Surface-related Features Research Articles

Surface electronic structure of monolayer Sb on InP(110)

The electronic band structure of an ordered 1 × 1 overlayer of Sb on InP(110) has been investigated by angle resolved photoelectron spectroscopy using synchrotron radiation. Experimental energy dispersion of the features in the spectra has been mapped along high symmetry directions in the surface Brillouin zone. A number of criteria is employed to distinguish surface-related features and these are compared with a tight-binding, total energy minimisation calculation based on a zig-zag chain model of Sb on the InP(110) surface. Two bands near the valence band maximum are found to be in reasonable agreement with predicted states with bonding character associated with the adsorption on anion and cation sites. The origin of these and the remaining bands is discussed with reference to measurements which probe the symmetry of the states with respect to the mirror plane and the surface normal.

Photoelectron bandstructure of InP(110)-Sb monolayers

The electronic bandstructure of an ordered 1*1 overlayer of Sb on InP(110) has been investigated by angle-resolved photoelectron spectroscopy using synchrotron radiation. The experimental energy dispersion of the features in the spectra has been mapped along high-symmetry directions in the surface Brillouin zone. An analysis based on a number of criteria is employed to distinguish surface-related features and these are compared with a 'tight-binding, total energy minimization' calculation based on a zig-zag chain model of Sb on the InP(110) surface. Two bands near the valence band maximum are found to be in reasonable agreement with predicted states with a bonding character associated with the adsorption on anion and cation sites. The nature of two further bands at higher binding energy is discussed.

Satellite structure in the photoemission spectra of MnO(100).

The satellite structure in both core-level and valence-band photoemission spectra from single-crystal MnO(100) has been studied by using both x-ray photoemission spectra and resonant photoemission. Only very weak satellites are present in the Mn 2p core-level spectra, while no satellite structure is evident in the Mn 3p and 3s core-level spectra. The small intensity of the satellite peaks in MnO is consistent with the trend predicted by a recent ligand charge-transfer screening model; such screening is quite weak in MnO in comparison to the heavier transition-metal oxides. The valence-band spectrum, however, exhibits a stronger satellite peak than predicted by the model, and its origin has been uncertain. We have found that, while the satellite in the valence-band spectrum can be resonantly enhanced across the Mn 3p\ensuremath{\rightarrow}3d optical excitation threshold, its intensity depends strongly upon surface treatment. The satellite disappears with only 0.2--1-langmuir exposure of oxygen at 340 \ifmmode^\circ\else\textdegree\fi{}C, confirming that it is essentially a surface-related feature. We suggest that it is associated with point defects on the surface, presumably surface Mn vacancies.

Surface electronic structure of CoSi2(111).

The surface electronic structure of ${\mathrm{CoSi}}_{2}$(111) surfaces is studied by angle-resolved photoemission using synchrotron radiation in the energy range 10\ensuremath{\le}\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\le}60 eV. Depending on preparation technique the crystal termination is either a Co or a Si(111) plane. The ${\mathrm{CoSi}}_{2}$(111)-Co terminated surface exhibits two surface-related features at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} at -1.4 and -2.7 eV. The prominent low-lying peak is a true surface state of the Shockley type located in an absolute Si3s3p--Co 3d hybridization gap of the projected bulk band structure at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} and shows an oscillating emission intensity in reciprocal space. The relevant surface-state band disperses toward the Fermi level with increasing ${k}_{?}$ and corresponds to bonding states of surface Co atoms with a reduced coordination shell. In contrast, the -1.4-eV feature is rather a Tamm surface state or resonance derived from surface Co 3d nonbonding orbitals. On ${\mathrm{CoSi}}_{2}$(111)-Si terminated surfaces only weak surface-related features can be identified.

Transfer optics for high spatial resolution electron spectroscopy

A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.

Experimental and theoretical investigations of Cr(001) surface electronic structure.

The surface electronic structure of Cr(001) is characterized by angle-resolved photoelectron spectroscopy. The spectral properties of surface-related photoemission features are found to be consistent with results from a comprehensive spin-polarized calculation of the Cr(001) surface electronic structure. The theory predicts the existence of a ferromagnetic Cr(001) surface phase characterized by a very large (3.00 electrons) surface spin polarization. The overall agreement between theory and experiment provides additional evidence that the Cr(001) surface is, in fact, ferromagnetic.