A study of amorphous hydrogenated titanium carbide films: Structure, stability, and role of hydrogen doping

Amorphous hydrogenated titanium carbide films (a-TiC :H , X y 0.88<x<0.95 and O.OS<y<0.12) were successfully prepared by low-temperature (150-300°C) and low-pressure (<10-S torr) metallorganic chemical vapor deposition (MOCVD) of the organometallic compound tetraneopentyl-titanium. X-ray and electron diffraction studies confirmed the amorphicity of the coatings, while controlled-heating experiments emphasized their stability against crystallization to higher temperatures (-1100°C) than typical glassy metals. Analyses of the coatings by Auger electron spectroscopy (AES), electron energy-loss spectroscopy (EELS), and x-ray photoelectron spectroscopy (XPS) led to an understanding of the film morphology and microchemistry, and to a quantitation of H concentrations in the coatings. This work necessitated, in a preliminary stage, performing MOCVD of the Ti-coordination compound titanium-bipyridine and completing the characterization studies started by Morancho and Constant on the corresponding deposited films. Other amorphous titanium carbide films (a-TiC), with X 0.91<x<0.93, were produced by electron beam evaporation (EBV) and were analyzed with various spectroscopies. EBV thus provided single phase a-TiC films to compare to TiC :H The X X y purpose was to investigate the local structure in both types of films and to confirm the critical role of hydrogen in the formation and stability of the amorphous structure obtained by MOCVD. A major investigative tool in this structural determination was the analysis of the extended fine structure above the Ti x-ray K-edge, the Ti energy-loss L 2 , 3 -edges and C energy-loss K-edge, using extended x-ray absorption fine structure (EXAFS), and extended energy-loss fine structure (EXELFS). The thesis presents a detailed description of the physical mechanism associated with EXAFS and EXELFS, a simple theoretical derivation of the EXAFS expression, a comparison of EXAFS and EXELFS, and a discussion of their suitability to structural investigations. Details of the first application of the combination EXAFS-EXELFS to perform structural studies on amorphous a-TiC and a-TiC :H films are then presented. This study yielded information on the dynamic and static disorder, local arrangement of both C and Ti atoms, location of hydrogen and its effect on the short-range order (SRO) in the films. Finally, a theoretical model, based on the Nagel-Tauc rule and Harrison formulation, is proposed to explain the stability of the amorphous phase. XPS valence band measurements confirmed the predictions of these theoretical calculations, and showed a transfer of charge from Ti to H in a-TiCx:Hy.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Kaloyeros, Alain Elie

Contributors dc:contributor

• Williams, W.S.

• amorphous hydrogenated titanium carbide films
• hydrogen doping
• metallorganic chemical vapor deposition
• tetraneopentyl-titanium

Statement dc:rights

• 1987 Alain Elie Kaloyeros

Language dc:language

en

Identifier

1322697

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25456