A. Taleb-Ibrahimi

Oxidized silicon surfaces studied by high resolution Si 2p core-level photoelectron spectroscopy using synchrotron radiation

Abstract The Si 2p soft X-ray photoemission study of various oxidized surfaces (thermal oxidation and room temperature (RT) oxidation) shows the benefit derived from the use of high-energy resolution (70 meV). Interesting structural information can be retrieved from an analysis of the line widths of the oxides, suboxides, and elemental Si peaks. In particular the binding energy (BE) of elemental silicon layers adjacent to the oxidized layer can be distinguished from that of deeper silicon layers (the two prominent `interfacial elemental Si lines are shifted by about +0.2 and −0.2 eV). These new data show a possible effect of oxygen second neighbors on elemental Si 2p binding energies. Moreover, changes in the oxide/suboxide line widths – as seen in a comparative study of the Si(1xa01xa01)-7×7 surface thermally oxidized in O2 and exposed at RT to O2 or H2O – may be attributed to static disorder, i.e., variations in Si–O bond lengths.

Photoelectron spectroscopy study of Ga 3d and As 3d core levels on MBE-grown GaAs surfaces

Abstract We have performed a photoemission study of GaAs MBE-grown surfaces, using UV radiation to investigate Ga 3d core levels (CLs) of (100) and (111)B surfaces in-situ, and using synchrotron radiation ex-situ for the As 3d and the Ga 3d CLs study. Different reconstructions were studied, from the As-saturated to the Ga-stabilized ones, and we focused on the surface contributions. A surface signal attributed to Ga atoms on the surface was found even on c(4 × 4) surfaces, where it was not expected. The capping/decapping method was found a good way to investigate GaAs(100) surfaces ex-situ, but such surfaces were extremely sensitive to the decapping procedure. Finally, the surface Fermi level was measured on the (100) surfaces, and was always found pinned, regardless of the reconstruction.

Preparation of clean reconstructed InAs(001) surfaces using HCl/isopropanol wet treatments

A simple treatment method using HCl/isopropanol solutions is given for preparation of high-quality InAs(001) surfaces. The surface structure and chemistry were characterized using low-energy electron diffraction and photoemission spectroscopy as a function of UHV temperature. The treatment removes the natural oxide and leaves on the surface a physisorbed overlayer containing arsenic and small amounts of InClx. Annealing at 330u200a°C induces desorption of this overlayer and reveals a clean arsenic-rich (2×4)/c(2×8) surface. The indium-rich (4×2)/c(8×2) reconstruction is obtained upon further annealing to 410u200a°C.

Local-order of chemically-prepared GaAs(100) surfaces

Abstract In the present work HCl–propanol treated and vacuum annealed GaAs(1xa00xa00) surfaces were studied by means of soft X-ray photoemission and reflectance anisotropy spectroscopies (SXPS, RAS). On the as-treated surface, Asxa03d and Gaxa03d core level spectra (CLs) are found to be similar to the ones observed on As-capped GaAs(1xa00xa00) surfaces after annealing at 350 °C, which desorbs most of the overlayer. RAS measurements of the as-treated surface and after annealing up to 350 °C show spectra similar to those detected on the as-grown surfaces with c(4×4) reconstruction. Anneals in the 380–470 °C temperature range lead to the appearance of a RAS line at 3 eV which is characteristic of As dimers. This finding coincides with the presence of a surface component in the Asxa03d core level spectrum with a chemical shift of −0.5 eV, which we attribute to As-dimers. Further annealing at 540 °C yields in RAS spectra an intense line at 2.2 eV due to Ga dimers, while the Gaxa03d CLs do not exhibit any appreciable change.

Adsorption sites at Cs nanowires grown on the InAs(110) surface

We present a high-resolution ultraviolet photoelectron spectroscopy study of the room temperature Cs chain formation on InAs(1 1 0), analysing the valence band spectra and core levels in the whole coverage range from the self-assembling of the Cs chains to the cluster uptake at saturation coverage. The valence band data shows an insulating behaviour up to saturation coverage. The adsorption sites have been monitored by means of Cs-4d, In-4d and As-3d core levels. The Cs-4d core-level data shows two distinct components, consistent with the presence of two unequivalent Cs adsorption sites in the Cs nanowire. The In-4d and As-3d levels show Cs-induced extra components due to electronic level re-hybridization to the substrate atoms, and predominant charge transfer from Cs adatoms to In, in agreement with recent theoretical calculations.

Oxidation of the H-Si(111)-1×1 surface: high resolution Si 2p core-level spectroscopy with synchrotron radiation

Abstract The room temperature oxidation of H-terminated Si(111) surfaces by activated oxygen has been investigated using high resolution (70xa0meV) Si 2p core-level spectroscopy with synchrotron radiation. The data are compared with previous studies using photoemission spectroscopy and high resolution electron energy loss spectroscopy. The metastability of the oxidized layer formed at room temperature is also examined.

Role of gold segregation in the growth mode and the morphology of Fe/Au(001) magnetic thin films

Abstract The growth mode of iron on Au(0xa00xa01) surface at room temperature has been studied by means of photoelectron spectroscopy and scanning photoemission microscopy. The analysis of Au4f core level shifts reveals the segregation of gold atoms during the growth, leading for high coverage to the floating of Au surface layer burying Fe thin film and AuFe interfacial alloy. The formation of such segregating layer is coherent with energetic criteria (low gold surface energy, negative interfacial mixing energy, size effect,…). The synergy between these effects may favour the intermixing at the interface and the gold segregation. Photoemission microscopy measurements have been carried out to characterize local morphological and compositional inhomogeneities. The growth proceeds via the segregation of small three-dimensional AuFe gold islands surrounded by a flat Fe/Au region.