Thin Solid Films, 161 (1988) 139 147 PREPARATION AND CHARACTERIZATION 139 EFFECT OF DEPOSITION RATE ON STRUCTURE AND PROPERTIES OF As2S 3 FILM KOTO WHITE Materials Laboratory, Wright-Patterson AFB, OH 45433 (U.S.A.) BINOD KUMAR University of Dayton Research Institute, Dayton, OH 45469 (U.S.A.) AMARENDRA K. RAI Universal Energy System, Dayton, OH 45432 (U.S.A.) (Received November 25, 1986; revised November 9, 1987; accepted November 24, 1987) Thin films of glassy As2S 3 were prepared by physical vapor deposition at deposition rates ranging from 15/~ s 1to 300/~ s- ~. The refractive index of the films was determined by a spectrophotometry and stylus technique. The films were characterized by X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry and transmission electron microscopy. The result was interpreted in terms of variation in stoichiometry and structure. 1. INTRODUCTION Arsenic trisulfide (As253) glass has been widely used in IR optical devices because of its good transparency in the wavelength region from 0.7 ~tm to 11.0 lam, and because of its excellent resistance against devitrification, moisture and corrosive chemicals. The vapor-deposited films of As2S3-based compositions, which have been used mainly as optical coatings, have found new applications in electronics, electro-optics and optical information storage in recent yearst-4. In general, the physical and structural properties of vapor-deposited films are greatly different from those of the corresponding bulks and are affected by deposition conditions such as the deposition rate, residual gas pressure, type and temperature of substrates, and the angle and velocity of incident vapor 5-1 o. Apling, Leadbetter and coworkerst 1-~3 examined the structural dissimilarity between bulk and thin film As2S3 and As2Se3, using a hot-stage X-ray diffraction technique. The first diffraction peaks for both compounds were found to be sharper and more intense in as-deposited films reflecting an enhanced longer range order, and their intensities decreased and approached that of the bulk on annealing. This was explained by the possible existence of As--As bonds and a sheet-like open structure in as-deposited films. This speculation was supported by an arsenic-rich stoichiome- try in their films and a considerable fragmentation of As2S 3 into S 2 and As4S4 during the evaporation process, as detected by mass spectroscopy 12,14 Nemanich and coworkersl 5,16, from extended X-ray absorption edge fine structure and Raman spectroscopic results, and Tohge et al.17, through IR spectroscopy, suggested that all the As--As bonds may be incorporated as S2As--AsS 2 units, as in As4S 4 molecules, 0040-6090/88/$3.50 © Elsevier Sequoia/Printed in The Netherlands