Abstract

Synthesized materials obtained by physical mixing are often used to generate de sired optical and mechanical properties. These properties often differ from the average of the properties of individual materials that make up the mixture.¹ In this paper we discuss the optical, structural, and mechanical properties of several composite IR material systems. SrF₂ films have a micro-structure with pronounced columnar grains that results in rough morphology and optical scatter. Films of pure ZnSe and mixtures of ZnSe with up to 70-vol % SrF₂ have very smooth morphologies. Films with alternating material layers, on the other hand, do not become smooth even in the ZnSe layers. Codeposition results in strongly oriented crystalline films where both ZnSe and SrF₂ crystalline phases are observed, indicating rapid segregation during deposition. In general, mixing reduces the crystalline grain size. Mixed intermediate composition films have crystalline orientations that differ from those of the pure components. Films rich in one material suppress the crystallinity of the other material and impose the preferred orientation of that material on the composite film. Intrinsic stress of the fluorides is small and tensile whereas the stress in thermally evaporated ZnSe is compressive. The stress in the composite films changes abruptly at 70% SrF₂ composition from compressive to low tensile.

© 1989 Optical Society of America