An n-type semiconducting diamond thin film was obtained by microwave enhanced plasma chemical vapor deposition using phosphine (PH3) as a dopant source. A homoepitaxial diamond thin film with a thickness of about 300 nm was grown on the {111} surface of a type Ib diamond with a variety of dopant concentrations. Over a wide range of dopant concentrations (PH3/CH4: 1000–20 000 ppm), the n-type conduction was confirmed by Hall-effect measurements. The activation energy of carriers was 0.43 eV. The Hall mobility of about 23 cm2/V s has been obtained at around 500 K for the 1000 ppm sample. No significant increase of hydrogen has been observed by secondary-ion-mass-spectroscopy analysis for the phosphorous doped layers.
Thermal oxidizing treatments of hydrogenated diamond surfaces have been performed in an O2 environment.Chemisorption of oxygen on diamond surfaces has been investigated by diffuse reflectance Fourier-transform infrared (FTIR), temperature-programmed desorption (TPD), temperature-programmed reaction (TPR) and thermogravimetry (TG). Oxidation of the hydrogenated diamond occurred above 300 "C and diamond started to burn out above 480 "C in 20% 0,. Diffuse reflectance FTIR spectra indicated that the oxidation gave species containing C -0 and C-0-C structures on t h e diamond surface above 300°C. The structures of t h e chemisorbed species changed with the oxidation temperature. The maximum coverage of oxygen was obtained between 480 and 500 "C. TPD spectra of oxidized diamond indicated that the oxygencontaining species were desorbed as CO and CO, above 480°C. This paper deals with t h e mechanistic considerations for the oxidation of diamond surfaces.
Microcrystalline diamond has been formed on silicon or molybdenum substrates by vapor deposition from a geseous mixture of methane and hydrogen. Cubo-octahedral or multiply-twinned crystals were obtained. The structure of the deposits was identified by electron diffraction and Raman scattering.
The chemisorbed species on diamond surfaces have been studied by Fourier-transform infrared (FTIR), temperature-programmed desorption (TPD) and laser Raman spectroscopy. Oxidized diamond powders were treated thermally in an H, environment. IR spectral changes were followed during the hydrogenation of oxidized diamond powders. We observed CH bonding on diamond surfaces. The amount of CH bonding increased with the temperature of treatment below 900°C. Above 9OO"C, the amount of the CH bonding decreased. Thermally desorbed species were analysed by mass spectrometry. H, was desorbed from hydrogenated diamond powders above ca. 800°C. Close agreement between FTIR and TPD results was obtained. Raman spectra indicated that the disordered graphitic carbon phase was formed above 900 "C.
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