AFM lecture 2
AFM lecture 2
Outline
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Deflection detection
AFM designs
Imaging modes
Cantilevers and tips
Imaging artefacts
References / links
light lever
interferometer
electron tunneling
capacitance
piezoresistive
piezoelectric
as in MHB
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AFM lecture 2
AFM lecture 2
Sample scanning
Tip scanning
from Veeco training manual
Difficulty in maintaining laser
position on tip
More flexibility in samples
Harder to make rigid
Veeco Multimode – sample scans x,y,z
from Veeco training manual
Asylum Research MFP-3D
– sample scans x,y
tip scans z
Veeco Dimension
from AR website
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Veeco Enviroscope
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AFM lecture 2
AFM lecture 2
Piezo scanner design
Tube piezo
Veeco SPM guide
Veeco SPM guide
• typical piezo response ~ 0.262 nm / V
• to elongate a bar of 1 cm by 1Pm,
apply a voltage of 380 V across 1 mm
RIGID
high resonant frequency
less sensitive to noise
faster scan rates possible
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BUT
cross-talk
difficult to integrate with sensors
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AFM lecture 2
AFM lecture 2
Flexure based
Controllers
Can be mostly hardware or
almost entirely software.
No cross talk,
Easier to integrate sensors
Larger scan areas possible
higher mass – lower resonant frequency
greater sensitivity to noise
slower scan speeds
Look for high sampling rates,
flexibility, and low electrical
noise
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AFM lecture 2
AFM lecture 2
Available AFMs
Imaging Modes
Warwick
static
Multimode – sample scanning, tube piezo
J scanner ~120Pm square and 5.5 Pm z (z noise < 0.5A)
E scanner ~ 5 Pm square x-y (I think!), and ~ 2.5 Pm z
A scanner ~ 1 Pm square x-y, z ? (not vertical engage)
Picoforce ~ 40 Pm x-y, and 20 Pm z closed loop
Nanoscope IIIa controller – 16 bit variable gain
Quadrex – dual phase lock-in amplifier
sample size limited to ~ 15 mm square by ~ 5 - 10 mm
contact
dynamic
contact mode
pulsed
force
mode
Enviroscope – tip scanning, tube piezo
Scan size 90 Pm square x-y, 5 Pm z
z noise ~ 0.5 - 1.0 A (greater in vacuum)
sample size – flexible depending on stage used
Nanoscope IV controller – similar specs to Nanoscope IIIa plus Quadrex
force modulation
ultrasonic
force
microscopy
torsional / shear mode
tapping mode
‘noncontact’ mode
Nottingham – lots including above and several
Asylum Research MFP-3D – sample x-y tip z
90 Pm square closed loop, z range 15 Pm closed loop,
controller - 16 bit variable gain
noncontact
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static
deflection
mode
EFM, MFM …
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AFM lecture 2
AFM lecture 2
Contact mode
Force curve
constant compliance
jump to contact
deflection
lateral force
Deflection (V)
height
adhesion force
z displacement (nm)
deflection sensitivity
(typical values ~ 100 – 200 nm -V 1)
1)
spring constant
(in contact typically 0.01 – 1 nN m
adhesion force
(typical values in ambient ~ 10 – 100 nN)
imaging force
large contact force => large lateral force when imaging
BAD FOR SOFT SAMPLES AND SHARP TIPS
5 Pm scans of pressure densified polycrystalline alumina, 50 nm height scale.
Sample courtesy of Geoff West.
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AFM lecture 2
AFM lecture 2
‘Tapping mode’
A0
A0
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Imaging in tapping mode
dynamic mode
driven oscillator
amplitude modulation
intermittent contact
z
A0 – free amplitude
A – imaging amplitude
A < A0
2A
A
A / A0 ~ 1
A / A0 << 1
height
amplitude
phase
‘Soft tapping’
‘Hard tapping’
Typical oscillation amplitudes
A ~ 5 – 50 nm
5 Pm scans of pressure densified polycrystalline alumina, 50 nm height scale.
Sample courtesy of Geoff West.
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AFM lecture 2
AFM lecture 2
Force curve – tm
TM vs CM
amplitude sensitivity
deflection sensitivity
0.0
TM deflection (V)
Am plitude (V)
0.10
β
α
-0.5
-1.0
150
175
200
z displacem ent(nm )
0.05
γ
0.00
150
175
200
z displacem ent(nm )
With Veeco AFM’s usually have 2 V target oscillation amplitude
amplitude sensitivity ~
Contact Mode
Tapping Mode
Cheap
Simple
Lower interaction forces
(especially lateral)
More versatile
Stable
More sensitive
Easy to implement
Higher resolution
(tip effects)
10 nm V-1 for 100 Pm cantilever
20 nm V-1 for 200 Pm cantilever
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AFM lecture 2
AFM lecture 2
Cantilevers and tips
V-shaped cantilever
the ‘tip’
diving board or
rectangular
cantilever
l
scale bar 1 mm
scale bar 20 Pm
scale bar 25 nm
t
w
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AFM lecture 2
AFM lecture 2
Critical parameters
Critical parameters
TIP
radius,
cone
angle,
cone
height,
tip setback,
material
coating
geometry
CANTILEVER
spring constant,
deflection sensitivity,
Q,
Q0,
length,
width,
thickness,
geometry,
reflectivity,
tolerances,
tip positions,
material
coatings
https://www.veecoprobes.com/
https://www.veecoprobes.com/
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AFM lecture 2
AFM lecture 2
Choosing cantilevers / tips
Tip effects – ‘resolution’
• 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, imaging
under solution ….
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AFM lecture 2
Tip wear
Common tip / imaging artefacts
Damage of the tip
‘picking – up’
contaminants
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double tip
blunt tip
streaking
contamination
optical interference
poor tracking
‘ringing’
‘noise’
Veeco SPM guide / NW
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AFM lecture 2
AFM lecture 2
Tip deconvolution
Imaging artefacts - piezo
• critical for quantitative force measurements
• deconvolution sample
• drawback – tip wear
Piezo’s without closed loop are liable to
• hysteresis
• creep
• bow
• drift
• ageing
Piezo’s should be calibrated in x-y and z regularly
• critical
• should be checked with relevant test sample
• best ~ few %
www.ntmdt.com
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AFM lecture 2
AFM lecture 2
Tip manufacturers
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Instrument manufacturers
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Nanoworld
MikroMasch (www.spmtips.com)
Budget Sensors – available through Windsor Scientific
Veeco
Nanosensors
www.nanoandmore.com
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Also do calibration samples etc.
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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AFM lecture 2
Image processing software
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
Giessibl
Rev. Mod. Phys. 75, 949-982, 2003
on CD
• 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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