Influence of Substrate Temperature on the Microstructure of Sc and ScD2 Films

Scandium films with thickness of ∼ 2∼3 μm were deposited on Mo substrates with a surface roughness Rq
• 5∼8.63 nm. Subsequently, the films were converted to scandium dideuteride (ScD2) in the Sievert's apparatus. A novel substrate preparation process has been developed for a simple observation of the cross-sectional images. The effects of substrate temperatures (623, 823, 1023 K) on the initial Sc-metal film microstructure and the following ScD2 microstructure were investigated. Results indicate that Sc films show a columnar microstructure with a preferred orientation of the crystallites along the [002] direction at all the three tempertures and the (002) texture increases with increasing of the temperature. The grain sizes of Sc films deposited at higher temperature are larger than those deposited at lower temperature, consistent with the published structure zone models (SZMs). As expected, the stronger (002) texture of Sc-metal film deposited at higher temperature results in the stronger (111) texture of deuteride film, indicating that the deuteride nuclei might inherit their texture from the initial metal grains' structure. Unexpectedly, an inverse correlation appears that larger Sc-metal grains lead to smaller deuteride grains due to the improved deuterium diffusion kinetics in the more defective and fine-grained metal structure