Thermally induced changes in refractive index of As-S and Ag-As-S thin films

Reflection measurements at infrared (IR) wavelengths are used to measure th ermally induced changes in the optical thickness of as-deposited and anneal ed As33S67 and As40S60 thin films of thicknesses similar to 1.5 and similar to 16 mu m, respectively, deposited by vacuum thermal evaporation at a rat e of similar to 0.1 nm s(-1). Measurements were also made on films of estim ated composition As21Ag26S53 derived from Ag diffusion into the As33S67 Obt ained by heating Ag/As33S67 bilayers. For annealed As-S films the relative change in optical thickness was approximately equal to the thermal expansio n coefficient for the melt-quenched glass between room temperature and simi lar to 160 degrees C, indicating that the refractive index, n, has a neglig ible dependence on temperature. Tn contrast, the Ag-As-S system was found t o have thermal coefficients similar to 2.5 times those for the annealed As- S films, which were not reduced by annealing. (C) 1999 Elsevier Science B.V . All rights reserved.