D. M. Zehner

Angular effects in Auger electron emission from Cu (110)

Abstract Angular variations in the emission intensities of M 2, 3 VV (62 eV) Auger electrons from a Cu (110) surface have been measured. Large changes are observed as a function of both polar and azimuthal angles. Effects of the incident beam energy and angle of incidence have been determined, and interpretations of the the data are proposed.

Characteristic energy gain and loss, double ionization, and ionization loss events in Be and BeO secondary electron spectra

Abstract Two satellite peaks have been observed on the high energy side of the Be KVV Auger peak. The lower energy satellite is attributed to coupling of energy from bulk plasmon de-excitations with Auger electrons, and the higher energy event to Auger electrons ejected from Be atoms with doubly ionized K levels. Following oxidation, the ionization loss spectra of BeO were observed to have structure which is interpreted as being related to the density of unfilled electron states above the BeO valence band. In addition, the characteristic loss and the low energy (“true secondary”) spectra of Be and BeO were determined. Peaks in these spectra are discussed in terms of characteristic energies related to excited electron states in the solids.

Chemisorption of hydrogen on the Ag(111) surface

The interaction of atomic hydrogen/deuterium with the Ag(111) surface was investigated with high‐resolution electron loss spectroscopy (HREELS), thermal desorption spectroscopy, low‐energy electron diffraction (LEED) and the results correlated with the work function change and an absolute coverage measurement. Dissociation of molecular hydrogen is an activated process on Ag(111) but atomic hydrogen chemisorbs and at a temperature of ∼185 K, recombines and desorbs as H2. Upon the adsorption of atomic hydrogen at 100 K, a sharp (2×2) LEED pattern is observed in the coverage range 0.25∼0.5 ML and is followed by combined (2×2)+(3×3) patterns with an increase in coverage of 0.1 ML. The saturation coverage is determined to be Θsat=0.6±0.1 ML. In contrast to other H/fcc(111) systems, the intensities of the fractional order diffraction beams are quite large, suggesting an H‐induced reconstruction. The work function increases monotonically with H‐exposure to a maximum value of Δφmax=+0.32 eV at saturation. Specula...

Formation of aluminum oxide thin films on FeAl(110) studied by STM

The surface morphology and atomic structure of clean and oxidized FeAl(1 1 0) surfaces have been investigated with scanning tunneling microscopy (STM). An incommensurate reconstructed structure, having FeAl2 stoichiometry confined to the outmost layer, is observed on the clean surface due to preferential Al segregation upon annealing to 1125 K. When the reconstructed clean surface is exposed to oxygen at elevated temperatures, an ordered ultra-thin aluminum oxide film is formed. Based on STM data, a structural model of the oxide film is proposed, which exhibits a quasi-hexagonal oxygen layer and accommodates an even mix of octahedral and tetrahedral occupancy of Al ions arranged in an alternating zigzag–stripe structure. STM imaging with tunnel voltages in the range of the bulkband gap implies that the thin film oxide electronic structure differs substantially from the bulkoxide, and indicates a local density of states around the oxide constituents within the bulkband gap. 2003 Elsevier Science B.V. All rights reserved.

A comparison of the surface electronic structure of Ta(100) and TaC(111) using Auger‐photoelectron coincidence spectroscopy

We present N7VV (4f7/25d5d) Auger spectra from TaC(111) taken in time coincidence with photoemitted bulk and surface‐shifted 4f7/2 core‐level electrons, and compare these data with self‐convolutions of calculated valence band d densities of states (SCDOS) for the surface (first) and bulk (exponential sum of second, fourth, and sixth subsurface) atomic layers of a 13‐layer slab. The Ta 4f levels of TaC(111) and Ta(100) both exhibit large surface core level shifts, but of opposite sign. Therefore, we compare the TaC(111) data and calculations with analogous N7VV Auger coincidence spectra and calculated SCDOS that we have previously published for Ta(100). The bulk Ta(100) and surface TaC(111) spectra show favorable agreement with the calculations; the surface Ta(100) and bulk TaC(111) spectra, on the other hand, exhibit marked disagreement with the calculations. These discrepancies are consistent with and provide added support for the presence of our proposed1 surface‐to‐bulk (bulk‐to‐surface) interatomic Au...

Plasmon energy gain and double ionization satellites in the Be Auger spectrum

Abstract Two relatively weak, higher energy satellites are observed at 18 and 38 eV above the Be KVV Auger spectrum. The lower energy satellite is assigned to coupling of energy from bulk plasmon de-excitations ( h ω ∼ 18 eV) with Auger electrons and the higher energy event to Auger electrons ejected from Be atoms with doubly ionized K levels.

Auger transitions initiated from singly and doubly ionized states in Li metal

Abstract Major events in Auger spectra from Li surfaces containing both Na and K have been identified. Li Auger transitions initiated from both singly and doubly ionized K shells of Li have been observed. However, no higher energy satellite corresponding to the coupling of the energy of a plasmon decay with that of the Li K VV Auger electrons was detected.

Surface morphology and electronic structure of Ni/Ag(100)

The growth morphology and electronic structure of Ni on Ag(100) has been studied with scanning tunneling microscopy (STM) and synchrotron based angle resolved photoemission spectroscopy. At deposition temperatures at or below 300 K, STM reveals Ni cluster growth on the surface along with some subsurface growth. Upon annealing to 420 K, virtually all Ni segregates into the subsurface region forming embedded nanoclusters. The electronic structure of Ni d bands in the unannealed surface shows dispersion only perpendicular to the surface whereas the annealed surface has Ni d bands that exhibit a three-dimensional-like structure. This is a result of the increased Ni d–Ag sp hybridization bonding and increased coordination of the embedded Ni nanoclusters.

Surface reconstruction of FeAl(110) studied by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy

The surface geometric and electronic structure of the FeAl(110) intermetallic alloy has been investigated by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy (ARPES). Preferential sputtering results in depletion of Al in the surface region and subsequent annealing promotes surface segregation of Al and gives rise to new reconstructed phases. A bulk terminated surface structure is obtained after annealing the surface to 400 °C. However, an incommensurate phase develops above 800 °C with a stoichiometry consistent with an FeAl2 structure in the topmost layer. The ARPES measurements confirm the Al segregation with increased density of states (DOS) near the Fermi level. The increased DOS is believed to be due to hybridization between the Fe d and Al sp states. The increased intensity of the Al 2p core level for the incommensurate phase also confirms the higher Al surface concentration for this phase.

Bismuth induced structures on copper (100)

Different submonolayer phases of bismuth on copper (100) have been investigated with low‐energy electron diffraction and Auger electron spectroscopy. The room temperature observations, made after depositing Bi onto well annealed Cu, agreed with those reported previously. Below room temperature, a low coverage c(2×4) phase was observed. With increasing Bi coverage, this phase was observed to coexist with the c(2×2) phase, until finally, only the c(2×2) phase was observed. Restructuring of the Cu substrate into {210} facets, at 26°34’ angle with the original (100) surface, was obtained by depositing Bi onto roughened Cu(100), and subsequently annealing. A possible explanation for the nucleation and growth of these facets is given.