afm: 6 must know measurements - mccrone · • afm provides true measurement of z (height) • (in...
TRANSCRIPT
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AFM: 6 Must Know
Measurements
Dalia Yablon
SurfaceChar LLC
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AFM - Principles of operation
piezo
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AFM can
measure many
other useful
surface
properties
10nm lateral resolution
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Must know
measurements with AFM
• Topography – 3 dimensional maps
• Mechanical contrast: Mapping with materials
contrast
• Mechanical properties: Nanoscale adhesion and
modulus
• Electrical properties: Mapping with electrical contrast
• Magnetic properties: Mapping with magnetic contrast
• Optical: Chemical information
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Topography – 3 dimensional maps
• Most common measurement
• AFM provides true measurement of z (height)
• (in contrast to electron/optical microscopy)
• Enables measurements like roughness analysis
• Topography is the backbone of all AFM imaging measurements
• Feedback is on the z piezo to provide topography
• Any other imaging mechanism contrast (mechanical, electrical, magnetic) are all collected simultaneously with the topography
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Materials contrast imaging:
Phase imagingTapping mode!
– Drive base of cantilever with a sinewave generator
– Phase lag between cantilever drive and response
– Response is due to complicated material response including
elastic and viscoelastic properties
– Key method to discriminate materials, though not well understood
driveresponse
f
D amplitude
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Differentiating materials via phase imaging
f
Df DfPhase lag image
Solution-cast triblock
copolymer film (equilibrated)
ABA block copolymer, solvent-vapor annealed:
poly (styrene-isobutylene-styrene) or SIBS
(styrene cylinders standing or lying down)
Relatively bright regions: glassy phase
of triblock copolymer → less dissipative
Stiffness, adhesion, viscosity,…can give dissipation
100 nm
From G. Haugstad
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Component
#1 and #2
Component
#3
Component
#4
Component
#5
Phase
Topography
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Single point mechanical measurements:
Force curve/force spectroscopy
Adhesion
Modulus
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Force curves on impact
copolymer
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Create force maps…
Height Adhesion
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Forcemaps on cells
Adhesion force (nN)
Elastic modulus (kPa)
cell
background
Data from nanosurf
Epithelial cells
Fibroblast cells
Adhesion
Elastic modulus
Elastic modulus
Data from Asylum Research
(online image gallery)
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Kelvin probe microscopy
• Maps surface potential
• What can it measure?
– Trapped charge, spontaneous
polarization, work function variation,
potential difference
• Requires cantilevers with electrically
conductive coating
• Two passes
– First pass: topography with typical piezo
actuation/tapping mode
– Second pass: AC electrical bias plus a
DC bias to vibrate the tip
[cantilever driven electrically]
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Electrical properties: surface potential
(Kelvin probe force microscopy KPFM)
BN
Graphene
Copper foil
Image courtesy of Asylum Research
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Magnetic Properties
(Magnetic force microscopy – MFM)
10um 10um
Topography MFM
Data and image courtesy of ParkAFM
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AFM-IR
• Combine AFM + IR
– Apertureless scattering method
– Photothermal method
Courtesy of Neaspec
• Adds chemical information
to the AFM topography
Courtesy of Anasys Instruments
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AFM-IR: Nanoscale spatial resolution
for polymer thin film
min
max
Nano-FTIR Absorption
min
max
200 nm
0nm
3.8nm
Topography
0nm
2.3nm
100 nm
1730 cm-1
ON Resonance
1650 cm-1
OFF
Resonance
High-resolution PMMA/PS diblock thin films (period: 50nm)
Data courtesy of Neaspec
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Summary
• Topography – 3 dimensional maps
• Mechanical contrast: Phase imaging
• Mechanical properties: Force spectroscopy
• Electrical properties: Kelvin probe microscopy
• Magnetic properties: Magnetic force microscopy
• Optical: AFM-IR
• Nanoscale Resolution
• Environmental flexibility
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