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Title:Mechanistic Studies of the Chemical Vapor Deposition of Ceramic and Metal Films From Organometallic Precursors
Author(s):Cheon, Jinwoo
Doctoral Committee Chair(s):Girolami, Gregory S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:Investigations of the thermolysis of tetra(neopentyl)titanium (TiNp$\sb4$) in solution have been carried out in parallel with studies of the chemical mechanism responsible for its conversion to titanium carbide under CVD conditions. A kinetic isotope effect $(k\sb{\rm\alpha (H)}/k\sb{\rm\alpha (D)} = 5.2 \pm 0.4)$ upon deuterating the alkyl groups at the $\alpha$ positions provides clear evidence that the initial step in the thermolysis is an $\alpha$-hydrogen elimination reaction to form neopentane. The activation parameters for this $\alpha$-hydrogen elimination process are $\rm\Delta H\sp\ddagger = 21.5 \pm 1.4$ kcal/mol and $\rm\Delta S\sp\ddagger = -16.6 \pm 3.8$ cal/mol K.
The chemical pathway responsible for the conversion of TiNp$\sb4$ to TiC has been studied. For every equivalent of TiNp$\sb4$ consumed in the deposition process, 3.25 equiv of neopentane and 0.16 equiv of isobutane are produced; other organic species are also formed but in relatively small amounts. Thermolysis of the specifically deuterated analogue TiNp$\sb4$-$d\sb8$ yields a 2.25:1 ratio of neopentane-$d\sb3$ and neopentane-$d\sb2$; this result combined with a kinetic isotope effect of 4.9 at 385 K shows that the first step in the deposition pathway under CVD conditions is $\alpha$-hydrogen elimination. The $\alpha$-hydrogen elimination step produces one equivalent of neopentane and a titanium alkylidene, which undergoes further $\alpha$- (and eventually $\gamma$-) hydrogen activation processes to generate the second and third equivalents of neopentane.
The deposition of amorphous MoS$\sb2$ and TiS$\sb2$ thin films from the metal-organic precursors Mo(S-t-Bu)$\sb4$ and Ti(S-t-Bu)$\sb4$ has been investigated. Stoichiometric films nearly free of oxygen and carbon contaminants can be grown at temperatures between 110 and 350$\sp\circ$C and low pressure. For TiS$\sb2$, the deposition apparatus was treated with TiCl$\sb4$ before the deposition runs to remove adventitious water and reduce the amount of oxygen impurities. The organic by-products generated during deposition consist principally of isobutylene and tert-butylthiol; smaller amounts of hydrogen sulfide, di(tert-butyl)sulfide, and di(tert-butyl)disulfide are also generated.
The organometallic compounds bis(allyl)zinc and bis(2-methylallyl)zinc have been investigated as MOCVD precursors for the deposition of zinc at temperatures as low as 150$\sp\circ$C. The deposits consist of aggregates of hexagonal plates and columns. Analyses of the organic byproduct distribution and in situ spectroscopic studies on single crystal Cu(111) surfaces show that bis(allyl)zinc adsorbs molecularly at temperatures below 200 K, but that the allyl groups transfer to the copper surface at 250 K; the surface-bound allyl groups are bound in a trihapto fashion. On fresh surfaces, the allyl groups fragment to adsorbed hydrogen atoms and hydrocarbon fragments; the former react with intact allyl groups to give propene while the latter eventually give rise to a carbonaceous overlayer. (Abstract shortened by UMI.)
Issue Date:1993
Description:158 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.
Other Identifier(s):(UMI)AAI9411588
Date Available in IDEALS:2014-12-17
Date Deposited:1993

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