G. Hollinger

Oxygen chemisorption and oxide formation on Si(111) and Si(100) surfaces

We have used photoemission techniques with synchrotron radiation to study the adsorption of oxygen on the Si(111)‐(7×7) and Si(100)‐(2×1) surfaces at room temperature in the submonolayer and monolayer regimes. High resolution Si 2p core‐level spectra, valence‐band spectra, work‐function, and Fermi‐level pinning positions have been measured for exposures between 1 and 1000 L and after annealing at 700u2009°C. Four oxidation states have been detected for the silicon surface atoms with Si 2p core‐level shifts of 0.9, 1.9, 2.6, and 3.4 eV which are assigned to silicon atoms bonded to 1, 2, 3, and 4 oxygen atoms. Both (111) and (100) surfaces are characterized by about the same sticking coefficient, a simple adsorption process for 1‐L exposures, the quenching of the surface states after 15 L and a saturation of the amount of oxygen after 100 L. Significant differences exist in the initial bonding geometries for the (111) and (100) surfaces. After 15‐L exposure, oxygen atoms are incorporated below the Si (111)‐(7×7...

Early stages in the formation of the oxide-InP(110) interface

Abstract The early stages in the formation of the InP(110)-oxide interface have been studied using high energy resolution photoemission with synchrotron radiation. Both unexcited and excited oxygen were used. Changes were observed in P 2p, In 4d and valence-band spectra. The oxidation of InP appears spatially inhomogeneous. Three stages were observed: a precursor chemisorption stage, a nucleation process, the formation of an oxide layer.

Angle-resolved photoemission and temperature dependence of 5f electronics states in uranium nitride

Abstract A 5f-like photoemission feature in normal emission from UN(100) appears for T N e el = 53 K . It arises from band states that are modified due to a halving of the Brillouin zone in the antiferromagnetic phase. This is the first observation for f electrons and proves their itinerant character in UN.

Electronic structure of Si(111) surfaces

Abstract The relation of surface states and surface core levels to the surface geometry is discussed for Si(111) surfaces by comparing photoemission and inverse photoemission results with calculations for different geometries. It is shown that several sets of recent angle-resolved photoemission data for Si(111)-(2 × 1) and Si(111)-(7 × 7) are very similar to each other despite the fact that they have been interpreted in terms of different geometries. This indicates that no unique conclusions about the surface geometry can be drawn from the surface electronic structure. At present, only the traditional ionic buckling models can be ruled out rather safely. New information about unoccupied urface states in the gap of Si(111)-(7 × 7) is obtained from inverse photoemission data. The quenching behavior of occupied surface states under hydrogen exposure shows an unexpected band narrowing which helps identify the origin of surface state bands from the energy level of a localized state at 0.2 eV below the valence band maximum.

On the applicability of the rigid band model to the metallic sodium tungsten bronzes: A photoemission study using synchrotron radiation

Abstract W4f, Na2p photoelectron spectra and valence band spectra are reported for a series of cubic metallic NaxWO3 (0.4