熱酸化に伴うCu<SUB>2</SUB>O皮膜内の応力発生挙動

Abstract

The stress generation behavior in Cu2O grown on Cu has been studied using an X-ray diffraction apparatus, which is provided with a newly designed hot stage unit. The oxidation run has been carried out at temperatures between 573 and 923 K and at oxygen pressures ranging from 25 to 110 Pa for (100) and (111) faces of single crystalline copper discs and surfaces of polycrysalline ones. The stress generation behavior varied depending on temperature and crystalline state of the specimen. At temperatures below the half of the melting point of Cu2O a compressive strain (7×10−3 at 573 K) larger than the fracture strain of the bulk oxide (2×10−3) was observed. This elastic strain diminished at higher temperatures. The oxide scale exhibited a pseudo brittle-ductile transformation between 573-673 K as the bulk oxdie did. A quantitative evaluation of the stress generated in the epitaxial oxide grown on Cu (100) showed values between 1.3 and 3.0±0.5×108 N·m−2, which were 30% larger than the elastic strain generated in the oxide grown on Cu (111). This will result from a new epitaxial effect which is probably due to epitaxial development of a mosaic structure in the oxide but not due to “lattice misfit” at the oxide/metal interface. The strain observed within the elastic range can alter grain to grain due to an elastic anisotropy in the Cu2O crystal. This implies a heterogeneous strain, instead of stress, distribution model to be probable. These observations together with those made by scanning electron microscopy allowed to conclude on the nature of strain generation and also on the athermal effect.