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 http://www.chembio.uoguelph.ca/educmat/chm729/afm/firstpag.htm

Hierarchy of Techniques Scanning Probe Microscopy Scanning Tunneling Microscopy Atomic Force Microscopy Contact Mode Tapping Mode Non-contact Mode 2 http://www.chembio.uoguelph.ca/educmat/chm729/afm/firstpag.htm

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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

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

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

Silicon Nitride Probe Spring Constant (k) 0.58, 0.32, 0.12, 0.06 N/m (1) Nominal Tip Radius of Curvature 20 - 60nm 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

Silicon Probe 8

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

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

AFM Imaging and Tip Shape Silicon probe 11

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

AFM height image of a semiconducting polymer thin film on SiO2

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

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