M. Gautier

Electronic structure of an AlN film produced by ion implantation, studied by electron spectroscopy

N+ ion implantation in a pure Al (111) monocrystal triggers a crystalline and stoichiometric thin AlN film. A complete description of the electronic states of the film is obtained by combining different spectroscopies carried out in situ. The density of electronic states in the valence band is given by x ray and UV photoemission spectroscopy; excitation of a core level (Al2p) by electrons provides information on the density of unoccupied states in the conduction band. Low‐electron energy‐loss spectroscopy allows one to study transitions between occupied and unoccupied states, as well as localized levels in the band gap, due to the presence of structural defects.

Electronic structure of the (0001) and (101̄0) quartz surfaces and of their defects as observed by reflection electron energy loss spectroscopy (REELS)

Abstract Reflection electron energy loss experiments were carried out on monocrystalline (1010) and (0001) quartz samples. Five bulk single loss structures appear at 10.5, 12.5, 14.3, 17.9 and 21.3 eV. The 10.5 eV peak is due to the SiO 2 exciton, the 21.3 eV peak to the SiO 2 plasmon, and the three other transitions are interband transitions, as confirmed by the calculated JDOS. Our experiments show that two electronic transitions at 5.1 and 7.2 eV appear in the gap of α-quartz under several excitations: by phonon excitation (UHV heating), by atomic excitation (collision between the 7 keV ions and the nuclei of the surface and near-surface atoms), and by electronic excitation (interaction with the 350 eV electron beam). The defects responsible for these structures are located at the surface and related to the neutral oxygen vacancy that is the precursor of the E

(011̄0) α-quartz surface: a LEED, XANES and ELS study☆

centre.

Study of the electronic structure of an AIN surface by electron spectroscopy

Abstract We studied the structure of the (0110) α-quartz surface after different treatments (900°C vacuum or air heating and ion bombardment). The long-range order was investigated by low-energy electron diffraction (LEED), the mean-range order by X-ray absorption spectroscopy at the oxygen K edge (XANES) and the electronic structure of the surface band gap by low-energy electron loss spectroscopy (ELS). The (1 × 1) structure is obtained only after a slight chemical etching in HF. A 900°C air-annealed sample exhibits a (3 × 1) or (1 × 3) LEED pattern associated with reconstructed surface regions, which structure is either related to the bulk α → β transition phase occurring at 573°C, or to a new SiO2 phase present only at the surface (tridymite). Finally, a 900°C heating in vacuum provides a glassy surface, also containing oxygen vacancies. These three structures lead to different surface electronic properties: the reconstructed surface presents a larger surface band gap than the (1 × 1) (9.5 instead of 8.6 eV). The disordered surface shows an 8.8 eV wide surface band gap, containing two electronic levels associated with surface oxygen vacancies.

Study of Non Stoichiometric Pure and Zr-Doped Yttria Surfaces by X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy

AlN is a wide band gap III–V semiconductor with piezoelectric properties. A thin AlN film was prepared in ultrahigh vacuum by nitrogen ion implantation in a pure AI(111) monocrystal. This procedure gives a stoichiometric and crystalline AIN film. A complete description of the electronic states of the compound is obtained by combining different spectroscopies, carried out in situ: (i) the density of electronic states in the valence band is given by photoemission experiments using different photon energies (corresponding to the He I, He II and AI K α lines). (ii) Excitation of a core level (AI 2p) and of secondary electrons, by an electron beam (Ep = 250 eV) provides information on the density of unoccupied states in the conduction band. (iii) Electron energy-loss spectroscopy allows one to study localized electronic levels in the band gap, due to the presence of structural defects.

Diffraction effects in the low energy electronic excitations of a clean Al(111) surface

Surfaces of oxygen-deficient yttrium oxide, pure or Zr-doped, have been studied by means of X-ray photoelectron spectroscopy and scanning electron microscopy.

α‐Al2O3 (0001) Surfaces: Atomic and Electronic Structure

The low energy electronic excitations of an Al(111) surface have been studied by means of Electron Energy Loss Spectroscopy (EELS) in the incident electron energy range 20 < Ep < 100 eV. Apart from the well known plasmon lines, two EELS peaks are observed A (1.5–2 eV) and B (4–5 eV). Diffraction effects are observed in the variation of the intensity of these peaks versus primary energy. They are interpreted in the frame of Dukes two-step model. Peak A is attributed to a bulk interband transition at the W point of the bulk Brillouin zone, while peak B is interpreted in terms of a transition involving surface states.