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Characterization of Silicon and Gold Surfaces Modified by New Methodologies

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Title: Characterization of Silicon and Gold Surfaces Modified by New Methodologies
Author: Koczkur, Kallum
Department: Department of Chemistry
Program: Chemistry
Advisor: Houmam, Abdelaziz
Abstract: With technology advancing at an incredible rate, especially in the microelectronics industry, there has been continuous research into finding new and ever more efficient ways to modify solid surfaces. The interaction of sulfur with metal surfaces has also been intensively studied owing to a direct impact on important areas such as environmental chemistry, fabrication of nanodevices, catalyst poisoning and corrosion. In my Ph. D. studies a new method for the modification of Si(111) surfaces without the use of heat, irradiation, or UHV conditions has been examined along with a new means of modifying Au(111) by a series of new sulfur source compounds in organic solvents. Modified surfaces were characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In an effort to explore a new and efficient means of modifying silicon, whose modification plays a vital role in electronic computer chips, freshly prepared Si(111)-H surfaces were used as the starting points. Our procedure is based on an electron transfer reaction from a good electron donor, ferrocene, to a good electron acceptor, N-bromosuccinimide (NBS) and N-bromophthalimide (NBP) that does not require the use of heat or irradiation. Characterization of the surface by XPS indicated the presence of the imidyl/phthalimidyl groups as well as bromine. Another signal which was detected was that of iron. This is important as it indicates that ferrocene is being incorporated onto the surface and ferrocene groups on modified silicon have been previously cited as potential computer memory storage devices. Nucleophilic substitution was successfully performed on the modified surfaces using succinimide, phthalimide, and pentachlorophenol anions. FTIR spectroscopy on the modified surfaces gave strong signals for a carbonyl stretch. AFM studies indicated the presence of multilayers on the silicon surfaces. Sulfur-gold interactions form the basis of what is probably the most studied self-assembled monolayer (SAM) system, organosulfur compounds and gold. SAMs have been cited for use in areas of study such as photoelectric catalysis, environmental chemistry and corrosion. By studying sulfur, which can be regarded as the shortest SAM, deposition in an organic solvent, new insights may be gained into the structure and dynamics of this phenomenon. Both polycrystalline gold and Au(111) were used to study the interaction of sulfur on gold surfaces using a series of new compounds (thiobisphthalimide, dithiobisphthalimide, p-iodobenzenesufonyl phthalimide, p-methoxybenzenesulfonyl phthalimide, p-fluorobenzenesulfonyl phthalimide, thiobis(hexamethyldisilazane) and hexamethyldisilathiane) in various organic solvents. CV studies were used to assess the rate at which sulfur was deposited on a gold electrode. XPS data for all compounds showed signals consistent with sulfur deposition. Imaging of the sample surfaces with STM showed several instances of new pattern formations and moving rectangles, the latter of which provides an answer to a long standing debate in the literature as to what the nature of the rectangular structures observed at high coverage is.
Date: 2011-12
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