Scanning Tunneling Microscopy and Digital Image Correlation in Nanomechanics Investigations

Citation

Huang, Ying (2001) Scanning Tunneling Microscopy and Digital Image Correlation in Nanomechanics Investigations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/exy7-5z58. https://resolver.caltech.edu/CaltechTHESIS:12212010-112400412

Abstract

Probe microscopy (scanning tunneling microscopy and atomic force microscopy) and digital image correlation together serve as a potentially powerful tool for experimentally investigating the mechanical behaviors of materials at the sub-micron and nanometer scales. Based on the tunneling effect in quantum physics, the scanning tunneling microscope (STM) records surface topography quantitatively and can achieve angstrom resolution. The digital image correlation (DIC) extracts the displacements and gradients from the undeformed and deformed topographical images. In this work, a calibration has been performed on the existing STM built "in-house" and the coefficients used in the STM system were confirmed. Major improvements on several components of the system have been made, including constructing a new actuator probe to decouple its in-plane and out-of-plane movements, designing and implementing a new first-stage amplifier to reduce the noise output by a factor of 10 and modeling of the controller in the STM feedback loop. Further, systematic study of the digital image correlation has been conducted. In the simple case of one-dimensional correlation, key parameters involved are the subset size, variables in the displacement representation, frequency content of the signal and noise. The one-dimensional study was then extended to two dimensions. In addition to those key parameters identified in the one-dimensional study, the sampling rate poses substantial influence on the correlation accuracy. Low amplitude, high frequency noise still increases the correlation error significantly.

Thesis Files