1. ATOMIC FORCE MICROSCOPY
Introduction and theoretical background
Jenny Malmstrom

2. AFM invented by Binning and co-workers in 1986.
Belongs to the Scanning Probe Microscopy family
Binning et al., Physics Review Letters 1986

3. AFM invented by Binning and co-workers in 1986.
Belongs to the Scanning Probe Microscopy family
AFM, atomic force microscopy [1]
Contact AFM
Non-contact AFM
Dynamic contact AFM
Tapping AFM
BEEM, ballistic electron emission microscopy[2]
CFM, chemical force microscopy
C-AFM, conductive atomic force microscopy[3]
ECSTM electrochemical scanning tunneling microscope[4]
EFM, electrostatic force microscopy[5]
FluidFM, Fluidic force microscopy[6][7][8][9]
FMM, force modulation microscopy[10]
FOSPM, feature-oriented scanning probe microscopy[11]
KPFM, kelvin probe force microscopy[12]
MFM, magnetic force microscopy[13]
MRFM, magnetic resonance force microscopy[14]
NSOM, near-field scanning optical microscopy (or SNOM, scanning near-field optical microscopy)[15]
PFM, Piezoresponse Force Microscopy[16]
PSTM, photon scanning tunneling microscopy[17]
PTMS, photothermal microspectroscopy/microscopy
SCM, scanning capacitance microscopy[18]
SECM, scanning electrochemical microscopy
SGM, scanning gate microscopy[19]
SHPM, scanning Hall probe microscopy[20]
SICM, scanning ion-conductance microscopy[21]
SPSM spin polarized scanning tunneling microscopy[22]
SSM, scanning SQUID microscopy
SSRM, scanning spreading resistance microscopy[23]
SThM, scanning thermal microscopy[24]
STM, scanning tunneling microscopy[25]
STP, scanning tunneling potentiometry[26]
SVM, scanning voltage microscopy[27]
SXSTM, synchrotron x-ray scanning tunneling microscopy[28]
SSET Scanning Single-Electron Transistor Microscopy [29]
(Wikipedia 2015)
Binning et al., Physics Review Letters 1986

4. PRINCIPLE Physical probe that raster scans a specimen Key elements:
2. Detector & Feedback
3. Piezo actuators

5. Scanning Probe Microscopy
Scanning Tunneling Microscopy (STM)
Atomic Force Microscopy (AFM)
Operate by using a small tip (the probe) to scan very closely across a surface, detecting forces present between the surface and the tip.
Atomic scale resolution possible
Can be operated in air and liquid
Slow

6. STM Allows: To see (1981) To manipulate (1988)
Signal origin is quantum tunneling effect
0.1 nm lateral resolution and 0.01 nm depth resolution
Can be used to manipulate individual atoms, trigger chemical reactions, or reversibly produce ions by removing or adding individual electrons from atoms or molecules.
Very small scan ranges
Image of reconstruction on
a clean Au(100) surface.
STM image of self-assembled supramolecular chains of the organic semiconductor Quinacridone on Graphite.

7. Scanning tunneling microscopy
no limitation to crystalline structures
ultimate resolution in ultra-high vacuum
also other environments possible such as air and liquids
but by far more difficult
limited to metal surface AFM
problem of sample preparation
Surface Science community has started to look at the adsorption of biologically relevant molecules which is interesting in the context of biocompatibility and molecular recognition

8. Atomic Force Microscopy (AFM)
Signal origin from short-range forces between the tip and the sample: van der Waals, capillary, electrostatic
1 nm lateral resolution and 0.1 nm depth resolution
Contact mode
Tapping mode

10. AFM COMPONENTS
feedback
Figures from Wikipedia 10

11. Cantilevers Length thickness
Cantilever dimensions determine how easy to bend it is.

12. Image quality depends on tip size and shape
trace
contact point
Slide courtesy of Duncan Sutherland

13. Influence of tip sharpness
trace
Tip
trace
Slide courtesy of Duncan Sutherland

14. Contact Mode AFM Laser Detector Z Cantilever Tip X,Y
Simple
In contact mode, the tip is mounted onto the end of a flexible cantilever and raster scans the surface of the sample. The tip-surface interaction deflects the cantilever, which gives information about the surface topography.  Samples can be analyzed in air, liquids or vacuum. Resolution in liquid and vacuum is increased because of the absence of strong capillary forces due to a thin liquid film on all samples in air.  Unfortunately, biological samples are challenging to study in contact mode because they are generally soft, weakly bound to the surface, and damaged easily.
Not too affected by humidity
Operation in liquid
Feedback: Deflection of cantilever
Damage to soft samples
Slide courtesy of Duncan Sutherland

15. Tapping Mode AFM Feedback: Oscillation amplitude Detector
Piezoelectric material
drives oscillations
Cantilever oscillates can be driven
at a resonant frequency ~ KHz
10-100nm
The surface acts to damp the resonance
Feedback: Oscillation amplitude
Slide courtesy of Duncan Sutherland

16. Repulsive regime
Attractive regime

17. Phase imaging in tapping mode
Delay related to tip surface interaction
Phase shift
Two regions on the surface with different
Tip- surface interactions
Slide courtesy of Duncan Sutherland

18. Phase only really means something in the repulsive mode (more contributions in the attractive mode)
Many of the more advanced imaging modes has to be run in the repulsive mode
Not always possible

20. MFP-3D Origin AFM
Imaging in contact and tapping mode. Force curves in single or multiple points.
Image large area with the Origin AFM (80um scan size), um z-piezo
Can do future liquid imaging (if we buy a ‘skirt’)

21. Cypher ES
Image relatively fast to a very high resolution of flat samples (e.g. nanofiber on mica)
Image samples with features up to 5 um in height
Flow inert gas into the imaging chamber
Control the temperature of the sample stage (0-150 deg)
Image by tapping mode in liquid (using blue drive)
Applications available that needs a bit of learning and that will not work for all samples:
AMFM
EAFM
SKPM
Things we can modify the system to do in the future:
Using perfusion cell to exchange solutions
Electrochemistry (ports for electrodes available)

22. AM-FM Viscoelastic Mapping Mode
Quantitatively maps both the storage modulus (elastic response) and loss modulus or loss tangent (viscous response) with nanoscale resolution based on tapping mode, so it’s gentle and high resolution.
Works in both gas and liquid environments
Using both ground tone resonance and first overtone. Several feedbacks (A, A1, f).
Need to calibrate tip on known sample.

23. EFM: Electrical AFM
High resolution technique. Has to be done in air.
Need conductive probe.
First tap along one raster line. Then do a non-contact trace (fly) with applied electric field and monitor forces on cantilever. “Nap” mode
Can “see” hidden conductive elements under the surface of the material (carbon nanotubes in polymer)
SKPM: Scanning Kelvin Probe Microscopy
Monitors surface potential. Less resolution than EFM. Uses a conductive probe and applied a bias to the tip. Detects potential difference between tip and sample. “Nap-mode”
SKPM is QUANTITATIVE
PFM: Piezo responsive force microscopy
Tune the tip in contact with the surface – which gives the resonance of the ‘combined system’. This can be used to investigate internal dipoles in the system and can also be used as lithography technique if the dipoles are rewritable.

24. Improved optics – smaller laser spot
New developments:
Improved optics – smaller laser spot
Smaller cantilevers – faster scanning
Fast scanning cantilevers are 10–20x shorter than conventional cantilevers
The Cypher laser spot is perfectly sized for even the smallest conventional cantilevers.

25. blueDrive Photothermal excitation

26. SUMMARY AFM is a member of the scanning probe family.
It uses a sharp tip on the end of a flexible cantilever
to ‘feel’ the sample surface.
Things AFM cannot do:
Image very rough samples
Image something inside another material
Image something that cannot be deposited on a solid material
Things AFM is particularly suitable for:
Imaging hard nanostructures
Imaging soft nanostructures (proteinfibers, polymers) Imaging single molecules on a flat substrate
Imaging adherent cells