Metal nanowires and hydrogen loading: An AFM-study

Metal nanowires (Nb, V, Pd and Fe) were studied by atomic force microscopy (AFM). The wires were produced by metal deposition onto faceted sapphire substrates. Periodic arrangements of wires of about 7 × 10−8 m width and 3 × 10−8 m height, accompanied with a wire length of about 1 × 10−3 m were analysed. The grain size was normally about 2 × 10−8 m.Prolonged scanning in contact mode leads to massive material agglomeration on the back of the substrate facet. Short-run measurements successfully image the wire morphology but impede an exact determination of the phase transition pressures.At 10−2 Pa hydrogen gas pressure, the formation of a hydride along the wire axis of Nb-wires was verified in short-run experiments by AFM images including contour-lines as well as height histograms. The lattice of a 30 nm thin Nb-wire locally expands upon hydride formation with about 2 nm in vertical direction. This result agrees with the predictions of a model assuming linear elasticity, an ideally rigid substrate, and infinitely strong adhesion of the nanowires. No lateral expansion was detectable.