Surface Core-level Binding-energy Shifts Research Articles

A (4×2) reconstruction of CuInSe2 (001) studied by low-energy electron diffraction and soft x-ray photoemission spectroscopy

Clean and flat (001) surfaces of CuInSe2∕GaAs grown by molecular-beam epitaxy could be prepared by the combination of a Se capping and decapping process and subsequent Ar+ ion sputtering and annealing. The formation of a (4×2) reconstruction was observed with low-energy electron diffraction. Soft x-ray photoemission spectroscopy was performed on the prepared surfaces and revealed surface core-level binding energy shifts in the Cu2p3∕2, Se3d, and In4d levels which are associated with surface atoms. The structure model of a combined metal adatom-Se dimer structure is proposed to refer to the (4×2) reconstruction.

Core-level shifts for two- and three-dimensional bimetallicPdxCu1−xandPdxAg1−xalloys on Ru(0001)

Core-level binding energy shifts (CLSs) and surface CLS (SCLSs) are determined by experiment and theory for ultrathin Pd as well as for PdCu and PdAg surface alloys which vary in thickness from 1 t ...

Investigation of the SMSI phenomenon with TiO 2/Ru/SiO 2 model-dispersed catalysts

The response of ternary SiO 2-supported Ru/TiO 2 catalysts to a series of characteristic treatments has been examined in detail by chemisorption measurements, XPS, SIMS, and HREM observations, appropriate comparisons being made with binary Ru/SiO 2 and Ru/TiO 2 reference samples. The SMSI state is shown to be air-sensitive and the active highly dispersed phases on the ternary TiO 2/ Ru/SiO 2 catalysts exhibit SMSI behavior even after low-temperature reduction. SIMS and XPS data indicate that the SMSI condition does not involve intermixing of the Ru and TiO 2 phases. Rather it is associated with highly dispersed metal entities whose XP spectra exhibit significant surface core-level binding energy shifts. Further aspects of the SMSI state are also discussed.

Surface core-level spectroscopy of Cu(100) and Al(100).

We present experimental and theoretical results for the surface core-level binding-energy shifts of Al(100), representative of an sp metal, and Cu(100), representative of a transition metal. Our analysis of these results leads to a unified interpretation for the different behavior of sp and transition metals. The d-electron contribution to smaller surface core-level binding energies is elucidated.

Constant final state measurements of surface core-level binding energy shifts: InP(110) and GaAs(110)

The surface core-level binding energy shifts have been obtained for the In4d and the P2p core-levels on the InP(110) surface. In agreement with previous studies of core-level shifts on the cleavage face of III–V semiconductors, the anion and cation shifts are of almost equal magnitude and are of opposite polarity (−0.31 and +0.30 eV respectively). The results are compared with a similar investigation of the GaAs(110) surface and discussed in terms of a recent calculation of surface core-level shifts for the (110) cleavage face of III–V semiconductors.

Constant final state measurements of surface core-level binding energy shifts: InP(110) and GaAs(110)

The surface core-level binding energy shifts have been obtained for the In 4d and the P2p core-levels on the InP(110) surface. In agreement with previous studies of core-level shifts on the cleavage face of III–V semiconductors, the anion and cation shifts are of almost equal magnitude and are of opposite polarity (−0.31 and +0.30 eV respectively). The results are compared with a similar investigation of the GaAs(110) surface and discussed in terms of a recent calculation of surface core-level shifts for the (110) cleavage face of III–V semiconductors.

Surface core-level binding-energy shifts for the cleaved GaP(110) surface.

Ga 3d and P 2p core-level photoemission spectra have been collected from cleaved GaP(110) surfaces and surface core-level binding-energy shifts of -0.41 and +0.31 eV have been obtained for the P 2p and Ga 3d core levels, respectively. The energy dependence of the P 2p core-level line shape has also been studied and estimates of the photoelectron escape depth in GaP are made for photoelectrons with kinetic energies in the range 10--60 eV.

Surface core-level binding-energy shifts in hydrogen-adsorbed nickel-copper alloy

The influence of adsorbates on the surface core-level binding-energy shifts in a Zx(Z+1)1-x alloy system (Z being the atomic number) has been studied in terms of the equivalent core approximation (ECA) and an electronic theory of chemisorption-induced surface segregation. For the H/NixCu1−x system it has been shown that at low bulk Ni concentration the surface core-level shift of Ni undergoes a sign reversal similar to the sign reversal in the heat of segregation found both theoretically and experimentally.

A core-level binding-energy shift analysis of CO, H, and O adsorption on Cu–Ni surfaces

The equivalent core approximation (Z+1) is used with a Born–Haber cycle analysis to analyze the Ni 2p3/2 surface core-level binding-energy shifts which occur upon adsorption of CO, H, and O on Ni(100). The analysis gives values for the heats of desorption of these gases from Cu–Ni alloy surfaces. Perhaps more importantly, it also provides a quantitative determination of how chemisorption of CO, H, and O modify the heats of surface segregation for Cu–Ni surfaces.

Comparison of calculated surface core-level energy shifts with empirical heats of segregation

Two seemingly disparate expressions for heats of surface segregation, one involving surface core-level binding-energy shifts, the other dominated by surface energy differences, are shown to agree across the d-band transition series. This result is generalized to predict differences in heats of adsorption on transition metals.

Surface core-level binding energy shifts in alloys

A simple theory for the core-level binding energy shifts at the surfaces of binary alloys A x B 1− x is presented. Results are given for the surface core-level shifts of Ni in Ni x Cu 1− x alloys and Pd in Pd x Ag 1− x alloys. It has been shown that the surface core-level shifts may depend sensitively on surface segregation.

Surface heat of segregation from surface core-level binding-energy shifts

Surface heat of segregation from surface core-level binding-energy shifts

Calculated transition-metal surface core-level binding-energy shifts

Calculated transition-metal surface core-level binding-energy shifts