NANO 230 Micro/Nano characterization Characterization: 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 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 http://www.chembio.uoguelph.ca/educmat/chm729/afm/firstpag.htm

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

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)

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

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

Silicon Probe

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

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

AFM Imaging and Tip Shape Silicon probe

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