Ni Alloy Surface Research Articles

Observation of CuNi alloy surfaces by low wattage glow discharge emission spectrometry

AbstractGlow discharge sputtering on CuNi alloy surfaces is studied by optical emission spectroscopy and Auger electron spectroscopy. The relative intensity of Cu emission lines against Ni lines increases with a decrease in supplied power in very low wattage regions. These changes of the relative intensities principally depend on the sputtering parameters of constituent elements in CuNi alloy; that is, the preferential sputtering of copper. Surface analysis by Auger electron spectroscopy shows that when samples are sputtered by glow discharges in very low power operations, the deformation layer which has a nickel‐enriched composition exists on alloy surfaces. We discuss the effect of glow discharge sputterings on surface compositions using the two analytical methods described above.

Adsorption and decomposition of CO ON Cu, Ni AND Cu-Ni single crystals

The adsorption of CO on Ni(100), Ni(111) and Cu-Ni surface alloys has been studied in the temperature range 300–600 K and pressures up to 10 −2 torr. Adsorption isotherms on pure nickel gave a coverage-independent heat of adsorption of 134 kJ mol −1. If, on Ni(111), some carbon was present on the surface this value decreased to 103 kJ mol −1. On Cu-Ni surface alloys no CO adsorption was found for Cu(100)-Ni, and on Cu(111)-Ni adsorption-induced segregation was so severe that no heat of adsorption could be determined. For low nickel content on Cu(110)-Ni the heat of adsorption is 62 kJ mol −1; at higher nickel fractions this value increases to 75 kJ mol −1, with a small amount of CO bound with 75–130 kJ mol −1. At very high nickel concentration, segregation of Ni made accurate determinations impossible. On Ni(100) and Ni(111), CO disproportionates, but more readily on Ni(100). On Cu-Ni surface alloys no carbon deposition took place. These results are compared with literature data and an explanation for the difference between Cu and Ni in the CO disproportionation reaction is given. The differences and similarities between the three low-index faces are also discussed.

Preparation and characterization of Cu(111)-Ni and Cu(110)-Ni surface alloys

The interaction of Ni(CO) 4/CO gas mixtures with Cu(111) and Cu(110) single crystal surfaces has been studied with ellipsometry. Auger electron spectroscopy, LEED and argon ion depth profiling. At room temperature Ni atoms with some CO ligands remain at the surface. The amount of Ni that can be deposited is less than one monolayer. The alloy surface is able to bind CO. After exposures above 220°C, the initially deposited amount of Ni resides below the first layer of Cu atoms. The amount of Ni that can be deposited is essentially unlimited. The alloy surfaces show no contamination of C or O at the surface or in deeper layers. The Ni concentration profile below the surface is bell shaped and is metastable up to 400–450°C. The ellipsometric data can be understood if one assumes that a significant fraction of voids are present in the Cu-Ni layer.

Preparation and characterization of Cu(111)-Ni and Cu(110)-Ni surface alloys

Preparation and characterization of Cu(111)-Ni and Cu(110)-Ni surface alloys

Adsorption of oxygen on a Cu(110)Ni surface alloy and its reaction with hydrogen and carbon monoxide

Ellipsometry, AES and LEED have been used to study the interaction of O 2 with a Cu(110)Ni surface alloy and the reaction of H 2 and CO with adsorbed oxygen. The surface alloys were prepared by dissociation of nickel carbony1 on a clean Cu(110) surface. The rate of chemisorption of oxygen on a freshly prepared Cu(110)Ni (1°) surface is independent of the crystal temperature and can be described by a precursor state model. The initial sticking probability is ∼0.07 and no saturation is observed at θ=0.5. For θ o > 0.5 the reaction probability of CO with adsorbed oxygen first increases and then decreases: its order of magnitude is ∼10 −5 and the apparent activation energy is ∼ 6.5 kcal/mole. The reaction rate of hydrogen with preadsorbed oxygen is more or less independent of the oxygen coverage at crystal temperatures above 220°C and θ O < 0.5. The reaction rate is limited by the dissociation of hydrogen. At lower crystal temperatures the reaction rate is no longer proportional to the hydrogen pressure and decreases with decreasing oxygen coverage. The reaction of hydroxyl groups at ‘nickel like’ sites appears to be the rate-determining step.

Adsorption of oxygen on a Cu(110)-Ni surface alloy and its reaction with hydrogen and carbon monoxide

Adsorption of oxygen on a Cu(110)-Ni surface alloy and its reaction with hydrogen and carbon monoxide

The adsorption of carbon monoxide on Cu(110)-Ni surfaces prepared by dissociation of nickel carbonyl

Cu(110)-Ni surface alloys were prepared by dissociation of nickel carbonyl on clean Cu(110). The adsorption of CO is reversible in the temperature region of 22–200°C and the pressure range of 5 × 10 −8-0.7 Torr, as monitored with ellipsometry and AES. The amount of adsorbed CO depends on the amount of preadsorbed oxygen but not on the amount of carbon present at the surface. The isosteric heat of adsorption decreases from 31 ± 3kcal/mole to 18 ± 2 kcal/mole with increasing CO coverage (up to θ = 0.14 θ max) but is constant for higher coverages (up to θ = 0.4θ max).

Hydrogen desorption from Ni sites on (110) CuNi surfaces

Hydrogen adsorption on Ni-rich (110) CuNi alloy surfaces has been studied by means of thermal desorption spectroscopy. After adsorption near room temperature the hydrogen desorption spectra exhibit a coverage dependence similar to that known from pure (110)Ni. Besides a slightly composition dependent desorption energy the alloy surfaces behave like a (110)Ni surface diluted by practically inert Cu. These results are compared to those reported by Yu Ling and Spicer.

SIMS, AES, work function and flash desorption measurements of the CO adsorption on NiCu alloy surfaces

The chemisorption of CO on Cu, Ni and CuNi alloy surfaces was examined by SIMS, work function measurements and desorption spectroscopy. Using a dynamic SIMS technique the M +, M + 2, MCO + and M 2CO + emission at different temperatures (100–400 K) was measured as a function of CO exposure. In agreement with the work function and desorption experiments an increase of M + and MCO + emission due to the CO adsorption on Cu was found only at low temperatures (100–190 K). On the Ni surface an increase of Ni +, NiCO + and Ni 2CO + was measured up to 400 K. The adsorption of CO on CuNi alloy surfaces — as derived from the work function measurements — can be described by the assumption of two different states of adsorbed carbon monoxide. They can be characterized by different binding energies and from sign and magnitude different work function changes. These states were interpreted as adsorption at Ni or Cu sites of the alloy surfaces, respectively. To a certain extent the SIMS results from the alloy surfaces are incompatible with the work function measurements and desorption spectroscopy and the SIMS studies on the pure metals. A Cu + emission with comparable intensity to the Ni + emission was found for alloys with bulk concentrations of 60 and 40 at% Cu at 300 K. The ratio Ni + Cu + was nearly independent of CO pressure and temperature. The measured ratios of Cu + 2 ( Cu + + Ni +) , Ni + 2 ( Cu + + Ni +) and CuNi + ( Cu + + Ni +) with values about 10 −2 can be explained the basis of a statistical arrangement of Cu and Ni atoms in the alloy surface. The intensities of the MCO + emissions are 10 2 times smaller than the corresponding values of the pure metals. No emission of M 2CO + was found on CuNi during CO adsorption.

Thickness and in-depth composition profile of altered layer caused on CuNi alloy surface due to preferential sputtering

Preferential sputtering on CuNi (50 wt%) alloy surfaces was studied by Auger electron spectroscopy. The CuNi (50 wt%) sample was prepared by electrolytically polishing the sample under some specific conditions so as to obtain a mirror surface and at the same time keeping the surface composition identical with that of the bulk. The average thickness of the altered layer produced on the CuNi surface due to the preferential sputtering has been estimated to be of the order of ~15 Å for normally incident 500 eV Ar ion bombardment according to the approach proposed by Ho et al. The individual sputtering yields of the constituent elements in the alloy have also been measured. The thickness of the altered layer and the individual sputtering yields in the alloy agree very well with those reported for evaporated Cu-Ni samples by Ho et al. It has also been found that the thickness of the altered layer decreases as the angle of incidence of sputtering ion beam increases. In-depth composition profile measurement of the altered layer has also been made according to the analysis reported by Watanabe et al., but paying particular attention to the estimation of signal intensities of the low energy Auger electrons (M 1M 45M 45 transitions). This mode of measurement has shown a higher enrichment of Ni on the sputtered Cu-Ni surface than those obtained from the high energy Auger signals.

Direction of electron transfer in FeNi alloy surface

The direction of electron transfer in FeNi alloys was studied by an infrared technique comparing CO interaction with CuNi and CoNi alloy systems. The results were interpreted by the d-hole relationship of the metals and the saturation magnetization of alloy systems. An electron transfer from Fe to Ni in the FeNi alloy system is proposed, whereas no electron transfer between alloying components is believed to occur in the CoNi alloy system. A critical point for the FeCO interaction on the FeNi alloy surface was observed at 75 Fe25 Ni atom percent; a critical point for CuCO interaction on the CaNi alloy surface was previously found at 85 Cu15 Ni atom percent. No similar critical composition was found on the CONi alloy surfaces. Some of Uhlig's corrosion theory of surface passivity was applied to the calculation of critical composition. Infrared band shifts on the alloy surfaces are shown. Infrared absorption bands for CO on silica-supported metal alloy surfaces were determined in the region from 2200 cm −1 to 1600 cm −1.