Electrospray Deposition of Uniform Thickness Ge[subscript 23]Sb[subscript 7]S[subscript 70] and As[subscript 40]S[subscript 60] Chalcogenide Glass Films

Abstract

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two chalcogenide compositions are demonstrated: Ge[subscript 23]Sb[subscript 7]S[subscript 70] and As[subscript 40]S[subscript 60] , which have both been studied extensively for planar mid-infrared (midIR) microphotonic devices. In this approach, uniform thickness films are fabricated through the use of computer numerical controlled (CNC) motion. Chalcogenide glass (ChG) is written over the substrate by a single nozzle along a serpentine path. Films were subjected to a series of heat treatments between 100 °C and 200 °C under vacuum to drive off residual solvent and densify the films. Based on transmission Fourier transform infrared (FTIR) spectroscopy and surface roughness measurements, both compositions were found to be suitable for the fabrication of planar devices operating in the mid-IR region. Residual solvent removal was found to be much quicker for the As[subscript 40]S[subscript 60] film as compared to Ge[subscript 23]Sb[subscript 7]S[subscript 70]. Based on the advantages of electrospray, direct printing of a gradient refractive index (GRIN) mid-IR transparent coating is envisioned, given the difference in refractive index of the two compositions in this study.