xe-100 user's manual 1.8.2 - unipr.it2010].pdf · this manual may not be reproduced in any...

XE-100

User’s Manual

Preliminary

Version 1.8.2

Copyright © 2009 Park Systems Corporation.

All rights reserved.

High Accuracy Small Sample SPM

Notice

This manual is copyrighted by Park Systems Corp. with all rights reserved.

This manual may not be reproduced in any form or translated into any other language,

in whole or in part, without written permission from Park Systems Corp. Park

Systems is not responsible for any mistakes or damages that may occur either

accidentally or willfully, as a result of using this manual.

Park Systems is not responsible for typographical errors. This manual may be

changed without prior notice, and it will be examined and revised regularly.

We welcome any user feedback that may result in future improvements to the quality

of this manual. If you have any suggestions, please contact Park Systems.

Park Systems Corp

KANC 4F lui-Dong 906-10

Suwon, Korea 443-766

Ph +82-31-546-6800

Fax +82-31-546-6805~7

Homepage: www.parkAFM.com

Park Systems Inc

3040 Olcott St.

Santa Clara, CA 95054

Ph 408-986-1110

Fax 408-986-1199

Homepage: www.parkAFM.com

Preface

The Scanning Probe Microscope (SPM) is not only at the top of the list of equipment

pioneering the nano scale world, it is also the most fundamental technology.

Succeeding the first generation optical microscope, and the second generation

electron microscope, the SPM has every right to be known as a “third generation”

microscope since it enables us to look into the nano scale world. At the same time it

has many advantages over manual microscopes which passively look at the samples.

The SPM is like a miniature robot, fabricating specific structures by manipulating

atoms on the sample surface and using a probe tip to take measurements of those

structures.

The SPM originated with the invention of the Scanning Tunneling microscope (STM).

The STM uses a tunneling current between a probe tip and a sample in a vacuum

state to measure surface topography. As a result, it is limited in that it can only

measure a sample which is a conductor or a semiconductor. Once the Atomic Force

Microscope (AFM) was developed, however, a whole new range of measurement

capabilities became possible. Now it is not only possible to measure non-conductors

in air, but also to measure the physical, chemical, mechanical, electrical, and

magnetic properties of a sample’s surface, and even measure live cells in solution.

The SPM is indeed the key to entering the world of nano technology that has yet to

flourish, and it is essential equipment for various research in the basic sciences –

physics, chemistry, and biology - and in applied industry - mechanical and electrical

engineering.

The importance of the SPM stands only to grow greater and greater in the future.

Safety Precautions of XE-100 system

i

Safety Precautions of System

This section describes the procedures related to the general operating safety

of the XE-100 in detail. This section should be thoroughly understood before

operating the XE-100 for your safety.

CAUTION!

If a user operates the XE-100 in a manner not specified in this User’s Manual,

serious damage to the instrument may result.

1. Definition of safety symbols

Table shown below explains the meaning of the safety symbols – WARNING,

CAUTION, NOTE.

Table. Safety terms and their meanings

Symbols Meaning

WARNING Alerts Users to potential danger. Consequences and

countermeasures are described. If users fail to follow the

procedures described in this manual, serious injury or instrument

damage may occur. Such damage will NOT be covered by

warranty.

CAUTION Calls attention to possible damage to the system that may result,

if users do not follow the procedures described in this manual.

NOTE Draws attention to a general procedure that is to be followed.

XE-100 User’s Manual

ii

Please understand these safety terms thoroughly, and follow the associated

instructions. It is important to read all safety terms very carefully. WARNINGs,

CAUTIONs, and NOTEs include information that, when followed, ensure the

operating safety of XE-100.

2. Operating Safety

2-1. General operating safety

The following are most of the WARNINGs, CAUTIONs, and NOTEs

necessary to operate the XE-100 safely.

WARNING!

The XE-100 should be grounded before its components are connected to

electric power. The main power plug needs to be connected to a three-prong outlet

which includes a protective earth ground contact.

WARNING!

Before the power is turned on, the power selections for the individual

components need to be inspected. The voltage selector switch is located on the rear

panel of the XE-100 Control Electronics, and it can be set to the following voltages: 100

V, 120 V, 230 V, or 240 V.

WARNING!

Do not open the XE-100 Control Electronics or the AFM head. Doing so may

result in serious electrical shock, as high voltages and electrostatic sensitive

componenst are used in the XE-100 Control Electronics and the AFM head.

CAUTION!

Check regularly to ensure that the XE-100’s cables are free from damage and

that all connections are secure. If any damaged cables or faulty connections are found,

contact your local Park Systems service representative. Never try to operate the

equipment under these conditions.

Safety Precautions of XE-100 system

iii

CAUTION!

All parts in the XE-100 system should be handled with extreme care. If not

handled properly, these parts can be easily damaged as they are made of fragile

electromagnetical equipment.

CAUTION!

An EMI filter must be installed to meet operating safety and EMC

(ElectroMagnetic Compatibility compliance).

CAUTION!

The AFM head should always be handled with care. When removed from the

XE system, the AFM head needs to be carefully placed on a flat surface. This will

protect the scanner, the cantilever, and the beam adjustment knobs. Never allow

anything to impact the AFM head. When separated from the main frame, it is safe to

keep the head in its storage box.

CAUTION!

Before the AFM head is mounted or unmounted from the Z stage, the ON/OFF

switch for the beam must be turned off. Otherwise, the laser beam diode in the AFM

head may be damaged.

CAUTION!

When the AFM head is mounted or unmounted from the Z stage, ensure that

the AFM head does not sustain any damage, and that it is properly grounded. The AFM

head is extremely sensitive to electrostatic discharge.

CAUTION!

To meet the EMC guidlines, the Acoustice Enclosure should be closed while

making measurements with the XE-100.

2-2. Laser Beam Safety Cautions

The Super Luminescence Diode (SLD) used in the XE-100 has a maximum

output power of 5mW, and a wavelength of 830nm.

WARNING!

Any deviations from the procedure described in this manual may result in

hazardous beam exposure.


iv

Figure i. Beam Warning Label

Figure i shown above is a laser beam warning labels found on the AFM head.

The warning labels must be strictly followed. Also, Figure ii shows the position of the

laser beam warning label that attached to the AFM head.

Figure ii. Location of warnings posted on the XE head

Contents

v

Contents

Safety Precautions of System ............................................................................................... i

1. DEFINITION OF SAFETY SYMBOLS ........................................................................................... I

2. OPERATING SAFETY...............................................................................................................II

2-1. General operating safety ............................................................................................ii

2-2. Laser Beam Safety Cautions ....................................................................................iii

Chapter 1. Introduction to XE-100 ................................................................................ 1

1-1. PRIMARY COMPONENTS OF XE-100 SYSTEM ...................................................................1

1-1-1. XE-100 SPM Stage ..................................................................................................2

1-1-2. XE-100 Control Electronics ....................................................................................8

1-1-3. Computer & Monitor.................................................................................................9

1-2. PRINCIPLES OF XE-100’S MEASUREMENTS ......................................................................9

1-2-1. Scanning Probe Microscope ..................................................................................9

1-2-2. Atomic Force Microscope .....................................................................................10

1-2-3. XE-system’s advantages.......................................................................................13

Chapter 2. Installation .................................................................................................. 21

2-1. ENVIRONMENT ..................................................................................................................21

2-2. PRE-INSTALLATION ...........................................................................................................22

2-3. COMPONENT LIST.............................................................................................................22

2-4. HARDWARE INSTALLATION................................................................................................23

2-4-1. Installation of an Air Table or an Active Vibration Isolation System ................23

2-4-2. Computer Installation.............................................................................................26

2-4-3. Unlocking the Optical Microscope .......................................................................27

2-4-4. XE Cable Connections ..........................................................................................28

2-4-5. Connection to Power supply.................................................................................37

2-4-6. Installation Checkup ..............................................................................................37

Chapter 3. Cantilever Selection .................................................................................. 39

3-1. CHARACTERISTICS OF THE CANTILEVER ..........................................................................39

3-2. CANTILEVER SELECTION ..................................................................................................41

Chapter 4. Operation Procedure ................................................................................. 43

4-1. TURN ON THE XE-100......................................................................................................43


vi

4-2. XEP SOFTWARE ...............................................................................................................43

4-3. MOVING THE Z AND FOCUS STAGES ................................................................................44

4-4. REMOVING THE XE HEAD.................................................................................................45

4-5. CANTILEVER PREPARATION ..............................................................................................46

4-6. LOCATING THE CANTILEVER .............................................................................................47

4-7. BEAM ALIGNMENT .............................................................................................................48

4-8. SAMPLE PREPARATION .....................................................................................................51

4-9. SOFTWARE CONFIGURATION ............................................................................................52

4-10. FREQUENCY SWEEP.......................................................................................................52

4-11. APPROACH ......................................................................................................................54

4-12. SCAN PARAMETER DEFINITIONS.....................................................................................57

Chapter 5. Set up Scanner Mode ................................................................................ 59

5-1. XE-100 SCANNER CONFIGURATION ................................................................................59

5-2. SELECT SCANNER MODE .................................................................................................59

5-2-1. High voltage mode .................................................................................................60

5-2-2. Low voltage mode ..................................................................................................62

5-2-3. Z scanner Range ....................................................................................................63

Chapter 6. AFM in Contact Mode ................................................................................ 65

6-1. PRINCIPLE OF CONTACT MODE AFM ...............................................................................65

6-2. CONTACT MODE SETUP.....................................................................................................66


6-4. SCANNER SETUP ..............................................................................................................69

6-5. MEASUREMENT PROCEDURE ...........................................................................................70

Chapter 7. Lateral Force Microscopy (LFM) .............................................................. 71

7-1. PRINCIPLE OF LATERAL FORCE MICROSCOPY (LFM) .....................................................71

7-2. CONVERSION TO LFM ......................................................................................................74



Chapter 8. AFM in Non-Contact Mode........................................................................ 77

8-1. PRINCIPLE OF NON-CONTACT MODE AFM.......................................................................77

8-2. NON-CONTACT MODE SETUP ............................................................................................81

8-3. RESONANT FREQUENCY SETUP .......................................................................................82

8-4. CANTILEVER SELECTION...................................................................................................83

8-5. SCANNER SETUP...............................................................................................................85

Contents

vii


Chapter 9. Dynamic Force Microscopy (DFM)........................................................... 87

9-1. PRINCIPLE OF DYNAMIC FORCE MICROSCOPY ...............................................................87

9-2. CONVERSION TO DFM .....................................................................................................90

9-3. RESONANT FREQUENCY SETUP .......................................................................................90



Chapter 10. Approach Spectroscopy ......................................................................... 95

10-1. ACQUIRING AN APPROACH CURVE.................................................................................97

10-1-1. F/D Mode ..............................................................................................................98

10-1-2. Tip Oscillation Mode ..........................................................................................104

10-2. CURVE ANALYSIS .........................................................................................................105

10-3. CURVE COMPUTATION ALGORITHM .............................................................................107

Chapter 11. Calibration .............................................................................................. 110

11-1. SCANNER CALIBRATION ............................................................................................... 110

11-1-1. Calibrating the X-Y scanner in the ‘Open Loop’ scan ................................... 110

11-1-2. Calibrating the X-Y scanner in the ‘Closed Loop’ scan................................. 114

11-1-3. Z scanner calibration ......................................................................................... 116

11-2. DETECTOR OFFSET CALIBRATION................................................................................120

11-2-1. X direction ...........................................................................................................120

11-2-2. Y direction............................................................................................................122

11-2-3. Z direction............................................................................................................123

11-3. SOFTWARE LINEARIZED CORRECTION.........................................................................129

11-3-1. Software Linearized Correction of XY scanner in Low voltage mode ........130

Appendix A. Aligning XE-100 AFM............................................................................ 137

Index ............................................................................................................................ 147


viii

Figure Contents

ix

Figure contents

Figure i. Beam Warning LabelFigure ii. Location of warnings posted on the XE head Figure 1-1. The XE-100 SPM System Figure 1-2. XE-100 Scanning Probe Microcope Figure 1-3. XE-100 HeadFigure 1-4. Dovetail Lock Head Mount Figure 1-5. Z scanner Assembly Figure 1-6. X-Y scannerFigure 1-7. X-Y scanners : 5µm × 5µm (left), 50µm × 50µm (middle),

100µm × 100µm (right) Figure 1-8. XE-100 XY StageFigure 1-9. Optical Microscope Frame Figure 1-10. XE-100 Control Electronics Figure 1-11. Diagram of conventional AFM’s scanning Figure 1-12. Nonlinearity and Hysteresis (a), and Cross Coupling (b) Observed in

Piezoelectric Tube Scanners Figure 1-13. Z scanner separated from X-Y scanner Figure 1-14. Background Flatness Images from a conventional AFM (a) and XE-

series AFM (b) Figure 1-15. Beam path related to the cantilever’s movement Figure 1-16. Captured optical microscope image Figure 1-17. Dovetail Lock Head Figure 1-18. EZ Snap Probe Tip Exchange Figure 1-19. XEP - Data Acquisition Program Figure 1-20. XEI - Image Processing Program Figure 2-1. Below Air Table Figure 2-2. (a) Compressed air lever (b) Air Table suspended in air Figure 2-3. Active Vibration Isolation System Figure 2-4. Rear panel of AVIS Figure 2-5. Front panel of AVIS Figure 2-6. Locks on Optical Microscope Figure 2-7. Unlocking locks on Optical Microscope Figure 2-8. Basic arrangement of XE-100


x

Figure 2-9. Cables needed to be checked prior to installation Figure 2-10. Connection between XE-100 SPM main body and the XE head and X-Y

scanner Figure 2-11. Rear panel of the XE-100 SPM Base Figure 2-12. Cable connections of the XE-100 Control Electronics Figure 2-13. Illuminator Figure 2-14. Diagram of cable connections for the XE system Figure 3-1. Cantilever chip Figure 3-2. SEM image of silicon cantilever Figure 4-1. XEP User Interface Figure 4-2. Motor Control WindowFigure 4-3. Removing the XE Head Figure 4-4. EZ Snap Tip ExchangeFigure 4-5. Probe Hand without and with Cantilever Chip Figure 4-6. Camera Panning Knobs Figure 4-7. Laser beam alignment on the cantilever Figure 4-8. Laser beam alignment display in XEP Figure 4-9. Amplitude Setting for Frequency Sweep Figure 4-10. Frequency Sweep Window Figure 4-11. Scan Control Window Figure 4-12. Proper Gain (top); Noise from Excessive Gain (bottom) Figure 5-1. Select Scanner mode Figure 5-2. XY Servoscan is ON Figure 5-3. Scanner’s observable areaFigure 5-4. XY Servoscan is OFF Figure 6-1. Relation between the force and the distance between atoms Figure 6-2. Contact mode AFM setup Figure 6-3. SEM image of the shorter cantilevers (A, B, C) from a chip of the NSC36

series Figure 6-4. Silicon chip of the NSC36 series has 3 rectangular cantilevers Figure 6-5. Contact AFM Part Selection Figure 7-1. Quad-cell PSPD Figure 7-2. AFM and LFM signal Figure 7-3. Conversion to LFMFigure 7-4. Setup for LFM mode Figure 8-1. Concept diagram of Contact mode and Non-Contact mode

Figure Contents

xi

Figure 8-2. Resonant frequency Figure 8-3. (a) Resonant frequency shift (b) Amplitude vs Z-feedback Figure 8-4. Non-contact mode AFM setup Figure 8-5. Resonant Frequency setup in Non-Contact Mode Figure 8-6. SEM image of ULTRASHARP silicon cantilever (the PPP-NCHR series) Figure 8-7. Silicon chip of the NCHR series has 1 rectangular cantilever Figure 8-8. Non-contact AFM setup and voltage mode selection Figure 9-1. Resonant frequency Figure 9-2. (a) Resonant frequency shift (b) Amplitude vs. Z-feedback Figure 9-3. Conversion to DFM Figure 9-4. Resonant frequency setup in DFM Figure 10-1. Auto Offset option Figure 10-2. Spectroscopy Config Figure 10-3. Input Config for F/D Measurements Figure 10-4. Moving the Tip Position Figure 10-5. Points List Dialog Figure 10-6. Use a Map Figure 10-7. Edit Map Dialog Figure 10-8. F/D Curves in Buffer Window Figure 10-9. Selecting a Region by Mouse Figure 10-10. Use Tip Oscillation Figure 10-11. Input Config for Tip Oscillation Approach Curves Figure 10-12. Export the data as other document format Figure 10-13. XEI Spectroscopy Mode Figure 10-14. Approach Curve Figure 10-15. Adhesion Energy Computation Figure 16. Force Volume Image (Left: Topography, Center: Hardness Image and

Right: Snap-In)


xii

Chapter 1. Introduction to XE-100

1


1-1. Primary Components of XE-100 system

The XE-100 SPM System consists of four primary components: the XE-100

SPM stage, the XE-100 Control Electronics, a computer & monitor, and an illuminator.

Figure 1-1. The XE-100 SPM System

The XE-100 SPM stage is where actual measurements are made, and the XE-100

Control Electronics controls the movement of the XE-100 SPM stage according to the

commands from the computer. In Figure 1-1, the SPM stage is hidden inside the Basic

Acoustic Enclosure which shields it from acoustic and electrical noise.

The monitor, which displays the image from the optical microscope that is mounted on

the XE-100 SPM stage, is used to locate the exact spot that is to be measured on the

sample surface. It is also used to view the cantilever that will be used to make the

measurement.


2

1-1-1. XE-100 SPM Stage

The XE-100 SPM is much easier to operate than a conventional SPM, and

measurements are made faster and more accurately. Figure 1-2 shows overall structure

of the XE-100 SPM stage with the acoustic enclosure open. The following explains the

individual components in detail.

Objective LensXE Head

CCD Camera

XY Stage

Optical Microscope Frame

SPM Frame

Z Stage

XY Scanner

Objective LensXE Head

CCD Camera

XY Stage

Optical Microscope Frame

SPM Frame

Z Stage

XY Scanner

Figure 1-2. XE-100 Scanning Probe Microcope

XE-100 Head

The XE-100 head is the component which actually interacts with the sample

and takes measurements. A unique characteristic of the XE-100 compared to that of

conventional SPM is that the Z scanner, which controls vertical movement of the SPM

tip, is completely separated from the X-Y scanner which moves in horizontal direction

on the sample.

This structural change provides the user with several operational advantages.


3

1. The Z scanner, being separate from the X-Y scanner, is designed to have a

higher resonant frequency than conventional piezoelectric tube scanners. This

enables the tip to precisely follow the topography of a sample surface at faster

rate and increases the speed of the measurement, and protects the tip,

resulting in the ability to acquire clear images for an extended period of time.

2. Since the tip wears out eventually, it is necessary to replace it after some

amount of usage. The XE-100 has a Kinematic Mount that makes tip

exchanges routine and easy.

3. Most SPMs detect probe’s movement to measure topographic data by

collecting a laser beam signal on a PSPD (Position-Sensitive Photo Detector)

after it is reflected from the back side of a cantilever. To align the laser beam,

conventional SPMs use additional positioning equipment, the operation which is

often difficult and cumbersome. However, laser beam alignment becomes very

easy and convenient, with the XE-100. Manageable control knobs on the XE-

100 head can be adjusted manually with the help of the control software and

the video monitor display, making location and movement of the laser beam

easy and accurate.

4. Whenever it is necessary to remove the XE-100 head from the main frame, it is

very easy to do so. This procedure can be accomplished by unlocking the

dovetail thumb locks and sliding the XE-100 head off the dovetail rail after

having disconnected the cable from between the head and the main frame.

Remounting the head is as easy as removing it.

CAUTION!

Before disconnecting the cable, the Laser beam switch on the XE-100 head

must first be turned off.

WARNING!

Do not disassemble the XE-100 head on your own. Park Systems will not be

responsible for any personal, physical damage or degraded performance that may

result from unauthorized disassembly.


4

Figure 1-3. XE-100 Head

Figure 1-4. Dovetail Lock Head Mount

XE-100 Z scanner

The Z scanner which is mounted on the XE-100 head makes it possible for the

tip to maintain constant feedback conditions (force or distance) as it is moved over a

sample surface. The maximum measurement range of sample surface’s height is

determined by the Z scanner range. The XE-100’s Z scanner can move up to 12µm. On

the other hand, the minimum obtainable vertical resolution is determined by the control

unit and the electric voltage that is applied to the Z scanner.


5

WARNING!

Never disassemble the Z scanner on your own Park Systems will not be

responsible for any personal, physical damage or degraded performance that may

result from unauthorized disassembly.

Figure 1-5. Z scanner Assembly

XE-100 X-Y scanner

The XE-100’s X-Y scanner is a Body Guided Flexure scanner. The X-Y

scanner is fabricated from a solid aluminum block. The desired area is cut out from

inside the aluminum block, and the lines indicated in Figure 1-6 are then fabricated with

a special technique called ‘Wire Electric Discharge Machining’ - this results in a flexure

hinge structure.

An X-Y scanner with a flexure hinge structure has the advantage of highly

orthogonal two-dimensional movement with minimal out-of-plane motion. Due to the

Parallel Kinematics design, the X-Y scanner has low inertia and axis-independent

performance. Hysteresis-correcting ServoScan (described in Chapter 5) scanning is

accomplished by means of an optical sensor in the flexure scanner.

There are three X-Y scanner models that may be used with the XE-100: 5 µm

× 5 µm, 50 µm × 50 µm, or 100 µm × 100 µm, depending on the desired maximum

measurement range (Figure 1-7).


6

WARNING!

Never disassemble the X-Y scanner on your own. Park Systems will not be

responsible for any personal, physical damage or reduced performance resulting from

unauthorized disassembly.

Flexure HingeFlexure Hinge

Figure 1-6. X-Y scanner

Figure 1-7. X-Y scanners : 5µµµµm ×××× 5µµµµm (left), 50µµµµm ×××× 50µµµµm (middle),

100µµµµm ×××× 100µµµµm (right)

XE-100 XY Stage

The X-Y scanner is affixed to the XY Stage. By adjusting manual micrometer

screws, the X-Y stage can be used to horizontally position the sample The X-Y stage

has a maximum range of 25mm in both X and Y with a resolution, or minimum unit of

movement, of 10µm.


7

Figure 1-8. XE-100 XY Stage

XE-100 Optical Microscope

The optical microscope is used to focus the beam onto the cantilever and to

locate regions of interest on the sample surface. Since the optical microscope is located

parallel to the Z-scanner, it is possible to have a direct on-axis view of the cantilever in

conjunction with the sample area that is to be scanned.

All of the components of the optical microscope - the objective lens, the tube

lens, and the CCD camera - are rigidly fixed on a single body. Since the entire assembly

moves together for focusing and panning, the axis aligning the sample and the CCD

camera is always fixed, and therefore the high quality optical view is preserved. With

the CCD camera, high quality resolution image could be produced.

The XE-100’s standard 10X objective lens yields about 500 times

magnification, and the optional 20X objective lens yields about 1000 times magnification.


8

Figure 1-9. Optical Microscope Frame

1-1-2. XE-100 Control Electronics

The Control Electronics plays an important role in mediating between the XE

SPM stage and the computer.

In order to maintain fast, effective communication between the computer and

the XE-100 Control Electronics, a USB or TCP/IP interface is used. The DSP contained

in the XE-100 Control Electronics is the TMS320C6415, running at 600MHz

(4,800MIPS).


9

Figure 1-10. XE-100 Control Electronics

1-1-3. Computer & Monitor

The computer is connected to the XE-100 Control Electronics, via USB or

crossed LAN cable. The computer is equipped with a Pentium IV CPU/Processor, 1GB

DDR RAM, and two 80GB HDDs. It uses a Windows XP operating system. The 19 inch

LCD monitor utilizes 12801024 pixels with 32 bit color. This monitor is digitally

connected to the computer via DVI (Digital Video Interface) port.

1-2. Principles of XE-100’s measurements

1-2-1. Scanning Probe Microscope

The Scanning Probe Microscope (SPM) proved false the prevailing concept

that an atom is too small to be observed with even the best microscope. It now has

every right to be called the third generation microscope, with optical and electron

microscopes named as the first and second generation microscope. Whereas the

maximum magnifying power of an optical microscope is several thousands and that of a

scanning electron microscope (SEM) is tens of thousands, an SPM has the magnifying

power of tens of millions, enough to observe individual atoms. Even though a

transmission electron microscope (TEM) has the lateral resolution high enough to

image at the atomic level, its vertical resolution is much weaker at observing individual

atoms. On the other hand, the vertical resolution of SPM is even better than its

horizontal resolution making it possible to measure on the scale of fractions of the

diameter of an atom (0.01nm). The SPM, with its exceptional resolution, not only makes


10

it possible to understand the various nanoscale worlds which heretofore were not

completely revealed, but also to bring the unbelievable into reality, providing such

capabilities as allowing a user to change the position of individual atoms or to write

letters by transforming the surface of a material at the atomic level.

1-2-2. Atomic Force Microscope

Among SPMs, the first to be invented was the Scanning Tunneling Microscope

(STM). The STM measures the tunneling current between a sharp, conducting tip and a

conducting sample. The STM can image the sample’s topography and also measure the

electrical properties of the sample by the “tunneling current” between them.

The STM technique, however, has a major disadvantage in that it cannot

measure non-conducting material. This problem has been solved by the invention of the

Atomic Force Microscope (AFM) which may be used to measure almost any sample,

regardless of its electrical properties. As a result, the AFM has greatly extended the

SPM’s applicability to all branches of scientific research.

Figure 1-11. Diagram of conventional AFM’s scanning

Instead of a conducting needle, the AFM uses a micro-machined cantilever

with a sharp tip to measure a sample’s surface. See the “Cantilever Selection” for more

information on the cantilever. Depending on the distance between the atoms at the tip of

the cantilever and those at the sample‘s surface, there exists either an attractive or


11

repulsive force/interaction that may be utilized to measure the sample surface. See the

“AFM in Contact Mode” and AFM in “Non-Contact Mode” chapters for a further

discussion on utilizing the atomic forces.

Figure 1-11 displays the basic configuration for most AFMs. This scanning

AFM is typically used to measure a wide variety of samples, which have relatively small

roughness. The force between the atoms at the sample’s surface and those at the

cantilever’s tip can be detected by monitoring how much the cantilever deflects. This

deflection of the cantilever can be quantified by the measurement of a beam that is

reflected off the backside of the cantilever and onto the Position Sensitive Photo

Detector (PSPD).

The tube-shaped scanner located under the sample moves a sample in the

horizontal direction (X-Y) and in the vertical direction (Z). It repetitively scans the

sample line by line, while the PSPD signal is used to establish a feedback loop which

controls the vertical movement of the scanner as the cantilever moves across the

sample surface.

The AFM can easily take a measurement of conductive, non-conductive, and

even some liquid samples without delicate sample preparation. This is a significant

advantage over the extensive preparation techniques required for TEM or SEM.

Despite its many advantages, the AFM does have some drawbacks as well.

1. Since the tip has to mechanically follow a sample surface, the measurement

speed of an AFM is much slower than that of an optical microscope or an

electron microscope.

2. In general, the scanners used in AFMs are piezoelectric ceramic tubes (Figure

1-11). Due to the non-linearity and hysteresis of piezoelectric materials, this

may result in measurement errors as seen in Figure 1-12.

3. The geometrical and structural restraints imposed by the tube type scanner

results in cross coupling of the individual scan axes. Thus, independent

movement in the x, y, and z directions is impossible.

4. Since the tip has a finite size, it is very difficult and sometimes impossible to

measure a narrow, deep indentation or a steep slope. Often, even though such

a measurement may be possible, the convolution effect due to the shape of the

tip and the sample profile may result in measurement errors.


12

Figure 1-12. Nonlinearity and Hysteresis (a), and Cross Coupling (b) Observed in

Piezoelectric Tube Scanners

The most inconvenient aspect of using the AFM is its slow speed. As

mentioned above, since the image is obtained by the tip’s mechanically following a

sample surface, it is much slower than other microscopes that use electrons or light.

The main factors slowing the speed of the AFM are the Z scanner’s response rate and

the response rate of the circuit which detects changes in the cantilever’s resonant

frequency. The resonant frequency of the typical tube scanner is several hundred Hz. In

order to accurately measure a sample area with 256×256 pixels (data points), it is

necessary to scan at a rate of about one line per second. Thus, it takes approximately 4

minutes to acquire an image.

For most cases, the second and third problems listed above can be minimized

by software calibration. This is a reasonably simple and inexpensive procedure that

involves imaging a standard sample, (usually a grid structure with a known pitch) in

order to create a calibration file that will be used to control the scanner’s movements

Extension of X axis

Extension of Y axis

Piezo Extension ( m

)

Applied bias (V)


13

when unknown samples are imaged. Correction using software, however, still depends

heavily on the scan speed and scan direction, and such a correction becomes accurate

only when the center of the scan range used to measure an unknown sample coincides

exactly with the center of the scanning range that was used to image the standard

sample and to create the calibration file.

1-2-3. XE-system’s advantages

X-Y scanner

Z scanner

Sample

X-Y scanner

Z scanner

X-Y scanner

Z scanner

Sample

X-Y scanner

Z scanner

Figure 1-13. Z scanner separated from X-Y scanner

Since the conventional tube type scanner cannot move in one direction

independently from other directions, movement in one direction will always

simultaneously affect the scanner’s movement in other directions. This cross talk and

non-linearity(see Figure 1-12) caused by the scanner’s three axes being non-orthogonal

to another has a more pronounced effect in the case of measuring larger areas or flat

samples. This intrinsic problem can be eliminated completely, however, by physical

separation of the Z scanner from the X-Y scanner.

The breakthrough that eliminated these cumbersome problems came when the

XE-series (Cross-talk Elimination) SPMs introduced a new concept of separating the Z

scanner from the X-Y scanner. The XE-scan system is designed so that the X-Y

scanner scans a sample in two-dimensional space, while the Z scanner moves the tip


14

only in the z direction. Figure 1-13 shows a diagram of the XE system, in which the Z

scanner separated from the X-Y scanner. The symmetrical flexure scanner used in the

XE-series SPM moves only in the X-Y plane, and has superb orthogonality. This

scanner’s design also makes it possible to place much larger samples on the sample

stage than could normally be accommodated by a piezoelectric tube type scanner.

Furthermore, since the flexure scanner only moves in the X-Y direction, it can be

scanned at much higher rates (10~50 Hz) than would be possible with a standard AFM.

Because the stacked piezoelectric actuator used for the Z scanner has a very fast

response speed, at least 10 kHz, it is able to respond to topographic changes on the

sample surface more than 10 times faster than is possible with a conventional tube type

scanner.

Having the X-Y scanner separated from the Z scanner in the uniquely designed

XE system not only increases the data collecting speed by at least 10 times compared

to a conventional tube type scanner, but also isolates the vertical and horizontal scan

axes, completely eliminating cross coupling, resulting in a very accurate measurement.

Moreover, this independent scanning system improves the error due to the inherent

non-linearity of the scanner itself. Figure 1-14 compares the background image of a

conventional tube scanner compared to that of the new XE scan system.

(a) Conventional AFM

(b) New scan system of XE







Figure 1-14. Background Flatness Images from a conventional AFM (a) and XE-

series AFM (b)


15

Figure 1-15 shows a diagram that explains the cantilever movement detection

mechanism used in the XE-series SPMs. This beam/PSPD configuration, which permits

the acquisition of stable images at high measurement speeds, is a distinguishing mark

of the XE-series and satisfies the following two important imaging conditions:

First, the PSPD should be able to measure only the deflection of the cantilever

without interference from the Z scanner.

Second, to improve the response rate in the Z direction, the weight of the Z

scanner must be minimized.

Figure 1-15. Beam path related to the cantilever’s movement

The cantilever and the PSPD move together with the Z scanner while the

beam, a steering mirror, and a fixed mirror in front of the PSPD are fixed relative to the

scanner frame. The beam, positioned at one side of the scanner, is aimed at a prism

that is situated above the cantilever. The prism reflects the beam downward and onto

the back surface of the cantilever. The beam will always hit the same spot on the

cantilever’s surface since the Z scanner only moves vertically. Therefore, once the

beam is aligned, there is no need to realign the beam, even after the Z scanner has

been moved up and down to change samples. The steering mirror, located at the front

of the Z scanner assembly, adjusts the reflection angle of the beam that is reflected off

the cantilever’s surface. The steering mirror reflects the beam to a fixed mirror which, in

turn, reflects the beam at once to the PSPD. Another clever feature of this alignment

design is that as a result of placing the second (fixed) mirror next to the PSPD, it allows


16

changing of the Z scanner position without having to readjust the position of the PSPD.

Therefore, only the deflection of the cantilever will be detected, independent of the Z

scanner movement.

Since there is nothing obstructing the view above the cantilever in the structure

(Figure 1-15), the optical microscope is located on the same axis as the beam that is

reflected at the prism as shown in Figure 1-13.

Figure 1-16. Captured optical microscope image

Figure 1-16 shows the cantilever with the beam focused on it, as it is displayed

on the video monitor. Since the CCD camera is aligned directly with the cantilever with

nothing blocking its view, it is very convenient to focus on or to observe the sample

while moving the camera up and down. This view also provides superb quality for an

optical microscope.

The superiority of the XE- system’s design, and its intention to accommodate

the convenience of the user, appears in many different aspects in addition to the optical

microscope. The AFM head, which includes the Z scanner, is easily inserted by sliding it

along a dovetail rail and locking it into place with a convenient turn of two thumb locks.

There are no additional knobs or springs to adjust as is common with other designs.

The replacement of the tip is just as easy, and no special tools are required for

this procedure. Figure 1-18 shows the easy operation of replacing a tip by hand.


17

Figure 1-17. Dovetail Lock Head

Figure 1-18. EZ Snap Probe Tip Exchange

The XE system not only achieved a structural design change that yielded

exemplary SPM efficiency, but it also brought lots of improvements to the electronic

controller and to the supporting software. The electronic controller has a fast and

powerful DSP (Digital Signal Processor), 14 DACs (Digital to Analog Converters), and 5

ADCs (Analog to Digital Converters). The XE Control Electronics are designed to

enable the scanner, the core unit of the AFM, to provide efficient, accurate and fast

control, and to facilitate the acquisition of a stable image even beyond a scan speed of

10Hz. In addition, the controller contains input/output terminals that provide a simple

means for users to design advanced experiments that extend far beyond and are much

more complicated than obtaining basic images.

Furthermore, the up to date computer is equipped with the most recent high-


18

power Pentium chip and Windows XP operating system. A 19” LCD monitor displays

crystal clear images using a DVI (Digital Video Interface). All necessary software,

including XEP, the Data Acquisition program, and XEI, the Image Processing program,

is installed on the computer. Figure 1-19 shows the XEP program’s clean and easy-to-

use interface, complete with safety functions and various measurement capabilities that

are required to perform advanced applications. Figure 1-20 shows the XEI program that

is used to convert acquired data into an image and to perform various analyses that

meet the user’s requirements.

Figure 1-19. XEP - Data Acquisition Program


19

Figure 1-20. XEI - Image Processing Program


20

Chapter 2. Installation

21


The installation procedure and environmental specifications for the XE-100 play

a significant role in the safe operation of XE-100. Since the durability, safety and overall

performance of the XE-100 depend on the environment and proper installation, please

pay close attention to the following installation environment and procedures that are

recommended in this chapter.

2-1. Environment

Temperature and Humidity

Recommended Temperature: 5 °C ~ 35 °C

Recommended Humidity: 30 % ~ 80 % (Not condensing)

The XE-100 should be installed in a clean, dry atmosphere with proper

ventilation.

Vibration

The XE-100 is extremely sensitive to external vibrations. Thus, it is important to

isolate all possible vibrations from the equipment’s surroundings. It is recommended

that an Air Table or Active Vibration Isolation System be installed to remove external

vibrations.

Floor Vibration: vertical floor vibration, less than 1×10-8

m/sec for 0-50 Hz.

Acoustic and Electromagnetic Noise

The XE-100 should be installed where outside noise and light can be minimized.

To eliminate noise and light interference, it is advisable to operate the XE-100 with the

Acoustic Enclosure closed.


22

Electrical Requirements

The XE-100 requires an AC power supply.

Power Supply: 100/120 V or 230/240V, 50/60 Hz, 300 W

Since the XE-100 SPM is highly sensitive equipment, it is ideal to use it with a

UPS (Uninterruptible Power Supply) installed to provide a stable power supply.

The resistance in the ground system should be less than 100 ohms to optimize

operation.

2-2. Pre-Installation

The XE series SPM (Scanning Probe Microscope) is a precision instrument that

can measure up to sub-nanometer scale features. Consequently, it is very susceptible

to surrounding noise and vibrations, and the following precautions need to be followed

very carefully in order to obtain stable operation and the best measurement results.

The optimal location to install the XE-100 is a room with no vibrations, such as

a basement or the lower floor of a building where the inside and outside

vibrations have the least effect.

If the XE-100 must be installed in a location where there is considerable air

flow or electrical noise caused by electromagnetic fluctuations, you may isolate

the noise by using an Acoustic Enclosure.

To protect the system from electric shock, the power supply, electric outlet,

extension cord, and plugs must be grounded.

2-3. Component List

XE-100 SPM Main Body

XE-100 Control Electronics

XE Manuals

XE Software Installation CD

XE Scanner

X-Y scanner : Single module parallel-kinematics flexure scanner

Z scanner : Guided flexure scanner


23

Illuminator

Input power : AC 90~130/180~260 V, Auto select 50/60 Hz

12V-100 W Halogen Lamp

XE Cables

from Control Electronics

Motor cable, 40pin 3 m

Analog cable, 68pin 3 m

XE Base to scanner

X-Y scanner cable, 20pin 25 cm

Z-scanner cable, 26pin 25 cm

Optical fiber cable 3 m

Acoustic Enclosure

Computer

Pentium IV, DDR RAM 1GB, 160GB HDD, Window XP Operating System

19inch LCD Monitor, DVI Type 2ea

Air Table (Air Compressor Included) or Active Vibration Isolation System

Standard Sample

3 µm x 3 µm Grating, Height: 130nm

Cantilevers

Silicon Cantilevers for Contact AFM 10ea

Silicon Cantilevers for Non-contact AFM 10ea

Power Strip – 110 V or Multi-Tap – 220V, Ground Type

Tweezers

for sample and cantilever 1ea

Sample disk (pucks) 15ea

Options may vary when purchasing Premium System.

2-4. Hardware Installation

2-4-1. Installation of an Air Table or an Active Vibration Isolation System

Air Table Installation (Optional)

The function of an Air Table is to suspend the XE-100 on a floating platform so

that it can be free from surrounding vibrations - the equipment is placed on a marble

table that “floats” on air.


24

At the bottom of each of the four corners of the Air Table, you will find a leg and

a wheel. To level the Air Table, the height of each of the four legs can be adjusted as

follows - suspend the legs by rotating the lower bolt in the frame of the wheel (Figure 2-

1) counterclockwise, and making sure that the Air Table is fixed properly, adjust the legs

using the levels on top of the table.

Figure 2-1. Below Air Table

Once the Air Table is properly leveled, connect the air compressor to the

compressed air line. There are three levers (as shown in Figure 2-2 (a)) on the Air Table.

Adjust these three levers, as shown in Figure 2-2 (b), so that the Air Table’s top plate is

suspended in air a few millimeters high. To be sure not to tilt the marble plate, use the

level.

Figure 2-2. (a) Compressed air lever (b) Air Table suspended in air


25

Active Vibration Isolation System (Optional)

An Active vibration Isolation System (AVIS) uses an electromagnetic transducer

to isolate any vibrations generated by the building as well as system. The AVIS (TS-

150) available with the XE system consumes in general under 10W, and in extreme

cases a maximum of 40W. Either AC 110V or 230V can be used for the power supply,

but it should always be connected to an electric outlet with a separate ground. The AVIS

can block the vibrations in the frequency range of 0.7Hz~1kHz, but vibrations above

1kHz will penetrate the AVIS.

Figure 2-3 shows the general view of the TS-150; an object of up to 150kg can

be placed on the table top. Figure 2-4 shows the power supply connection located on

the TS-150’s rear panel. On the left hand side of the rear panel, there are two fuses

1.6A/230V. On the right hand side, a BNC socket gives a multiplexed output showing

the signals from all six accelerometers that are used to isolate vibrations, and an

oscilloscope may be used to display changes due to the AVIS.

Figure 2-3. Active Vibration Isolation System


26

Figure 2-4. Rear panel of AVIS

Before being installed, the AVIS should be in “Lock” mode in order to protect the

TS-150 from outside impacts that may occur during shipping or storage.

When the AVIS is initially installed, or after the lock condition has been selected

prior to system transport or long-term storage, the lock mode will be automatically

released once power is supplied to the AVIS. Be sure to securely place the four corners

of the TS-150 on a solid flat surface before turning on the power supply. When the

power switch is on, and after the inside motor stops turning, the upper table will be

floating, and the “Isolation Disable” sign will be displayed. At this time, if you push the

button labeled “E” on the front panel, the active vibration isolation will begin and the red

LED will turn on.

Figure 2-5. Front panel of AVIS

If the AVIS is to be kept in storage again or transported, you may scroll the

screen while the power is still on, until the message “to lock push ” appears. Pushing

the “ ” button will initialize the motor which slowly lowers the isolation stage until it

finally halts. You may turn off the power when the “System locked’ message appears.

The AVIS will remain locked until the power supply is turned on again.

2-4-2. Computer Installation

Please refer to the manual supplied by the computer manufacturer.

Fuses


27

2-4-3. Unlocking the Optical Microscope

For the safety during the shipping, Optical microscope of XE-100 is locked by

two locks indicated in the figure below.

Figure 2-6. Locks on Optical Microscope

After placing the SPM at the installation site, optical microscope should be

unlocked. To unlock the optical microscope follow the instructions below. These lock

should be locked again when the system is moved from one place to another.

Figure 2-7. Unlocking locks on Optical Microscope

Pull out the loosened lock while supporting optical microscope with the other hand

Unlock the two screws fixing the lock

Unlocked lock


28

2-4-4. XE Cable Connections

Before connecting the XE-100 SPM components, for easy connection and

operation, please arrange them as shown in Figure 2-8.

Figure 2-9 shows the cables to be checked before the initial installation.

Figure 2-8. Basic arrangement of XE-100


29

Figure 2-9. Cables needed to be checked prior to installation

A : Analog Cable

B : Motor Cable

C : Head Cable

D : Scanner Cable

E : Optical Fiber

F : LAN Cable (for TCP/IP)

G : Power Cable

H : IEEE 1394 Cable

LAN Cable(F) is replaced with USB Cable when control electronics connects to PC

using USB.

XE-100 SPM Main Body

As shown in Figure 2-8, there are two connectors on the side of the XE SPM

main body. Connect the upper connector to the Z scanner head using the Head cable

(26pin). Connect the lower connector to the X-Y scanner using the X-Y scanner cable

(20pin).

The rear panel of the SPM main body has 6 connectors as shown in Figure 20-

11. Connect these cables to where as follows: Connect Motor connector to the rear

panel of Control electronics using Motor cable. Connect Analog connector to the rear

panel of Control electronics using Analog cable. Connect Illuminator connector to the

illuminator using optical fiber. Connect Camera connector to the IEEE 1394 port of

Computer using the IEEE 1394 Cable.


30

Figure 2-10. Connection between XE-100 SPM main body and the XE head and X-

Y scanner


31

Figure 2-11. Rear panel of the XE-100 SPM Base

XE-100 Control Electronics

As shown in Figure 2-12 below, the XE-100 AFM Control Electronics has three

parts on the rear panel. The upper right and left corner has a fan. The mid of controller

has BNC Input and Output connectors for the external application modes and auxiliary

Analog Digital converters. The lower part of the XE-70 Control electronics has several

connectors for cables.

As shown in Figure 2-10 and 11, connect the “Analog” connector (B) on the rear

panel of the XE-100 Control Electronics to the 68 pin connector on the back of the main

body using the Analog cable (68 pin).

Connect the “Motor” output (C) on the rear panel of the XE-100 Control

Electronics to the 40pin connector on the back of the main body using the 40pin Motor

cable.

Connect the USB connector (D) on the rear panel of the XE-100 Control

Electronics to the USB port of the computer using the standard USB cable.

Or, connect the Ethernet connector (E) on the rear panel of the XE-70 Control

Electronics to the LAN port of the computer using the LAN cable.

Fan

BNC Output

Cable Connectors


32

Figure 2-12. Cable connections of the XE-100 Control Electronics

A : Power

B : Analog

C : Motor

D : USB

E: Ethernet

Connector

Label Type

Connection

to Purpose/ specification

Analog DDK-

DHA-RC68 Frame PCB

Analog signal I/O (+/-15V , PSPD,

Detector, Piezo drive signal, Tip bias ,

Sample bias, Modulation)

Motor DDK-

DHA-RC40 Frame PCB

Digital signal I/O (+5V, Z motor, Focus

motor, Limit sensor, SPI)

Sync DDK-

DHA-RC20 None Digital I/O (Line, Pixel, Frame, SPI)

Aux ADC

1, 2, 3 BNC None

Inputs connector for user-supplied

signals. External signals are introduced

through these connectors can be viewed

alongside SPM parameters, each being

assigned to a channel selectable from the

“Input Config” menu. These auxiliary

signals can also be captured as an image

in XEP for analysis. The three signal

paths are identical and independent.

Input voltage range: -10V to +10V

Full Power Bandwidth: 50kHz

Impedance: 50kΩ impedance


33

Frame

Line

Pixel

BNC None

DIGITAL OUTPUTS EOF (End-Of-

Frame), EOL (End-Of-Line), and EOP (End

of Pixel). Provides transistor-transistor

logic (TTL) synchronization pulses for both

upward and downward frames, forward

and backward lines, and each pixel.

TTL reference signal negative-going

pulse, +3.3 to 0V

Impedance: 50 Ω

A-B BNC None

Difference between the voltage from

upper and lower cells of the quad cell

PSPD. Experimenter can use this

connector to process the A-B signal from

external device such as lock-in amplifier.

Output range: -10V ~ +10 V

Small Signal Bandwidth: 600kHz

Impedance: 50 Ω

Error BNC None

Difference between A-B signal and its

reference value (setpoint). Used for

external feedback. (Currently

inaccessible).

Ext. Tip

Bias

Ext. Sample

Bias

BNC None

Input connector used when the

experimenter wants to apply bias from the

external source to the sample. Input range

is limited to -10 to +10 V. If experimenter

wants to apply higher bias to the sample,

user can use ‘External High Voltage toolkit’

Input voltage range: -10V to ~ +10V

Full Power Bandwidth: 50kHz

Impedance: 50kΩ


34

Aux

DAC 1 BNC None

Outputs from the Aux DAC can be

accessed from this connector. However,

output from Aux DAC is only available in

form of DC signal with voltage value preset

from the XEP software. Dynamic

controllable outputs will be available

through Aux DAC channel in future.

Output range: -10V ~ +10V

Small Signal Bandwidth: 1kHz

Impedance: 50 Ω

Table 4-2 AFM Control Electronics Connection List

The power to the AFM controller is not free voltage.So to change the input power

voltage configuration has to be made as below.

1. Remove power cord.

2. Pry door open at socket.


35

3. Lift and swing door into socket.

4. Lift fuse holder out of housing.

5. Install one (1) AG fuse or two (2) metric fuses*.

6. Replace fuse holder into housing.

7. Swing and snap door back in place.

Removing the Fuse Holder

1. Insert a pocket screwdriver at point "X" as shown

Gently lift UP until the entire door lifts up approximately 1/4" (minimum)

2. Once lifted, the door will pivot on it's hinges and expose the fuse holder

3. When the fuse holder is installed in the single fuse position, apply the screwdriver as

shown and gently pry up. Insert screwdriver as shown - do not use fingers to pry unit

loose.


36

When the fuse holder is installed in the dual fuse position, it will normally release as

soon as the door is opened.

Fuse Changing

European Fusing Arrangement

North American Fusing Arrangement

Install fuses on one side only. Do not install both AG and Metric fuses at the same time.

lluminator

As shown in Figure 2-13, connect the illuminator to the illuminator connector

(referred to as “D” in Figure 2-9) using the Optical fiber and fix the Optical fiber by

turning the upper knob.


37

Figure 2-13. Illuminator

2-4-5. Connection to Power supply

Connect the XE-100 Control Electronics, the illuminator, the computer, and the

video monitor to the grounded power supply. Make sure all the switches are turned off

to prevent any damage to the equipment.

2-4-6. Installation Checkup

After the installation is complete, turn the power supply on. If you click the XEP

icon on the main window screen or in the folder C:\Park Systems\Bin, the program

will start and you can check to ensure that system initialization completes without any

error messages. If there is a problem, check whether the power supply is on, and make

sure all the components are arranged correctly as shown in Figure 2-13.

Optical Fiber


38

Figure 2-14. Diagram of cable connections for the XE system

Chapter 3. Cantilever Selection

39


3-1. Characteristics of the cantilever

In general, the term ‘cantilever’ includes the silicon chip, a cantilever hanging from the

chip, and a tip hanging from the end of the cantilever. Figure 3-1 below shows the

overall view and the names of the parts of the cantilever used in the SPM.

Figure 3-1. Cantilever chip

The chip, the cantilever, and the tip are made from Silicon (Si) or Silicon Nitride (Si3N4),

and are manufactured using macro-machining techniques.

Because a cantilever has very small dimensions - 10 width, 100 length, and

several thickness - it is very difficult to handle in the process of attaching to the SPM.


40

To make it easier to use, the SPM uses a relatively large chip of size several millimeters.

Figure 3-2 is the SEM image of a cantilever manufactured this way.

Figure 3-2. SEM image of silicon cantilever

The cantilever is the part sensing the surface properties (for example, the

topographic distribution, the physical solidity, electrical properties, magnetic properties,

chemical properties, etc.) by detecting the degree of deflection due to the interaction

with the sample surface, and is very important component determining the sample

resolution.

When viewed from the top, the structures of cantilevers are divided into two

groups: those with a rectangular shape and those with a triangular shape. Each design

has a different force constant depending on the width, depth, thickness, and the

composition of the material. Among them, the Silicon Nitride cantilever is stronger that

the Silicon cantilever, but it has some disadvantages:

1. When the thickness is more than 1 , contortion may occur.

2. The curvature of the end of the tip is large – on the order of tens of

nanometers.

3. It has a low aspect ratio.

Compared to the Silicon Nitride cantilever, the Silicon cantilever has a

curvature of the tip of less than 10nm, and is more commonly used. Moreover, in non-

contact mode, which has a high resonant frequency, and the cantilever with the high

force constant, the rectangular shaped cantilever with a bigger Q-factor is used more

than the V shape. The cantilever provided with the XE-100 as a default is a Silicon,

rectangular shaped cantilever for use in both contact mode and non-contact mode.


41

In addition, the upper surface of the cantilever (the opposite side of the tip) is coated

very thinly with a metal such as gold (Au) or aluminum (Al) to enhance the high

reflectivity. However, for EFM (Electrostatic Force Microscopy) or MFM (Magnetic Force

Microscopy), when the whole cantilever and tip is coated to measure the electric or

magnetic properties, there is no extra coating on the cantilever to enhance the high

reflectivity.

3-2. Cantilever Selection

There are several types of cantilevers varying in material, shape, softness

(represented by the spring constant), intrinsic frequency, and Q-factor. The choice of a

cantilever from among these is primarily determined by the type of the measurement

mode.

In the contact mode, a “soft” cantilever, which has a small spring constant of

about 0.01 N/m ~ 3N/m to respond sensitively to the tiny force between atoms is usually

chosen. The probe tip used in the contact mode has a thickness of about 1 to

achieve a small spring constant. This is because a cantilever with a small spring

constant makes a relatively large deflection to a small force, and can thus provide a

very fine image of the surface structure.

On the other hand, in non-contact mode, a cantilever has a greater thickness,

~ 4 , compared to contact mode. It has a spring constant of 40N/m which is very “stiff”,

and a relatively large resonant frequency. While contact mode detects the bending of a

cantilever, the non-contact mode vibrates a cantilever at a high resonant frequency, and

measures the force gradient by the amplitude and phase change due to the interaction

between the probe and the sample, which yields the topography of the sample. When

an AFM is operating in the atmosphere, or if the probe tip is situated on a moist or

contaminated layer, it may often stick to the layer due to the surface tension of the tip.

This happens more frequently if the spring constant of the cantilever is smaller.

Because of the small spring constant, it is difficult to bring it back to the original position.

Therefore we need a cantilever with a spring constant which can overcome the surface

tension. The sharper the tip, the more stable operation can be expected because the

surface area of the tip and the surface tension are reduced.


42

Chapter 4. Operation Procedure

43


Once you are ready to use your XE SPM to obtain sample data, you can follow

the procedure described in this chapter to get started. This chapter describes the

basic procedures required for taking any SPM measurement with your XE system.

4-1. Turn on the XE-100

The following components of your XE system need to be turned on. The

order that these are turned on does not matter.

Computer and monitors

Control Electronics

Illuminator

NOTE!

The Control Electronics must be turned on before the XEP Program is started;

otherwise, you will receive a initialization error message and will need to restart XEP.

4-2. XEP Software

The XE-100 is operated by the XEP software. When you click the XEP icon

in C:\Park Systems\Bin or on your desktop, the program will start.


44

NOTE!

The Control Electronics must be turned on before the XEP Program is started;

otherwise, you will receive a initialization error message and will need to restart XEP.

Figure 4-1. XEP User Interface

The XEP user interface is divided into several windows and panels. For a

complete description of each component, refer to the XEP Software Manual.

4-3. Moving the Z and Focus Stages

The Motor Control window (Figure 4-2) contains the Z Stage and Focus

components. These control pads are used to lower or raise the Z Stage and Focus

Stages.

Clicking above the center bar will raise that stage, and clicking below the center

bar will lower it. The speed depends on how far away from the bar you click.


45

NOTE!

The cantilever depiction in the Z Stage pad is not the center bar. Treating it

as the center bar will result in unintended movement of the Z Stage.

Slow

Fast

Slow

Fast

Figure 4-2. Motor Control Window

WARNING!

When the cantilever and the sample are very close, a rapid movement of the Z

Stage may cause the Z Scanner to collide with the sample. This may result in severe

damage to the probe tip, the sample, and/or the scanner itself.

If “Focus Follow” is selected, the Focus stage movement will be synchronized

with that of the Z stage. This is useful for following the cantilever with the optical

microscope.

4-4. Removing the XE Head

During the imaging procedure, some steps may become easier if you remove

the XE Head. Removing and replacing the Head is very easy.

First, confirm that the Head has clearance. If it is too close to the sample,


46

raise the Z Stage. If the Focus Stage is too close to the Head, raise the Focus Stage.

Remove the Head Cable and unlock the dovetail locks on the sides of the Head.

Then, slide the Head out to the right.

Figure 4-3. Removing the XE Head

Replacing the head is as easy as removal: slide it in, engage the dovetail locks,

and reconnect the Head Cable by pushing it in.

4-5. Cantilever Preparation

There are different kinds of cantilevers for use in different modes of operations

and for different samples. The XE System is provided with pre-mounted general

Contact and general Non-Contact cantilevers. See the Cantilever Selection chapter for

more information on cantilever choice.

Cantilevers must be mounted on Chip Carriers before use. Both pre-mounted

and unmounted cantilevers are available. If your cantilever is not mounted onto a Chip

Carrier, you must do so with an adhesive. Cyanoacrylate (superglue) adhesives are

recommended. Place a dab of the adhesive on the Chip Carrier, and use forceps to

place the Cantilever Chip on top of the adhesive. You should allow several hours for

the adhesive to completely dry; otherwise, Non-Contact mode images may be affected.

Once your cantilever is on a Chip Carrier, simply attach it to the Probe Hand,

where it will be held in place by magnets. As shown in Figure 4-4, this can be done by

simply raising the Z Stage until you have enough space to access the Probe Hand. If

this is difficult, you can remove the XE Head for clear access to the Probe Hand.


47

Otherwise, the sample surface or the tip can be damaged.

Figure 4-4. EZ Snap Tip Exchange

There are two holes in a cantilever chip; a round hole, and an elongated slot.

When you overlay the two ruby nodules located on the end of the probe arm with these

holes, the cantilever chip will be attached into place by a magnet, and the position of the

cantilever will be firmly fixed in one position.

Figure 4-5. Probe Hand without and with Cantilever Chip

4-6. Locating the Cantilever

Now that the cantilever has been mounted on the system, it must be found on

the Optical on-axis camera. The view from the Optical Microscope can be seen in the

Vision Panel of XEP or in the XEC software. You can turn on the XEC by clicking the

icon and turn on the Vision panel by clicking the button in XEP. You can click

this button a second time and drag the window to the second monitor for a convenience.

The Vision mode of XEP and the XEC software cannot be opened at the same time.

The camera panning knobs on the XE Stage are used to move the field of view

in the X and Y directions, while the Focus Stage control in the Motor Control Window is

used to adjust the focus.


48

Figure 4-6. Camera Panning Knobs

4-7. Beam Alignment

The AFM obtains an image by monitoring the deflection of a cantilever. Since

this deflection is too tiny to be measured, the actual measurement is made indirectly by

utilizing a laser beam. The laser beam is reflected off the backside of the cantilever and

onto a PSPD (position sensitive photo detector). When the cantilever deflects, the

reflection angle of the laser beam will change, resulting in a change of the location

where the laser beam enters the PSPD. This change is, in general, much greater than

the deflection of the cantilever (usually smaller than a radius of an atom), which makes

the position detection much easier.

There are two major steps in aligning the laser beam on the top of the cantilever.

At first, adjust the laser beam so that it strikes the backside of the cantilever. This

procedure is facilitated by bringing the cantilever relatively close to the sample so that it

is easy to find the laser beam spot when it reflects off of the sample surface.

1. As shown in Figure 4-7, using the two laser beam aligning screws which are

Y X


49

located on the upper part of the XE head, move the laser beam vertically and

horizontally on the LCD monitor.

2. Move the laser beam from the outside area of the cantilever chip to the outer

edge of the chip (from the lower part of the monitor to the upper part

accordingly). Once the laser beam reaches the cantilever chip, you will be able

to see the reflected laser beam light at the chip’s edge.

3. After the laser beam touches the edge of the cantilever chip, adjust the laser

beam (by moving horizontally on the LCD monitor) to focus it on the cantilever.

4. Bring the laser beam to the tip of the cantilever.

Figure 4-7. Laser beam alignment on the cantilever

Secondly, place the reflected laser beam on the center of the PSPD as follows.

1. Adjust the steering mirror located on the front side of the XE head so that the

path of the reflected laser beam will reach the PSPD as shown in Figure 4-8.

Generally the “A+B” value will be more than 2V when the alignment is

optimized (the A+B value indicates the total intensity of the laser beam

detected by the PSPD). When the cantilever surface is not coated with metal,

the “A+B” value is closer to 1V because of the difference in surface reflectivity.

2. To position the laser beam on the center of the PSPD, adjust the knobs located


50

on the front of the scanner head (see Figure 4-7) so that the “A-B” value is

smaller than 0.5V (the A-B value indicates the difference in the laser beam

intensity detected in the upper half and the lower half of the PSPD cell). During

imaging, this value is related to the deflection of the cantilever. When the above

alignment condition is met, there will be an increase in the intensity of the small

red circle on the PSPD display (see Figure 4-8).

Figure 4-8. Laser beam alignment display in XEP

3. Even if the “A-B” value is within the acceptable range, if the “A+B” value is too

small, then it may be difficult for the laser beam to approach the center of the

PSPD. It should be done first to get a proper “A+B” value before adjusting the

“A-B”. If the “A+B” value is too small and not adjusted to ~2V(~1V for uncoated

Z scanner

X-Y scanner


51

cantilevers), then the laser beam path depicted in Figure 4-8 is not optimized.

In order to maximize the “A+B” signal, try to adjust each of the mirror

positioning knobs on the front of the scanner head one at once. Adjust one of

the knobs until a peak in the “A+B” value is observed, and then follow the same

process with the other knob. Try fine tuning these knobs individually, until the

“A+B” value increases to the appropriate range. If this procedure does not work,

other trouble shooting steps may be required. For SLD head, SLD detector

card is used to show a laser beam very brightly - like a piece of paper - check

to make sure that the laser beam being reflected from the cantilever strikes the

fixed mirror, located in the rear of the Head, after it passes through the hole in

the center of the probe arm. If you cannot locate the laser beam properly with

maximum turns of the mirror adjusting knobs, it may be that either the

cantilever is not properly placed, or the cantilever arm is broken. If the

cantilever is broken, you can easily see this on the LCD monitor. In this case,

you should exchange the broken cantilever for a new one. Even if the

cantilever is not broken, it is still a good idea to try another cantilever before

proceeding to troubleshoot other potential alignment problem sources. Also,

check to ensure that the cantilever chip is properly mounted at the end of the

scanner arm and is being firmly held in place with the backside of the cantilever

facing upwards.

4-8. Sample Preparation

The sample loading procedure for using the magnetic sample holder is as follows.

1. Raise the Head and the Focus stage high enough that you have easy access

to the sample holder.

CAUTION!

If the Head and the Focus stage are not rasied high enough, the sample or the

cantilever may be damaged.

2. Fix the sample on a sample disk using an adhesive. Hard-setting adhesives


52

such as cyanoacrylate glues are recommended; otherwise, the sample may

move significantly during the imaging procedure.

3. Place the disk on the magnetic sample holder. The magnet will keep the

sample disk in place.

4-9. Software Configuration

The hardware setup has been completed. You must now determine several

software settings.

Turn off the XE Head by clicking the button. This will enable Part

Selection. Open the Part Selection dialog by clicking the button. See the “Set up

Scanner Mode” chapter for more information on the Z Scanner and XY Scanner settings.

Change the Cantilever and Head Mode to reflect which type of measurement you wish

to make.

Turn the head back on.

Open the Input Configuration dialog by clicking the button. Select the

input channels required for your experiment. For more information on which input

channels are needed for your experiment, consult your Mode Manual or the “AFM in

Contact Mode,” “Lateral Force Microscopy,” “AFM in Non-Contact Mode,” or “Dynamic

Force Microscopy” chapters.

4-10. Frequency Sweep

The hardware and software setup has been completed. You must now

determine the Set Point which is reference signal for Z servo. In Contact mode, you can

skip this section since the Set Point is automatically selected by setting the cantilever

type. In Non Contact mode, you have to follow the step below: Input near 13nm on the

Amplitude text field on Scan Control Window of XEP. Refer to the Figure 4-9. Click the

NCM ASetup button . Check if the selected frequency is within the

resonant frequency of the cantilever and if the amplitude of the peak is near 13 nm.

If needed to change those parameters, zoom out until the X-axis grid is

100kHz per division. Select the resonant frequency of the cantilever by clicking the

desired frequency on the mouse. Then the red cross hair will move its position to the


53

selected point and zoom in until you can see the peak well like Figure 4-10. Adjust the

Drive% until the amplitude of the peak becomes near 13nm. You can change the

amplitude depending on your sample by adjusting Drive %.

Figure 4-9. Amplitude Setting for Frequency Sweep


54

Figure 4-10. Frequency Sweep Window

4-11. Approach

The cantilever must be placed near the sample surface in order to measure it.

This process is not very simple, as the distance that the cantilever must be moved is on

the order of centimeters, and the required precision is on the order of micrometers.

In order to position the cantilever so that it is close to the sample, place the

mouse pointer at the lower edge of the Z stage pad button and click the left mouse

button. This will move the Z stage down very quickly. Visually monitor the cantilever,

and stop moving the Z stage when the distance between the cantilever and the sample

surface is several millimeters.

WARNING!

If the Z stage is lowered too fast, the cantilever may “crash” into the sample

surface. Such a forceful interaction may break the probe tip, damage or destroy the

sample, and/or seriously damage the Z scanner.


55

Uncheck the Focus Follow box, and move down the Focus Stage until you

locate the sample surface. Use the Sample Stage knobs to locate a point of interest

that you wish to image.

CAUTION!

If the cantilever is too far from the sample surface, it may be very difficult to

adjust the focus. In this case, bring the cantilever closer to the surface with the Z stage

control pad.

Once the cantilever is above the correct location, finish the approach. Slowly

lower the Z stage until the cantilever starts to appear faintly.

CAUTION!

When lowering the cantilever, do so very slowly to avoid a potential collision

with the sample.

Click the “Approach” button . All possible software selections will be

restricted until the completion of a system controlled tip approach except for the “Stop”

button .

NOTE!

It might take a long time to complete the Approach process, because the Z

stage moves only a few microns per step. Therefore, to minimize the time required to

complete tip’s approach, the cantilever must first be brought very close to the sample

surface. In order to decrease the approach time, practice using the optical microscope

to bring the probe very close to the sample surface.

After an Auto Approach is completed, several parameters in the “Scan Control”

window should be adjusted to minimize noise and artifacts from acquired images.


56

Figure 4-11. Scan Control Window

Input a value for the “Scan Size.” This will be the size of your image. Your

XY Scanner will begin moving back and forth by this amount, and this movement may

be visible on the Vision panel or XEC.

Select a “Scan Rate.” Keep in mind that the speed of the tip will be (2 * Scan

Size) / (Scan Rate), and too high of a speed will result in tip and sample damage.

Observe a Trace Control Window. If none are open, open one by clicking the

button. Select the Topography input.

Adjust the “Z Servo Gain” field until the trace line is stable. If this is difficult, try

lowering the Scan Rate.


57

Figure 4-12. Proper Gain (top); Noise from Excessive Gain (bottom)

Once the trace line is stabilized, click the “Image” button . Now the

measurement will begin.

4-12. Scan parameter Definitions

An abridged list of the parameters in the Scan Control Windows follows. For

a complete list, see the XEP Software Manual.

Repeat: If selected, the system will continue taking images in the same

location after finishing acquisition of the previous image.

Two way: Successive images will be acquired by alternating the slow scan

direction.

X,Y: The fast scan direction can be chosen to be either the X or Y axis.

Slope: The slope of the tip/sample interaction can be adjusted by software.

Scan OFF: The X-Y scanner is stopped while the Z scanner continues to


58

operate and maintain feedback conditions.

Offset X, Y: Specifies the center of the scan area in a relative coordinate

system with (0,0) being the center of the X-Y scanner.

Rotation: Allows the direction of scanning to be changed within the range of –

45˚~ 45˚.

Z Servo: Select Z scanner feedback on/off. The Z Servo must be on for most

SPM modes.

Z Servo Gain: Controls the sensitivity of the Z scanner feedback loop. If this

value is too high, the Z scanner will oscillate, producing noise in the image or

line scan. If it is too small, then the SPM probe will not track the sample

surface properly.

Set point: In Contact mode, specifies the force that will be applied by the end

of the tip to the sample surface when the system is in feedback.

In Non-Contact mode, the set point represents the amplitude of tip oscillation.

Tip Bias: Controls the voltage applied to the tip when EFM or C-AFM modes

are used.

Chapter 5. Set up Scanner Mode

59


5-1. XE-100 Scanner Configuration

The XE-100 scanner is separated into an X-Y scanner and a Z scanner instead

of a single piezoelectric tube scanner used in most other SPM. The X-Y scanner moves

the sample in horizontal direction for the range you want to image. The Z scanner

moves the cantilever in vertical direction to trace the morphology of the sample. These

independent movements of the X-Y direction and the Z direction are combined to make

a three-dimensional image.

The XE-100 can be used over a broad range of scan sizes. The High Voltage

mode is used to investigate large areas, while the Low Voltage mode is commonly used

to acquire high resolution scans of small scan areas down to atomic scales. This

chapter offers detailed description about how to set up these two modes as well as their

functions.

5-2. Select Scanner Mode

When selecting between High and Low Voltage mode, it is important to

consider several factors including the surface’s roughness, structure fluctuation, and the

size of the scan area. The proper mode selection will allow you to acquire the best

image. Although the High Voltage mode is most commonly used, the Low Voltage mode

should be used in cases where you want to investigate a very small area, a very smooth

surface, or possibly atomic level structure.

Both the XY Scanner and the Z Scanner can change voltage modes

independently.


60

1. Turn off the beam by clicking the beam On/Off icon in the Tool bar

2. Open the “XEP Part selection” window by clicking the ‘Select Parts’ icon

and then select HIGH or LOW.

Figure 5-1. Select Scanner mode

5-2-1. High voltage mode

In the High voltage mode, two measurement types, ‘Closed Loop’ and ‘Open

Loop’, are possible depending on the status of the XY Servoscan. ‘Closed loop’ refers to

when XY Servoscan is “ON” and ‘Open loop’ is when XY Servoscan is “OFF”.

In general, piezoelectric materials display nonlinear behavior in response to an

applied voltage. Therefore, the scanner, which is made of a piezoelectric material

displays nonlinearity and hysteresis (Refer to Chapter 1). When the scanner’s range of

motion increases, nonlinearity and hysteresis can be calibrated by means of hardware

corrections.

In the XE system, detectors are used to measure the actual movement of the

XY or Z scanners. This information is compared with the desired movement, and

discrepancies are corrected for by modifying the voltage applied to the scanner. This

ServoScan system effectively eliminates the nonlinearity of the piezoelectric actuators,

but also introduces noise that becomes significant as the signal (i.e. scan size)

becomes very small.


61

Figure 5-2. XY Servoscan is ON

XE-100 scanners, both X-Y scanner and Z scanner, have a maximum range of

movement. X-Y scanner’s maximum movable range is 50µm and Z scanner’s maximum

movable range is 12µm. In the High voltage mode, the applied voltage allows the

scanner to reach this maximum range.

Figure 5-3 depicts the maximum XY range as a solid gray-shaded square. The

area outside of this square cannot be observed. For example, if the scanner’s maximum

range is 50 µm, it is not possible to scan area A, even though it has the same scan size

as area C (15 µm). Area A’s offset (the black midpoint) extends A’s range over the

maximum range of the scanner. Area C, however, is possible to scan. Also, although B

and D have the same size and the same offset, it is impossible to scan area B which

extends over the maximum range due to its different angle of rotation. Whenever the

user enters an “excessive range” like A and B, the scan range will be changed

automatically to an observable area that falls within the scanners maximum allowable

range.

Figure 5-3. Scanner’s observable area


62

5-2-2. Low voltage mode

Aside from the High voltage mode, which enables investigation of a wide range

of surface structures, from several micrometers to the maximum range the scanner can

move, the Low voltage mode can investigate tiny scales and very fine structure with

high resolution. In the Low voltage mode the resolving power increases, but the

maximum allowable scan range decreases. For the XE-100, the maximum range of the

XY and the Z scanner in the Low voltage mode is reduced to approximately 1/10th and

1/7th respectively of that in the High voltage mode.

In the Low voltage mode, the nonlinearity and hysteresis is less than in the

High voltage mode because the X-Y scanner’s moving distance is much smaller. Also,

the detectors used for ServoScan are not much more accurate on such a scale, and the

noise introduced by ServoScan on this small scale is significant. Therefore, it is

recommended that you turn off XY ServoScan when operating in Low voltage mode.

Figure 5-4. XY Servoscan is OFF

The lateral resolution of an image acquired by AFM is calculated by dividing

the scan size by the pixel size. If you measure a 10 µm square image with 256 256

pixels, the lateral resolution is 10 µm/256 = 39.1 nm. This means the size of one data

point in the 10 µm square image is 39.1 nm. Even though you can increase an image’s

pixel count to get higher lateral resolution, it will take a much longer time to acquire an

image. Another solution to get higher resolution data is to decrease the scan size. If you

measure a 100 nm image with 256 256 pixels, you can get a lateral resolution of 3.91 per data point. Therefore, when you want to measure fine structure, it is desirable to

reduce the scan size.


63

Also, the scanner’s ability to make elaborate motions is another factor that

influences the lateral resolution. The scanner expands or shrinks in proportion to an

applied voltage. Hence, you can manage the scanner’s motion more precisely by

dividing the applied voltage into smaller units in the DAC (digital-to-analog converter).

This is effectively done by operating in Low voltage mode.

The XE-100 system uses a 16-bit DAC for controlling scan movement in X and

in Y. A 12-bit DAC is used for determining offset and scale so that the scanner’s motion

and position can be controlled to a maximum of 228

bits. When an applied voltage that

can make the scanner move 50µm is controlled using a simple 16-bit DAC, the lateral

resolution is 50 µm / 216

= 7.6

. As mentioned above, the High voltage mode will parse

the allowable 16 bits over the scanner’s maximum range. On the other hand, in Low

voltage mode, the scanner’s maximum motion is limited, and the 16-bit DAC is then

applied to a much smaller range thus offering higher lateral resolution. This principle

can be carried over to the macro-scale for easier interpretation. For example, in

measuring a distance of 10cm, a 50cm ruler would make an adequate measurement. To

measure a 1cm distance, however, a 5cm ruler would be more sensible. The XE-100’s

X-Y scanner ratio of high voltage to low voltage is set to 1/10th. Therefore, the XY

scanner’s lateral resolution can be improved by a factor of 10 (5 µm / 216

= 0.76

resolution in Low voltage mode). Thus, Low voltage mode can provide more detailed

and better control than the High Voltage Mode.

5-2-3. Z scanner Range

The resolution of the Z scanner can be adjusted by limiting the Z scanner’s

motion range in addition to selecting between the High and Low voltage mode.

The number entered in the text box labeled Z scanner Range can be regarded

as a proportionality factor related to the Z scanner’s maximum movable range in the

user selected mode (High or Low voltage). Basically, if the Z scanner Range is 1.0, then

the Z scanner can move through a 12µm range in the High voltage mode and a 1.7µm

range in the Low voltage mode. However, if the Z scanner Range is 0.5, then the Z

scanner’s maximum movable range would be reduced to 6µm and 0.85µm in the High

and Low voltage mode, respectively. This adjustment that effectively reduces the Z

scanner’s maximum range results in an increase in vertical resolution. The vertical

resolution, which is 1.8

in the High voltage mode and 0.25

in the Low voltage mode

will be improved to 0.9

and 0.125

respectively when the Z scanner range is set to

0.5. To use the Z scanner Range feature effectively, two points should be considered:

the z-scanner’s available maximum range and the vertical resolution. Before adjusting


64

the scanner range, consider at first the overall height variation of the sample surface. Of

course, this height difference must not be greater than the Z scanner’s maximum

available range. For example, if a sample has a 3µm height difference, it cannot be

measured in the Low voltage mode since the Z scanner’s maximum range will be only

1.7µm. Secondly, the smallest height difference on the sample surface should be

greater than the vertical resolution. For example, it is not possible to distinguish atomic

scale steps with height differences of 1 in the High voltage mode which has a vertical

resolution of 1.8 . Therefore, it should be changed to Low voltage mode. Also,

changing the Z scanner Range from 1.0 to 0.5 will produce even better vertical

resolution. If the Z scanner Range is set to 0.5, the height of 1 would be indicated by

eight 0.125 scaled pixels. When the Z scanner Range is set at 1.0, however, a 1

step would be indicated by only four 0. 25 scaled pixels.

Chapter 6. AFM in Contact Mode

65


6-1. Principle of Contact Mode AFM

The AFM (Atomic Force Microscope) is an instrument that is used to study the

surface structure of a sample by measuring the force between atoms.

At the lower end of the Z scanner, there is a cantilever of very tiny dimensions:

100 µm long, 10 µm wide and 1 µm thick, which is manufactured by means of micro-

machining techniques. At the free end of the cantilever, there is a very sharp cone-

shaped or pyramid-shaped tip. As the distance between the atoms at this tip and the

atoms on the surface of the sample becomes shorter, these two sets of atoms will

interact with each other. As shown in Figure 6-1, when the distance between the tip and

the surface atoms becomes very short, the interaction force is repulsive due to

electrostatic repulsion, and when the distance gets relatively longer, the interatomic

force becomes attractive due to the long-range van der Waals forces.

This interatomic force between atoms can bend or deflect the cantilever, and

the amount of the deflection will cause a change in the reflection angle of the beam that

is bounced off the upper surface of the cantilever. This change in beam path will in turn

be detected by the PSPD (Position Sensitive Photo Detector), thus enabling the

computer to generate a map of the surface topography.


66

Figure 6-1. Relation between the force and the distance between atoms

In contact mode AFM the probe makes “soft contact” with the sample surface,

and the study of the sample’s topography is then conducted by utilizing the repulsive

force that is exerted vertically between the sample and the probe tip. Even though the

interatomic repulsive force in this case is very small, on the order of 1~10 nN, the spring

constant of the cantilever is also sufficiently small (less than 1 N/m), thus allowing the

cantilever to react very sensitively to very minute forces. The SPM is able to detect

even the slightest amount of a cantilever’s deflection as it moves across a sample

surface. Therefore, when the cantilever scans a convex area ( )of a sample, it will

deflect upward, and when it scans a concave area ( ), it will deflect downward. This

probe deflection will be used as a feedback loop input that is sent to an actuator (z-

piezo). In order to produce an image of the surface topography, the z-piezo will maintain

the same cantilever deflection by keeping a constant distance between the probe and

the sample – if the cantilever tip reaches a lower area, the Z actuator will move the

cantilever down by that distance, or back up if the cantilever’s tip begins rising.

6-2. Contact mode setup

To use contact mode AFM, select the appropriate Head mode as follows:

1. Turn off the beam by clicking the “Beam On/Off “ button in the Tool bar.

2. Once the beam is off, set the Head mode to C-AFM after clicking the


67

“Select Parts” button .

3. Turn on the beam by clicking the “Beam On/Off” button .

Figure 6-2. Contact mode AFM setup


Selecting the appropriate probe is a critical aspect of using AFM. Choosing a

probe means determining the combination of a tip, which interacts with sample surface

atoms, and a cantilever, which deflects depending on the interatomic forces and

quantifies the deflection. Generally, the upper surface of a cantilever is coated with a

metal such as gold (Au) or aluminum (Al). This coating, which enhances the surfaces

reflectivity, has a thickness of about 1000 . There are several types of cantilevers that

vary in material, shape, softness (represented by the spring constant), intrinsic

frequency, and Q-factor. The type of cantilever selected is primarily determined by the

measurement mode. As mentioned in Chapter 3, a “soft” cantilever is used for contact

mode AFM. Typically, such cantilevers are made of silicon and have a spring constant

less than 1~3 N/m. With such a low spring constant, the contact mode cantilever is

sensitive to extremely small forces, and it will bend more significantly than a cantilever

with a higher spring constant when exposed to an equal force. This allows the AFM to

measure even extremely tiny structures.

Figure 6-3 shows the SEM image of a cantilever commonly used for contact

mode, the NSC36 series. To improve the beam reflectivity, the upper surface of the

cantilever (the opposite side of the tip) is coated with aluminum.


68

Figure 6-3. SEM image of the shorter cantilevers (A, B, C) from a chip of the

NSC36 series

Figure 6-4 shows the detailed standardized gauge of the NSC36 series chip.

Altogether, this chip contains three cantilevers, all with different spring constants.. If the

unmounted cantilevers are purchased separately, you may choose set of cantilevers

A,B,C.

Figure 6-4. Silicon chip of the NSC36 series has 3 rectangular cantilevers

Table 6-1 shows the specification for the three cantilevers in the NSC36 series.


69

Table 6-1. NSC36 Series Cantilever Specifications

M in Ty pic al M ax Mi n Ty pi c al M ax M in T y pic al M ax

Lengt h, l ±5, µm 110 90 130

w idt h, w ±3, µm 35 35 35

Th ic k nes s, µ m 0 .7 1 1. 3 0. 7 1 1. 3 0. 7 1 1.3R es onant frequ enc y,

k H z 65 105 150 95 155 230 50 75 105

Fo rc e c ons ta nt, N /m 0 .3 0. 95 2. 5 0. 5 1 .75 5 0. 2 0.6 1.5

A B CC ant il ev er T y pe

6-4. Scanner Setup

Depending on the roughness of the sample or the measurement range, it is

necessary to select either the High voltage mode or the Low voltage mode.

In general, High voltage mode is selected, but when measuring small areas, or

when imaging samples with a low degree of roughness, switching to the Low voltage

mode may produce a higher resolution image.

Figure 6-5. Contact AFM Part Selection

To change the voltage mode, as is the case with a change to contact mode,

click the button to open the “XEP Part selection” box as shown above, and choose

“High” or “Low” in the “XY voltage mode” and/or the “Z voltage mode”.

See the “Set up Scanner Mode” chapter for more information on scanner setup.


70

6-5. Measurement Procedure

The measurement procedure hereafter is the same as in Chapter 4. Please

refer to Chapter 4.

Chapter 7. Lateral Force Microscopy

71

Chapter 7. Lateral Force Microscopy (LFM)

7-1. Principle of Lateral Force Microscopy (LFM)

The principle of Lateral Force Microscopy (LFM) is very similar to that of

Contact mode AFM. Whereas in contact mode we measure the deflection of the

cantilever in the vertical direction to gather sample surface information, we measure the

deflection of the cantilever in the horizontal direction in LFM. The lateral deflection of the

cantilever is a result of the force applied to the cantilever when it moves horizontally

across the sample surface, and the magnitude of this deflection is determined by the

frictional coefficient, the topography of the sample surface, the direction of the cantilever

movement, and the cantilever’s lateral spring constant. Lateral Force Microscopy is very

useful for studying a sample whose surface consists of inhomogeneous compounds. It

is also used to enhance contrast at the edge of an abruptly changing slope of a sample

surface, or at a boundary between different compounds.

Since the LFM measures the cantilever movement in the horizontal direction as

well as the vertical one to quantitatively indicate the surface friction between the probe

tip and the sample, it uses a PSPD (position sensitive photo detector) that consists of

four domains (quad-cell), as shown in Figure 7-1.


72

Figure 7-1. Quad-cell PSPD

Generally, in AFM, to measure the topography of a sample surface, the “A-B”

signal is used. This signal is related to the difference between the upper cells (A+C) and

the lower cells (B+D) of the PSPD.

Topographic information = (A+C)-(B+D)

The LFM signal, which is related to the change in the surface friction on a

sample surface, measures the deflection of the cantilever in the horizontal direction and

can be represented as the difference in the signals recorded in the right cells (A+B) and

the left cells (C+D).

Frictional information = (A+B) – (C+D)

C

D B

A


73

Figure 7-2. AFM and LFM signal

Figure 7-2 (a) shows a surface structure with a centrally located step with low,

smooth areas on either side. The flat part on the left contains a domain with a relatively

high frictional coefficient. Profile b indicates the cantilever’s deflection as it encounters

topographic features as well as different frictional coefficients as it scans from left to

right. Profile c is an AFM image of the surface topography and structure; it is

represented by the change in the vertical deflection of the cantilever which does not

include the horizontal deflection. Profile d and Profile e show the LFM signal which

indicates the horizontal deflection of the cantilever. When scanning left-to-right, the

surface structure of a sudden peak will instantaneously twist the cantilever to the right.

This results in a lateral force signal with a convex shape as seen in Figure 7-2 (d) .

The opposite occurs when the probe encounters a sudden downward step as depicted

at location . The region between and indicates an area on the sample surface

AFMSignal

LFMSignal

LFMSignal

a)

b)

c)

d)

e)

Scan Direction


74

where there is a material with a higher surface frictional coefficient compared to the

surrounding area. There are no distinguishable surface features that will allow the user

to differentiate this region utilizing the topography signal. Even though the topographical

information is the same between and , there will be a conspicuous difference

noticeable in the LFM signal. When the cantilever scans this area from left to right, an

increase in relative friction will cause it to tilt to the right, thus producing an increase in

the LFM signal.

Figure 7-2 (e) shows the LFM signal when the scan direction is reversed. If the

cantilever scans direction as indicated by the arrow, there will be no change in the LFM

signal at region and which are related to the topographic features of the sample

surface. However, when the scan direction is reversed, the cantilever will now tilt to the

left in the area where the frictional coefficient between and is larger, yielding a

decrease in the LFM signal in this area.

Considering the simple comparison described above, the LFM result contains

the surface frictional information as well as the surface topographical information.

Hence, when you analyze the result of the LFM measurement, it is necessary to

distinguish the information due to difference in the frictional coefficient from the

information due to the change in the sample surface topography by taking the AFM

image into account.

7-2. Conversion to LFM

As mentioned above, since lateral force mode is an extension of contact mode,

the Head mode will be set to “Contact mode”.

1. Turn off the beam switch by clicking the “Beam On/Off “ button in the Tool

bar.

2. Once the beam is off, set the Head mode to C-AFM by clicking the “Select

Parts” button .

3. Turn on the beam by clicking the “Beam on/off” button .


75

Figure 7-3. Conversion to LFM


The Lateral Force Microscope (LFM) measures the horizontal deflection of

cantilever under the same conditions as the contact AFM. Therefore, LFM uses the

same type of cantilever as is used for contact AFM. Please refer to Chapter 6, section 3

“Cantilever selection” in contact mode.


You can obtain an LFM image and a topography image simultaneously when

you measure in contact mode. If you press the ”Input Config” button , the “Input

Configuration” window will appear as shown in Figure 7-4 below. You can take an LFM

image if you selected ‘Lateral Force’ option in this “Input Configuration” box. When the

selected input signal, the ‘Lateral Force’, does not appear, press the “Setup”

button which will open the “Select Input” window. There you can choose ‘Lateral Force”.

Also, LPF, Flattening, and Scan Directions (forward and/or backward) should be

selected based on the sample. How to set them is recommended to consult the

software manual for XEP.


76

Figure 7-4. Setup for LFM mode

The procedure to measure in the ‘Lateral Force’ mode is the same as that in

contact mode. The measurement method hereafter can be consulted by Chapter 4.

Chapter 8. AFM in Non-Contact Mode

77


8-1. Principle of Non-contact Mode AFM

There are two major forces, the static electric repulsive force and attractive force,

existing between atoms a short distance apart: The static electric repulsive forces (Fion)

between ion cores and the static electric attractive forces (Fel) between valence electrons

and ion cores. When the distance between the atoms at the end of the probe tip and the

atoms on the sample surface becomes much shorter, the repulsive forces between them

become dominant, and the force change due to the distance change becomes greater and

greater. Therefore, contact AFM measures surface topography by utilizing the system’s

sensitive response to the Repulsive Coulomb Interactions that exist between the ion cores

when the distance between the probe tip and the sample surface atoms is very small.

However, as shown in Figure 8-1, when the distance between the probe tip and the

sample atoms is relatively large, the attractive force Fel becomes dominant. Ion cores

become electric dipoles due to the valence electrons in the other atoms, and the force

induced by the dipole-dipole interaction is the van der Waals Force. Non-contact AFM

(NC-AFM) measures surface topography by utilizing this attractive atomic force in the

relatively larger distance between the tip and a sample surface.


78

Figure 8-1. Concept diagram of Contact mode and Non-Contact mode

Figure 8-1 compares the movement of the probe tip relative to the sample surface

for images being acquired between in contact AFM and in non-contact AFM. Contact AFM

uses the “physical contact” between the probe tip and the sample surface, whereas non-

contact AFM does not require this contact with the sample. In Non-Contact mode, the force

between the tip and the sample is very weak so that there is no unexpected change in the

sample during the measurement. Therefore, Non-Contact AFM is very useful when a

biological sample or other very soft sample is being measured; the tip will also have an

extended lifetime because it is not abraded during the scanning process. On the other

hand, the force between the tip and the sample in the non-contact regime is very low, and

it is not possible to measure the deflection of the cantilever directly. So, Non-Contact AFM

detects the changes in the phase or the vibration amplitude of the cantilever that are

induced by the attractive force between the probe tip and the sample while the cantilever

is mechanically oscillated near its resonant frequency.

A cantilever used in Non-Contact AFM typically has a resonant frequency between

100 kHz and 400 kHz with vibration amplitude of a few nanometers. Because of the

attractive force between the probe tip and the surface atoms, the cantilever vibration at its


79

resonant frequency near the sample surface experiences a shift in spring constant from its

intrinsic spring constant ( ok ). This is called the effective spring constant (keff), and the

following equation holds:

'Fkk oeff −= (1)

When the attractive force is applied, keff becomes smaller than k0 since the force

gradient F’ (=∂F/∂) is positive. Accordingly, the stronger the interaction between the

surface and the tip (in other words, the closer the tip is brought to the surface), the smaller

the effective spring constant becomes. This alternating current method (AC detection)

makes more sensitive responds to the force gradient as opposed to the force itself. Thus,

it is also applied in such techniques as MFM (Magnetic Force Microscopy) and DFM

(Dynamic Force Microscopy).

A bimorph is used to mechanically vibrate the cantilever. When the bimorph’s drive

frequency reaches the vicinity of the cantilever’s natural/intrinsic vibration frequency (f0),

resonance will take place, and the vibration that is transferred to the cantilever becomes

very large. This intrinsic frequency can be detected by measuring and recording the

amplitude of the cantilever vibration while scanning the drive frequency of the voltage

being applied to the bimorph. Figure 9-2 displays the relationship between the cantilever’s

amplitude and the vibration frequency. From this output, we can determine the cantilever’s

intrinsic frequency.

Figure 8-2. Resonant frequency

On the other hand, the spring constant affects the resonant frequency (f0) of the

cantilever, and the relation between the spring constant (k0) in free space and the resonant

f0 frequency

amplitude


80

frequency (f0) is as in Equation (2).

m

kf 0

0 = (2)

As in Equation (1), since keff becomes smaller than k0 due to the attractive force,

feff too becomes smaller than f0 as shown in Figure 8-3 (a). If you vibrate the cantilever at

the frequency f1 (a little larger than f0) where a steep slope is observed in the graph

representing free space frequency vs. amplitude, the amplitude change ( A) at f1 becomes

very large even with a small change of intrinsic frequency caused by atomic attractions.

Therefore, the amplitude change measured in f1 reflects the distance change ( d) between

the probe tip and the surface atoms.

If the change in the intrinsic frequency resulting from the interaction between the

surface atoms and the probe or the amplitude change ( A) at a given frequency (f1) can

be measured, the non-contact mode feedback loop will then compensate for the distance

change between the tip and the sample surface as shown in Figure 8-3 (b). By maintaining

constant cantilever’s amplitude (A0) and distance (d0), non-contact mode can measure the

topography of the sample surface by using the feedback mechanism to control the Z

scanner movement following the measurement of the force gradient represented in

Equation (1).

f1

A0

∆∆∆∆A=A0-A1

A1

amplitude

frequency

feff f0


81

Figure 8-3. (a) Resonant frequency shift (b) Amplitude vs Z-feedback

8-2. Non-contact mode setup

The non-contact mode setup can be done easily by selecting NC-AFM as the

Head mode, similar to the setup for contact mode explained in Section 2 of Chapter 6.

1. Turn off the beam switch by clicking the “Beam On/Off” button in the Tool bar.

2. Once the beam is Off, set the Head mode to NC-AFM by clicking the “Select

Parts” button .

3. Turn on the beam by clicking the “Beam On/Off” button .


82

Figure 8-4. Non-contact mode AFM setup

8-3. Resonant Frequency setup

Once the Head mode is selected as NC-AFM, turn on the beam by clicking the

“Beam On/Off” button . The system will then automatically find the resonant frequency.

When all selections are completed, click the “OK” button .

Besides the method of turning the beam on and off, you can access the

Frequency Sweep dialog by clicking the NCM ASetup button in the Scan Control Window.

Figure 8-5. Resonant Frequency setup in Non-Contact Mode

When the “NCM Frequency Setup” window opens, you can manually select the


83

resonant frequency as follows.

1. If the ‘Refresh’” button or ‘Zoom Out’ button is clicked, one unit

on the X-axis represents 5 kHz as shown above.

2. Select the resonant frequency as follows: At first, press the ‘Refresh’ button

and then the graph of frequency vs amplitude will appear. Press the

‘Refresh’ button while adjusting the drive % to make the strongest

peak fall within 20nm in the y-axis. After adjusting the height of the peak, press the

(Zoom) “In” button until the x-axis unit is 1kHz/div.

3. After positioning the mouse pointer on the slope just to the right hand side of the

strongest peak as shown in Figure 8-5, click there with the left mouse button and a

‘+’ sign will appear. The location of the ‘+’ sign corresponds to the selected

frequency f1 at which the cantilever will vibrate in non-contact mode. After

positioning the mouse pointer on the red horizontal line, move this red line up and

down while holding the left mouse button; this will allow you to change the set

point value. In general, make the set point just higher than half of the peak height,

and press the “OK” button once to enter the selection.

The value of the drive amplitude(%) and set point can also be changed in the

“Scan Control” window.

8-4. Cantilever selection

The non-contact mode cantilever has a relatively large frequency since the non-

contact mode use the vibrating cantilever method which enables to measure the force

gradient by the amplitude and phase change due to the interaction between the probe and

a sample surface. Figure 8-6 shown below is a SEM image of a typical non-contact mode

cantilever, the PPP-NCHR series. The upper surface of the cantilever (the opposite side of

the tip) is coated with aluminum (Al) to enhance the beam reflectivity.


84

Figure 8-6. SEM image of ULTRASHARP silicon cantilever (the PPP-NCHR series)

Figure 8-7 shows the standard dimensions of the NCHR series chip. The

thickness of the chip is 0.4 mm, and a rectangular shaped cantilever is at the end of the

chip. Table 8-1 lists the specifications for this cantilever. The non-contact mode cantilever

has a thickness of about 4 , and the spring constant is very large (42N/m) relative to that

of a contact mode cantilever.

Figure 8-7. Silicon chip of the NCHR series has 1 rectangular cantilever

Table 8-1. NCHR series Cantilever Specifications

Cantilever

Thickness, µm

Resonant

Frequency, kHz

Force Constant,

N/m

Cantilever

Type

Cantilever

Length,

l ± 5, µm

Cantilever

Width,

w ± 3, µm min typical max min typical max min typical max

A 125 30 3.0 4.0 5.0 204 330 497 10 42 130


85

8-5. Scanner setup

Before measuring a sample surface, you first need to select either the High

voltage mode or the Low voltage mode, depending on the roughness of the sample and

the size of the measurement area.

In general, the High voltage mode is selected, but to measure fine features on

samples with a low surface’s roughness, the Low voltage mode is used. Changing the

voltage mode was already introduced in Chapter 5.

Click the “Select part” button to open the “XEP part selection” box as below,

and choose “High” or “Low” for the “XY Voltage mode” and/or the “Z Voltage mode”.

Figure 8-8. Non-contact AFM setup and voltage mode selection


The measurement procedure hereafter is the same as in Chapter 4. Please refer

to Chapter 4.


86

Chapter 9. Dynamic Force Microscopy(DFM)

87

Chapter 9. Dynamic Force Microscopy (DFM)

9-1. Principle of Dynamic Force Microscopy

Dynamic Force Microscopy (DFM) is very similar to Non-contact mode AFM in

many ways such as the applied force and the measurement principle. Before you read this

chapter, please read carefully “Chapter 8 Non-contact Mode measurement”.

DFM is a hybrid of the two most fundamental measurement methods, represented

by contact mode and non-contact mode. In LFM, the cantilever vibrates in free-space in

the vicinity of the resonant frequency like in non-contact mode. At the same time, since the

vibrating cantilever gets very close to the sample surface, it taps the surface repeatedly,

and the tip “contacts” the sample surface as in contact mode.

If you measure the amplitude of vibration of the cantilever used in DFM while

changing the frequency, as shown in Figure 9-1, there appears a special frequency where

the amplitude resonates and amplifies greatly. This is called the intrinsic frequency (f0).


88

Figure 9-1. Resonant frequency

DFM uses the non-contact mode feedback circuit with keeping the vibrating

frequency (f1) a little bit lower than the resonant frequency while oscillating in free-space.

Then, as the tip is lowered, the real spring constant reduces due to the attractive van der

Waals force which becomes larger as the tip comes closer to the sample surface, as

shown in Figure 9-2 (a). Therefore the resonant frequency changes to effective

frequency(feff) in non-contact regime and the amplitude at the frequency f1 increases by

A. Since the amplitude increases by A, the non-contact mode feedback circuit decreases

the distance between the tip and the sample surface by d, indicated in the graph of

vibration amplitude vs tip-sample distance and z-feedback as shown in Figure 9-2 (b) (This

part was explained in detail in Chapter 8, so please refer to Chapter 8, section 1).

Therefore, the vibrating cantilever, which is oscillating above the sample, approaches the

sample almost in contact or in collision with the surface. This method, keeping intermittent

contact between the sample surface and the vibrating cantilever is called Dynamic force

microscopy (DFM).

Similar to the initial approach of making contact with the sample, while scanning,

larger amplitude reduces the distance between the tip and sample, and smaller amplitude

increases the distance depending on the surface roughness to determine the surface

topology.

fo frequency

amplitude


89

Figure 9-2. (a) Resonant frequency shift (b) Amplitude vs. Z-feedback

For certain samples, DFM yields better measurements than contact mode or non-

contact mode AFM. Dynamic force microscopy (DFM) has an advantage over contact

mode in the sense that it will damage the sample less since there is no frictional force as

the cantilever “skips” across the sample surface instead of “dragging” across it. Since the

amplitude of oscillation is so large, there is a much better chance that the probe will not be

caught by the meniscus forces of moisture condensed on the sample surface, as there is

with NC-AFM.

f1

f0 feff

∆∆∆∆A=A1-A0

A0

A1

frequency

amplitude


90

9-2. Conversion to DFM

In dynamic force microscopy, the Head mode will be set to NC-AFM just as in non-

contact mode. However, the “Intermittent” checkbox in the Scan Control Window must be

selected.

Figure 9-3. Conversion to DFM

9-3. Resonant Frequency setup

As explained in section 1, DFM uses non-contact mode feedback, but, as opposed

to non-contact mode, the driving frequency should be selected at the left part of the peak

in the graph. The other conditions are the same as the non-contact mode.


91

Figure 9-4. Resonant frequency setup in DFM


Since DFM uses the same method as non-contact AFM, which is to vibrate the

cantilever when measuring the sample surface, the same type of cantilevers are used in

DFM as in non-contact mode unless the user prefers a different type of cantilever for a

specific purpose. See the Cantilever Selection section in the Non-Contact AFM chapter.


The method of measurement of DFM is the same as that of non-contact mode.

The absolute value of the set point also means the distance between the probe tip and the

sample surface, just as in non-contact mode, but the value is much smaller. As explained

in Chapter 8, section 1, the vibrating probe tip moves as if it is pecking the sample surface

using the same feedback circuit. Determining the set point plays a very important role in

obtaining the best image.

The measurement method hereafter is the same as in Chapter 4. Please refer to

Chapter 4.


92


93

Acquiring an Approach Curve

95

Chapter 10. Approach Spectroscopy

Approach Spectroscopy are used in the investigation of a sample’s

mechanical properties. An approach curve(call as F/D curve) plots how the

cantilever’s interaction with the sample changes as its distance from sample

changes.

This chapter assumes that the operator is familiar with the XE SPM

system, as well as the XEP software. Otherwise, it is recommended that you

consult this XE User’s Manual and the XEP Software Manual while going

through this tutorial.

Modes

Approach curves can be acquired in several different modes. These

modes and their differences are as follows:

In F/D Mode(Force/Distance Mode), the cantilever is simply

approached to the sample to find where the surface is, then raised to

the MIN position, lowered to the MAX position, and raised again to the

MIN position. Only the cantilever’s deflection vs. the Z scanner’s

position is measured.

In Tip Oscillation Mode, the cantilever is oscillated near its resonance

frequency as it is being raised and lowered. The amplitude and

phase of the oscillating cantilever are considered with respect to the Z

scanner’s position. To use Tip Oscillation Mode, the Head Mode

(from Parts Config) must be one that uses tip oscillation, such as NC-

AFM, and the “Use Tip Oscillation in Spectroscopy” option in

Preferences must be selected.


96

Other Considerations

The actuator which moves the cantilever closer and farther from the

sample surface consists of a stacked PZT material. This material is controlled

by varying an electric field. However, the PZT actuator does not actually

move in a linear relationship to the control voltage, but rather displays

hysteresis and other nonlinearity. This deviation from the assumed linear

movement, although small on the nanometer scale, becomes significant on the

micrometer scale.

To correct for these deviations, XEP implements “Z ServoScan”, a

corrective feedback loop. Z ServoScan compares the Z Scan signal to the

actual movement of the Z Scanner, which is measured by the Z Detector.

When there is a discrepancy, the ServoScan modifies the Z Scan signal (now

known as the Z Scan Corrected signal) to eliminate the nonlinearity. The

drawback to the Z ServoScan system is that it introduces electrical noise,

which may become significant when the scan size decreases.

It is up to you to decide whether the nonlinearity of the actuator or the

Z ServoScan system’s noise is more significant for your experiment. You can

select Z ServoScan by deselecting the “Auto Offset” item in the Spectroscopy

Control Panel and selecting “ON” in Z ServoScan Setup which is shown in the

Setup.


97

Figure 10-1. Auto Offset option

10-1. Acquiring an Approach Curve

No hardware modifications are required for taking approach curve

measurements with an XE SPM system.

It is typical to obtain an SPM image of the sample to identify regions of

interest for approach curve acquisition. You may skip this process and instead

identify the region of interest by optical microscope, or image a random point on

the sample.

For more information on SPM imaging procedures, consult your XE

User’s Manual or the relevant Operation Manual for your SPM mode. The

following sections describe the procedures for taking approach curves.


98

10-1-1. F/D Mode

1. To take Force-Distance measurements, deselect the “Use Tip Oscillation

in Spectroscopy” option in the Scan Control page of the Preferences

dialog.

2. Switch to F/D Spectroscopy Mode by clicking on the icon in the

toolbar, or by selecting F/D Spectroscopy from the Mode menu.

3. Open Spectroscopy Config by clicking the icon, or by selecting

Spectroscopy Config from the Setup menu.

The options in the upper half of the dialog are used to prevent the tip from

crashing into the sample surface as it is being moved to a new

measurement location. For more information on the Spectroscopy Config

options, see the XEP Software Manual.

Figure 10-2. Spectroscopy Config

4. If you have taken an SPM image of your sample, select which image you


99

wish to use using the “Reference Image” dropdown menu. This image will

be saved together in the same file with any approach curves you acquire.

The example shown in Figure 10-2 has selected the Topography that was

acquired in the Forward direction. If you want to select the image acquired

in the Backward direction, select the ‘B’ image. For example, ‘Topography

B’.

Select OK and exit the Spectroscopy Config dialog.

5. Open the Input Config dialog. Select the Force, Z Detector, and Z Scan

inputs.

6. Change the settings in the FD Spectroscopy Control panel to suit your

measurement. For a complete description of each control, refer to XEP

Software Manual.

7. If the tip has not already been approached to the sample surface,

approach it now.

Figure 10-3. Input Config for F/D Measurements


100

8. Select the point or points at which to take F/D measurements. There are

several ways to do this.

Clicking the “Start” button will approach the tip and perform a F/D

measurement at the current location of the tip. You can change the

current location of the tip by right-clicking on a position in the

reference image and selecting the “Move Here” item. The green

crosshair indicates the position of the tip.

Note that any curves acquiring this will not be saved, as this function

is meant to help locate points of interest. However, you can export

each data point of the acquired curve. Copy the curve data to a

clipboard by clicking “Clipboard” button and paste the copied data to

Notepad or Spreadsheet.

Figure 10-4. Moving the Tip Position

You can add points to a list. Right-clicking on a location in the

reference image and selecting the “Add Point” item will add a point to

the list at that location. You can also add points by directly entering

values into the Points List, which is accessible by selecting the Edit

Points item in the context menu.


101

Figure 10-5. Points List Dialog

The third way to designate F/D measurement points is to use the Map,

which designates evenly spaced points on matrix that is overlaid on

the sample surface. F/D curves are automatically acquired at all

intersection points of the matrix by clicking “Acquire” button. This

matrix can be stretched and moved by the mouse. You can also

change the number of measurement points by selecting the “Edit

Map” item from the context menu.


102

Figure 10-6. Use a Map

Figure 10-7. Edit Map Dialog

9. Execute the F/D measurements by clicking the “Acquire” button, if you

designated the points of interest by using the Points List or a Map. Click

‘Start’ button if you want to measure the current location.

10. Once all of the measurements are complete, they will be saved to a file

represented in the Buffer Window. You can perform a curve analysis by

right-clicking on the file in the Buffer Window and selecting “Send to XEI.”


103

Figure 10-8. F/D Curves in Buffer Window

11. After taking an FD measurement, you may wish to refine the Min and Max

range for the measurement and re-acquire a new curve. To do this,

select an area on the Trace Window by left-clicking and dragging the

region, then click the “Apply” button. The Min and Max values will

change to reflect the selected region.

Figure 10-9. Selecting a Region by Mouse


104

10-1-2. Tip Oscillation Mode

Approach curves can also be taken while oscillating the tip near its

resonance frequency. Such measurements compare the phase shift and

amplitude change of the oscillation as the distance changes.

Although the procedure for taking Tip Oscillation approach curves is

very similar to taking F/D curves, a few important differences exist.

Figure 10-10. Use Tip Oscillation

In Step 1, the option “Use Tip Oscillation in Spectroscopy” must be

checked.

Before Step 2 (entering Spectroscopy Mode), the Head Mode must be

one that uses tip oscillation, such as NC-AFM or MFM.

In Step 5, select the NCM Amplitude and NCM Phase inputs in

addition to the Z Scan, Z Detector, and Force inputs.


105

Figure 10-11. Input Config for Tip Oscillation Approach Curves

10-2. Curve Analysis

Once you have acquired F/D curves, you can perform analyses on them by

exporting the data as text, to a spreadsheet, or by opening the .tiff file in XEI.

To export the data as text or to a spreadsheet, right-click on the acquired curve in

the buffer window and select “View Information”. In Image Information Dialog, select the

desired image and click “Export” button. Select a new document in the format that you

wish to export to, and save the data.


106

Figure 10-12. Export the data as other document format

To open the file in XEI, right-click on the buffer window image and select “Send to

XEI.” Alternatively, open XEI and find the file on your hard drive.

In XEI, opening the file for analysis will automatically turn XEI into Spectroscopy

Mode. In Spectroscopy Mode, there are 3 views; the Information, Batch, and Multi views

allow for different types of analyses.


107

Figure 10-13. XEI Spectroscopy Mode

For a full explanation of each view, see the XEI software manual.

10-3. Curve Computation Algorithm

Approach Spectroscopy mode is measure interaction between tip and sample on

one point through Z scanner movement. Therefore, Z scanner will decline and incline, so

tip will pull down on one point of sample (red line) and pull off (blue line). At this point,

shown as picture below, there are changes on cantilever defection, also force value.

Figure 10-14. Approach Curve


108

A. Approach: tip is approaching to sample. Tip did not make any contact with sample.

B. Jump to Contact (Snap-In): Tip is pulled down by attractive force near surface.

C. Contact: tip is pushing down sample, so tip is bent. Lowering Z scanner will bent

tip even more.

D. Adhesion: when pulling up Z scanner, due to interaction between tip and sample,

Adhesion force occurs. This force occurs until critical point. Due to this, tip is bent

down.

E. Pull-Off: distance between tip and sample is so far that it reaches critical point, so

there are no contact between sample and tip.

Basic Information Data of F/D Curve is calculated as below method on XEI. Basic

Information Data is calculated between changes on movement of Z scanner signal (Z

detector signal and X axis) and Force signal (Y signal).

1. Maximum Load

Y-axis maximum value of trace data (Z Scanner extends). It simply displays value,

hence if offset or etc are adjusted the value will be changed.

2. Snap-In

Y-axis minimum value of Trace data (Z Scanner extends). It simply displays value,

hence if offset or etc are adjusted the value will be changed.

3. Pull-Off

Y-axis minimum value of retrace data (Z scanner retracts). It simply displays

value, hence if offset or etc are adjusted the value will be changed.

4. Adhesion Energy

According to last value of Retrace Data (Z scanner retracts), all the points that

are below Retrace Data will be added up (green area).


109

Figure 10-15. Adhesion Energy Computation

You can automatically acquire F/D Curve at all the intersection points of the map

on sample topography and display above parameter image such as Snap-In, Pull-Off,

Adhesion Energy, Hardness and so on. Below image is topography of polymer on glass

sample (left). Original scan size is 15 then zoomed in for F/D curve on 128 X 128 (total

16384 point) and acquired Force Volume Image (middle: Hardness, right: Snap-In). With

this image, sample’s Hardness, Snap-In and so on can be compared.

Figure 16. Force Volume Image (Left: Topography, Center: Hardness Image and

Right: Snap-In)


110

Chapter 11. Calibration

11-1. Scanner Calibration

This section describes how to calibrate the XY scanner and Z scanner introduced

in the previous chapter as details.

11-1-1. Calibrating the X-Y scanner in the ‘Open Loop’ scan

High Voltage mode

1) Install a 50 or 100 X-Y scanner and the XE head as described in Section 1-

1-1.

2) Place the calibration sample on the X-Y scanner. The calibration sample you

need depends on the image size that you use most frequently. If you don’t need

a special calibration sample, you can use the standard grating sample(3 or

10 grating) included with your system. Rotate the square sample so that the

edge directions of the grating are parallel with the x and y scan direction.

3) Open the XEP program by double-clicking the XEP icon on your computer’s

desktop

4) Open the ‘XY ServoScan’ dialog by selecting ‘XY ServoScan’ from the Setup

menu. Turn off the x, y feedback by selecting the ‘OFF’ option and then clicking

the ‘Done’ button.


111

5) Go to calibration mode which you can go by clicking icon and uncheck Item 1,

2, 3 in “High” voltage mode in this window.

6) Turn off the laser by either deselecting ‘Head On’ from the Mode menu or by

clicking the Head On/Off icon .


112

7) Open the ‘XEP Part selection’ dialog by selecting ‘Part Config’ from the Setup

menu or by clicking the ‘Part Config’ icon on the Toolbar. Switch the ‘XY

Voltage mode’ to ‘High’.

8) Confirm that ‘Head mode’ is ‘C-AFM’ and you are using the corresponding contact

mode cantilever.

9) Turn on the laser by either selecting ‘Head On’ from the Mode menu or by clicking

the Head On/Off icon .

10) Assign the maximum value for ‘Scan Size’ and select a scan rate appropriate for

the scan size.

11) Adjust the set point, gain, and slope parameters until the signal trace on the

Trace window is stable and represents the sample topography. Note the

orientation of the features on the sample with respect to the x and y direction.

12) Once you have an image, send the data to the XEI program by clicking the right

button of your mouse on the image and selecting ‘Send to XEI’.


113

13) Using the XEI program, measure the spacing between the largest number of

maxima for the x direction of the calibration grid image. Refer to XEI manual for

details.

14) The measured spacing in this example is 26.836 between nine maxima. For

the 3 grating sample, the spacing should be 27 . Enter the calibration mode

and select XY scanner tab.

15) Input the measured x spacing, 26.836 to the ‘Measured value’ box of the ‘X

Scanner’ and input the actual spacing, 27 into the ‘Desired value’ box. Click

the ‘Calibrate’ button..


114

16) Repeat the same procedures 12) ~ 14) for the y direction.

17) Save the calibrated data base by clicking the ‘Save Calibration’ icon .

Low Voltage mode

Procedure for XY scanner calibration is same as in High voltage mode, except the

voltage ode should be set to ‘Low’ from the Part Selection and from ‘Software

Linearized Correction’. If you want to use ‘Software Linearized Correction’ in Low

voltage mode, refer to Section 11-3.

11-1-2. Calibrating the X-Y scanner in the ‘Closed Loop’ scan

1) Install a 50 or 100 X-Y scanner and the XE head as described in Section 1-1-1.

2) Place the calibration sample on the X-Y scanner. The calibration sample you

need depends on the image size that you use most frequently. If you don’t need

a special calibration sample, you can use the standard grating sample(3

grating) included with your system. Since is the sample area is square, rotate the

sample so that the edge directions of the grating are parallel with the x and y scan

direction.

For calibration in

open loop scan

For calibration in

closed loop scan


115


desktop

4) Open the ‘XY ServoScan’ dialog by selecting ‘XY ServoScan’ from the Setup

menu. Turn on the x, y feedback by selecting the ‘ON’ option and clicking the

‘Done’ button. Now, the XY detector will correct the non-linearity of the XY

scanner.






7) Next are the same as steps 7~13 in ‘Open Loop’ calibration mode.


116

8) Input the measured spacing and desired spacing into the appropriate boxes in the

‘X Detector’ window. This window is for calibration in closed loop scan.

9) Repeat the same procedures for calibration of the y scan direction.

10) Save the calibration data base by clicking the ‘Save Calibration’ icon .

11-1-3. Z scanner calibration

Usually, Z scanner motion is much smaller than that of the XY scanner. So, the Z

detector does not correct the Z scanner motion but only monitors the Z scanner motion.

Because of this characteristic of the Z scanner motion, calibration process of Z scanner

same for both open and closed loop scan.

When you need to measure heights greater than several hundreds of nanometers, you

may then use the ‘Z detector’ signal which is the motion of Z scanner measured by Z

detector for more accurate measurements.

High Voltage mode

1) Install a 50 or 100 X-Y scanner and the XE head as described in Section 1-

1-1.

2) Place the calibration sample on the X-Y scanner. Usually, the topography

variation is close to 100nm. If you don’t need a special calibration sample for

much smaller/larger heights, you can use the standard grating sample included

with your system.


117


desktop.




menu or by clicking the ‘Part Config’ icon from the Toolbar. Switch the ‘Z


6) Make sure that ‘Head mode’ is set to ‘C-AFM’ and you are using the

corresponding contact mode cantilever.



8) Open the ‘Input Config’ dialog and select the ‘Z Detector’ and ‘Topography’ as an

input signal. If you are not able to see some signals in your dialog, click setup

button to open the signal list, find the missing signals and add them to the dialog.


118

9) Set the Scan size to be the size of the calibration sample and select a scan rate

appropriate for this scan size.

10) Adjust the set point, gain, and slope parameters until the signal trace on the

Trace window is stable and represents the sample topography.

11) Once you have images of the ‘Topography’ and ‘Z Detector’ signal, send the data

to the XEI program by clicking the right button of your mouse on the image and

selecting ‘Send to XEI’.

12) Using the XEI program, measure the height of the grating from both ‘Topography’

image’ ad ‘Z detector’ image’. If you need to perform image processing such as

flattening, refer to the XEI manual.


119

13) The height of the gratings in the above example is 129nm when measured from

the ‘Topography’ image and 138nm when measured from the ‘Z detector’ image.

According to the specification of this grating sample, the height should be 142nm.

Enter the calibration mode and select Z Scanner tab.

14) Input the height of gratings measured from Topography image, 0.129 . in the

‘Measured value’ box of the ‘Topography’ window and input the actual height,

0.142 into the ‘Desired value’ box. Click the ‘Calibrate’ button.

15) Input the height of gratings measured from Z detector image, 0.138 into the

‘Measured value’ box of the ‘Z Detector’ window, and input the actual height,

0.142 into the ‘Desired value’ box. Click the ‘Calibrate’ button.


120

16) Save the calibration data base by clicking the ‘Save Calibration’ icon .

Low Voltage mode

Procedure for Z scanner calibration is same as in High voltage mode, except the

voltage mode should be set to ‘Low’ from the ‘Part Selection’ and only the

"Topography" should be selected for the input signal in the "input Config"

11-2. Detector Offset Calibration

This section describes how to adjust the Detector signal. The scanner cannot

move in a full range if the detector signal is too deviated.

11-2-1. X direction

1) Set the Scan Size to be zero and the Scan Direction to “X” in the XEP Scan Control

window.

2) Open the Input Config window, select ‘X Detector’ as an input signal and assign

to the units of the X Detector and click OK.


121

3) Open the Trace Control window and select X detector from the signal name list.

4) Select [Setup] -> [XY ServoScan] from the menu bar to open the XY ServoScan

Setup window and choose “OFF” and click “OK”

5) Adjust the Y scale unit of the Trace control window to 1 by clicking on the window

and turning the mouse wheel. Y scale of the window is shown on the upper left

corner of the window.

6) Click the right button of your mouse on the Trace control window and select “Show

Set the input signal

Set the scan parameters

Select the signal Turn off the XY servo


122

Line Cursor”. You will see the X[ ] and Y[ ] value of the point selected by cursor

in the upper right corner of the Trace Bar. Check the Y[ ] value of the X Detector

trace. If the Y[ ] value changes with the position of the line cursor, use the

average of the two Y[ ] value at the leftmost and right most of the trace control

window.

7) Enter the Calibration mode, select XY scanner tab and assign the Y[ ] value of the

X Detector trace from the step 6 to the X Detector Offset and click the ‘Coarse cal’

button.

8) Check that the Y[ ] value of the X Detector is now zero.

11-2-2. Y direction

For the Y direction, follow the same procedure as in X direction.

Show the line cursor Check the Y value


123

11-2-3. Z direction

When you use Z scanner in the closed loop(Refer to Section 8-6), the scanner

cannot move in a full range if the detector signal is too deviated. In this case, you need to

adjust Z detector offset.

High Voltage mode


desktop








5) Uncheck ‘Z Servo’ check box and ‘Z ServoScan Setup’ is activated in Setup menu.


124

6) Click the ‘Z ServoScan Setup’. Turn off Z Servo by selecting the ‘OFF’ and then

clicking the ‘OK’ button.

7) Open the Input Config window, select ‘Z Det. Corrected’ and ‘Z Detector’ as an

input signal and click ‘OK’ button.

*Z Detector signal is the untainted movement of the scanner which is dependent


125

of the given voltage, whereas the Z Det. Corrected signal changes according to

how the scanner was calibrated.

8) Go to Trace Mode by selecting ‘Trace Mode’ in Mode menu.

9) Select the Driving Source as Z scan. Click ‘XY Scanner Off’ and ‘Z Servo Off’

button.

10) Perform the Z Scanner sweep by click ‘Sweep’ button.

11) When the Z Det. Corrected signal is off the center like figure below, the Z Detector

offset needs to be adjusted. Go to Calibration mode and select ‘Z Scanner’ tab.


126

12) Input Offset textfield according to deviation and click ‘Calibrate’ button. For

example, Z Det. Corrected signal is like figure above. You should input ‘-3’(µm) on

the ‘Offset’ textfield.

13) Repeat 8)~12) until the Z Det. Corrected signal is on the center.


127

14) Click the ‘Z ServoScan Setup’. Turn on Z Servo by selecting the ‘OFF’ and then

clicking the ‘OK’ button.

15) If the Z Detector offset is correctly adjusted, you can see that the Z Detector signal

is moved linear like figure below.


128

Low Voltage mode

Procedure for Low Voltage mode is same as in High voltage mode, except the voltage

mode should be set to ‘Low’ from the Part Selection.


129

11-3. Software Linearized Correction

XY scanner consists of piezoelectric material, it shows non-linearity and hysteresis

according to the voltage applied to XY scanner.

Hardware Correction

XE-XY scanner has the feedback loop designated to correct the non-linearity of

the XY scanner. This feedback loop uses an XY detector signal, which is XY scanner

movement detected by PSPD. By monitoring this detector signal, the feedback loop

corrects for scanner non-linearity in X and Y directions by adding a correction to the

voltage that is sent to the scanner. This feedback loop says as “Close loop” which you can

set by clicking ‘On’ on XY Servo Scan Setup. Selecting the ‘Off’ option turns off this

feedback loop. This process says “Open loop” and it doesn’t correct non-linearity in the

scanner’s X, Y position.

Software Correction

Close loop has higher noise level than Open loop since it uses the feedback loop

with XY detector. Therefore, when measuring small scan area(<500nm for 50 XY

scanner and 1 for 100 XY scanner), you can measure better images in Open loop.

However, in this case, non-linearity of XY scanner is shown.

This non-linearity of XY scanner can be corrected by software using the XY

detector signal. This software correction mechanism saves the X, Y position according to

the voltage applied to XY scanner to DB and calculate the applied voltage to the XY

scanner movement. The figure below shows 500nm topography image of nano particles.


130

Left is image with software linearized correction off and right is on. Software linearized

correction uses XY detector signal, and you have to calibrate XY detector calibration

before software linearized correction calibration.

NOTE!

Piezoelectric material is sensitive to temperature and XY scanner drift can be

generated. In this case, software linearized correction calibration may not be correct. So,

please do warming up the system.

Example:

Lift the tip away from the sample surface and make the XY scanner moving up &

down around 30 minutes. (Set [Scan Size: 5 , Fast Scan Direction: X, Two Way: On,

Repeat: On] and acquire image).

11-3-1. Software Linearized Correction of XY scanner in Low voltage mode

1) Before starting calibration, backup the database files in computer under path

C:\Park Systems\XEP\DB. The contents of these files will be changed during the

calibration process.

2) Calibrate XY scanner in the ‘Closed Loop’ Scan. For detail information, refer to

Section 11-2.


131

3) Change the mode to ‘Calibration mode’ by clicking the Calibration mode icon

in the toolbar. The Calibration mode icon is activated in the Maintenance mode.

4) Select ‘XY scanner’ tab in ‘Calibration’ mode and change the voltage mode to the

‘low voltage’ in ‘Software linearization correction’ panel.

5) Disable software correction function by unchecking check box beside Item 1, 2, 3.

6) Press ‘Save’ button by clicking icon and change the mode to ‘Scan mode’ by

clicking icon.

7) Turn off the head by clicking the button and enter part selection dialog by

clicking button. Set Low voltage mode in XY voltage mode and turn on the

head by clicking the button.


132

8) Open Input Config dialog and select X Detector and Y Detector in both scan

direction. Make sure that scan directions are checked both direction(Forward and

Backward).

9) Open ‘Session manager’ in Tools menu and create session named ‘5 ’ in which

image data will be saved.


133

10) Follow below setting and press start button to acquire 4

image data(bottom to top). No need for approaching to

sample.

Scan Rate: 2Hz

Fast Scan Direction: X

Scan Size: 5

Two way: On (with Slow Scan Reverse: Off)

When scan size is not set to 5 , open Scan Config by

clicking icon and set over scan to 0%.

11) After step 10) is finished, using same settings, press start button to acquire 4

images data which scan direction is opposite(top to bottom).

12) Change fast scan direction to Y and follow step 10)~11) to acquire 4 images.

13) Change scan size to 3 and make the ‘3 ’ folder using Session manager.

Repeat step 9)~12).

14) Change scan size to 1 and make the ‘1 ’ folder using Session manager.

Repeat step 9)~12).

15) Switch to Calibration mode and make sure that the voltage mode is set to ‘Low’.

16) In Software Linearized Correction panel, click on ‘Calibrate’ button next to Item 1

and find ‘5 ’ folder which you saved and select the 16 data acquire from step

10)~12) and calibrate.


134

17) Click on ‘Calibrate’ button next to Item 2 and find ‘3 ’ folder which you saved and

select the 16 data acquire from step 13) and calibrate.

18) Click on ‘Calibrate’ button next to Item 3 and find ‘1 ’ folder which you saved and

select the 16 data acquire from step 14) and calibrate.

19) Check all three Calibration Item 1, 2, 3 check box and press save button.


135

20) Calibrate XY scanner in Low Voltage mode. Follow all the steps in ‘’Low voltage

Mode’ of Section 11-1-1, except you should check all the items from ‘Software

Linearized Correction’. Use standard grating sample according to your scan range

and sample.


136

Appendix A. Aligning XE-100 AFM

137


Fundamentals:

1. Power On

2. Load sample

3. Load cantilever

4. Find cantilever

5. Align laser beam on cantilever

6. Center laser beam on PSPD

7. Approach tip to sample

Instructions:

IMPORTANT: Please turn only one knob at a time (refer to the “Section 4-7.

Beam Alignment in XE-100 User’s Manual” to verify the correct adjustment).

1. Power On

a) Turn on the Power to the entire AFM System. [Electronics, Computer,

Monitor, and Illuminator]

b) Each part may be turned on at any desired order, however the Control

Electronics should be turned on before the XEP Software is run.

2. Load sample

a) Mount sample onto sample plate using tape or glue. If possible, the best

method is to glue the sample using hard-setting instant adhesives.

b) Load sample on magnetic sample holder. If the sample is large, unscrew


138

the magnetic sample holder from the XY scanner and place sample

directly on the XY scanner.

3. Load cantilever onto probe hand (Figure 1)

a) Mount cantilever onto probe hand on head. To ensure no damage to

cantilever, cantilever chip mount recommended to be held between your

thumb and your index finger. The alignment is simple since two holes on

the chip mount should fit directly over the two ruby balls on the magnetic

tip holder on probe hand.

b) The center of the camera on the monitor screen is the approximate position

of the last user’s cantilever, and therefore the laser beam. It is very

important NOT to adjust the objective knobs in order to make Step 5 much

easier.

c) Turn off the laser by clicking the Laser icon and click the Part Config

icon in XEP software. Select the desired mode and the cantilever type

in this XEP Part Selection Dialog. Then, turn on the laser again.

Figure 1

4. Find cantilever

a) Move down focus stage nearby head (see Figure 2) moving the focus stage

in XEP. As you click upper or lower position from the center bar on the

stage pad, the stage will move upper or lower. If you cannot move the

focus stage, please move down the Z stage a little in maintenance

mode(mode->maintenance mode) and try again.


139

Figure 2

b) You can see the cantilever when the distance between head and optics is

approximately 3mm. (see Figure 3) If you cannot see the cantilever in this

distance, please perform c).

Figure 3

c) Turn the X and Y objective adjustments to find the cantilever on the

camera. Pay close attention to how much you turn in order to perform Step

5.

d) Cantilever is on cantilever chip and cantilever chip is mounted on chip


140

carrier. Therefore, if you focus on cantilever, the cantilever chip substrate

is beside the point.(see Figure 4)

Figure 4

5. Align laser beam on cantilever

a) You would remember how much you turn the X and Y objective

adjustments to find the cantilever on the camera. Repeat the EXACT

translation, but with the laser adjustment knobs.

b) Depending how accurate your movements are, the laser beam should be

near the edge of the cantilever or cantilever chip substrate.

c) It is easier to find the laser beam by placing it on the edge of the cantilever

chip substrate with Y laser adjustment knob. (see Figure 5) After then, you

can easily fine tune the X and Y laser adjustments so the laser beam is on

the front half of the cantilever (see Figure 6).

d) Laser intensity on camera depends on focus position.

e) If the laser beam spot cannot be found, locate laser beam by placing the IR

detection card where the sample would normally be. Otherwise, locate

laser beam where it should normally be according to the laser beam path.

(see Figure 7).


141

Figure 5

Figure 6

Figure 7


142

6. Center laser beam on PSPD

a) Turn PSPD mirror adjustments (small knobs on front of head) to move the

red dot to the center of the cross hairs on the PSPD (in XEP).

b) Verify A+B (on the right of the PSPD in the software) is about 2-3 V.

c) If A+B < 2V then refer to the Troubleshooting Alignment Procedure and

double check that the direct laser beam spot is on the cantilever and is

centered on the PSPD.

7. Perform frequency sweep (NCM ASetup) if imaging in non-contact mode.

Please make sure if the selected frequency is within the range of resonant

frequency. The amplitude of the selected peak(red cross) is recommended to be set

near 1 .

8. Verify that the Z-scanner is fully extended (i.e. the Z scanner bar in the

“Monitor Window” should be completely green). If not, refer to Troubleshooting if

Z Scanner is Retracted.

9. Bring tip a few millimeters from sample

a) Move head towards sample using the Z-stage motor control in software.

Visually inspect the tip-sample separation. Stop when the tip is a few

millimeters from sample.

b) Focus on cantilever.

10. Bring tip 50-100 microns from sample

a) After the cantilever is focused, go down the focus stage until the sample is

focused.

b) Move the focus stage up about 50~100 from the sample surface.

c) Move the Z stage down until the cantilever comes into focus after uncheck

the focus follow option, and the distance between the cantilever and the

sample is approximately 50~100 . (see Figure 8)

d) Focus on the sample surface using the focus stage motor control in

software.

e) If the cantilever and sample are in focus at the same time, the tip has

crashed the sample. The cantilever and sample should NOT be in focus at

the same time.

f) Click “Approach” (underneath the Z-stage motor control). When the light


143

to the right of the motor controls stops blinking, the tip will be completed

to approach to sample and in feedback on the surface.

g) The upper half of Z scanner bar in the PSPD window will be green if

“Approach” is successful. Before approach, it is recommended to be set

the scan size to 0 and Z servo gain to 1 in the scan control window.

Figure 8

11. After the imaging is complete, set the Scan Size to zero in order to avoid the

damage of tip and the sample and lift the Z Stage. Then close the XEP

program and turn off XE controller.


144

Troubleshooting Alignment Procedure:

IMPORTANT: Please turn only one knob at a time and verify that you adjust the

appropriate knob, the correct axis and in the desired direction(refer to the “Section

4-7. Beam Alignment in XE-100 User’s Manual” to verify the correct adjustment.).

VERIFYING DIRECT LASER BEAM SPOT IS ON CANTILEVER

When the direct laser beam spot is on the cantilever you should observe the

following: While turning Y laser position (large knob on the left side of head)

CLOCKWISE, you should see the laser beam spot move UP on the

cantilever. A bright spot (see Figure 9) when the laser beam hits the edge of the

cantilever chip substrate. With the laser beam spot on the edge of cantilever substrate, turn the X

laser position. You should see the laser beam spot move along the edge of

the cantilever chip substrate (see Figure 9). If you don’t observe ALL of the above, then the spot you see on the

cantilever is not the direct laser beam.

Figure 9

VERIFYING DIRECT LASER BEAM SPOT ON PSPD

When the mirror is properly aligned, you should see the following: Turning X mirror adjustment (small right knob on front of head)

CLOCKWISE will move the red spot on PSPD to the LEFT. Turning Y mirror adjustment (small left knob on front of head)


145

CLOCKWISE will move the red spot on PSPD UP. Turning X or Y mirror adjustment can make A+B(laser intensity) sudden

smaller. In this case, stop turning X or Y mirror adjustment and turn the

adjustment knob to opposite direction.

If the laser doesn’t move up-down and left-right as described above, then:

1. Turn Y laser position adjustment (large knobs on head) to maximize A+B.

2. When A+B is maximized, X adjustment knob to maximize A+B.

3. Repeat steps 1 and 2 until laser beam intensity become 2-3V on PSPD.

4. Sometimes if the laser beam is severely misaligned, A+B may go through

a minimum point.

After adjusting the direct laser beam spot on the cantilever and on the PSPD, verify

that A+B is 2-3V, and proceed to step 6 of the alignment procedure. Sometimes if

the backside of cantilever is rough or coated, A+B can be smaller and bigger.

Troubleshooting if Z Scanner is Retracted:

After aligning the laser beam and PSPD, and executing the frequency sweep the Z

scanner bar in the software should be completely green. If the Z scanner is

completely or partially retracted, the “auto approach” function will not work.

Do the following in the order given until the Z scanner completely extends (all

green):

Non-contact Mode

1. Verify A+B = 2-3V. If not, see Troubleshooting Alignment Procedure.

2. Redo the frequency sweep.

3. Select a different peak in the frequency sweep (make sure it’s within the

range of the spec given for the cantilever you are using) by double clicking

on the desired peak and Zoom In. You may have to try a few different

peaks.


146

Contact Mode

1. Verify A+B = 2-3V. If not, see Troubleshooting Alignment Procedure.

2. Make sure the cantilever is properly set in the head mode.

Index

147

Index

A

A+B value, 49

A-B value, 50

Acoustic Enclosure, 21

Active vibration Isolation System, 25

Air Table, 23

amplitude change, 80

Approach, 55

Atomic Force Microscope, 10

B

bimorph, 79

BNC socket, 25

C

Calibration, 110

cantilever, 39

cantilever vibration, 78

CCD camera, 16

chip, 39

Closed loop, 60

Contact Mode, 65

Control Electronics, 8, 31

cross coupling, 11

D

Diagram of cable connections for the XE

system, 38

dovetail rail, 3

drive amplitude, 83

drive frequency, 79

E

effective spring constant, 79

electrostatic repulsion, 65

excessive range, 61

external vibration, 21

EZ snap, 47

F

flexure hinge, 5

Floor Vibration, 21

Focus Follow, 45

force gradient, 79

frictional coefficient, 71

Fuse, 35

H

Head mode, 66

High voltage mode, 60

hysteresis, 11


148

I

illuminator, 36

Input Configuration, 75

interatomic force, 65

intrinsic frequency, 79

intrinsic spring constant, 79

K

Kinematic Mount, 3

L

Laser beam alignment, 48

lateral deflection, 71

Lateral Force Microscopy, 71

lateral force mode, 74

lateral resolution, 9, 62

Locating Cantilever, 47

Low voltage mode, 62

LPF, 75

M

Magnetic Force Microscopy, 79

maximum movable range, 61

N

Non-contact Mode, 77

non-linearity, 11

O

objective lens, 7

Offset X, Y, 58

Open loop, 60

Optical fiber, 36

optical microscope, 7

orthogonality, 14

P

piezoelectric, 11

piezoelectric tube scanner, 3

power supply, 37

PSPD, 3, 49

Q

Q-factor, 67

Quad-cell PSPD, 72

R

reflection angle, 48

Refresh, 83

Removing XE Head, 46

Repeat, 57

resonance, 79

resonant frequency, 78

response rate, 12

Rotation, 58

S

Scan Control, 55

Scan Direction, 75

Scan OFF, 57

Scanner Mode, 59

Scanning Probe Microscope, 9

Scanning Tunneling Microscope, 10

SEM, 9

Set point, 58

set point value, 83

Silicon cantilever, 40

Silicon Nitride cantilever, 40

Slope, 57

software calibration, 12

spring constant, 67

standard sample, 12

Index

149

steering mirror, 15

T

TEM, 9

Tip Bias, 58

tube scanner, 12

tunneling current, 10

Two way, 57

V

van der Waals Force, 77

vertical resolution, 9, 64

X

X,Y, 57

XE-100 Head, 2

XEI, 18

XEP, 18, 43

XEP Part selection, 60

XY Detector Offset Calibration, 120

X-Y scanner, 5

XY Scanner Calibration

Closed Loop, 114

Open Loop, 110

XY Servoscan, 60

XY Stage, 6

Z

Z Detector Offset Calibration, 123

Z scanner, 3, 4

Z scanner Range, 63

Z Servo, 58

Z Servo Gain, 58

Z stage pad, 54

Zoom Out, 83


150

Customer’s Document Feedback Form

In an effort to ensure that the content of this manual is updated and accurate, Park

Systems welcomes any and all customer feedback.

If, during the course of using this manual, you come upon any errors, inaccuracies, or procedural

inconsistencies, or if you have other content suggestions, please take the time to forward your

comments to us for consideration in future manual revisions.

Please check that you think this comment is critical ( ) or moderate ( ) or minor ( ).

Comments:

Customer Information

Name:

Company/Institution:

Address:

Country:

Date:

System

model:

E-mail:

Fax:

Phone:

You may fax this form or e-mail to Park Systems:

Homepage:

E-mail:

Address:

Fax:

Phone:

www.parkAFM.com

[email protected]

KANC 4F Iui-Dong 906-10, Suwon, Korea 443-766

+82-31-546-6805

+82-31-546-6800


In an effort to ensure that the content of this manual is updated and accurate, Park Systems

welcomes any and all customer feedback.

If, during the course of using this manual, you come upon any errors, inaccuracies, or procedural

inconsistencies, or if you have other content suggestions, please take the time to forward your

comments to us for consideration in future manual revisions.

Please check that you think this comment is critical ( ) or moderate ( ) or minor ( ).

Comments:

Customer Information

Name:

Company/Institution:

Address:

Country:

Date:

System model:

E-mail:

Fax:

Phone:

You may fax this form or e-mail to Park Systems:

Homepage:

E-mail:

Address:

Fax:

Phone:

www.parkAFM.com

[email protected]

KANC 4F Iui-Dong 906-10, Suwon, Korea 443-766

+82-31-546-6805

+82-31-546-6800

xe-100 user's manual 1.8.2 - unipr.it2010].pdf · this manual may not be reproduced in any...

Documents