Date of Award

1972

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering

Department

Chemical Engineering

First Advisor

P. J. Gielisse

Abstract

Semiconducting diamond has been synthesized from carbon-metal melts in a 600 ton tetrahedral anvil press at about 60 kbar and 1400°c. The experimental set up, pressure and temperature calibrations, and the growth region in the pressure-temperature regime are indicated. Micrographs of synthesized crystals are shown.

The semiconducting properties of diamond, doped with boron, aluminum and titanium have been interpreted using the log R versus l/T curves. In boron-doped diamond ''high concentration" type impurity conduction occurs and the activation energies vary from 0.15 eV to 0.30 eV. The activation energies for aluminum and titanium-doped samples are found to be 0.31 eV and 0.40 eV respectively. The results are consistent with those obtained from optical methods where data were available.

Properties of diamond irradiated with 17-18.3 MeV protons have been investigated. Raman spectral measurements indicate an increase in the lattice constant of 0.0032 Å. The infrared absorption spectrum of proton irradiated diamond shows a characteristic absorption at 6.92 microns. The optical absorption edge of diamond does not seem to be affected by the irradiation.

Boron phosphide has been synthesized from the elements at pressures and temperatures above 20 kbar and 1200°c. The crystal growth rate has been determined as a function of temperature and pressure from which an activation energy for the process is derived. Optical and Scanning Electron Micrographs of the crystals synthesized revealed a poorly developed morphology with voids present under all conditions of pressure and temperature.

The effect of thermal neutron irradiation on the electrical conductivity of boron phosphide, hexagonal boron nitride and boron oxide (B2O3) has been observed by studying the current-voltage characteristics before and during irradiation with a neutron flux of about 108n/cm2.sec. In all these compounds, currents were higher, for the same voltage setting, during irradiation. The differences observed during irradiation in current values for the three boron compounds have been explained as being due to the "boron to anion ratio" being different in them.

The Appendix to this thesis includes an introduction to the foregoing investigations and describes the equipment used with recommendations for future work.

Share

COinS