S.A. Flodström

Atomic geometry and electronic structure of CdTe(110)

Abstract A sp 3 tight-binding model for CdTe is constructed and validated by comparison with optical absorption and X-ray photoemission data. The energy minimization method is applied to determine the surface structure of the (110) cleavage face. The predicted surface atomic geometry compares well with that obtained from low-energy electron diffraction intensity analysis. The calculated electronic surface states give a good description of angle-resolved photoemission data.

Experimental surface state bands of the Si(111) 2 × 1 reconstruction

Abstract The surface state bands of the Si(111) 2 × 1 reconstruction have been measured using angle-resolved photoemission. The dangling bond band and several back bond bands have been detected and their initial state energies as a function of momentum parallel to the surface, E i ( k ∥) , have been obtained. For the (2 × 1) reconstruction, the initial state dispersions were measured along the Γ-J and Γ-K symmetry lines in the (2 × 1) surface Brillouin zone. In these two directions the dangling bond band disperses to higher initial state energies, which is in strong disagreement with single particle bands calculated using the Haneman buckling model for the (2 × 1) reconstruction.

Photoemission from surface states on the (101̄0) and (112̄0) surfaces of CdSe

Abstract Using a reparameterized tight binding model the symmetry resolved charge densities of electronic surface-state bands for the (1010) and (1120) cleavage faces of CdSe are calculated and compared with photoelectron spectroscopy measurements. This comparison reveals that using the relaxed surface atomic geometries predicted by the model the calculations describe the angle-resolved and angle-integrated spectra semiquantitatively for both surfaces, thereby confirming explicitly the electronic-surface-state mechanism for the reconstructions of the cleavage surfaces of wurtzite structure materials.

ELECTRONIC-STRUCTURE OF NIO(1 0 0) WITH ADSORBED NA

Adsorption of Na on single crystals of NiO(1 0 0) at room temperature has been investigated via angle-resolved photoemission spectroscopy and measurements of work-function changes. The drastic changes in the valence band spectra upon Na deposition are assigned to a chemical reaction between Na and O where metallic Ni is left as by-product. At short deposition times, Na mainly acts as an inert electron donor, and at these coverages no dispersion is observed in the angle-resolved photoemission spectra which indicates that the electronic states are localized. The measurements were performed both for a polished and an in-situ cleaved NiO crystal.

ELECTRONIC-STRUCTURE OF THE HCP PHASE OF SILVER-ALUMINUM ALLOYS

The close-packed (0001) surface of the ζ-phase of the AgAl alloy has been studied with angle-resolved photoelectron spectroscopy. The ζ-phase was obtained by evaporating Ag onto an A1(111) crystal face and was verified by LEED. The polar angle dependence of the photoelectron emission was recorded along the two symmetry lines ΓM and ΓK of the surface Brillouin zone. The creation of the hcp lattice gives two new structures in the spectra. These structures are found around Γ and M in the surface Brillouin zone and are assigned to be emission from surface states located in band gaps induced by the hep structure. The 4d band emission observed from the ζ-phase AgAl alloy is structureless and shows no similarity with the 4d band emission from Ag 4d in crystalline phase.