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Processing effects on microstructure in Er and ErD2 thin-films

Journal of Nuclear Materials

Parish, Chad M.; Snow, Clark S.; Kammler, Daniel K.; Brewer, Luke N.

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. © 2010 Elsevier B.V. All rights reserved.

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The manifestation of oxygen contamination in ErD2

Proposed for publication in the International Journal of Hydrogen Energy.

Parish, Chad M.; Snow, Clark S.; Brewer, Luke N.

Erbium dihydride Er(H,D,T){sub 2} is a fluorite structure rare-earth dihydride useful for the storage of hydrogen isotopes in the solid state. However, thermodynamic predictions indicate that erbium oxide formation will proceed readily during processing, which may detrimentally contaminate Er(H,D,T){sub 2} films. In this work, transmission electron microscopy (TEM) techniques including energy-dispersive x-ray spectroscopy, energy-filtered TEM, selected area electron diffraction, and high-resolution TEM are used to examine the manifestation of oxygen contamination in ErD{sub 2} thin films. An oxide layer {approx}30-130 nm thick was found on top of the underlying ErD{sub 2} film, and showed a cube-on-cube epitaxial orientation to the underlying ErD{sub 2}. Electron diffraction confirmed the oxide layer to be Er{sub 2}O{sub 3}. While the majority of the film was observed to have the expected fluorite structure for ErD{sub 2}, secondary diffraction spots suggested the possibility of either nanoscale oxide inclusions or hydrogen ordering. In situ heating experiments combined with electron diffraction ruled out the possibility of hydrogen ordering, so epitaxial oxide nanoinclusions within the ErD{sub 2} matrix are hypothesized. TEM techniques were applied to examine this oxide nanoinclusion hypothesis.

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30 Results
30 Results