0000000000049617
AUTHOR
V. Kempter
Atomic and electronic structure of the corundum (0001) surface: comparison with surface spectroscopies
Abstract The electronic structure and geometry of the Al-terminated corundum (0001) surface were studied using a slab model within the ab-initio Hartree-Fock technique. The distance between the top Al plane and the next O basal plane is found to be considerably reduced on relaxation (by 0.57 A, i.e. by 68% of the corresponding interlayer distance in the bulk). An interpretation of experimental photoelectron spectra (UPS He I) and metastable impact electron spectra (MIES) is given using the calculated total density of states of the slab and the projections to the atoms, atomic orbitals, and He 1s floating atomic orbital at different positions above the surface. Calculated projected densities…
A comparative analysis of electron spectroscopy and first-principles studies on Cu(Pd) adsorption on MgO
Ultrathin MgO films were grown on a W(1 1 0) substrate while metastable impact electron (MIES) and photoelectron (UPS) spectra were measured in situ; apart from the valence band emission, no additional spectral features were detected. The oxide surface was exposed to metal atoms (Cu, Pd) at RT. A comparison with the DOS extracted from first-principles DFT calculations shows that the metal-induced intensity developing above the top of the O 2p valence band in the UP spectra under Cu(Pd) exposure is caused by Cu 3d (Pd 4d) emission. The emission seen in the MIES spectra is attributed to the ionization of Cu 3d and 4s states of adsorbed neutral Cu atoms in an Auger process, Auger neutralizatio…
Study of the electronic and atomic structure of thermally treated SrTiO3(110) surfaces
The electronic structure of heated SrTiO3(110) surfaces was investigated with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (He(I). Scanning tunnelling microscopy and atomic force microscopy (AFM) were used to study the topology of the surface. The crystals were heated up to 1000 °C under reducing conditions in ultrahigh vacuum or under oxidizing conditions in synthetic air for 1 h, respectively. Under both conditions microfacetting of the surface is observed. The experimental results are compared with ab initio Hartree-Fock calculations, also presented here, carried out for both ideal and reconstructed SrTiO 3(110) surfaces. The results give direct evid…
The surface electronic structure of stoichiometric and defective LiF surfaces studied with MIES and UPS in combination with ab-initio calculations
Abstract UPS (He I) and metastable impact electron spectroscopy (MIES) spectra of the LiF(100) single crystal surface and stoichiometric LiF films are presented. The spectra are interpreted on the basis of ab-initio electronic structure calculations. Defective surfaces, produced by electron dosing, were studied in the same manner. The MIES spectra reveal that the electron dosing produces metallic patches on the surface, but no uniform Li adlayer. The calculation show that the F-center contribution to the electron emission is very close in energy to that from the metallic patches; thus, the two contributions cannot be distinguished by the present experimental techniques.
Characterization of LiF and CaF2 surfaces using MIES and UPS (HeI)
Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination with ab initio calculations (CRYSTALcode) were applied to study surface and bulk defects in LiF and CaF2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W (110) and CaF2 (111) is discussed on the basis of the ab initio calculations. MIES spectra show features from Li agglomerates on the surface of electron bombarded LiF. The electronic structure of the LiF:Mg single crystal shows additional features above the valence band maximum caused b…