an undergraduate nanotechnology engineering laboratory course on atomic force microscopy

14
428 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011 An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy Daniel Russo, Randal D. Fagan, and Thorsten Hesjedal, Senior Member, IEEE Abstract—The University of Waterloo, Waterloo, ON, Canada, is home to North America’s first undergraduate program in nan- otechnology. As part of the Nanotechnology Engineering degree program, a scanning probe microscopy (SPM)-based laboratory has been developed for students in their fourth year. The one-term laboratory course “Nanoprobing and Lithography” is accompa- nied by a preceding one-term lecture course, “Nanoprobing and Lithography.” The lecture course lays the theoretical foundation for the concepts covered in the laboratory course. The students work in groups of two and obtain hands-on experience in biweekly 3-h laboratory sessions. The labs use a dedicated undergraduate SPM teaching facility consisting of five atomic force microscope stations. The laboratory course covers all common standard modes of operation, as well as force spectroscopy, electrostatic force mi- croscopy, magnetic force microscopy, and scanning probe lithog- raphy by electrochemical oxidation and scratching/ploughing of resist. In light of the breadth of the nanotechnology engineering educational program in terms of synthesis and characterization of nanomaterials, the authors designed a dedicated SPM lab with a capacity of up to 130 students per term. Index Terms—Atomic force microscopy (AFM), laboratory course, nanotechnology education, scanning probe microscopy (SPM), SPM education. I. INTRODUCTION S INCE September 2005, the University of Waterloo (UW) has offered an undergraduate-level engineering degree in the discipline of nanotechnology engineering (NE). 1 Due to the nature of the field of nanotechnology, the program is multidisci- plinary. It consists of courses spanning the areas of electronics, materials, and biochemistry, as well as courses covering the relevant synthesis and/or fabrication techniques. The program Manuscript received May 28, 2010; accepted July 28, 2010. Date of publica- tion September 02, 2010; date of current version August 03, 2011. This work was supported in part by the CFI (Leaders Opportunity fund) and NSERC (Dis- covery grant). D. Russo was with the Nanotechnology Engineering Program, University of Waterloo, Waterloo, ON N2L 3G1, Canada. He is now with Polar Mobile, Toronto, ON M5J 2L6, Canada (e-mail: [email protected]). R. D. Fagan is with the Nanotechnology Engineering Program, University of Waterloo, Waterloo, ON N2L 3G1, Canada (e-mail: rdfagan@sciborg. uwaterloo.ca). T. Hesjedal is with the Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada (e-mail: thesjeda@ece. uwaterloo.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TE.2010.2066566 1 The Nanotechnology Engineering honors degree program at the University of Waterloo leads to a Bachelor of Applied Science (B.A.Sc.) in Nan- otechnology Engineering. [Online]. Available: http://nanotech.uwaterloo.ca/ (accessed Jul. 31, 2010). is administered jointly by the Departments of Electrical and Computer Engineering and Chemical Engineering in the Fac- ulty of Engineering and the Department of Chemistry in the Fac- ulty of Science. During the four-and-two-thirds-year program (14 trimesters), the NE students have the opportunity to work in academia or industry and gain valuable practical experience during their five cooperative work terms (two four-month work terms in years 1 and 2, followed by two eight-month work terms in years 3 and 4). 2 The nanotechnology core lecture course on “Nanoprobing and Lithography” (NE 353) prepares the student for the subse- quent laboratory course and covers the following topics: theory and application of nanoprobing based on scanning probe mi- croscopy (SPM) and nanolithography techniques ranging from extreme-UV lithography, X-ray lithography, e-beam lithog- raphy, focused ion beam lithography, nano-imprint lithography, to SPM-based lithography. NE 353 is taught one year before the lab course in the NE curriculum. The lab course provides the students with relevant, hands-on experience with SPM and, more specifically, atomic force microscopy (AFM). The labo- ratory course reinforces the key concepts of AFM, which are taught in the lecture course, through practical demonstrations, examples, and hands-on use. All common AFM imaging modes are covered. The students exploit the versatility of the SPM instrumentation, expanding the use of AFM beyond topography imaging into the spatially resolved characterization of electric and magnetic properties, and nanolithography (by oxidation and mechanical ploughing). The authors’ task was to develop and deliver the AFM labora- tory class to a group consisting of 70–130 students per trimester term. Each student participates in six sessions, each 3 h in du- ration. One dedicated SPM room was designed specifically for the laboratory course and allows one lab instructor to deliver the course to five pairs of students simultaneously by using a projector for demonstrating the key concepts and practical as- pects of AFM operation on one of the AFM workstations. The SPM room is equipped with educational-level AFM models sup- plied by Anfatec Instruments AG [1]. The six lab course ses- sions (modules) were delivered in biweekly sessions. The AFM lab is further used for the “Nanosystems Design Project” that the students carry out in groups of four in the last two terms of the program (NE 408 and 409, preceded by NE 307, “In- troduction to Nanosystems Design”), and that concludes with a “Nanosystems Design Project Symposium.” In this context the 2 Cooperative education is an educational model that formally integrates aca- demic studies with relevant work experience. Co-op students alternate terms of school and work in appropriate fields of business, industry, government, social services, or the professions. [Online]. Available: http://www.cecs.uwaterloo.ca/ (accessed Jul. 31, 2010). 0018-9359/$26.00 © 2010 IEEE

Upload: t

Post on 23-Sep-2016

219 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

428 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

An Undergraduate Nanotechnology EngineeringLaboratory Course on Atomic Force Microscopy

Daniel Russo, Randal D. Fagan, and Thorsten Hesjedal, Senior Member, IEEE

Abstract—The University of Waterloo, Waterloo, ON, Canada,is home to North America’s first undergraduate program in nan-otechnology. As part of the Nanotechnology Engineering degreeprogram, a scanning probe microscopy (SPM)-based laboratoryhas been developed for students in their fourth year. The one-termlaboratory course “Nanoprobing and Lithography” is accompa-nied by a preceding one-term lecture course, “Nanoprobing andLithography.” The lecture course lays the theoretical foundationfor the concepts covered in the laboratory course. The studentswork in groups of two and obtain hands-on experience in biweekly3-h laboratory sessions. The labs use a dedicated undergraduateSPM teaching facility consisting of five atomic force microscopestations. The laboratory course covers all common standard modesof operation, as well as force spectroscopy, electrostatic force mi-croscopy, magnetic force microscopy, and scanning probe lithog-raphy by electrochemical oxidation and scratching/ploughing ofresist. In light of the breadth of the nanotechnology engineeringeducational program in terms of synthesis and characterization ofnanomaterials, the authors designed a dedicated SPM lab with acapacity of up to 130 students per term.

Index Terms—Atomic force microscopy (AFM), laboratorycourse, nanotechnology education, scanning probe microscopy(SPM), SPM education.

I. INTRODUCTION

S INCE September 2005, the University of Waterloo (UW)has offered an undergraduate-level engineering degree in

the discipline of nanotechnology engineering (NE).1 Due to thenature of the field of nanotechnology, the program is multidisci-plinary. It consists of courses spanning the areas of electronics,materials, and biochemistry, as well as courses covering therelevant synthesis and/or fabrication techniques. The program

Manuscript received May 28, 2010; accepted July 28, 2010. Date of publica-tion September 02, 2010; date of current version August 03, 2011. This workwas supported in part by the CFI (Leaders Opportunity fund) and NSERC (Dis-covery grant).

D. Russo was with the Nanotechnology Engineering Program, Universityof Waterloo, Waterloo, ON N2L 3G1, Canada. He is now with Polar Mobile,Toronto, ON M5J 2L6, Canada (e-mail: [email protected]).

R. D. Fagan is with the Nanotechnology Engineering Program, Universityof Waterloo, Waterloo, ON N2L 3G1, Canada (e-mail: [email protected]).

T. Hesjedal is with the Department of Electrical and Computer Engineering,University of Waterloo, Waterloo, ON N2L 3G1, Canada (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TE.2010.2066566

1The Nanotechnology Engineering honors degree program at the Universityof Waterloo leads to a Bachelor of Applied Science (B.A.Sc.) in Nan-otechnology Engineering. [Online]. Available: http://nanotech.uwaterloo.ca/(accessed Jul. 31, 2010).

is administered jointly by the Departments of Electrical andComputer Engineering and Chemical Engineering in the Fac-ulty of Engineering and the Department of Chemistry in the Fac-ulty of Science. During the four-and-two-thirds-year program(14 trimesters), the NE students have the opportunity to workin academia or industry and gain valuable practical experienceduring their five cooperative work terms (two four-month workterms in years 1 and 2, followed by two eight-month work termsin years 3 and 4).2

The nanotechnology core lecture course on “Nanoprobingand Lithography” (NE 353) prepares the student for the subse-quent laboratory course and covers the following topics: theoryand application of nanoprobing based on scanning probe mi-croscopy (SPM) and nanolithography techniques ranging fromextreme-UV lithography, X-ray lithography, e-beam lithog-raphy, focused ion beam lithography, nano-imprint lithography,to SPM-based lithography. NE 353 is taught one year beforethe lab course in the NE curriculum. The lab course providesthe students with relevant, hands-on experience with SPM and,more specifically, atomic force microscopy (AFM). The labo-ratory course reinforces the key concepts of AFM, which aretaught in the lecture course, through practical demonstrations,examples, and hands-on use. All common AFM imaging modesare covered. The students exploit the versatility of the SPMinstrumentation, expanding the use of AFM beyond topographyimaging into the spatially resolved characterization of electricand magnetic properties, and nanolithography (by oxidationand mechanical ploughing).

The authors’ task was to develop and deliver the AFM labora-tory class to a group consisting of 70–130 students per trimesterterm. Each student participates in six sessions, each 3 h in du-ration. One dedicated SPM room was designed specifically forthe laboratory course and allows one lab instructor to deliverthe course to five pairs of students simultaneously by using aprojector for demonstrating the key concepts and practical as-pects of AFM operation on one of the AFM workstations. TheSPM room is equipped with educational-level AFM models sup-plied by Anfatec Instruments AG [1]. The six lab course ses-sions (modules) were delivered in biweekly sessions. The AFMlab is further used for the “Nanosystems Design Project” thatthe students carry out in groups of four in the last two termsof the program (NE 408 and 409, preceded by NE 307, “In-troduction to Nanosystems Design”), and that concludes with a“Nanosystems Design Project Symposium.” In this context the

2Cooperative education is an educational model that formally integrates aca-demic studies with relevant work experience. Co-op students alternate terms ofschool and work in appropriate fields of business, industry, government, socialservices, or the professions. [Online]. Available: http://www.cecs.uwaterloo.ca/(accessed Jul. 31, 2010).

0018-9359/$26.00 © 2010 IEEE

Page 2: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 429

AFMs form a part of a metrology and cleanroom suite that isopen for the students to use for the projects.3

AFM, and more generally SPM, offers a suite of surface char-acterization and molecular/atomic manipulation tools and tech-niques important to science and engineering. For details of AFMinstrumentation and characterization techniques, please refer to[2] and [3], or to one of the many excellent textbooks in thefield, e.g., [4] or [5]. Applicability to fields spanning electronics,biotechnology, chemistry, and physics are a testament to theimportance and power of the AFM to micro- and nanoscalescience and technology. Typical AFM instruments comprise ananoprobe (a micromachined cantilever with a sharp tip affixedat the end, where the tip diameter at its point may measure a fewto tens of nanometers) and a three-dimensional (3-D) nanopo-sitioning system. In principle, AFM instrumentation is capableof subnanometer and, in special cases, even atomic resolution.Practically, resolution is dictated by the particulars of the inter-actions between the sample surface and the tip, the tip diameter,and the tip-sample distance. In many ways, due to its ability toaccess the micro- and nanoscales, the AFM may appropriatelybe considered as a Swiss Army knife for the nanoscale.

The AFM is the cornerstone of the “Nanoprobing and Nano-lithography” laboratory. An in-depth study of the tool’s appli-cability and versatility for accessing the nanoscale is the pri-mary goal of the laboratory. The course aims to teach studentsthe operational and practical principles of the AFM and extendthese principles toward advanced imaging and lithography tech-niques. It is not the intent that the students should become ex-perts in the field of AFM through their enrollment in the 18-hcourse. Rather, the primary goal is to provide the students withstrong background knowledge of the technique and instrumen-tation a notion of what AFM operation typically entails, un-derstanding of when and where the instrument is applicable,and how to interpret SPM results. Courses at other universitieshave been developed for nanoscience and AFM [6]–[13]. How-ever, these are not delivered at the same scale, or with the samefocus and goals, as the laboratory course discussed here. Thisarticle outlines aspects of and the development of the labora-tory course.

II. DESIGN OF THE SPM LAB

Delivery of the AFM laboratory required selection of theAFM instrumentation, design of the laboratory space, selectionof course material, development of the laboratory manuals,and acquisition and/or design and development of the relevantconsumables, samples, and tools needed. The layout of thelaboratory space is provided in Fig. 1.

A. SPM Equipment

The instrument used for the laboratory course is the educa-tional AFM model “Eddy” from Anfatec Instruments [1]. The

3The fourth-year design project is spread over two terms, and the work forthe project is proposed a year earlier (NE 307). See the NE curriculum fordetails. [Online]. Available: http://www.nanotech.uwaterloo.ca/Undergrad-uate_Studies/Course_List/ (accessed Jul. 31, 2010). News coverage of thedesign symposium is available. [Online]. Available: http://newsrelease.uwa-terloo.ca/news.php?id=5173 (accessed Mar. 18, 2010).

Fig. 1. Layout of the dedicated SPM room for the undergraduate students.(a) Floor plan showing five AFM setups, two cabinets for supply storage, and a6 projector screen. The 6 project screen is connected to one of the five AFMtables for demonstration purposes. The two desks located in the middle of theroom are worktables for the students, where they may place their notes and/orlaptops. (b) AFM station photograph and (c) layout. Each AFM station consistsof two adjacent but separated tables: one to hold the AFM and its electronics(measuring �� � �� ), and the other for the PC, keyboard, mouse, and twomonitors (measuring �� � �� ). The two students at each AFM station eachsit at one of the two tables.

instrument is capable of all standard AFM modes of opera-tion, including contact (static) and dynamic modes (noncon-tact, intermittent contact, force modulation), as well as extendedtwo-pass capabilities for electrostatic force microscopy (EFM)and magnetic force microscopy (MFM). The tool additionallyaccommodates experiments where environmental control is re-quired (e.g., a nitrogen-purged AFM chamber, though vacuumexperiments are not directly possible with this education-levelversion). Additionally, a bell jar provides a first level of acousticisolation.

The instruments are delivered on marble tabletops that areisolated from the underlying tables by a foamy damping layer.During operation, the heavy tabletops reduce the instrument’ssusceptibility to vibrations (low-frequency building vibrations,closing doors, people walking, etc.). Vibrational damping,using the provided tabletops, had proven to be sufficient formost experiments. Active damping, which would add between$6000 and $10 000 CAD to the cost of a single AFM unit, is notabsolutely required for the purposes of this laboratory course.From an educational point of view, the presence of noise andthe hands-on implementation of countermeasures is central tothis lab—not the optimal suppression of mechanical noise. Themajor drawback, however, is the limited success in imaging

Page 3: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

430 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

Fig. 2. Photographs of the AFM setup. (a) AFM body (houses the coarse mo-tors, ���-piezo, and sample stage), AFM head (houses the photodetector, laser,camera, probe mount, and dither-piezo for exciting cantilever oscillations), andthe AFM control electronics. (b) Bottom view of the AFM head. The clip holdsthe probe; the laser and the photodetector (not visible in the picture) are lo-cated within the AFM head. (c) Side view of the AFM head. The position of thecamera is indicated in the picture.

DNA and atomic steps in lab module IV (High-ResolutionImaging).

The Anfatec AFM is an ideal choice for the undergraduatelaboratory training since the instrumentation is not enclosed.All components of the instrument can be explained and demon-strated to the students: the laser diode, photodetector, micro-scope and camera, stage, -piezo scanner, and coarse mo-tors for 3-D positioning. Nevertheless, the construction is solidenough to withstand day-to-day handling in an undergraduatelab.

Additional infrastructure required for the offering of the lab-oratory is custom-built tables. Each of the five AFM stationsconsists of two detached tables and two chairs (for a maximumof two students at each AFM station). The first table holds theAFM, stone tabletop, and AFM electronics, and the second tableholds the computer (mounted below the table) and two monitors(attached to table-mounted stands). The two adjacent tables aredetached to minimize vibrational disturbances to the AFM. Themain AFM components are depicted in Fig. 2.

Each AFM station is also equipped with a high-purity ni-trogen line that will allow AFM experiments in a controlledenvironment in the future. For example, tip-sample adhesionexperiments could be carried out in an environment with con-trolled relative humidity levels.

The total cost for setting up the AFM laboratory (includingtables, chairs, etc.) was $180 000 CAD (September 2008). In-cluded in the package are five AFMs with control electronicsand PCs, additional probes, and the necessary calibration andtest gratings.

B. AFM Software

The control software for the AFM instrumentation, SxM, isprovided by Anfatec (see Fig. 3), and it is a fully featured suitefor a wide array of SPM techniques. SPM modes include contactmodes (including force modulation), dynamic modes (ampli-tude- and frequency-modulated), two-pass techniques, conduc-tive AFM (CAFM), Kelvin probe force microscopy (KPFM),and so forth. The software is very flexible in that all instru-mentation and software can be manually configured and set up.Nonetheless, the software conveniently comes with preset con-figurations for contact, dynamic, KPFM modes, and so on. Ad-ditionally, the software allows the user to run scripts, whichis useful for running lithography experiments and for imple-menting new measurement techniques.

Two important features of the software, highly relevant to thedelivery of an undergraduate lab with a significant throughput ofstudents, are theadministrator andusermodes. Thead-ministrator mode is password-protected and provides fullaccess to the configuration of the software. The user mode al-lows the administrator or lab manager to control the permissionsavailable to the students. Only those features that are needed tooperate modules I–VI are available to the students. In this way,there is no risk of their altering important configuration and/orcalibration data. In order to reduce the risk of an infection witha computer virus, none of the AFM computers is connected toa network at this point. Instead, a USB flash drive is used totransfer the data at the end of the lab day.

C. AFM Probes and Consumables

All AFM probes (tips) used throughout the labs are suppliedby MikroMasch [14] and selected appropriately for the type ofexperiment. Specific details are discussed for each lab module inSection III. Probes utilized are CSC17/AlBS for contact modes,NSC15/AlBS for dynamic modes, and NSC18/Co-Cr for elec-trical and magnetic dynamic modes. Each of the five AFM sta-tions is equipped with tweezers, magnetic sample mounts, AFMprobes of various types, and silver adhesive paste for samplepreparation. The typical tip consumption for lab modules I–IV,assuming that the lab instructor is exchanging the tips, is negli-gible given that new tips are supplied for each station before thedelivery of the course. Module V (Nanolithography) consumeson average one tip per station per lab day. Furthermore, the re-quired metal-coated tips are the most costly consumables in thecourse. Module VI requires on average four tips for the wholelab course. Special training was offered to the students after theregular lab hours to train them in the tip exchange procedurewith broken cantilevers.

D. Analysis Software

Analysis software is available on the AFM computers for useby the students. Image analysis and processing is a crucial com-

Page 4: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 431

Fig. 3. Overview of the SxM software used for data acquisition. (a)–(c) Image acquisition windows. The images acquired are chosen according to the AFM mode ofoperation. Each acquisition window allows the operator to display the data with slope correction and false color contrast on line-by-line or full image bases. (d) Theparameter window provides the main controls for feedback, scan parameters, acquisition start/stop, coarse and auto-approach, and scan rotation. (e) Cross-hairswindow displaying graphically the position of the laser dot on the photodetector. (f) Oscilloscope window that provides real-time display of up to three signals.(g) Image capture of the microscope, revealing the cantilever and sample surface. (h) Dynamic window for obtaining frequency response spectra of the cantilevers.The user selects the operating frequency and amplitude. Filter controls are provided. (i) Spectroscopy window allows the user to obtain force-distance, amplitude-and phase-distance, I-V curves, and so forth. (j) Select window allows the user to zoom-in to specific regions of an obtained image, move the cantilever to a fixedpoint to obtain spectroscopy data, and run preset scripts (useful for lithography).

ponent of the laboratory course. Two software packages wereused: Present (supplied by Anfatec4) and Gwyddion (freeand open-source software5). As Gwyddion is available on mul-

4FreePresent is the free version of Present, available under the An-fatec Freeware License Agreement. [Online]. Available: http://www.anfatec.net/anfatec/freepresent.html (accessed Jul. 31, 2010).

5Gwyddion is a modular program for SPM data visualization and analysis.Gwyddion is free and open-source software, covered by GNU General PublicLicense. [Online]. Available: http://gwyddion.net/ (accessed Jul. 31, 2010).

tiple platforms (Windows, Linux, and OS X), students are en-couraged to download the software to their personal computers.

E. Simulation Tools

Students are directed to basic simulation tools they can useto help them understand the concepts of AFM. The simulationtools, courtesy of Dr. J. Griffith and available for download fromthe Web site listed in [15], include the following:

Page 5: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

432 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

Fig. 4. Internet portal for the AFM lab course developed for the Nanotech-nology Engineering program at the University of Waterloo. All course materials,as well as supporting projects and additional information, can be downloadedfrom this site (see [16] for the URL).

• Probe simulator—(tip-shape modeling) demonstrating tip-surface convolution in topography imaging;

• Driven oscillator—damped, driven harmonic mechanicaloscillator modeling for demonstrating behavior of theAFM cantilever probe;

• AFM model—a general AFM model where feedback gain,feedback setpoint, tip-sample separation, and scan speedare user-controlled, demonstrating AFM behavior duringimaging and the operational principles.

F. Online Course Material

The entire course material is available online from the SPMlab site [16]. A screenshot of the online portal is shown in Fig. 4.

As part of this lab development effort, the authors were de-signing AFM and MFM demonstrations for K–12 and otheron-campus outreach activities. The designs for the demonstra-tions and the educational approach are explained on the SPMlab Web site6 [16]. The designs are available for download fromthe same site.

III. SPM LAB MODULES

The laboratory course is subdivided into six modules, whereeach module occupies a single 3-h laboratory session. Eachmodule has a unique focus and aims to demonstrate new andalternative information about the instrument and its capabilities.As the principles taught in modules I–III build upon each other,these modules were delivered in order. Modules IV–VI requireinformation taught only in modules I–III and can be delivered

6Username: “spm”; password: “lab2010”

Fig. 5. Organizational flowchart of the lab modules. Note that while mod-ules I–III have to be taught in this sequence, modules IV–VI, as well as futureexpansion modules (e.g., the magnetic force microscopy module VII), can betaught independently, allowing perhaps for the establishment of electives forupper-year courses.

as independent entities. Fig. 5 illustrates the arrangement of themodules.

The first module, focusing on contact mode AFM, delivers thefoundational concepts of the instrumental operation and tech-niques. Contact mode AFM is selected for the introduction, asopposed to dynamic AFM modes, since contact modes are rel-atively easier to understand and apply. Exposure to dynamicmodes begins in module III.

The grading for all of the modules is based on a seriesof questions related to the laboratory exercises, instrument,and techniques. The students are encouraged to answer thequestions during the laboratory exercise (electronic copiesof the question sheets are provided on the AFM computersequipped with OpenOffice). The two-monitor setup assures thatthe students can conveniently handle the documents and thecontrol software. Following module II (which first introducespost-processing techniques of the acquired AFM images), allimages included in the students’ responses are expected to bepost-processed.

The students are prepared for the individual lab modules in athree-step process that consists of their studying the respectivechapter in the lab manual (the manual is available for downloadfollowing the link provided in [16]), reading the mandatory sci-entific publication(s) on the topic, and passing a prelab exam-ination. This examination takes place in the AFM room and iscarried out as a constructive dialog between the lab instructorand the students (a lab group consists of 10 students). This is toassure that the students are sufficiently prepared to understandthe objectives of the lab, to be aware of the risks and dangers forthe instruments and the operator, and to help them to transfer thetheoretical knowledge into practical knowledge. The mandatoryreading comprises scientific articles that are referenced in the re-spective sections.

Page 6: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 433

Fig. 6. Examples of data obtained during module I. The data are raw and have not been processed. (a) Topography AFM image of the Si sample used in module Iobtained using contact mode AFM. The image is taken after the students have had the opportunity to determine the effects of feedback and scan parameters onimage quality. While exploring their effects on image contrast, the students would obtain topography and error signal images similar to (b) and (c), respectively.The images are obtained simultaneously, while the students vary the integral gain parameter during image acquisition. In the images, the integral gain parameteris increasing toward the bottom of the scan. It is clear that the image quality in the topography image (b) degrades while the contrast in the error signal, i.e., thedifference between the deflection (force) setpoint and the topography (deflection) signal, in (c) increases. (d) Force-distance curve. The slope of the curve from�� � � nm to approximately 400 nm is used to calculate applied contact force between the tip and the sample. The shape and characteristics of the retract andapproach curves are typical for force spectroscopy, and the origin of the curve is explained elsewhere [17]. The importance of the force-distance curve is stressedsince it characterizes the force acting in the system. All AFM techniques function by exploiting these forces (this idea is reinforced to the students in modules IIIand VI).

The following sections outline each of the modules, the con-tent delivered, lab tasks, and details of their development.

A. Module I—Atomic Force Microscopy in Contact Mode andForce Spectroscopy

Module I focuses on fundamental AFM concepts andpractices. Though the concepts are applied with the specificinstrument used in the laboratory, the AFM concepts aregeneral and transfer to any AFM system. Topics covered are:cantilever beam bending and Hooke’s Law, instrumentation(optical beam-bounce technique, four-quadrant photode-tector, piezo-scanner, etc.), probe mounting (if time permits),tip-sample approach, constant force and constant height modesof contact AFM, force spectroscopy principles, measurement ofthe contact force, imaging and associated imaging parameters,feedback, and feedback parameter optimization in constantforce AFM. Fig. 6 illustrates some experimental results typi-cally obtained in the lab.

The students operate the instrument in constant force con-tact mode AFM using a MikroMasch CSC-17 AlBS probe (witha force constant of 0.15 N/m and a nominal tip diameter of20 nm). The sample analyzed by the students was selected to berelatively easy to image so that the students could focus on un-derstanding the operation of the AFM. The sample is patternedSi, with periodic features having 50 nm depth and 2 m lat-eral pitch. In this way, the students would first not have to dedi-cate a significant portion of the 3-h lab session searching for thefeatures, and then would have no difficulty obtaining a suitableAFM image.

The procedure for module I guides the student through theprocess, beginning with instrumental setup and ending withimage acquisition. To save time, the AFM probes are mountedonto the AFM head and samples prepared by the instructorprior to the students’ entry into the session. Then, throughout

module I (or during module II if time does not permit comple-tion during the module-I session), the instructor or teachingassistant would address each group individually and walk thestudents through probe mounting and sample preparation. Bythis method, the students can begin working with the AFMsas soon as they enter the lab. The module-I instruction manualis written with sufficient detail that the students would beable to follow it without the assistance of the instructor and,in principle, obtain an image. Nonetheless, the instructor isalways available to aid the students.

The first task in module I is to align the laser and pho-todetector. Once the laser and photodetector alignments arecomplete, the students would set the relevant feedback parame-ters (deflection setpoint, integral gain, proportional gain). Notethat the values set at this point serve as initial guesses until theparameters are optimized by the students. The next task is toapproach the tip manually toward the sample surface, followedby an automatic approach. During the automatic approach, thestudents are to observe, through the Oscilloscope tool,exactly what the instrument is monitoring and doing. Theymust pay particular attention to the “Top-Minus-Bottom” signal(T-B signal) and see that the automatic approach ends when theT-B signal reaches the deflection setpoint value.

Once the tips are engaged, the students are then required touse force spectroscopy. The concepts of contact and adhesionforces are illustrated [17], [18]. Before moving onto the sub-sequent steps, the students use Hooke’s Law to determine thecontact force of the AFM probe. Errors in the contact force mea-surement are highlighted; these are mainly due to nonoverlap-ping approach and retract lines and to error in the force constantgiven by the cantilever manufacturer.

When the tip is engaged at the surface, the feedback param-eters that the students are initially told to use have to be op-timized. The students take a scan with these incorrect feed-

Page 7: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

434 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

Fig. 7. Module II sample data obtained during the operation of the lab. (a) Unprocessed topography image of an integrated circuit. This image is provided to thestudents at the start of the laboratory session, and the students are guided through the process of improving the quality of this image. The image contains tilting andstreaking errors. In order to improve the image, the students can experiment with leveling by first- and second-order lines and planes. Streaking and other errorsare shown to be removed with mean filtering. Students can also adjust the contrast (false coloring scheme) by using a histogram tool. (b) Example of the end resultof the students’ experimentation with the image in (a): The image is flattened with a mean filtering algorithm applied. (c) Topography and (d) lateral force imagesof a spin-cast polystyrene and poly(methyl methacrylate) blend. The students image a blend during the laboratory session. They use the contrast generated duringlateral force imaging to highlight topographical and material changes. (e), (f) Plots of the measured displacement of the piezo-scanner in the �-direction using astrain gauge ��� � and the applied signal corresponding to the piezo-displacement in the �-direction scaled to a distance unit, used internally in the software ����.Over short distances, as in plot (e), the relationship between �� and �� is roughly linear. Over greater distances, however, as in plot (f), the piezo-scanner beginsto exhibit nonlinearities. The students take these plots, and they serve as a warning that piezo-scanner nonlinearities and hysteresis should never be neglected.

back parameter values, and the resulting “topography” image isblurry. The primary cause for the blurry image is that the initialvalue set for the integral gain is significantly below the workingrange. The students are instructed to observe the T-B signal andinterpret it as the “error” signal: Correctly set feedback parame-ters significantly reduce any contrast observed in the T-B imagesince the T-B signal is the feedback input.

Understanding the effect of the feedback and scan parameterson image quality is a primary goal of module I. The primary taskof the students is to systematically vary the integral gain, de-flection setpoint (and hence contact force), line scan frequency,scan window size, and pixel resolution (up to 256 256 pixelsper image) in order to obtain the best topography image pos-sible. They must understand the role of each feedback and scanparameter and the sensitivity of the image quality to the param-eter. In general, the students should observe the following rela-tionships. They are required to discuss their observations in thepost-lab exercise.

• A low integral gain results in a blurry image and a signifi-cant error signal at and around the edges of the surface fea-tures. Increasing the integral gain reduces the magnitudeand span of the error signals. Increasing the integral gainfurther eventually results in feedback oscillations, whichare noticeable in both the topography and error signals.

• A low contact force would result in poor tracking of thesample edges and pits, in which case features appear “outof focus” in the topography image. Increasing the contactforce improves image quality. However, too large contactforces may wear and/or damage the tip and sample surface.

• Increased pixel resolution affects image quality at the costof image acquisition time.

• Increased scan window size, without reducing scan fre-quency (number of lines acquired per second), or viceversa, degrades image quality due to increased tip flightvelocity. Students should explore the possibility of coun-tering this image degradation by increasing the integralgain value. Students may also observe streaking andpiezo-scanner image artifacts.

Finally, if time permits, the students would obtain two imagesusing the optimized feedback parameters that they would havedetermined in the previous steps. The first image requires a rel-atively large scan window of 10 m. The second image is to betaken at a step edge, with a maximum window size of 2 m. Thesmall window size allows the students to observe, in finer detail,the surface characteristics of the Si sample imaged. Students donot use analysis or processing software until module II, wherethe concepts are introduced in full.

The module is graded by having the students, post-laboratorysession, answer questions on the concepts covered in the labsession. In addition to answering the questions, the students areexpected to discuss the results obtained. Students are gradedbased on the depth and accuracy of their statements.

B. Module II—Image Analysis and Processing and LateralForce Microscopy

The aim of module II is twofold (see Fig. 7). First, commonpractices and tools for image analysis and processing are

Page 8: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 435

demonstrated. Second, lateral force microscopy (LFM), orfrictional contrast AFM, is demonstrated and applied.

Image analysis and processing (first part of module) is done inoffline mode. It is stressed to the students that processing shouldnot be excessive, as each processing step commonly has adverseeffects on the data. It is best practice to obtain the best imagepossible during AFM operation before moving onto the analysisand processing stage.

The processing tools demonstrated are the following:• leveling (first-, second-order line-fitting for tilt and

bowing, plane-fitting);• histogram;• mean and noise filtering;• image arithmetic;• fast Fourier transform (FFT) filtering techniques (intro-

duced in module IV).The analysis tools demonstrated are line analysis for step

height measurements and surface roughness measurements.These tools were demonstrated by supplying the same topog-

raphy images to the students. They are then guided through a se-ries of steps using Anfatec’s Present software. The task is toimprove the image quality using the supplied image for practice.There are two significant problems that are corrected: sampletilt and skipped pixels (streaking). The students are asked tocompare different techniques that are used to achieve the sameend results. For each step, they must comment on the positiveand/or negative effects that result through use of the respectiveprocessing tools. Tilt is corrected using both the line-fitting andplane-fitting techniques. Streaking is corrected using histogramand mean filtering techniques.

Students are introduced to the idea that AFM modes arehinged upon the principle of actuating and/or transducingadditional signals, e.g., the T-B deflection (the error signal dis-cussed prior) or the piezo-scanner -position (the topographysignal). Dynamic AFM (including noncontact or intermittentcontact AFM) is accomplished by actuating the AFM cantileverwith an AC oscillation, and images are constructed simply bymonitoring the signal associated with the resulting oscillation(i.e., the magnitude and phase of the cantilever’s oscillation).

In module II, the example of the acquisition of the “Left-Minus-Right” (L-R) signal is used. The L-R signal is correlatedto the torsion of cantilever. The extent of lateral “bending” re-veals frictional information, i.e., the greater the degree of can-tilever torsion, the stronger the frictional forces. While the stu-dents operate the AFM, they will learn the following.

• The operational principles of the instrument remain thesame, with the exception that the L-R signal is simultane-ously acquired,

• The L-R, or frictional, contrast is enhanced when the fast-scan direction is perpendicular to the cantilever’s long axis(since the twisting of the cantilever is maximized).

• L-R contrast in LFM is sensitive to topographic changes(slope of the surface) as well as compositional changes.

It is stressed to the students that all information obtainedabout a sample (whether it be signals related to topography, fric-tion/lateral, AC amplitude and phase, magnetic, electrostatic,forces) must be interpreted simultaneously. Relevant discus-sions are required for the graded post-laboratory assignments.

It is not enough to look at a frictional (L-R) image of a sampleand conclude that the observed contrast is associated with ma-terial contrast or a secondary phase present on the sample sur-face. Frictional (L-R signal) contrast may be due to changingtopographical conditions. In order to correctly interpret com-positional changes on the sample surface using L-R contrast inLFM (for example, in spin-casted polymer blends or patternedself-assembled monolayers), information from the topographyimage must be used simultaneously to aid the interpretation.

In module II, the students again use the MikroMasch CSC-17AlBS probe in order to analyze spin-cast a phase-separatedpolystyrene and poly-(methyl methacrylate) (PMMA) blend.Using their experience obtained in module I, the students areexpected to set up the instrument by themselves and adjustthe feedback and scan parameters as needed, so as to obtainthe best image possible. Once the best possible image hasbeen obtained, signal processing is conducted for the imageacquired using Present. Students are asked to identify anyproblem(s) that they observed with the image(s); discuss thesource of the problem(s) and if any such may be corrected byscanning again with new conditions; propose and conduct anoffline fix to the problem(s) using tools such as line-fitting,histogram, and filtering; and finally discuss if the fixes wereor were not successful and what issues or errors that they mayhave introduced.

C. Module III—Dynamic Modes of Atomic Force Microscopy

Module III first exposes the students to the dynamic modes ofAFM, namely an AFM mode that employs an oscillating can-tilever. For examples of data, see Fig. 8. Dynamic modes includeintermittent contact and noncontact operation. Oscillation am-plitudes may range from a few nanometers to tens of nanome-ters. When the oscillating cantilever approaches the sample sur-face, the tip-sample interaction forces result in a damped oscil-lation, producing a phase shift and/or amplitude change. Thecharacteristics of the oscillation (amplitude and phase lag) areused to construct the images. Unlike contact AFM (covered inmodules I and II), where the (static) T-B signal is used as thefeedback signal, amplitude-modulated AFM uses the oscillationamplitude (of the T-B signal) for feedback input.

The theories and instrumentation related to dynamic AFMare introduced, and topics specifically cover the mechanics ofcantilever motion (approximated as a damped, driven harmonicmechanical oscillator), the origin of phase contrast, powerlosses during the cantilever oscillation cycle, and amplitude-and phase-distance spectroscopies (for further reading, see[19]–[22]). Using the amplitude-distance curve, students ap-proximate the oscillation amplitudes of the cantilever whenfreely oscillating and after having approached the samplesurface.

First, students image patterned Au on a glass substrate. Mar-ginal phase contrast is observed between the Au and glass sur-faces. However, topography and phase images reveal surfacedefects and contaminants on the surfaces. The format of thelab tasks is very similar to module I. With respect to the setupof the experiment, the change from module I is that the stu-dents must determine the driving amplitude and frequency ofthe cantilever. The driving frequency is selected (on or near

Page 9: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

436 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

Fig. 8. Examples of data obtained during module III. (a) Topography image and (b) corresponding phase image of patterned Au on a glass substrate obtainedusing dynamic AFM (amplitude-modulated feedback). The scale bars correspond to 10 �m. During the lab session, the students also acquire amplitude-distanceand phase-distance curves at various free oscillation amplitudes. In (c), the free oscillation amplitude of the cantilever is approximately an order of magnitudesmaller than the free oscillation amplitude in (d). As seen in the plots, the students would observe that the stability of oscillations is generally dependent on the freeoscillation amplitude (and of course, it is sensitive to the system and environmental conditions such as humidity, vacuum, and so forth). Acquisition of topographyand phase images requires a stable cantilever oscillation. Additionally, the students are required to alter the feedback parameters, similar to the procedures outlinedin module I, so as to improve the image quality during acquisition. They explore the effect of altering the free oscillation amplitude, setpoint reference, and thefeedback gain parameters. The amplitude- and phase-distance curves obtained are typical, and the theory is described elsewhere [19].

resonance) after the frequency response of the cantilever is de-termined. Once selecting a setpoint oscillation amplitude, thesample is approached toward the surface. Then, the students ac-quire amplitude- and phase-distance curves, from which theycan determine their oscillation amplitude (free amplitude andsetpoint amplitude used for feedback). The initial oscillationamplitude is roughly 10 nm. Students begin imaging and ex-plore the effects of the feedback and scan parameters. Once theparameters are set, the students acquire topography, amplitude,and phase signals, with the amplitude signal being treated asthe error signal. When the scan(s) is (are) complete, the stu-dents increase their free oscillation amplitude to a significantlygreater value and repeat the amplitude-distance and phase-dis-tance spectroscopy, parameter optimization, and image acquisi-tion. The students can compare the results of imaging with smalland large amplitudes.

For the graded post-lab exercise, the students are required toprovide their obtained images and their processed images and todiscuss the steps and concepts covered during the lab session.

D. Module IV—High Resolution Imaging

Module IV pushes the AFM to its practical limits under am-bient conditions. Issues related to vibrational isolation, thermalnoise/drifting, and electrical noise are introduced as challengesto acquiring high-resolution images (with subnanometer resolu-tion in the -direction). Examples of student data taken duringthe lab are shown in Fig. 9.

First, the students image in dynamic AFM a freshly cleavedmica surface. The mica samples are supplied by NTMDT [23].The students prepare the mica by applying adhesive tape to thesurface and “peeling” it off, resulting in a cleaved, atomicallyflat mica surface. The atomically flat surface is ideal for studyingnoise sources present in AFM: It is not unreasonable to assumethat any contrast observed in the obtained images is a direct re-sult of noise present in the system. The students can explore howthe noise “maps” into a spatial image depending on the line scanfrequency, scan window, scan angle, and so forth. Any noisesobserved in the image may be studied using discrete FFT anal-ysis, either one-dimensional (1-D) or two-dimensional (2-D).

Page 10: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 437

Fig. 9. Student data obtained during module IV is summarized. Unless otherwise specified, the scale bar represents 250 nm. Note that the FFT images are croppedalong the �-axis direction only. (a) Dynamic mode topography image on a freshly cleaved mica surface. The origin of observed contrast is attributed to noisesources, including electronic and vibrational noise. (b) Corresponding 2-D FFT image, showing a significant noise band. (c), (d) Phase and topography images ofDNA on a mica substrate, also obtained using dynamic AFM. (e) 2-D FFT image corresponding to the topography image in (d). The noise in the topography imageof the DNA image has manifested itself similarly to the image of mica in (a), as it is seen that there are matching bands in the 2-D FFT images (b) and (e). Thesenoise bands are selected in (f) and are used to filter the noise in the topography image. (g) Filtering result. The topography image, after subtraction of the noiseimage in (f) from (h) the original DNA topography image shows much improvement in image quality.

Typically, low-frequency noise (less than 2 Hz) can be attributedto building vibrations.

Next, the students image DNA strands on the mica surface,again in a dynamic AFM mode (DNA samples are providedby NTMDT). They study the topography, phase, and amplitude(error) images to draw conclusions about the sample; they alsoidentify the noise that disrupts the image quality. Improving theimage quality is explored by varying scan, feedback, and oscil-lation parameters. The image quality is further improved using2-D discrete FFT filtering in Gwyddion as a way to eliminateany spatial frequencies associated with the noise of the system,which is primarily due to mechanical vibrations. Other samplesthat are imaged, as time permits, are monatomic steps of sil-icon or sapphire. The monatomic steps can be observed undernormal, ambient operating conditions. It has to be noted, how-ever, that the use of a more sophisticated vibration isolation tableis in fact able to decrease the noise level significantly.

E. Module V—Nanolithography

Module V introduces SPM as a suite of tools not only for ma-terial characterization, but also for manipulation and fabrication.The AFM instrument provides the user with control over a mi-croactuator (the cantilever) outfitted with a nanoprobe (the tip).The nanoprobe may be modified and used in any way that theuser desires. Numerous applications of the AFM for less con-ventional approaches to nanolithography have been discussedin the literature [24]–[34].

For the delivery of module V, mechanical scratching (alsoknown as ploughing) of a spin-casted PMMA film and oxidationof ultra-thin titanium films were carried out. Both the mechan-ical scratching route and oxidation route are repeatable and re-liable methods. Other systems of interest, which have not been

made part of the module, are based on the reduction of plat-inum and gold salts and polymerization of conducting polymers.Dip-pen lithography [24]–[26] of alkanethiols on gold surfacesis one of the established lithography techniques. However, it wasnot selected for module V since the deposition of the alkanethioloccurs whenever the tip makes contact with the Au surface.Imaging the patterned monolayer layer structures would thenrequire changing to a tip not coated with ink and relocating thefabricated patterns on the sample surface. Changing tips and re-locating patterns is a time-consuming procedure and deemed notsuitable for a 3-h lab session. The lithography techniques (me-chanical scratching, oxidation of titanium, reduction of metalsalts, and polymerizations) are activated by increasing contactforce or applying a voltage.

Oxidation of titanium surfaces was selected for the first de-livery of the course. The titanium surface was prepared by elec-tron beam evaporation onto oxidized Si wafers. The Ti filmforms a protective oxide upon exposure to air subsequent tothe deposition in ultrahigh vacuum. An NSC18/Co-Cr probe isused for module V. It is a silicon probe with a bilayer coating ofcobalt and chromium (the chromium layer is exterior to protectthe cobalt from oxidizing). The tip radius is a nominal 90 nm,and the resonant frequency and spring constant are approxi-mately 100 kHz and 3.5 N/m, respectively. An example of apattern written into resist by the ploughing process is providedin Fig. 10(f).

F. Module VI—Electrostatic Force Microscopy and MagneticForce Microscopy

Module VI concludes the laboratory course. Its aim is todemonstrate extended modes of dynamic AFM operation: EFM[35]–[37] and MFM (see Fig. 11). The concepts and techniques

Page 11: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

438 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

Fig. 10. The AFM lithography module V was developed using two techniques: oxidation and nanoploughing. (a) Schematic of the oxidation technique. Adsorbedwater on the sample surface (e.g., titanium that forms a native, protective oxide) acts as the electrochemical cell, and an applied potential between tip and sampleinduces oxidation of the thin film. The applied voltage and time of exposure of the sample surface to the applied voltage control the oxide depth and width. Patternscan be generated by controlling the path of the tip, and selectively controlling when the voltage is applied between tip and sample. (b) Example of oxide lineswritten on titanium at various write speeds and applied voltages. (c) Result produced by a student during module V of the laboratory course, again by oxidizing atitanium surface. (d) Schematic of the nanoploughing technique. In contact mode, a soft polymer or metal surface can be scratched when a large contact force isapplied. By controlling the tip path, and by modulating the contact force, the pattern created in the polymer or metal can be controlled. (e) Example data obtainedusing the nanoploughing technique with a high-force constant cantilever. The results show that with increasing contact force, both the pit depth and width increase.(f) Potential fabrication scheme using nanoploughing as the pattern-defining step. In step � , the desired pattern is ploughed into the resist layer. It is not necessaryto plough through to the underlying substrate, as in step � , a gentle plasma etch will uniformly etch the polymer through to the surface. Where the resist layerwas not ploughed, the resist layer remains and acts as a mask. Next, a thin metal layer is deposited by electron beam evaporation (step � ) and, finally, liftoff ofthe metal-coated resist (step �) leaves the patterned structures.

are taught in the context of two-pass methods, where in eachline of the scan, the topography is first scanned using conven-tional means (intermittent contact or noncontact), then the sameline is repeated with the tip lifted a fixed distance from thesurface. The tip is lifted at distances where long-range forcesdominate (electrostatic and magnetic). If the tip is magnetizedor charged, then during the second pass, the amplitude andphase changes of the oscillating cantilever can be associatedwith electrostatic/magnetic forces acting between the tip andsample. Such modulation reveals electrostatic and/or magneticinformation about the sample.

The theory and technique of Kelvin probe microscopy isdemonstrated, as well as its advantages over two-pass EFM.KPFM is not practiced by the students during the laboratorysession since it requires a second lock-in amplifier that notall of the AFMs are equipped with. Furthermore, due to timeconstraints, MFM is not regularly included as part of the labmodule. Unless the lab is extended by an additional lab day,these modules are taught only to students specifically interestedin MFM.

The laboratory procedure for module VI is to obtain two-passEFM amplitude and phase images, along with the topography,amplitude, and phase images. The students select an appropriateoscillation amplitude, as well as tip-sample separation distance

during the second pass. As always, the students are required tooptimize their feedback and scan parameters to obtain the bestimage possible. The sample imaged is a set of interdigitated Auelectrode fingers on a glass substrate. One set of fingers and thetip are held at system ground. The other set of fingers is con-nected with the sample stage, which is held at a software-con-trolled bias. With this setup, the students can control the biasof one of the electrodes with respect to the tip, while the otherelectrode set is always grounded. The effect of the applied biascan be observed in the amplitude and phase images: Contrastincreases for increasing applied bias, and the amplitude andphase changes occur only on the electrode finger held at the ap-plied bias. Contrast is also observed at the grounded electrode.Though both the tip and electrode are grounded, a built-in fieldis established across the air gap due to the Fermi level offset ofthe gold electrode and chromium tip.

IV. DISCUSSION

While the manuals were written with sufficient detail to guidethe students through the entire laboratory procedure without theaid of the instructor, it was found that, due to the 3-h time con-straint per lab session, the most efficient method of deliveringthe course was to guide the students as a group through the ini-tial setup steps. When the initial setup steps are completed, the

Page 12: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 439

Fig. 11. Two-pass EFM images obtained during the lab module VI. The scale bars are 7.5 �m. The sample is a set of Au electrodes on a glass substrate. Inthis experiment, both the tip and left electrode shown in (a)–(c) are at system ground, while the right electrode is held at some positive or negative applied bias(controlled through the software). (a) Topography, (b) second-pass amplitude, and (c) second-pass phase images. During the image acquisition, the bias appliedto the right electrode is varied. At nonzero biases, a reduction in the oscillation amplitude can be seen during the second pass (the amplitude change may be onlya few nanometers or less), and a positive phase shift during the second pass. The magnitudes of the change of amplitude and phase are a function of the appliedvoltage and, hence, the magnitude of the electrical force between the tip and sample. Note that, independent of the sign of the applied voltage, the interaction forceis always attractive. The topography image is obtained using standard dynamic mode AFM techniques, while the amplitude and phase images in (b) and (c) aresecond-pass images. While this second-pass technique for electrical imaging is not as powerful as the KPFM alternative for electrical force imaging, it nonethelessdemonstrates to the students the role of the long-range electrical forces. A magnetic system, using MFM, would behave similarly. In the topography image, we seethat for large applied biases, the topography data is inadvertently altered: The topography image shows two false step heights near the bottom of the image on theright electrode. When the applied bias is significant, generating strong-enough electrical attractive force, convolution of these electrical forces with shorter rangeforces used for constructing topography images affects the feedback and hence produces incorrect data. Such behavior is intended to demonstrate to the studentshow the AFM instrumentation, techniques, and behavior truly depend on the forces acting between tip and sample, which are characterized by the force-distancecurve. The students should never lose sight of this fact that all imaging depends on the force-distance curve.

groups independently explore the instrument and continue withthe tasks set out in the manual.

Judging from the submitted laboratory reports, it is suspectedthat six 6-h sessions would allow for better retention of the ma-terial covered. Increasing the total course time from 18 to 36 hwould not entail an increase in the amount of course material. Incontrast, the students may spend more time to achieve a bettercomfort level with the AFM, the material covered in the lectureand laboratory courses, and ultimately to understand what theinstrument is capable of and how to interpret images obtainedwith the techniques.

Surveys were conducted prior to the start of the laboratorycourse and after the end of the course. The surveys were usedto gauge the students’ expectations going into the course, and atthe end of the course, if those expectations were met and whatthe overall satisfaction with the course was. The same ques-tions were asked in the pre- and post-laboratory course surveys.The survey questions were posed as statements, and the studentshad to choose their level of disagreement or agreement with thestatements. Statements include: “The course is of educationalvalue to me”; “The course covers an adequate amount of mate-rial”; “The time allocated for completing the labs (three hoursper lab day) is/was sufficient”; “The course contains enoughhands-on experience”; “The lab manuals are useful”; “I will beusing the lab manuals in my future workplace”; “The samplesdemonstrated the AFM techniques well”; “I am able to obtain ahigh-quality image”; “From a set of recorded images, I am con-fident to distinguish a real feature from an artifact”; and “Theknowledge gained is advantageous for my career.”

Based on both the survey results and personal discussionswith the students, they were generally enthusiastic about thecourse. At the onset of the course, they had the expectation

that from the course, they would garner new practical skillsand knowledge in the realm of AFM instrumentation and tech-niques. Enthusiasm toward the course was expected since pre-vious courses in the NE curriculum (including the lecture courseon “Nanoprobing and Nanolithography”) would have exposedthe students to the relevance, importance, and applicability ofthe AFM technique. When the labs were concluded, student re-sponse to and feedback on the labs was overall positive: Theyfelt they had learned new and useful material and had sufficienthands-on experience and practice and, importantly, the coursewas enjoyable.

The survey responses indicated that a large number of stu-dents did not feel that they could obtain high-quality, artifact-free images. The survey responses from a large fraction of thestudents also indicated that the time allocated for completing thelabs (3 h per day) is not adequate: The material covered per labsession is too compressed. The inability to obtain high-qualityimages is perhaps a manifestation of this problem. One possiblesolution is to increase the duration of the lab session from 3 to6 h and reduce the number of groups to four.

In fact, there are some topics that the authors feel are missingfrom the laboratory course curriculum. Some advanced topicsinclude, but are not limited to: force spectroscopy for adhe-sion studies, KPFM (including surface and contact potentialmeasurements), dip-pen lithography, electrochemical dip-penlithography, conductive AFM, elastic force microscopy, andpiezoresponse force microscopy. The students would certainlybenefit from a second, follow-up lab in the following term tocover the more advanced topics—for instance, in the form ofan AFM-based nanoelectronics course.

Finally, the SPM lab infrastructure is not limited to use in theNE 450L laboratory. The SPM lab is particularly useful for in-

Page 13: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

440 IEEE TRANSACTIONS ON EDUCATION, VOL. 54, NO. 3, AUGUST 2011

tegration into other fourth-year laboratory courses offered in thecurriculum, where topics range from nanoelectronics, nanoma-terials, nanobiotechnology, to nanoinstruments. NE 450L actsas a stepping stone, or introduction, for the application of AFMin the other laboratory courses. For example, one can considera nanoelectronics lab where single-electron device structuresare fabricated using the AFM as a nanolithography tool [38],[39]. Starting from simple back-gated electronic transport struc-tures—which are fabricated in the NE cleanroom facility (aspart of the “Microfabrication and Thin Film Technology Labo-ratory,” NE 340L)—scanning probe lithography allows, for in-stance, for the fabrication of Coulomb blockade structures [40]that can be conveniently investigated even at liquid nitrogentemperatures [41].

In summary, it has to be stressed that the intent is not that stu-dents become experts with AFM in the short 18-h span. Such aduration is just enough to expose the students to the instrument,provide them with an understanding of operational and theoret-ical principles, and allow them to understand how these can beapplied to work in metrology or lithography in their future ca-reers. Based on the feedback, and in spite of the improvementsthat may be made to the course, this task is felt to have beensuccessfully accomplished.

ACKNOWLEDGMENT

The authors would like to thank Dr. A.-D. Müller of AnfatecInstruments AG, Oelsnitz, Germany, for her assistance withthe development of the laboratory; as well as Prof. J. Barby(Electrical and Computer Engineering Department, UW) andDr. S. Forsey (Chemistry Department, UW) for their contribu-tions to setting up this lab course.

REFERENCES

[1] “Anfatec Instruments AG,” Oelsnitz, Germany, accessed Jul. 31, 2010[Online]. Available: http://www.anfatec.de

[2] Y. Seo and W. Jhe, “Atomic force microscopy and spectroscopy,” Rep.Prog. Phys., vol. 71, no. 1, p. 016101, Jan. 2008.

[3] R. García and R. Pérez, “Dynamic atomic force microscopy methods,”Surf. Sci. Rep., vol. 47, no. 6–8, pp. 197–301, Sep. 2002.

[4] E. Meyer, H. J. Hug, and R. Bennewitz, Scanning Probe Microscopy:The Lab on a Tip. Berlin, Germany: Springer, 2003.

[5] P. Eaton and P. West, Atomic Force Microscopy. Oxford, U.K.: Ox-ford Univ. Press, 2010.

[6] K. Winkelmann, “Practical aspects of creating an interdisciplinary nan-otechnology laboratory course for freshmen,” J. Nano Educ., vol. 1, pp.34–41, Jan. 2009.

[7] J. D. Adams, B. S. Rogers, and L. J. Leifer, “Microtechnology,nanotechnology, and the scanning probe microscope: An innovativecourse,” IEEE Trans. Educ., vol. 47, no. 1, pp. 51–56, Feb. 2004.

[8] M. Guggisberg, P. Fornaro, T. Gyalog, and H. Burkhart, “An interdis-ciplinary virtual laboratory on nanoscience,” Future Gener. Comput.Syst., vol. 19, no. 1, pp. 133–141, Jan. 2003.

[9] C. Tahan, R. Leung, G. M. Zenner, K. D. Ellison, W. C. Crone, andC. A. Miller, “Nanotechnology and society: A discussion-based un-dergraduate course,” Amer. J. Phys., vol. 74, no. 5, pp. 443–448, May2006.

[10] D. W. Lehmpuhl, “Incorporating scanning probe microscopy into theundergraduate chemistry curriculum,” J. Chem. Educ., vol. 80, no. 5,pp. 478–479, May 2003.

[11] M. M. Maye, J. Luo, L. Han, and C.-J. Zhong, “Chemical analysis usingscanning force microscopy. An undergraduate laboratory experiment,”J. Chem. Educ., vol. 79, no. 2, pp. 207–210, Feb. 2002.

[12] C.-J. Zhong, L. Han, M. M. Maye, J. Luo, N. N. Kariuki, and W. E.Jones, Jr., “Atomic scale imaging: A hands-on scanning probe mi-croscopy laboratory for undergraduates,” J. Chem. Educ., vol. 80, no.2, pp. 194–197, Feb. 2002.

[13] T. S. Sullivan, M. S. Geiger, J. S. Keller, J. T. Klopcic, F. C. Peiris,B. W. Schumacher, J. S. Spater, and P. C. Turner, “Innovations innanoscience education at Kenyon College,” IEEE Trans. Educ., vol.51, no. 2, pp. 234–241, May 2008.

[14] “Mikromasch USA,” San Jose, CA, accessed Jul. 31, 2010 [Online].Available: http://www.spmtips.com

[15] “AFM Simulation Programs by Joe Griffith,” Nanoscience In-struments, Inc., Phoenix, AZ, Jul. 31, 2010 [Online]. Available:http://www.nanoscience.com/education/software.html

[16] “Nanoprobing & nanolithography teaching lab,” NE Program, Univ.Waterloo, Waterloo, ON, Canada, accessed Jul. 31, 2010 [Online].Available: http://spm.uwaterloo.ca

[17] H.-J. Butt, B. Cappella, and M. Kappl, “Force measurements with theatomic force microscope: Technique, interpretation and applications,”Surf. Sci. Rep., vol. 59, no. 1–6, pp. 1–152, Oct. 2005.

[18] X. Xiao and L. Qian, “Investigation of humidity-dependent capillaryforce,” Langmuir, vol. 16, no. 21, pp. 8153–8158, Sep. 2000.

[19] A. San Paulo and R. García, “Attractive and repulsive tip-sample inter-action regimes in tapping-mode atomic force microscopy,” Phys. Rev.B., Condens. Matter, vol. 60, no. 7, pp. 4961–4967, Aug. 1999.

[20] A. San Paulo and R. García, “Amplitude, deformation and phase shiftin amplitude modulation atomic force microscopy: A numerical studyfor compliant materials,” Surf. Sci., vol. 471, pp. 71–79, 2001.

[21] J. P. Cleveland, B. Anczykowski, A. E. Schmid, and V. B. Elings,“Energy dissipation in tapping-mode atomic force microscopy,” Appl.Phys. Lett., vol. 72, no. 20, pp. 2613–2615, May 1998.

[22] L. Zitzler, S. Herminghaus, and F. Mugele, “Capillary forces in tappingmode atomic force microscopy,” Phys. Rev. B, Condens. Matter, vol.66, no. 15, p. 155436, Oct. 2002.

[23] “NT-MDT Co.,” Moscow, Russia, accessed Jul. 31, 2010 [Online].Available: http://www.ntmdt.com

[24] D. S. Ginger, H. Zhang, and C. A. Mirkin, “The evolution of dip-pennanolithography,” Angew. Chem. Int. Ed., vol. 43, no. 1, pp. 30–45, Jan.2004.

[25] K. Salaita, Y. H. Wang, and C. A. Mirkin, “Applications of dip-pennanolithography,” Nature Nanotechmol., vol. 2, no. 3, pp. 145–155,Feb. 2007.

[26] Y. Li, B. W. Maynor, and J. Liu, “Electrochemical AFM dip-pen nano-lithography,” J. Amer. Chem. Soc., vol. 123, no. 9, pp. 2105–2106, Feb.2001.

[27] B. W. Maynor, S. F. Filocamo, M. W. Grinstaff, and J. Liu, “Di-rect-writing of polymer nanostructures: Poly(thiophene) nanowires onsemiconducting and insulating surfaces,” J. Amer. Chem. Soc., vol.124, no. 4, pp. 522–523, Jan. 2002.

[28] B. Klehn and U. Kunze, “Nanolithography with an atomic force micro-scope by means of vector-scan controlled dynamic plowing,” J. Appl.Phys., vol. 85, no. 7, pp. 3897–3903, Apr. 1999.

[29] L. Santinacci, T. Djenizian, H. Hildebrand, S. Ecoffey, H. Mokdad,T. Campanella, and P. Schmuki, “Selective palladium electrochemicaldeposition onto AFM-scratched silicon surfaces,” Electrochim. Acta,vol. 48, no. 20–22, pp. 3123–3130, Sep. 2003.

[30] B. Irmer, R. H. Blick, F. Simmel, W. Gödel, H. Lorenz, and J. P.Kotthaus, “Josephson junctions defined by a nanoplough,” Appl. Phys.Lett., vol. 73, no. 14, pp. 2051–2053, Oct. 1998.

[31] C. Balocco, A. G. Jones, J. M. Kingsley, J. R. Chan, X. Q. Huang, andA. M. Song, “Scanning probe microscope based nanolithography onconducting polymer films,” Jpn. J. Appl. Phys., vol. 45, no. 3B, pp.2095–2098, Mar. 2006.

[32] M. Heyde, K. Rademann, B. Cappella, M. Geuss, H. Sturm, T. Span-genberg, and H. Niehus, “Dynamic plowing nanolithography on poly-methylmethacrylate using an atomic force microscope,” Rev. Sci. In-strum., vol. 71, no. 1, pp. 136–141, Jan. 2001.

[33] P. Avouris, R. Martel, T. Hertel, and R. Sandstrom, “AFM-tip-inducedand current-induced local oxidation of silicon and metals,” Appl. Phys.A, Solids Surf., vol. 66, no. S1, pp. 659–667, Mar. 1998.

[34] K. Wilder, C. F. Quate, B. Singh, and D. F. Kyser, “Electron beam andscanning probe lithography: A comparison,” J. Vac. Sci. Technol. B,Microelectron. Process. Phenom., vol. 16, no. 6, pp. 3864–3873, Nov.1998.

[35] P. Girard, “Electrostatic force microscopy: Principles and someapplications to semiconductors,” Nanotechnology, vol. 12, no. 4, pp.485–490, Dec. 2001.

Page 14: An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

RUSSO et al.: UNDERGRADUATE NANOTECHNOLOGY ENGINEERING LAB COURSE ON ATOMIC FORCE MICROSCOPY 441

[36] S. Watanabe, K. Hane, T. Ohye, M. Ito, and T. Goto, “Electrostaticforce microscope imaging analyzed by the surface charge method,” J.Vac. Sci. Technol. B, Microelectron. Process. Phenom., vol. 11, no. 5,pp. 1774–1781, Sep. 1993.

[37] C. H. Lei, A. Das, M. Elliott, and J. E. Macdonald, “Quantitative elec-trostatic force microscopy-phase measurements,” Nanotechnology,vol. 15, no. 5, pp. 627–634, May 2004.

[38] R. Held, T. Heinzel, P. Studerus, K. Ensslin, and M. Holland, “Semi-conductor quantum point contact fabricated by lithography with anatomic force microscope,” Appl. Phys. Lett., vol. 71, no. 18, pp.2689–2691, Nov. 1997.

[39] J. A. Vicary and M. J. Miles, “Pushing the boundaries of local oxidationnanolithography: Short timescales and high speeds,” Ultramicroscopy,vol. 108, no. 10, pp. 1120–1123, Sep. 2008.

[40] C. Fricke, J. Regul, F. Hohls, D. Reuter, A. D. Wieck, and R. J. Haug,“Transport spectroscopy of a quantum point contact created by anatomic force microscope,” Physica E, vol. 34, no. 1–2, pp. 519–521,Aug. 2006.

[41] K. Matsumoto, M. Ishii, K. Segawa, Y. Oka, B. J. Vartanian, and J.S. Harris, “Room temperature operation of a single electron transistormade by the scanning tunneling microscope nanooxidation process forthe ��� ��� system,” Appl. Phys. Lett., vol. 68, no. 1, pp. 34–36, Jan.1996.

Daniel Russo received the B.A.Sc. degree in nanotechnology engineering fromthe University of Waterloo, Waterloo, ON, Canada, in 2010.

He is currently with Polar Mobile, Toronto, ON, Canada.

Randal D. Fagan received the B.Sc. degree in science from the University ofWaterloo, Waterloo, ON, Canada, in 1997.

He is currently a Lab Instructor with the Nanotechnology Engineering Pro-gram at the University of Waterloo.

Thorsten Hesjedal (S’96–A’97–SM’03) received the Ph.D. degree in physicsfrom the Humboldt University, Berlin, Germany, in 1997.

He is currently an Associate Professor of electrical and computer engineeringwith the University of Waterloo, Waterloo, ON, Canada. He is involved with thedevelopment of the Nanotechnology Engineering Program and specializes inthis context in materials characterization by electron microscopy, X-ray diffrac-tion, and spectroscopy techniques, as well as scanning probe microscopy.