afm 2 notes - university of warwickveeco spm guide afm lecture 2 6 tube piezo but cross-talk...
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![Page 1: AFM 2 notes - University of WarwickVeeco SPM guide AFM lecture 2 6 Tube piezo BUT cross-talk difficult to integrate with sensors RIGID high resonant frequency less sensitive to noise](https://reader033.vdocuments.us/reader033/viewer/2022041608/5e35cdd4d421a11179524b23/html5/thumbnails/1.jpg)
AFM lecture 2
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Outline
• AFM designs• Imaging modes• Cantilevers and tips• Imaging artefacts• References / links
AFM lecture 2
2
Deflection detection
as in MHB
light lever
interferometer
electron tunneling
capacitance
piezoresistive
piezoelectric
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AFM lecture 2
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Sample scanning
Veeco Multimode – sample scans x,y,z Asylum Research MFP-3D – sample scans x,ytip scans z
from Veeco training manual from AR website
AFM lecture 2
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Tip scanning
Difficulty in maintaining laser position on tip
More flexibility in samples
Harder to make rigid
from Veeco training manual
Veeco Dimension Veeco Enviroscope
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AFM lecture 2
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Piezo scanner design
• typical piezo response ~ 0.262 nm / V
• to elongate a bar of 1 cm by 1 m,apply a voltage of 380 V across 1 mm
Veeco SPM guide
AFM lecture 2
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Tube piezo
BUTcross-talkdifficult to integrate with sensors
RIGIDhigh resonant frequencyless sensitive to noisefaster scan rates possible
Veeco SPM guide
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Flexure based
No cross talk,Easier to integrate sensorsLarger scan areas possible
higher mass – lower resonant frequencygreater sensitivity to noiseslower scan speeds
AFM lecture 2
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Controllers
Can be mostly hardware or almost entirely software.
Look for high sampling rates, flexibility, and low electrical noise
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Available AFMs
Asylum Research MFP-3D – sample x-y tip z90 m square closed loop, z range 15 m closed loop, controller - 16 bit variable gain
Enviroscope – tip scanning, tube piezoScan size 90 m square x-y, 5 m zz noise ~ 0.5 - 1.0 A (greater in vacuum)sample size – flexible depending on stage usedNanoscope IV controller – similar specs to Nanoscope IIIa plus Quadrex
Multimode – sample scanning, tube piezoJ scanner ~120 m square and 5.5 m z (z noise < 0.5A)E scanner ~ 5 m square x-y (I think!), and ~ 2.5 m zA scanner ~ 1 m square x-y, z ? (not vertical engage)Picoforce ~ 40 m x-y, and 20 m z closed loopNanoscope IIIa controller – 16 bit variable gainQuadrex – dual phase lock-in amplifiersample size limited to ~ 15 mm square by ~ 5 - 10 mm
Warwick
Nottingham – lots including above and several
AFM lecture 2
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Imaging Modesstatic dynamic
contact
noncontact
contact mode force modulation ultrasonic force
microscopy
tapping mode
‘noncontact’ mode
torsional / shear mode
static deflection
mode
pulsed force mode
EFM, MFM …
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Contact mode
height deflection lateral force
5 m scans of pressure densified polycrystalline alumina, 50 nm height scale. Sample courtesy of Geoff West.
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Force curve
deflection sensitivity (typical values ~ 100 – 200 nm V- 1)
spring constant (in contact typically 0.01 – 1 nN m- 1)
adhesion force (typical values in ambient ~ 10 – 100 nN)
imaging forcelarge contact force => large lateral force when imaging
BAD FOR SOFT SAMPLES AND SHARP TIPS
Def
lect
ion
(V)
z displacement (nm)
constant compliancejump to contact
adhesion force
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‘Tapping mode’
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• dynamic mode• driven oscillator• amplitude modulation• intermittent contact
A0 – free amplitudeA – imaging amplitudeA < A0
A / A0 ~ 1 ‘Soft tapping’A / A0 << 1 ‘Hard tapping’
Typical oscillation amplitudes A ~ 5 – 50 nm
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Imaging in tapping mode
height amplitude phase
5 m scans of pressure densified polycrystalline alumina, 50 nm height scale. Sample courtesy of Geoff West.
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Force curve – tm
150 175 200-1.0
-0.5
0.0βα
Amplitude(V)
z displacem ent(nm )150 175 200
0.00
0.05
0.10
γTM deflection(V)
z displacem ent(nm )
amplitude sensitivitydeflection sensitivity
With Veeco AFM’s usually have 2 V target oscillation amplitude
amplitude sensitivity ~ 10 nm V-1 for 100 m cantilever20 nm V-1 for 200 m cantilever
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TM vs CM
Tapping ModeContact Mode
Lower interaction forces (especially lateral)
Cheap
More versatileSimple
More sensitiveStable
Higher resolution (tip effects)
Easy to implement
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Cantilevers and tips
l
wt
V-shaped cantileverdiving board or rectangularcantilever
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the ‘tip’
scale bar 1 mm scale bar 20 m scale bar 25 nm
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Critical parameters
CANTILEVERspring constant, deflection sensitivity, Q,
0,length,width,thickness,geometry,reflectivity,tolerances,tip positions, materialcoatings
https://www.veecoprobes.com/
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Critical parameters
TIPradius,coneangle,coneheight,tip setback, materialcoatinggeometry
https://www.veecoprobes.com/
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Choosing cantilevers / tips
• contact mode – force (spring constant and length), wear resistance, surface functionality, thermal drift, lateral stability, cost ….
• tapping mode – resonant frequency, Q, k,length, resolution, coatings, cost, imagingunder solution ….
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Tip effects – ‘resolution’
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Tip wear
Damage of the tip
‘picking – up’ contaminants
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Common tip / imaging artefacts
• double tip• blunt tip• streaking• contamination• optical interference• poor tracking• ‘ringing’• ‘noise’
Veeco SPM guide / NW
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Tip deconvolution
• critical for quantitative force measurements• deconvolution sample• drawback – tip wear
www.ntmdt.com
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Imaging artefacts - piezo
Piezo’s should be calibrated in x-y and z regularly
• critical• should be checked with relevant test sample• best ~ few %
Piezo’s without closed loop are liable to• hysteresis• creep• bow• drift• ageing
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Tip manufacturers
• Nanoworld• MikroMasch (www.spmtips.com)• Budget Sensors – available through Windsor Scientific• Veeco• Nanosensors• www.nanoandmore.com• ……
Also do calibration samples etc.
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Instrument manufacturers
• Agilent Technologies• Asylum Research• Jeol• JPK• Omicron• Nanonis and Nanosurf for controllers• Park Systems • Veeco (used to be DI)• ……….
Also usually have application notes and educational materials
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Image processing software
• WSXM freeware available from www.nanotec.es• Nanoscope Software (on CD) for Veeco files• SPIP – from Image Metrology
http://www.imagemet.com/• Image J - general image analysis software with plug-ins
for SPM analysis http://rsb.info.nih.gov/ij/
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References and links
• Veeco ‘A practical Guide to SPM’ available from their website (hopefully on CD as well)
• http://www.novascan.com/education/• http://virlab.virginia.edu/VL/easyScan_AFM.htm• For calibration standards see
http://www.pacificnano.com/standards-references.html• How AFM works
http://stm2.nrl.navy.mil/how-afm/how-afm.html• Advances in AFM
GiessiblRev. Mod. Phys. 75, 949-982, 2003on CD