Date on Master's Thesis/Doctoral Dissertation
Physics and Astronomy
Ouseph, P. J.
The scanning tunneling microscope has been in commercial use just over a decade. Due to its Quantum Mechanical nature, experiments in this area have been widely publicized to the scientific community. The apparatus is steadily growing easier to use, though fundamental problems are still present. In the first chapter, an address is given on the modem theory of tunneling to rationalize the conclusions Physicists made long ago about this phenomenon. The expanded theory generalizes the mathematical motivation for attempting such unique experiments and serves as a lead-in for the major components of the apparatus. Many texts do not quantize what the purpose is for each unit in the STM system, nor do they illustrate the process of preparation for probe shaping. It is the objective of the second and third chapters to detail this information. With as much as researchers know about the STM, there still remains an abundance of imaging problems which can develop. A study of graphite will be given in the fourth chapter dealing with one such issue - incorrect topograph scaling. Calibration techniques are provided to effectively determine the scaling needed for images using the horizontal and verticle lattice constants. Steps which appear as layering transitions are used for vertical calibration while B-atom spacing is used for horizontal calibration. Due to the conductive nature of the probe, particulate fragments are more likely to attach to the apex of the probe than to uncharged material in the system. Thus, since the probe's shape is the most important item to control in STM experiments, atomic resolutions of topographs are often in danger. One of many consequences of having two III atoms on the apex of the probe is a duplication of sample structures on the topographic image. In the fifth chapter, it is proposed that one could determine the structure of a double tip if an imperfection existed on the sample surface for reference. The imperfection used for this study is a hole created by prior tip contact with the graphite sample. The original and duplicate images of the cavity are used to determine this double tip structure.
Gossman, Michael Stephen, "Calibration methodology and multiple tip structure by scanning tunneling microscopy." (1997). Electronic Theses and Dissertations. Paper 2738.