Optical properties of X-ray irradiated Cu<sub>6</sub>PS<sub>5</sub>I-based thin films deposited by magnetron sputtering

Abstract

Introduction . Cu 6 PS 5 I crystals belong to a big family of compounds with argyrodite structure. They are characterized by high ionic conductivity. That’s why these materials are promising for creation of different type of modern devices such as batteries, supercapacitors, electrochemical sensors, etc. Studies of the influence of external factors on physical properties of Cu 6 PS 5 I materials are important to predict endurance, wear resistance and safety of devices made on their basis. Purpose . The purpose of the paper is to investigate the influence of X-ray irradiation on the optical properties of Cu 6 PS 5 I-based thin films as well as to perform the quantative and qualitative evaluation of the changes that have taken place in the structure “film-substrate” as a result of X-ray irradiation. Methods . Cu 6 PS 5 I-based thin films were deposited onto silicate glass substrates by non-reactive radio frequency magnetron sputtering. The film chemical composition was investigated by energy-dispersive X-ray spectroscopy. X-ray irradiation was performed at different exposition times (30, 60 and 120 min) using wideband radiation of Cu-anode X-ray tube with approx 400 W of power applied (33 kV, 13 mA). Optical transmission spectra of Cu 6 PS 5 I-based thin films were studied using MDR-3 grating monochromator. Results . Optical transmission spectra of X-ray irradiated Cu 5.6 P 1.7 S 4.9 I 0.8 , Cu 6.4 P 1.1 S 4.6 I 0.9 and Cu 8.0 P 0.7 S 3.6 I 0.7 thin films were studied at various irradiation times at room temperature. With irradiation time increase the red shift of the short-wavelength part of transmission spectra and interference maxima is revealed. In the X-ray irradiated thin films the Uhrbach behavior of the optical absorption edge is observed. Optical absorption edge for X-ray irradiated thin films is shifted to the long-wavelength region with irradiation time increase. It leads to the energy pseudogap decrease and Uhrbach energy increase. Dispersion dependences of the refractive index for the X-ray irradiated thin films have shown a slight dispersion of the refractive indices in the transparency region, increasing with approaching the optical absorption edge. With irradiation time increase the nonlinear increase of the refractive indices in the X-ray irradiated thin films is revealed. Conclusions. The influence of X-ray irradiation on optical properties of Cu 6 PS 5 I-based thin films was studied. Changes in optical parameters of the thin films were investigated and described. With irradiation time increase the decrease of energy pseudogap as well as increase of Uhrbach energy and refractive index values was observed. It was determined that with irradiation time increase the darkening and densitification of the thin films occur. The increase of Uhrbach energy indicates on increase of structural disordering induced by the influence of X-ray irradiation.