Scanning Tunneling Microscopy and Spectroscopy of Silicon and Carbon Surfaces

Citation

Baker, Shenda Mary (1992) Scanning Tunneling Microscopy and Spectroscopy of Silicon and Carbon Surfaces. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5JGQ-4X60. https://resolver.caltech.edu/CaltechTHESIS:09012011-151648229

Abstract

Scanning Tunneling Microscopy (STM) investigations and additional surface analyses were performed on carbon and silicon surfaces. A number of anomalies have been observed on highly oriented pyrolytic graphite (HOPG), including large corrugations, distorted images, large range of tip motion and the absence of defects. A mechanism involving direct contact between tip and sample or contact through a contamination layer to provide an additional conduction pathway is proposed. This model of point-contact imaging provides an explanation for added stability of the STM system, a mechanism for producing multiple tips or sliding graphite planes and an explanation for the observed anomalies. These observations indicate that the use of HOPG for testing and calibration of STM instrumentation may be misleading. Designs for the atmospheric STM used in this study are also presented.

The conditions necessary for preparing a dean silicon(111) (7x7) surface are discussed. The design and analysis of heaters necessary to prepare the silicon reconstructed surface at ultrahigh vacuum (UHV) are described. Results from both radiatively and resistively heated samples are shown in addition to a comparision of topographic and barrier height images of the boron (√3 x√3) reconstructed surfaces. A spectroscopic distinction between sites of boron, silicon or contaminants is demonstrated.

A synthetic boron-doped diamond was examined by a number of analytical techniques in order to determine its composition and surface morphology. Current-voltage spectroscopy taken with the STM indicates that the diamond Fermi level can be pinned in atmospheric conditions. In ultrahigh vacuum, band bending is observed, but the strength of the electric field experienced by the diamond semiconductor is less than expected; introduction of surface charges is shown to account for the field screening.

Presentation of an STM study of a protein-antibody complex on a gold surface illustrates the requirements for and difficulties of imaging large biomolecules. A flat, conducting substrate and sample stability on the surface are shown and discussed. Molecular manipulation by the STM tip is also presented. Although routine imaging of large adsorbates on surfaces is not yet possible, this study presents the obstacles and the potential afforded by the STM in attaining this goal.

Thesis Files