UIC Atomic Force Microscopy (AFM) Stephen Fahey Ph.D. Advisor: Professor Sivananthan October 16, 2009

UIC Outline Scanning Tunneling Microscope (STM) Atomic Force Microscope (AFM) Today’s Sample

UIC Tunneling Charge carriers can apparently violate E conservation!

UIC Scanning Tunneling Microscope Exponential dependence of J Piezoelectric materials Amplifier circuitry Low oxide tip 1981 Binnig and Rohrer observe tunneling between a metal tip and a flat surface This observation led to the first STM shortly thereafter (~ 1982)

UIC STM Observations Si (111) 7x7 reconstruction (1983) Nobel Prize (1986) (1982)

UIC More STM Scanning Tunneling Spectroscopy (STS) Single atom manipulation Multiple probes

UIC Atomic Force Microscope (AFM) STM not good for insulators ~ 1985 Binnig, Quate, and Gerber used STM as feedback of first AFM AFMs can typically be operated in either tapping- mode or contact-mode

UIC Prevalence of the Harmonic Oscillator Taylor Series and Potential Energy Inter-atomic potential Separation

UIC Damped and Driven Harmonic Oscillator Complementary Function ( F = 0 ), plus Particular Solution Motion has resonance frequencies Motion is phase shifted Less damping increases “Q” and sharpens phase vs. frequency curve More damping decreases resonance frequency Resonance frequency shifts under an external applied field gradient

UIC Tip-Sample Forces Pauli and Coulomb repulsive Van der Waals attractive Tip-Sample Cantilever Deflection Piezo Height

UIC Typical AFM data GaN Northwestern U. 2 μm Carbon Nanotubes Unidym BaF 2 / CaF 2 / Si

UIC Artifacts Large scale tip shape –Tip radius –Tip side-wall angles Double tip (or more) Contamination of tip Bow from Piezoelectric elements Background noise Feedback laser interference Response time limited errors (t ~ seconds)

UIC AFM System from Veeco Dimension 3100 Etched Si probe tips with Al back coating Movable sample stage with optical microscope for course positioning Stepper motors for micrometer postioning of tip Friendly software and feedback control circuitry

UIC Interferrometrically Patterned Today’s Sample

UIC Pattern Transfer and Oxide Removal

UIC 5 μm Final Sample

UIC Conclusion STM ~ 1982 led to AFM ~ 1986 Both are powerful and beautiful characterization techniques