The core-level and valence band electronic structure of the well-defined near-surface layer of n-GaAs (100) has been studied by synchrotron-based high-resolution photoelectron spectroscopy before and after modification of the layer by an Ar+ ion beam in the 1.5 - 2.5 keV energy range. Conversion of the conductivity type from n into p has been revealed in the irradiated layer several nm thick. The effect manifests itself in shifts of the core-levels and valence band edge by the value comparable to the bandgap width. Transformation on the conductivity type has been assumed to be caused by Ga-antisite point defects generated by ion bombardment. The possibility of local formation of a p-n nanojunction within the ion-beam spot has been shown.

Large-scale graphene fabrication by thermal and chemical reductions of graphene oxide has faced the problem of defect formation. To solve the problem, we have considered a physically alternative reduction process including electronic excitation followed by the oxygen group detachment from the carbon sheet without capturing a sheet of carbon atoms. Single-layer graphene oxide films were studied by photoemission spectroscopy in the course of monochromatic synchrotron X-ray radiation with in situ control of the layer thickness, chemical composition, atomic ordering, and defect concentration exactly in the modified area. The radiation flux was too low to heat the film. A non-thermal and low-destructive effect of X-ray induced graphene oxide reduction has been revealed. Transformation of the sp3 σ bonds into sp2 π ordered bonds, bandgap closing, and significant diminishing of the oxygen content (below 5 at. %) have been observed without any signs of defects in the photoemission spectra. The effective cross section of the oxygen group detachment induced by a soft X-ray photon (hν = 130 eV) was estimated to be σ* ∼ 3 × 10−18 cm2. A reduced single-layer graphene oxide with a narrow bandgap (0.4 – 0.8 eV) attractive for many applications was obtained, as well as almost pure graphene.

Detailed information on GaAs oxide properties is important for solving the problem of passivating and dielectric layers in the GaAs-based electronics. The elemental and chemical compositions of the native oxide layer grown on the atomically clean surface of an n-GaAs (100) wafer etched by Ar+ ions have been studied by synchrotron-based photoelectron spectroscopy. It has been revealed that the oxide layer is essentially enriched in the Ga2O3 phase which is known to be a quite good dielectric as compared to As2O3. The gallium to arsenic ratio reaches the value as high as [Ga]/[As] = 1.5 in the course of oxidation. The Ga-enrichment occurs supposedly due to diffusion away of As released in preferential oxidation of Ga atoms. A band diagram was constructed for the native oxide nanolayer on the n-GaAs wafer. It has been shown that this natural nanostructure has features of a p–n heterojunction.

We have observed the energy structure in the density of occupied states of graphene grown on n-type 6H-SiC (0001). The structure revealed with photoelectron spectroscopy is described by creation of the quantum well states whose number and the energy position (E1 = 0.3 eV, E2 = 1.2 eV, E3 = 2.6 eV ) coincide with the calculated ones for deep (V = 2.9 eV) and narrow (d = 2.15 A) quantum well formed by potential relief of the valence bands in the structure graphene/n-SiC. We believe that the quantum well states should be formed also in graphene on dielectric and in suspended graphene.

Thermal reduction in molecular hydrogen of the graphene oxide films has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. The restoration process was revealed to be accompanied by hydrogenation due to collisionally induced interaction of molecular hydrogen with carbon atoms. One side hydrogenated graphene films consisting of 20 μm one monolayer flakes were fabricated on SiO2/Si surface with hydrogen concentration as far as 40 at. %, at which the 0.3 eV bandgap opening was observed. It was shown that both H-coverage and bandgap width of the films can be controlled by varying the temperature of the heat treatment.

A nitride nanolayer fabricated on a GaAs (100) surface by implanting ions N 2 + (E i = 1.5 keV) has been studied by high-resolution photoelectron spectroscopy with the use of synchrotron radiation. It has been found that, apart from the dominant GaN wide-gap semiconductor phase, an additional phase of the GaAs1 − x N x narrow-gap solid solution (x < 0.10) is present in the nitride layer. It has been shown that the nitride layer created by ion implantation is a nanostructure with an attribute of a system of quantum dots, since it consists of nanoclusters of the narrow-gap semiconductor in the wide-gap matrix.

Transformation of the chemical composition and electron structure of graphite oxide (GO) nanolayers as a result of their annealing in hydrogen has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that both the chemical composition and bandgap width of GO can be controlled by varying the temperature and duration of heat treatment. By this means, the properties of GO nanolayers can be smoothly changed from dielectric to semiconductor.

At present time only the epitaxial growth technology based on high temperature annealing of SiC substrates has a real potential for mass production of wafer-scaled and high quality graphene films [1]. Despite the quickly increasing number of publications developing fundamental and applied aspects of this technology, it is still far from being accomplished. In this work we demonstrate that our original technique of substrate pre-growth treatment may promote considerable progress in this field. To this effect we investigated graphene films grown on a high quality commercial 6H-SiC (0001) substrates which were preliminary subjected to pre-growth treatment, that is, were annealed for 30 minutes in a high-vacuum chamber in a quasi-closed growth cell at a temperature about 1300°C. Then, the substrate was again annealed for 30 minutes, but at an ambient argon pressure of 1 atm. and at temperature 2000°C [2]. Properties of the film thus grown were studied by atomic force microscopy (AFM), low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. AFM study showed that substrate surface consists of flat and wide (~1 m) terraces covered with sufficiently large and continuous graphene domains. Numerous LEED patterns (see example in the figure) obtained from different points of the sample demonstrate concurrent presence of a well-ordered graphite (1×1) pattern and (6 3×6 3)R30 pattern inherent to the underlying buffer layer [1] and, thereby, evidence mainly bilayer character of the grown film. XPS and NEXAFS data obtained on synchrotron BESSY II (Berlin) allowed us to specify a chemical composition and electron structure of grown graphene film and confirmed its high quality and mostly bilayer nature. The research was supported by the RussianGerman Laboratory at BESSY II, by the FASR contract 02.740.11.0108 and by the program “Quantum physics of condensed matter” of the Russian Academy of Sciences.

Photoemission spectra of valence electrons of solid C60F18 were measured in X-ray photon energy range being close to the excitation of fluorine F 1s core electron into the first unoccupied state. Enhancement of photoemission cross sections was revealed due to Auger decay of fluorine vacancy in which electron of neighboring carbon atom takes part.

The concentration and chemical state of copper in the subsurface region of Cu/SiO 2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO 2 ) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO 2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.