1. NANO 230 Micro/Nano characterization
Characterization: Scanning Probe Microscopy

2. History
Scanning Tunneling Microscope invented in 1982 by, Binning, Rohrer, Gerber and Weibel
Binning and Rohrer won Nobel prize in 1986
AFM developed in 1986 by Binning, Quate and Gerber

3. Hierarchy of Techniques
Scanning Probe Microscopy
Scanning Tunneling Microscopy
Atomic Force Microscopy
Contact Mode
Tapping Mode
Non-contact Mode

5. STM It ~ Ve-cd Feedback loop keeps current constant
therefore d is constant
Sample must conduct electricity
Capable of detecting atomic scale defects

6. AFM Contact Mode Hook’s law F=-kx Scan tip along surface
Tip contacts sample through adsorbed fluid layer
Maintains constant cantilever deflection (force) using a split photo diode
Samples can be in liquid state
Works in ambient conditions
Hook’s law F=-kx
k limits sensitivity
(want low k)

7. AFM Tapping Mode Cantilever oscillates at or below resonance frequency
Maintains constant RMS of tip movement
amplitude
Position of scanner stored to create image
Tip must breakthrough water layer without getting stuck
Also works in ambient or liquid

8. AFM Non-Contact Mode Tip oscillates but does not touch sample
above resonance frequency
The resonant frequency is decreased by van der Waals forces
Position of scanner used to map 3-D plot of surface

9. Silicon Probe

10. AFM Imaging and Tip Shape
The radius of curvature of the tip limits the resolution of the image that can be taken

11. AFM Imaging and Tip Shape
The probe cannot image a sidewall that is steeper than the angle of the tip

12. AFM Imaging and Tip Shape
Silicon probe

13. Surface Roughness Measurements
Rz : average difference in height between the five highest peaks and five lowest valleys relative to the mean plane
Image Ra : average of the absolute values of the surface height deviations measured from the mean plane
Image Rq : Root mean square average of height deviations taken from the mean plane.
NanoScope Software 6.13 User Guide, Section 6.4.3