Optical properties of amorphous compounds As 2S 3 and As 2Se 3 in the infrared region

Abstract

Optical properties of amorphous As 2S 3 and As 2Se 3 at room temperature in the region between 30 and 8000 cm −1 are described. Absorption peaks at 38 cm −1 for both As 2S 3 and As 2Se 3 are assigned as vibration modes v AS concerning with only arsenic atoms. Kramers-Kronig analysis of reflectivity indicates only one reststrahlen band at 301 cm −1 for As 2S 3 or at 226 cm −1 for As 2Se 3 which is assigned as AsS or AsSe stretching vibration v R. Bands at 698 and 991 cm −1 for As 2S 3 or 487 and 732 cm −1 for As 2Se 3 are interpreted as overtones of v R. The shape of the reststrahlen bands fits to a Gaussian form, and broadening of the band can be attributed to a Gaussian distribution of oscillator frequencies. It is found from the value of the force constants (1.18 and 1.19 md/Å for As 2Se 3 for the stretching vibration and the difference between low and high frequency dielectric constants (1.63 and 1.92 for As 2S 3 and As 2Se 3) that the compounds have a large degree of covalency.