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Volume 32, Issue 3, May 2014
Samples of cerium were exposed to hydrogen under controlled conditions causing cerium hydride sites to nucleate and grow on the surface. The hydriding rate was measured in situ, and the hydrides were characterised using secondary ion mass spectrometry, scanning electron microscopy, and optical microscopy. The results show that the hydriding rate proceeded more quickly than earlier studies. Characterisation confirmed that the hydrogen is confined to the sites. The morphology of the hydrides was confirmed to be oblate, and stressed material was observed surrounding the hydride, in a number of cases lathlike features were observed surrounding the hydride sites laterally with cracking in the surface oxide above them. It is proposed that during growth the increased lattice parameter of the CeH2 induces a lateral compressive stress around the hydride, which relieves by the ca. 16% volume collapse of the γ-Ce to α-Ce pressure induced phase transition. Cracking of the surface oxide above the laths reduces the diffusion barrier to hydrogen reaching the metal/oxide interface surrounding the hydride site and contributes to the anisotropic growth of the hydrides.
Control of the interfacial abruptness of Au-catalyzed Si-Si1−xGex heterostructured nanowires grown by vapor–liquid–solid32(2014); http://dx.doi.org/10.1116/1.4867264View Description Hide Description
Axial Si-Si1−x Ge x heterostructured nanowires were grown by Au-catalyzed vapor–liquid–solid method. In this work, the authors examine the changes in growth parameters on the interfacial-abruptness of Si-Si1−x Ge x heterointerfaces in nanowires. The authors have investigated the effect of temperature drop, pressure change, and growth stop on the droplet stability which in turn modifies nanowire morphology and interfacial abruptness. The authors found that Si/Si1−x Ge x heterointerface is relatively sharp while Si1−x Ge x/Si is much broader. They demonstrate that a short growth stop is a good way to minimize reservoir effect resulting in small interfacial abruptness value. Our observations reveal that Si/Si1−x Ge x interfacial abruptness is 20 ± 5 nm irrespective of the nanowire diameter while interfacial abruptness for Si1−x Ge x/Si is linearly dependent on nanowire diameter.