Publications

A simplified surface reaction mechanism is presented for the CVD of diamond thin films. The mechanism also accounts for formation of point defects in the diamond lattice, an alternate, undesirable reaction pathway. Both methyl radicals and atomic C are considered as growth precursors. While not rigorous in all details, the mechanism is useful in describing the CVD diamond process over a wide range of reaction conditions. It should find utility in reactor modeling studies, for example in optimizing diamond growth rate while minimizing defect formation. This report also presents a simple model relating the diamond point-defect density to the thermal conductivity of the material.

This paper presents an analysis of the Chemical Vapor Deposition of diamond thin films in a direct-current (dc) arc-jet reactor. The analysis discussed here includes a model of the performance of the arc-jet hydrogen excitation source, chemistry in the free-stream region, diffusive transport and chemistry in the boundary layer and at the surface. The surface chemistry model includes pathways for deposition of diamond, as well as creation of defects in the diamond lattice.

This report documents the Surftherm program that analyzes transport coefficient, thermochemical- and kinetic rate information in complex gas-phase and surface chemical reaction mechanisms. The program is designed for use with the Chemkin (gas-phase chemistry) and Surface Chemkin (heterogeneous chemistry) programs. It was developed as a ``chemist`s companion`` in using the Chemkin packages with complex chemical reaction mechanisms. It presents in tabular form detailed information about the temperature and pressure dependence of chemical reaction rate constants and their reverse rate constants, reaction equilibrium constants, reaction thermochemistry, chemical species thermochemistry and transport properties. This report serves as a user`s manual for use of the program, explaining the required input and the output.

We have developed a novel molecular beam mass spectrometry technique that can quantitatively analyze the gas-phase composition in a CVD reactor. The technique simultaneously monitors a wide variety of radical and stable species, and their concentrations can be determined with sensitivities approaching 1 ppM. Measurements performed in a diamond deposition system have given us keen insights into the important phenomena that affect the growth environment. This paper first discusses the primary gas sampling design issues. In the second part, the details of the experimental results and their implications will be described.

CRESLAF is a Fortran program that predicts the velocity, temperature, and species profiles in two-dimensional (planar or axisymmetric) channels. The program accounts for finite-rate gas-phase and surface chemical kinetics and molecular transport. The model employs the boundary-layer approximations for the fluid-flow equations, coupled to gas-phase and surface species continuity equations. The program runs in conjunction with the Chemkin preprocessors for the gas-phase and surface chemical reaction mechanisms and the transport properties. This report presents the equations defining the model, the method of solution, the input parameters to the program, and a sample problem illustrating its use. Applications of CRESLAF include chemical vapor deposition (CVD) reactors, heterogeneous catalysis on reactor walls, and corrosion processes.