Leonard M. Hanssen

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.

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.

Effects of restricting the detector field of view when using integrating spheres

Integrating sphere theory is developed for restricted field of view (FOV) detectors using a simple series solution technique. The sphere throughput, sample reflectance, and sphere wall reflectance are calculated. The effects of the samples scattering characteristics on sphere measurements are determined. It is shown that although the generalized equations incorporating detector FOV dependence reduce to the hemispherical FOV equations in some cases, in general integrating sphere behavior is altered through restriction of the detector FOV.

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.

Diamond growth in O2+C2H4 and O2+C2H2 flames

Croissance de cristallites de diamant sur support Si si les rapports de flux et la temperature du support sont maintenus. Le taux de croissance pour un melange O 2 +C 2 H 2 est plus elue que pour un melange O 2 +C 2 H 4 , ce qui serait lie a la temperature de flamme, plus elevee dans le premier cas

Hemispherical Transmittance Of Several Free Standing Diamond Films

The hemispherical transmittance of free standing films (1-20 microns thick) of polycrystalline diamond grown with a filament assisted chemical vapor deposition (FACVD) system and an oxygen-acetylene torch has been measured. Measurements were performed in the infrared (2-16 microns) with a Fourier Transform Infrared Spectrophotometer (FTIR) equipped with a diffuse gold integrating sphere and in the ultraviolet, visible and near infrared (0.20 - 2.5 microns) by a dispersive spectrophotometer used with an integrating sphere attachment. For FACVD films of approximately 1 micron thickness grown with a small amount of oxygen in the chamber, strong interference effects are observed in both spectral regions, and the total transmittance was above 60% in the visible and MR. The best films grown in the oxygen-acetylene flame show a sharp band edge at 220-222 nm, and a transmittance at long wavelengths (> 16 microns) which approaches 70%, for film thicknesses of 10-20 microns. These features are comparable to type IIA natural diamond. The optical transparency of the flame grown films is sufficient to read newsprint when held next to the text, however the large grain size (2-5 microns) and rough surfaces introduce sufficient scatter to blur the image of the text as the film and text are separated.

Infrared Diffuse Reflectometer For Spectral, Angular And Temperature Resolved Measurements

This paper describes an integrating sphere - Fourier Transform Spectrophotometer (FTS) instrument and its measurements of directional hemispherical reflectance as a function of angle, temperature and wavelength in the infrared. Samples can be mounted in the center of the sphere or on the wall of the sphere. The center mounted samples can be tilted to vary the beam incidence angle from 0° to 60°; wall mounted samples can be heated to temperatures of 250°C. Measurements on samples using both sample mounts are presented and compared. A discussion of the measurement techniques used to obtain round robin results (presented in an accompanying paper) is also given. A study of the temperature dependence of a single round robin sample is presented. Detailed measurements of a ruled gold sample are given and the importance of the detectors field-of-view in explaining this data is demonstrated with a simple experiment.

9 - Reflectance Measurements of Diffusing Surfaces Using Conic Mirror Reflectometers

This chapter provides a comprehensive review of the published literature on conic mirror reflectometers. Based on this review, the significant sources of measurement error present with conic mirror devices have been systematically analyzed, including important magnification effects. Recent developments in the design of hemispherical sources and detectors using nonimaging compound parabolic concentrators (CPCs) have been reviewed in the chapter. Extensive raytracing studies of the effect of sample positioning on the throughput of the primary conic mirrors have shown that for modestly sized mirrors, the positioning error is small (< 0.25 %) if the sample offset from the conic mirror base plane can be controlled to <0.1-0.2 mm. However, the correction factor associated with interreflection effects can easily exceed 1.1 if the reflectance of the source (2π/θ) or the detector (θ/2π) is above 20 %. Techniques for minimizing and correcting for the interreflection error is also reviewed in the chapter. All the reflectometer designs and equations discussed can be easily modified to perform and analyze transmittance measurements of diffusing samples.