Processing effects on microstructure in Er and ErD2 thin-films

Erbium metal thin-films have been deposited on molybdenum-on-silicon substrates and then converted to erbium dideuteride (ErD2). 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 ErD2 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. ErD2 grain sizes are strongly influenced by the prior-metal grain size, with small metal grains leading to large ErD2 grains. A novel sample preparation technique for electron backscatter diffraction of air-sensitive ErD2 was developed, and allowed the quantitative measurement of ErD2 grain size and crystallographic texture. Finer-grained ErD2 showed a strong (1 1 1) fiber texture, whereas larger grained ErD2 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.