C. Coluzza

Photoemission Spectromicroscopy - a New Insight in the Chemistry of Snox Films for Gas Sensors

We used the novel experimental technique of photoemission spectromicroscopy to investigate the active area of SnO(x) thin films for gas sensors, deposited by dc sputtering. First, we analyzed the degree of oxidation and the homogeneity of as-deposited films in a high lateral resolution (30 mum) spectromicroscopy mode with an energy resolution of 0.4 eV. This led to a surprising discovery of a large amount of tin monoxide on the film surface. Then we studied the interaction of H-2 and H2O with the surface of polycrystalline SnO2 films used as sensitive layers in actual gas sensor devices. These results have been related to the resistivity changes of the corresponding devices: we found that such changes are primarily due to a reduction process in the film rather than to mere chemisorption.

Novel spectromicroscopy: Pt–GaP studies by spatially resolved internal photoemission with near‐field optics

The combination of internal photoemission and near‐field optics is proposed as a generally applicable approach to study the lateral variations of solid interface properties such as energy barriers and electron‐hole recombination rates. A successful test on Pt–GaP is described in which topographic and nontopographic phenomena are revealed, in particular recombination rate variations and small lateral changes of the Schottky barrier height.

Microscopic Manipulation of Homojunction Band Lineups

We tested the theoretical prediction that the band structures on the opposite sides of a homojunction can be artificially displaced in energy with respect to each other by means of double intralayers of atomiclike thickness, producing band discontinuities of potential interest for practical applications. Evidence of such discontinuities was found when Ga‐As, Al‐As, Ga‐P, or Al‐P intralayers were inserted between Si and Si or Ge and Ge.

Review of the development of cesium iodide photocathodes for application to large RICH detectors

CsI photocathodes were studied in order to evaluate their potential use as large photoconverters in RICH detectors for the PID system at ALICE (LHC in heavy ion collider mode). It has been demonstrated that a quantum efficiency comparable to the reference value obtained on small samples can be obtained on CsI layers evaporated on large pad electrodes operated in a MWPC at atmospheric pressure. We present a survey of the results obtained in the laboratory on small samples irradiated with UV-monochromatic beams and with RICH detectors of proximity-focusing geometry at a 3 GeV/c pion beam.

AU/GAAS(100) INTERFACE SCHOTTKY BARRIER MODIFICATION BY A SILICON NITRIDE INTRALAYER

We report a modification by thin silicon nitride intralayers of the Au/n-GaAs(100) Schottky barrier height. Thin intralayers were obtained by nitridation of evaporated Si films on decapped GaAs substrates in an argon–nitrogen mixture plasma. The nitridation was performed at a beam energy <40 eV, with 573 K sample temperature. Gold was deposited to study in situ the Schottky barrier formation process with x-ray photoelectron spectroscopy. Internal photoemission spectroscopy and current–voltage measurements were used to evaluate the barrier modification on fully formed interfaces. Such a modification was analyzed in terms of theoretical calculations of the dipole created by the substrate–intralayer bonds.

Recent results on the properties of CsI photocathodes

We report here on the results obtained by the CERN RD26 collaboration on the production and characterization of large area photocathodes, susceptible to equip fast UV-photon imaging devices. Such detectors are planned for some Ring Imaging Cherenkov (RICH) detector projects, in particular HADES at SIS Darmstadt, BABAR at the SLAG asymmetric B-factory, and ALICE at the LHC (CERN).

Spatially Localized Energy Shifts in the Photoemission Spectroscopy of Insulators

Core‐level photoemission peaks taken on several insulators with spatial resolution of 30–300 μm rigidly shift in energy from place to place, most likely because of local charging effects. Such phenomena can affect the linewidth and the general lineshape of conventional, spatially integrated spectra even when a flood gun is used, which is one of the standard remedies against charging. This may require a critical revision of photoemission linewidths and lineshapes for many past experiments on insulators.

Internal photoemission studies of artificial band discontinuities at buried GaAs(100)/GaAs(100) homojunctions

Internal photoemission phototransport measurements revealed 0.27±0.04 eV conduction‐ and valence‐band discontinuities induced by a Si intralayer at p‐GaAs(100)/n‐GaAs(100) homojunctions. The interface dipole originating from the heterovalent character of the Si—GaAs bonds raises the bands of the GaAs overlayer above that of the GaAs substrate.

Ar+ bombardment of Si(100) in oxygen atmosphere: Room temperature oxide formation studied by x‐ray photoelectron spectroscopy

We report the formation of silicon oxide thin films at room temperature obtained by Ar+ ion bombardment of Si(100) wafers in partial oxygen atmosphere. Samples have been prepared at several ion beam energies (0≤Eb≤400 eV) and characterized by x‐ray photoelectron spectroscopy. The oxidation rate, as well as the SiO2/SiOx (x=0.5, x=1, and x=1.5) ratio, have been found to increase with the ion beam energy. For the highest energy bombardment, Eb=400 eV, we observed the formation of a uniform, electrically insulating, SiO2 top layer about 37 A thick.

Intrinsic and Extrinsic Charge Neutrality Levels in Semiconductors - an Empirical-Approach

We discuss an empirical method to estimate the positions of intrinsic charge neutrality levels of semiconductors. The method, based on the relation between intrinsic and extrinsic charge neutrality levels, has been applied to Si, Ge, GaAs, GaP and InP.