Physical Electronics Dept.

You are invited to attend a lecture

By

Gilad Cohen

(M.Sc. student under the supervision of Prof. Yossi Rosenwaks)

on the subject:

Reconstruction of Kelvin Probe Force Microscopy images

Kelvin Probe Force Microscopy (KPFM) has already been demonstrated as a powerful tool for measuring electrostatic potential distribution with nanometer spatial resolution. However, due to the long range electrostatic forces the measured potential is a weighted average of the real surface potential distribution. The overall objective of this thesis is to develop an algorithm for reconstructing a sample surface potential from its KPFM image.

In order to reconstruct the real surface potential we extract the system noise statistics and calculate the exact point spread function (PSF) for the KPFM measurement. The image reconstruction is then performed by deconvolution in the frequency domain using the Wiener filter and the power spectra of the KPFM image and the noise. The reconstruction algorithm is validated by measuring a calibration sample under a defined bias. In addition, we develop a method to calculate the PSF of frequency modulation KPFM (FM-KPFM) and compare it with amplitude modulation KPFM (AM-KPFM). In FM-KPFM the probe measures the force-gradient rather than the force and thus demonstrates better spatial resolution than in AM-KPFM. We apply our algorithm to surface potential measurements of CdS-PbS nanorods and FM-KPFM measurements of Graphene layers conducted under ultra-high vacuum. We show that in AM-KPFM measurements the averaging effect is substantial whereas FM-KPFM measurements demonstrate hardly any probe averaging effect.