Nickel lattice orientation

The films are epitaxial in the sense that the lattice constant is intermediate between those of copper and nickel. As indicated above, that modulated strain is probably responsible for the increased hardness. Other authors (5) have tried to explain similar effects by stating that the layers were specifically oriented. Our example (6) demonstrates that these considerations must be reexamined since it was possible to achieve the effect in a crystalline multilayer deposited on an amorphous nickel-phosphorus underlayer. It appears that layer thickness is the important parameter here. 

Nickel oxide, like MgO, usually adopts the relatively simple rocksalt lattice. The natural cleavage plane of NiO is (100), and studies have shown that the resulting surfaces are of high quality, relaxing only slightly away from the ideal bulk terminated (100) surface (see Fig. 1). Structural determinations of adsorbates have been performed on both this surface and the polar (111) surface. To circumvent surface charging problems almost all of these studies have been performed on highly oriented NiO thin films. 

Chemically these catalysts contain metallic nickel along with 1-8% aluminum and up to 20% aluminum oxide or hydroxide. The surface is 50-100% metallic nickel which is present in an fee crystalline lattice, the same crystal orientation found for the bulk nickel. The use of low hydroxide ion concentrations and reaction temperatures in the reaction with the alloy gives catalysts containing more aluminum and aluminum oxide. The alumina in these preparations is occluded in the metallic skeleton and is difficult to remove even when later exposed to higher hydroxide concentrations. High temperature digestion is needed to remove all of the alumina from these catalysts. 

Nickel is one of the few materials possessing a close lattice match with diamond. However, its high carbon solubility and strong catalytic effect on hydrocarbon decomposition may be the reason that graphite layers develop on Ni substrates under the typical diamond CVD conditions. This effect impedes the direct nucleation of diamond on Ni substrates and excludes the eventual development of an orientational relationship between the diamond films and the Ni substrates, although diamond may eventually nucleate and grow on the graphite interlayers. 

Summary. An STM study has been initiated to investigate the various processes associated with electrodeposition of Cu-Ni multilayers on Cu(100). The substrates were prepared by electropolishing in phosphoric acid followed by immersion in 10 mmol/1 HCl. A (V2 x V2)R45° adlattice of oxidatively adsorbed chlorine is formed under these conditions. The adlayer stabilizes the surface steps in the <100> direction which corresponds to the close packed direction of the chloride adlattice. In dilute (millimolar) solutions of cuprous ion, reduction occurs under mass transport control with the electrocrystallization reaction proceeding by step flow in the <100> direction. At more negative potentials chloride is partially desorbed. Coincidentally, the highly kinked metal steps become Mzzy and move towards adopting the close-packed <110> orientation of the metal lattice. Preliminary experiments on heteroepitaxial nickel deposition reveal regions where electrocrystallization on Cu(100) occurs via step flow in the <110> direction. 

For thicker films of NiO formed at higher temperatures (e.g. 600°C), ex-situ RHEED is useful to examine the structure of the oxide which forms [7]. Figure 4.2 compares the oxidation of electropolished (112), (111) and (100) monocrystals with electropolished polycrystaUine nickel at 600°C. Only -lOiim of oxide has formed on (112)Ni after 1 h from RHEED, the single orientation prior oxide [(111) antiparallel NiO on (111) steps of the (112) macrosurface] persists during oxidation. The lower growth rate is the result of formation of oxide by lattice diffusion only. The increased rate of oxidation... 

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