Study of a polycrystalline Ni/Cr alloy .5. Hydrogen-atom exposure

An air-exposed polycrystalline nichrome (Ni/Cr) alloy was exposed to a hydrogen-atom flux at room temperature and then sputtered with Ar+ for 15 min. X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to examine the changes, which occur at the surface of the sample during these treatments. The near-surface region of the alloy initially consists primarily of nickel hydroxide and carbon contamination. Small amounts of Na and Cl contaminants an also present on the surface, according to the ISS data. The amount of carbon contamination and oxygen in the near-surface region is decreased by the H-atom exposure, and the Ni and Cr concentrations are increased. The hydroxyl groups are rapidly removed during the exposure to if atoms presumably through formation of water molecules, which desorb. Ni(OH)(2), NiO, Ni-0, CrO2 and Cr-0 are present in the near-surface region after the Ii-atom exposure. A subsequent 15-min, 1-keV Ar+ sputter removes the remaining carbon, nearly all of the oxygen, as well as the Na and Cl contaminants. The Ni is mostly metallic, and Cr is present as Cr-0 and CrO2. In previous studies, multiple ion-beam sputtering and annealing cycles were necessary to obtain this level of cleanliness. The process using a H-atom beam flux provides an alternative and less time-consuming method for cleaning Ni/Cr alloy surfaces. (C) 1997 Elsevier Science S.A.