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We report the studies of electronic structure of the InAs(0 0 1)4 × 2-c(8 × 2) surface by performing angle-resolved photoemission spectroscopy, LEED and STM measurements. The reconstruction of the clean surface was obtained by ion bombardment and annealing procedure. STM pictures show an ordered array of In-chains, and the photoemission experiments reveal new electronic surface structures. The intensity of these structures, which are located at binding energy of −2.94 and −1.05 eV, strongly depend on the surface preparation, and on the light polarization. They are non-dispersive with the photon energy.

We have performed angle-resolved photoemission spectroscopy on InAs(0 0 1)4×2-c(8×2) clean surfaces in order to investigate two new electronic surface states related to the In-terminated InAs(0 0 1)4×2-c(8×2) clean surface. The experiments were carried out at normal emission as a function of photon energy using s- and p-polarized light. The surface states are strongly resonant at photon energies of 31 and 61 eV, respectively. These energies correspond also to transitions from bulk electronic states localized at high symmetry points X6, X7 and Γ7, Γ6 of the calculated InAs band structure. The intensities of the two surface states decrease when passing from s- to p-polarization of the radiation: such behaviour directly establishes the orientation of the surface state bonds.

An Sb/Si(lll)root 3x root3 surface has been studied by high-resolution core-level spectroscopy. All the components of the Si 2p core level related to the clean surface have disappeared, and one strong Sb-induced component could be identified at a binding energy +0.13 eV with respect to the bulk peak. Such a component is mainly due to charge transfer between Si atoms at the top layer and Sb trimers. Two more small components are observed: one at +0.29 eV, due to Sb atoms residing at a different position, and one at -0.14 eV, due to local disorder. On the Si 2p core level taken in bulk sensitive mode, we found a very narrow bulk component with a total full width at half maximum of 130 meV at T=100 K.

We report here on the electronic properties of the Ge/Sb/Si(001) interface formation studied by very high-energy-resolution photoemission spectro-scopy using synchrotron radiation. Surface- and bulk-sensitive measurements of the core levels of the different atomic species give a clear indication of the occurrence of a site exchange process between germanium and antimony, when Ge is deposited on the already prepared Sb/Si(001) interface. We demonstrate that the use of surfactant atoms like Sb at the strained Ge/Si(001) interface produces a perfect epitaxial interface, where the Si atoms are in register with the bulk geometrical positions.

The photoabsorption spectra of neon and argon in the energy region of the and doubly excited states have been studied. The resolution and flux of the new VUV undulator beam line at ELETTRA allowed the resolution of new features for Ne and the first observation for Ar. A comparison of the measured photoabsorption spectra and of the threshold photoelectron spectra in the energy region of the and satellite states provides information on the decay routes of the inner-shell doubly excited states.

High resolution resonant Auger spectra have been measured at the vacuum-ultraviolet beam line at Sincrotrone Trieste while tuning the photon energy across the 2{ital p}{sub 3/2}{sup {minus}1}3{ital d} resonance of argon. A large variation of the branching ratio for decay into the spectator 3{ital p}{sup {minus}2}3{ital d} and shakeup 3{ital p}{sup {minus}2}4{ital d} channels is observed. The effect has not been seen previously in resonant inner-shell excitation and is attributed to the interference between the direct photoionization process and resonant Auger decay leading to the same final state. {copyright} {ital 1996 The American Physical Society.}

We report on inverse photoemission studies (IPES) obtained on freshly pealed InSe. The spectra have been taken with a Geiger-Muller-type detector and a resulting resolution of about 0.4 eV. The electron beam was not collimated thus leading to angle-integrated spectra. The data show peaks at 2.3, 5.1 and a broad feature at 7.5 eV above E F . The results are compared with previous theoretical calculations.

Negative bias stress experiments on a-Si:H/a-SiO 2 Thin Film Transistors show that the instability is predominantly related to charge injection in the gate insulator. We propose that charge injection is occurring in a defected region of the gate insulator adjacent to a-Si:H, caused by the effect of activated hydrogen on a-SiO 2 surface during deposition. To investigate the hydrogen influence, we have studied low-energy (100 eV) hydrogen-ion and Ar-ion bombardment effects on a-SiO 2 using synchrotron radiation photoemission spectroscopies. Comparing the two kind of treatments, we show that hydrogen treatment produces predominantly Si-H defects, which are observed to induce gap states in a-SiO 2 .

We investigated the electronic structure of ultra thin interface of organic titanium bis-phthalocyanine TiPc 2 deposited on InAs(001)(4 x 2)c-(8 x 2) clean surface, by means of high-resolution core-levels and valence band (VB) photoelectron spectroscopies. In4d, As3d, and Cls core levels were measured for different TiPc 2 thicknesses up to 1 monolayer. Surface core level shifts were found on both In4d andAs3d core levels. These shifts originate from the interaction between 4 x 2-c(8 x 2) InAs reconstruction and organic molecules suggesting the presence of strong bounds. C1 core level exhibits a line shape attributed to the C-C and C-N bonds. The VB spectroscopy shows dramatic changes related to the interaction of the TiPc 2 molecule with the InAs related surface states.

We have performed photoemission experiments to determine the surface versus bulk contributions of In4 d , Ga 3 d and P 2 p core level spectra in InP and GaP. The experiments were performed at the new VUV High Energy Resolution Photoemission beamline at the storage ring ELETTRA in Trieste. We obtained the values Δ E In 4 d =−0.32 eV and ΔE P 2 p =0.31 eV for the surface core level shifts of Indium and Phosphorous in InP(110), while the shifts for Ga 3d and P 2p in GaP(110) were −0.30 eV and 0.40 eV respectively. These results are discussed in terms of a simple model based on the difference between bulk and surface Madelung potentials.

We report the first results obtained from the high energy resolution beam line at the storage ring ELETTRA of Trieste. The beam line has been designed to perform photoemission experiments in the vacuum ultraviolet (VUV) and soft X-ray (SXR) energy range. The radiation source is an undulator which consists of three sections, with 36 periods and a period length of 12.5 cm. It allows scanning of an energy range 17–900 eV using the 1st, 3rd and 5th harmonics. The monochromator is a spherical grating type and the resolving power at 400 eV, estimated from the K-shell photoabsorption of the N2 molecule is well above 10 000. The spectra are better than any other spectra taken while operating with high flux, i.e. first order diffraction and grating not masked. Measurements taken at the oxygen and neon K-edges, the argon L23 edges and of the helium double ionization spectra, indicate that the resolution is excellent from 65 to 870 eV.

A study of silicon-oxynitride materials and their interfaces with amorphous silicon using synchrotron radiation photoemission is discussed. The effect of the hydrogen atoms as an intralayer at the silicon-oxynitride-a-Si interface is also analyzed. The data relative to the bulk silicon oxynitride show that the valence band edge gradually shifts toward a higher binding energy as the (O)/(N) ratio (A) is increased. For the silicon-oxynitride-a-Si heterojunctions, the valence band discontinuities Delta E/sub v/ ranged from 1.1+or-0.15 eV in the case of A=0.08 up to 4.6+or-0.15 eV in the case of A=2.02. The effect of the hydrogen intralayer was to reduce the Delta E/sub v/ by 0.5+or-0.15 eV. The observed intralayer-induced effect is attributed to modification of the interface dipoles. A simple model calculation, based on electronegativity arguments, gives a reduction of 0.4 eV for A=0 and 0.46 for A corresponding to pure silicon dioxide (SiO/sub 2/). >

Enhanced electron-emission yield was observed in GaP(110)-cleaved crystals, by constant-final-state, constant-initial-state and energy-distribution-curve spectroscopies at photon energies which excite transitions from the Ga $3d$ levels to empty surface states. We prove that the resonance is mainly due to direct recombination involving filled surface states \ensuremath{\simeq} -2 eV below the top of the valence band. We observed an inversion of the intensity ratio between Ga $3{d}_{\frac{5}{2}}$ and $3{d}_{\frac{3}{2}}$ with respect to the statistical value due to the contribution of localized states to the optical transitions. In particular, different intensity ratios in constant-initial-state spectra at different initial-state energies have been interpreted as being due to different localization of the filled states participating to the resonant process.

SiOx materials and their interfaces with a-Si have been studied using synchrotron radiation photoemission. We have also analyzed the effect of hydrogen atom either embedded in the SiOx matrix or at the SiOx-Si interface. The effect of hydrogen and bulk SiOx is to decrease by 0.5 eV the distance between the top of the valence band and the Fermi level. An opposite effect has been observed at SiOxSi interface, where a hydrogen intralayer decreases the valence band discontinuity.

We present energy loss spectra of Si–Ge heterojunctions. The early stage of formation of the interface has been studied by successive evaporations of small amounts of germanium on a silicon substrate heated at 350 °C. The results, compared with theoretical calculations, show that the interface is abrupt on a microscope scale and that germanium induces extrinsic interface states in the main and partial gaps of the projected bulk band structure of silicon on the (111) surface.

The electronic structure of carbon overlayers on Ni(111) has been investigated by using photoemission, energy-loss, and ionization-loss spectroscopy techniques. The combined use of these spectroscopies gives a detailed picture of these surfaces which have important catalytic implications. The carbidic carbon overlayer shows states at \ensuremath{\sim}1-, 4.2-, and 13-eV binding energy. Of particular significance is the detection (both in photoemission and in ionization-loss spectroscopy) of a carbon-derived state very near the Fermi level, in excellent agreement with recent theoretical predictions. The graphitic overlayer has an electronic structure very close to the electronic structure of pure graphite. We detect, however, an almost rigid shift of both valence and conduction bands which points to a charge transfer of about 0.02 electrons per carbon atom between the nickel substrate and the graphitic overlayer.

By using photoemission and partial yield spectroscopies the conduction band edge, the valence band and the 3d core levels of amorphous germanium hydrogenated and nonhydrogenated are studied and compared to that of crystalline Ge. We measure a 0.25 eV shift of the 3d core levels of amorphous Ge as compared to crystalline Ge whereas a smaller shift and a slight line - broadening are found in hydrogenated amorphous samples with low H content. These results are discussed in term of the contribution to the self-energy due to relaxation of the valence electrons when a core hole is created.

We performed resonant photoemission experiments on a-SiNx:H, with x close to the stoichiometric value, using photon energies close to the transition energy between N2s core level and empty conduction band states. Resonant enhancement was observed for nitrogen p-like lone-pair states at 2.2eV below the top of the valence band, the effect is attributed to the excitonic localization of N p-like conduction states.

Note: Univ wisconsin,dept phys,madison,wi 53706. ist nazl fis nucl,lab nazl frascati,grp nazl struttura mat,frascati,italy.ISI Document Delivery No.: SR778 Reference LSE-ARTICLE-1984-017doi:10.1103/PhysRevB.29.5941 Record created on 2006-10-03, modified on 2017-05-12

The geometry of adsorbed atoms on ordered surfaces may be determined by different experimental techniques. Among them the most used are ion scattering spectroscopy-(ISS) [1,2], surface extended X-ray absorption fine structure (SEXAFS) [3], low energy electron diffraction (LEED) [4] and normal photoelectron diffraction (NPD) [5]. All these techiques show limits in the number of possible systems to be exploited. In particular in the case of adsorbed carbon atoms the ISS suffers of low back-scattering amplitude while the carbon contamination of the optical elements [6] is the most limiting factor in SEXAFS and NPD techniques. LEED analysis is not affected by the above limits, nevertheless it requires careful and time-consuming computer analysis.