Hydrogen-related surface modifications of 20 nm thin straight-sided niobium nano-wires and niobium meander-films

Nano-wire arrays of Niobium were produced by small angle sputtering on facetted sapphire, using the self shadowing effect of the facets. A wire width of about 80 nm was adjusted, the mean (maximum) wire height was about 20 nm (30 nm), the length can be in the cm range. Meander-film morphologies of 20 nm mean (26 run maximum) thickness were produced by conventional sputtering onto smooth sapphire substrates at elevated temperatures. The morphology of the wires was investigated with atomic force microscopy (AFM), using contact mode. Meander-films were studied by scanning tunnelling microscopy (STM). Hydrogen loading was performed by instantaneously increasing the hydrogen gas pressure above the solubility limit. Thus, an elongated hydride could be monitored in an about 30 nm thick wire. STM studies on meander-films show the presence of cylindrical hydrides. Local out-of-plane and in-plane expansion can be explained by the formation of hydrides, being coherent with the matrix. This was verified by finite-element calculations. The surface morphology modification associated with these coherent hydrides disappears reversibly, as soon as the hydrogen gas pressure is reduced. This indicates that plastic deformation does not occur in thin wires and meander films. (C) 2007 Elsevier B.V. All rights reserved.