1. Scanning Probe Microscopy 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 1

2. Hierarchy of Techniques
Scanning Probe Microscopy
Scanning Tunneling Microscopy
Atomic Force Microscopy
Contact Mode
Tapping Mode
Non-contact Mode 2

3. 3

4. STM It ~ Ve-cd Feedback loop keeps current constant
therefore d is constant
Sample must conduct electricity
Capable of detecting atomic scale defects 4 4

5. AFM Contact Mode Hook’s law F=-kx Scan tip along surface
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) 5 5

6. AFM Tapping Mode Cantilever oscillates at or below resonance frequency
Maintains constant tip movement
amplitude
Position of scanner stored to create image
Tip must breakthrough water layer without getting stuck
Also works in ambient or liquid 6 6

7. Silicon Nitride Probe Spring Constant (k)
0.58, 0.32, 0.12, 0.06 N/m (1)
Nominal Tip Radius of Curvature nm
Cantilever Lengths
100 & 200μm
Cantilever Configuration
V-shaped
Reflective Coating
Gold
Sidewall angles
35° on all 4 sides
(1)Calculated spring constant values are based on the 0.6μm silicon nitride thickness; however, this value can actually vary from 0.4μm to 0.7μm. Thickness is cubed in the spring constant calculation, thus, actual values can vary substantially. 7

8. Silicon Probe 8

9. AFM Imaging and Tip Shape
The radius of curvature of the tip limits the resolution of the image that can be taken 9

10. AFM Imaging and Tip Shape
The probe cannot image a sidewall that is steeper than the angle of the tip
Silicon nitride probe 10

11. AFM Imaging and Tip Shape
Silicon probe 11

12. 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. 12
NanoScope Software 6.13 User Guide, Section 6.4.3

13. AFM height image of a semiconducting polymer thin film on SiO2

14. AFM images of SiO2 substrates for FET’s
8/4/08
AFM images of SiO2 substrates for FET’s
Uncleaned SiO2
Mean Roughness: 0.44 nm
5 nm
0 nm
-5 nm
5 nm
No detergent, No Plasma SiO2
Mean Roughness: 0.19 nm
6nm tall particle on surface
0 nm
-5 nm

15. AFM images of SiO2 substrates for FET’s
8/4/08
AFM images of SiO2 substrates for FET’s
5 nm
No detergent, Airplasma 5min SiO2
Mean Roughness: 0.27 nm
0 nm
-5 nm
5 nm
detergent, air plasma 5min SiO2
Mean Roughness: 0.17 nm
6nm tall particles on surface
0 nm
-5 nm