Valence band photoemission from the GaN(0001) surface

A detailed investigation by one-step photoemission calculations of the GaN(0001)-(1x1) surface in comparison with recent experiments is presented in order to clarify its structural properties and electronic structure. The discussion of normal and off-normal spectra reveals through the identified surface states clear fingerprints for the applicability of a surface model proposed by Smith et al. Especially the predicted metallic bonds are confirmed. In the context of direct transitions the calculated spectra allow to determine the valence band width and to argue in favor of one of two theoretical bulk band structures. Furthermore a commonly used experimental method to fix the valence band maximum is critically tested.Comment: 8 pages, 11 eps files, submitted to PR

Energetic and spatial bonding properties from angular distributions of ultraviolet photoelectrons: application to the GaAs(110) surface

Angle-resolved ultraviolet photoemission spectra are interpreted by combining the energetics and spatial properties of the contributing states. One-step calculations are in excellent agreement with new azimuthal experimental data for GaAs(110). Strong variations caused by the dispersion of the surface bands permit an accurate mapping of the electronic structure. The delocalization of the valence states is discussed analogous to photoelectron diffraction. The spatial origin of the electrons is determined, and found to be strongly energy dependent, with uv excitation probing the bonding region.Comment: 5 pages, 3 figures, submitted for publicatio

Interfacial effects on the electrical properties of multiferroic BiFeO/Pt/Si thin film heterostructures

Polycrystalline BiFeO3 thin films of various thickness were fabricated on (111)Pt/Ti/SiO2/Si substrates via chemical solution deposition. The electrical properties were investigated using impedance and leakage current measurements. X-ray photoelectron spectroscopy (XPS) combined with Ar ion milling (depth profiling) was used to investigate elemental distribution near the electrode–film interface. It is shown that the dielectric constant depends on film thickness due to the presence of an interfacial film–electrode layer evidenced by XPS investigation. Direct current conductivity is found to be governed by Schottky and/or Poole-Frenkel mechanism

Electronic Structure of the CdTe(100)-(1×1) Surface

Unreconstructed CdTe(100) surface prepared by ion bombardment and annealing is investigated by angle-resolved photoemission. The experimental band structure E(k$\text{}_{∥}$) is determined along high-symmetry lines of the surface Brillouin zone by measuring energy-distribution curves of photoelectrons. Different criteria were applied to separate surface and bulk related spectral features, e.g. calculating the position of bulk-derived emissions in the frame of the free-electron final state approximation assuming k conservation. In this way, most dispersing features could be explained. All remaining features were compared with theoretical surface band structures for different polar surface terminations which were calculated within a layer doubling procedure on the basis of an EHT-fit to the bulk band structure. The investigated CdTe(100)-(1×1) surface could be identified as Cd terminated. Two surface bands were observed, one located above the valence-band edge and the second in the open pocket of the projected bulk band structure along the Γ̅K̅ direction. At 4.6 eV binding energy an additional weakly dispersing band was found, which contains mixed surface and bulk character. The high density of bulk states associated with this edge of the heteropolar gap is also expected to contribute to this feature

Element a hybnost rozlišená elektronická struktura zředěného magnetického polovodiče: manganem dopovaného gallium arsenidu

Zředěné magnetické polovodiče slibují v aplikacích založených na spinových elektronických zařízeních na jejich potenciál pro feromagnetický pořádek při pokojové teplotě a různé unikátní přepínání a spin-závislé vodivosti. Nicméně přesný mechanismus, kterým dopování z přechodného kovu způsobuje, že ferromagnetismus je kontroverzní. Tady máme studoval zředěný magnetický polovodič (5% manganem dopovaný gallium arsenid) s Braggův reflexní stojatý vlnový paprsek s pevným rentgenovým paprskem se spektrální rozlišovací schopností a vyřešila svou elektronickou strukturu na součásti, které byly vyřešeny prvkem a momentem. The měřené intenzity valenčního pásma byly promítány do prvků vyřešených prvkem pomocí analogových energetických skenů Ga 3d, Mn 2p a As 3D úrovní jádra, s vynikajícími výsledky dohodu s elementy-projektované Bloch spektrální funkce a objasnění elektronické struktury tohoto prototypového materiálu. Tato technika by měla být široce použitelná pro jiné vícevrstvých materiálů.The dilute magnetic semiconductors have promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. Here we have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy, and resolved its electronic structure into element- and momentum- resolved components. The measured valence band intensities have been projected into element-resolved components using analogous energy scans of Ga 3d, Mn 2 p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions and clarification of the electronic structure of this prototypical material. This technique should be broadly applicable to other multi-element materials