Processing effects on microstructure in Er and ErD 2 thin-films

Abstract

Erbium metal thin-films have been deposited on molybdenum-on-silicon substrates and then converted to erbium dideuteride (ErD 2). Here, we study the effects of deposition temperature (≈300 or 723 K) and deposition rate (1 or 20 nm/s) upon the initial Er metal microstructure and subsequent ErD 2 microstructure. We find that low deposition temperature and low deposition rate lead to small Er metal grain sizes, and high deposition temperature and deposition rate led to larger Er metal grain sizes, consistent with published models of metal thin-film growth. ErD 2 grain sizes are strongly influenced by the prior-metal grain size, with small metal grains leading to large ErD 2 grains. A novel sample preparation technique for electron backscatter diffraction of air-sensitive ErD 2 was developed, and allowed the quantitative measurement of ErD 2 grain size and crystallographic texture. Finer-grained ErD 2 showed a strong (1 1 1) fiber texture, whereas larger grained ErD 2 had only weak texture. We hypothesize that this inverse correlation may arise from improved hydrogen diffusion kinetics in the more defective fine-grained metal structure or due to improved nucleation in the textured large-grain Er.