<title>Rain erosion behavior of germanium carbide films grown on ZnS substrates</title>

Abstract

Thick germanium carbine films (GeC) are successfully grown on various Zinc Sulfide and Germanium substrates at temperatures up to 350 degree(s)C by two methods: Plasma Enhanced Chemical Vapor Deposition (PECVD) in gas mixtures of methane and germane and by Reactive Radio-Frequency Sputtering (RRFS) starting from a germanium target in a sputtering medium of methane and argon. The optical and mechanical properties of the GeC coatings depend on the composition determined by the deposition parameters. The refractive index at 633 nm varies from 4.9 to 4.3 for a carbon content ranging from 3 to 25% and the correlated refractive index in the 8 to 12 micrometers range is found to be between 3.96 and 3.1. For these coatings, the absorption coefficient is ranging from 270 to 40 cm<SUP>-1</SUP>. All films are amorphous in nature with domains ranging from 13 to 20 angstroms. The hydrogen content varies from 2 to 25% coming from C:H, Ge:H and C:Ge:H bonding. The XPS analysis shows the Ge:C precipitation kinetic for high deposition temperature or annealed films. The rain erosion resistance of GeC films and GeC with a protective diamond like-carbon (DLC) coating on top is measured for 1.2 mm water drop with an impact velocity ranging from 210 to 265 m/s on the Saab-Scania whirling-arm rig (Linkoping, Sweden).