Scanning Tunneling Microscopy
Abstract
The entire research program has been taken in two steps. In the first part of the dissertation, the researcher has successfully designed and constructed a UHV compatible scanning tunneling microscope which is capable of producing atomic resolution images. The design of the microscope which was based on the concept of two-stage spring suspension with magnetic damping on one of the two stages. By using a piezoelectric tube scanner, the researcher found that the mechanical stability of the tunneling gap distance is of the order of 0.01 A at most frequency components with the exception of resonance frequency of 4.5 Hz at which the noise level is of the order of 0.1 A at best. Electronic noise of the STM control system was mainly of the order of 0.5 A at 60 Hz, which was found to be induced by the noise in the x and y driving voltages and can be significantly reduced by introducing a resistance divider. In the second part of the dissertation, the researcher has used the constructed microscope to study surfaces of beta-SiC(001) grown by CVD on the Si(001) substrate, ion-bombarded semiconductor surfaces and the PbS(001) cleavage surface. On the beta -SiC(001) surface, atomic resolution images have been obtained for the first time with the scanning tunneling microscopy. Besides LEED phases, the researcher has also seen the short-ranged 5 x 2 which was stabilized by the carbon contaminations and is probably the cause for the streaked 3 x 2 LEED pattern. On the ion-bombarded semiconductor surfaces, i.e., Si(001) and PbS(001), the researcher has observed individual ion-impact. In the case of PbS, atomic resolution has been achieved in the region around a single ion-impact. The STM results were in good agreement with the theoretical prediction of the lateral damage by the incident ion on the surface. On the PbS(001) cleavage surface, dislocations with Burgers vector of a/2(1,0,0) have been observed on the atomic scale and were probably generated during the cleavage process. The effect of tip -surface interaction has been exclusively observed and could be qualitatively explained by the resonant-tunneling theory proposed in Chapter 3. (Abstract shortened with permission of author.).
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1990
- Bibcode:
- 1990PhDT........41Z
- Keywords:
-
- MICROSCOPY;
- SILICON CARBIDE;
- LEAD SULFIDE;
- Physics: Condensed Matter