Keith A. Snail

Diamond synthesis using an oxygen-acetylene torch

Diamond microcrystallites and polycrystalline films were grown on various substrates in the ambient atmosphere with an oxygen-acetylene welding torch. Growth is examined as a function of substrate position and temperature, and gas flow ratio. The deposited material was analyzed with Raman spectroscopy, X-ray diffraction and electron microscopy.

Diamond synthesis in oxygen‐acetylene flames: Inhomogeneities and the effects of hydrogen addition

Micro‐Raman spectroscopy, scanning electron microscopy and a surface density counting technique have been used to probe the inhomogeneities of diamond crystallites grown with an oxygen‐acetylene flame on a scratched Si(100) surface. The surface temperature profile was measured using a thermal imaging camera and compared with the observed inhomogeneities in the diamond crystallites. It is concluded that the flame species flux to the surface is the dominant factor contributing to the diamond crystallite inhomogeneities. Hydrogen addition to the oxygen‐acetylene flame was studied. The addition of hydrogen reduced the amount of ‘‘amorphous’’ carbon contained in the diamond crystallites as measured with Raman spectroscopy. Growth density profiles were determined as a function of the inner flame front to substrate distance. For uniform growth density in the oxygen‐acetylene flame the substrate must be placed in the acetylene feather at a sufficient distance from the inner flame to avoid annular growth.

Diamond and non-diamond carbon synthesis in an oxygen-acetylene flame

diamond and non-diamond carbon deposition in an oxygen-acetylene combustion flame has been analyzed over a range of oxidizer:fuel ratios (Rf) and substrate temperatures (Ts). The effects on diamond deposition of substrate preparation and position in the oxygen-acetylene flame have been examined. Diagrams relating diamond, microcrystalline graphite and amorphous carbon growth to the oxygen:acetylene flow ratio and substrate temperature have been developed. In addition, the dependences of particle morphology and growth rate on Ts and Rf were examined. Micro-Raman spectroscopy, optical microscopy and scanning electron microscopy were used to analyze the growth.

In situ diamond growth rate measurement using emission interferometry

The growth rate of diamond synthesized in an oxygen‐acetylene flame has been measured in situ with an infrared pyrometer. During the growth, the sample’s emitted radiation intensity is modulated in time by interference phenomena in the growing diamond film, causing a periodic variation of the pyrometer’s apparent temperature reading. Diamond film growth rates determined from the period of these oscillations agree well with rates derived from the film thickness. This technique is used to determine the variation of diamond growth rate with substrate temperature over the range of 444–1200 °C. An Arrhenius analysis of the data shows two distinct diamond growth regimes.

High temperature, high rate homoepitaxial growth of diamond in an atmospheric pressure flame

Abstract Homoepitaxial growth of diamond at temperatures in the range of 1150–1500°C has been achieved on millimeter sized {100} and {110} natural diamond seed crystals using a laminar, premixed oxygen-acetylene flame in air. Growth rates of 100–200 μm/h have been observed. Microscope and naked eye observations show the original cylindrical shaped seed crystals growing into polyhedral shaped crystals with identifiable {100}, {110} and {111} faces. examination under optical and scanning electron microscopes reveals terraces on the {100} faces. The deposited diamond is clear and exhibits Raman spectra almost identical to that of natural diamond. Laue X-ray diffraction analyses have confirmed the epitaxial nature of the growth. The deposition temperatures and growth rates reported are the highest ever observed for the homoepitaxial synthesis of diamond crystals at low pressures.

Integrating sphere designs with isotropic throughput

An ideal diffuse reflectometer can be defined as a reflectometer with a throughput which is independent of the angle of reflected radiation, as measured at the sample. For integrating spheres, effects related to the detectors field of view (FOV), the beam port, and internal baffles can result in a throughput which is nonisotropic. This paper analyzes these three sources of nonideal behavior and suggests three sphere designs using nonimaging concentrators which minimize FOV related errors. A technique for measuring the error due to the beam port is also discussed as well as ways of minimizing perturbations caused by baffles.

Synthesis of high quality diamond films in a turbulent flame

High quality polycrystalline diamond films have been synthesized in a premixed, turbulent oxygen‐acetylene flame, using a commercial brazing torch. The quality of the films was measured by Raman spectroscopy, electron microscopy, and hemispherical transmittance measurements in the ultraviolet, visible, and infrared. Turbulence was achieved by operating the torch with a sufficiently high Reynolds number. The presence of turbulence was confirmed by observations of changes in the flame shape, the characteristic sound of the flame, and calculation of the Reynold’s number.

A thin‐film Schottky diode fabricated from flame‐grown diamond

Schottky diodes have been fabricated out of polycrystalline diamond thin films grown in an atmospheric pressure turbulent flame. Doping was accomplished by bubbling the source gas through a solution of diboric trioxide in acetone. The diodes were grown on metallic, noncrystalline substrates. A device fabrication technique utilizing carbide‐forming refractory metals as a buffer layer was used to bond the diamond film to the substrate and act as an ohmic contact. The resulting structure avoided the difficulties in flame growth of working with thin detached films. Diode rectification ratios in excess of 300 were observed.

Diamond growth in turbulent oxygen‐acetylene flames

Turbulent premixed oxygen‐acetylene flames have been used to synthesize polycrystalline diamond films on molybdenum substrates at temperatures ranging from 500 to 1300 °C and facetted single crystals on mm‐sized natural diamond substrates at temperatures of 1200–1300 °C. Turbulence was achieved by increasing the torch’s orifice diameter and/or the flow velocity; the presence of turbulence was confirmed by observations of changes in the flame shape, measurements of the flame’s noise spectrum, and calculations of the Reynolds number. The optical emission spectra of several diamond‐growing turbulent flames were also compared to the spectra of laminar flames. The variation in diamond quality with temperature and oxygen acetylene flow ratio was studied with one or more of the following techniques: Raman spectroscopy, scanning and transmission electron microscopy, infrared spectroscopy, and photoluminescence spectroscopy. Crystals grown on molybdenum at temperatures of 600–1100 °C were observed to be transparen...

High-temperature epitaxy of diamond in a turbulent flame

Abstract Diamond has been grown epitaxially on 1.5 mm diameter, natural diamond seed crystals at temperatures of 1200–1300 °C in a premixed, turbulent oxyacetylene flame. During a typical 1 h deposition, a polyhedral-shaped single crystal was observed to grow on top of a 〈100〉 oriented cylindrical seed crystal. The growth surface is composed of both {100} terraces and {110} ridges, arranged into well-formed pyramidal shaped structures with very long range order. Raman analyses show a lack of non-diamond carbon and a 1332 cm −1 peak which is indistinguishable from natural type IIa diamond. Low-temperature photoluminescence measurements indicate a greatly reduced level of localized radiative defects. Laue X-ray diffraction measurements have confirmed the epitaxial nature of the deposit, and preliminary X-ray rocking curve analyses are presented. This is the first report of the high-temperature epitaxial growth of diamond in a turbulent flame.