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Title: Scanning tunnelling microscopy of metal reactions with silicon
Author: Gray, Struan Marc
ISNI:       0000 0001 3513 7363
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1992
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I present the results of several investigations into the reactions that take place behveen transition metals and the silicon (111) surface. The ability of the STM to measure physical and electronic structure on an atomic-scale permitted the detailed study of several new phenomena. The reactions divide into hvo categories: a regime where less than a monolayer of metal was present; and a second one where enough metal was deposited on the surface to form a silicide. Silicides of cobalt and iron were grown from thin evaporated metal films, and the structures seen with the STM agreed \vith the results obtained previously by other groups using different techniques. In addition, two new effects were observed. Strongly localised noise, confined to the boundaries between iron silicide grains, indicated that the band structure was being distorted in these regions. Also, a new structure was discovered, involving the growth of a pure silicon overlayer on the surface of the silicide at high temperatures. The layer is thin enough for the interface between it and the buried silicide to perturb the surface, permitting details of the buried interface and its misfit dislocation netv.;ork to be inferred. Tungsten, tantalum and cobalt all adopted similar structures at submonolayer coverages. Domains of 7x7 reconstructed silicon were separated by surface dislocations, with metal islands at the nodes of the dislocation nehvork. The interiors of the islands were comprised of a 1ich variety of reconstructions, stabilised by the presence of the metal atoms. Areas of 5x5, 7x7, 9x9, 2x2, c(4x2). and ,/3xv3-R30 reconstructed surface could all be seen; and, for the first time, an l lxl 1 reconstruction was found. To set this ,vork in perspectiYe, a description of the clean silicon (111) surface and its 7x7 reconstruction is also given, and the theoretical and technological background to the microscope's operation discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Solid-state physics