Robert E. Witkowski

Cryogenic cathodoluminescence of plasma‐deposited polycrystalline diamond coatings

The cathodoluminescence spectra of microwave plasma‐deposited polycrystalline diamond films have been measured at liquid‐nitrogen temperatures over the spectral region of 230–800 nm. The diamond coatings had been deposited under several different deposition temperatures and reactant compositions. Measurements on natural type‐IIB diamond crystals were made for comparison. The intrinsic exciton emission bands which fall in the UV just below the band edge were observed, as well as several defect and impurity bands which extend throughout the visible part of the spectrum. SEM micrographs and Raman spectra were obtained for the same set of samples used for the cathodoluminescence measurements. It was found that the diamond‐related cathodoluminescence features were most intense in samples whose Raman spectra exhibited the most intense cubic diamond line at 1332 cm−1 and the least intense graphitic band at about 1500 cm−1.

CVD Diamond Coatings for the Infrared by Optical Brazing

Abstract Protective coatings of chemical vapor-deposited (CVD) diamond have been thermally bonded to soft infrared-transmitting optical windows of ZnSe and ZnS with chalcogenide glasses by the “optical brazing” process1. The diamond coatings were deposited on silicon by a microwave-excited plasma process, and transferred to the infrared optics. The silicon was subsequently removed, exposing the smooth nucleation surface. This approach to coating optical components accomplishes several purposes at once. The infrared optical components components are not subjected to the high temperature, reactive environment in which CVD diamond is deposited. Also, the rough diamond growth surface does not need to be polished because it is concealed in the chalcogenide bonding glass whose refractive index is made to closely match that of diamond. Measurements of reflectance and transmittance with a scanning infrared spectrophotometer confirmed that scatterering losses were greatly reduced, and were too small over most of the infrared spectrum to be detected by this technique. Windows as large as 3.8 cm have been diamond-coated by the optical brazing technique, and larger sizes are under development.

Cyclohexane-based optical coatings of diamond-like carbon

Protective and anti-reflective optical coatings of diamond-like carbon have been deposited on germanium and silicon substrates from glow discharges of cyclohexane. Films of excellent quality were obtained with high deposition rates using this non-hazardous feed gas. A parametric study was carried out to determine the dependence of the process characteristics and the optical properties of the films on the electrode bias gas pressure and flow. The study determined the contours for film refractive index and deposition rates over the parameter space and also revealed information on the dependence of infrared absorption and film adhesion. Important information on process scaling was determined. A simple dependence of negative self-bias on electrode design was obtained by using electrodes of different sizes. Changes in bias as a result of the coating of grounded reactor surfaces were measured. The effect of feed gas flow on the film and process properties provided insight into the impact of reactant depletion on the deposition process. 258 / SPIE Vol. 1325 Diamond Optics 111(1990)