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We report results obtained by resonant photoemission (RPE) and X-ray magnetic circular dichroism (XMCD) in absorption with photon energies around the L 2/3 edges of manganese. The samples contain manganese in different environments and details about the dynamics of electronic structure on one side, magnetic structure on the other side are being discussed. We will present studies on the following samples: submonolayers of Mn on Cu(100), Mn in InAs and thin films of the manganese perovskite LSMO.

FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR–ENEA–INFN–University of Roma “Tor Vergata” study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, leading to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S-band normal conducting linac with high-brightness photoinjector integrated in an RF compressor.

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.

We have studied Mn/InAs(0 0 1)(4×2) c (8×2) interfaces by high-resolution core-level spectroscopy, surface EXAFS and by X-ray magnetic circular dichroism (XMCD). The growth of manganese is found to depend strongly on the temperature of InAs. At low temperatures (room and liquid nitrogen temperature (LNT)), Mn atoms form the compound MnAs in the surface region leaving metallic In islands on the surface. Manganese deposition at 530 K results in strong diffusion of Mn into the substrate followed by formation of the compound In 1− x Mn x As in which Mn atoms are substituted in indium-sites. We show by XMCD that In 1− x Mn x As is ferromagnetic with a relatively high value of an average magnetic moment per Mn atom, exceeding 0.7 μB at low temperatures and with an individual magnetic moment of about 2.4 μB. The temperature dependence of the Mn magnetic moment follows the Brillouin function and it drops to zero at temperature of about 150 K for measurements in an external magnetic field of 5 T.

We have performed core-level photoemission measurements on Sb/Si(111) ?3×?3, Sb/Si(100) 2×1, Sb/Si(110) 2×3 and Ag/Si(111) ?3×?3R(30°) surfaces with the improved energy resolution of the 'VUV Photoemission' beamline at the ELETTRA third generation SR facility. In the case of antimony on Si(111), Si(100) and Si(110) our results show the presence of a strong Si2p interfacial component (S) whose shift with respect to the bulk peak is +130, +200 and +240 meV, respectively. A small component (C) was present in all surfaces on the high kinetic energy side. In the case of Ag/Si(111) ?3×?3R(30°) the Si 2p spectrum shows the presence of three components in addition to the bulk peak, shifted respectively by +450, +250, -220 meV. We assign the surface components to charge transfer and to the reconstruction structural elements. © 2001 Elsevier Science B.V. All rights reserved.

The deposition of 1 ML of As on Si(0 0 1)-(2×1) surface and the heteroepitaxial Ge/As/Si(0 0 1)-(2×1) growth were studied by using high resolution core-level spectroscopy and transmission electron microscopy (TEM). From the spectral decomposition of the Si2p core levels, collected on the Ge/Si interfaces obtained by codepositing As and Ge atoms at different Ge thickness, we identify the contribution of different Si layers to the Si2p lineshape, in agreement with recent theoretical final-state pseudopotential calculations. The bulk-like Ge3d core levels reflected the occurrence of a complete Ge–As site-exchange process, while the pseudomorphic layer-by-layer Ge/Si growth was confirmed by TEM investigation.

We have investigated clean In-terminated InAs(0 0 1)(4×2)-c(8×2) surface by LEED, STM and high-resolution core-level and valence band (VB) spectroscopies. The In4d and As3d core levels showed the presence of chemically shifted components. The decomposition of In4d core level exhibited a new surface component located close to that of free indium metal. This indicates that the origin of the electron emission at the Fermi level measured in the VB spectra is probably due to the free In charge. STM measurements showed a uniform distribution of charge on the In-rows, which are highly ordered over large areas of the surface.

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.

The adsorption of three monolayers (3 MLs) of Sb at −120°C on the Si(001)c(4×2) surface and the subsequent annealing up to 650°C were followed by high resolution core level spectroscopy and RHEED analysis. By relating the electron diffraction patterns to the Si2p and Sb4d core level spectra measured after each annealing cycle, it was possible to monitor the evolution of the Sb/Si interface structure up to the achievement of a diffuse (2×1) reconstruction. Even after the annealing to 650°C, the quality of the surface reconstruction remained poor, as attested by the RHEED pattern, by the intensity of the Si2p surface component and by the broadening of the Sb4d lineshape.

Ge epitaxy on $\mathrm{Si}(001)c(4\ifmmode\times\else\texttimes\fi{}2)$ was monitored by high-resolution core-level spectroscopy up to the deposition of 20 ML. Ge $3d$ and Si $2p$ core-level spectra were acquired at normal- and grazing-emission angles. Taking into account the whole evolution of the Ge $3d$ core-level line shape during growth, in addition to the three surface components previously reported for thin Ge layers, a fourth component was identified and attributed to bulklike Ge atoms. For submonolayer coverage, the difference between the number of up- and down-dimer sites occupied by Ge unequivocally indicated the formation of mixed Si-Ge dimers. The presence in the Ge $3d$ core level of the component related to second-layer atoms demonstrated that Ge starts to diffuse below the surface before all the dimer sites are occupied. During deposition of the second ML, the behavior of the bulklike component indicated that Ge diffuses to layers deeper than the second, probably in order to occupy sites under tensile stress. At a Ge coverage of 20 ML, the persistence of surface components in the Si $2p$ core level is related to segregation of Si in the Ge layer or, more appropriately, to Stranski-Krastanov growth, which determines an inhomogeneous Ge coverage, locally as low as 1\char21{}2 ML.

The adsorption of Ge on the Bi/Si(001)2×5 surface (Bi saturation coverage of 0.7 ML) and on Sb/Si(001)2×1 (Sb saturation coverage of 0.9 ML), was investigated by core level photoemission spectroscopy. For the Bi/Si(001)2×5 interface, at submonolayer Ge coverage, the presence of a bulk component largely dominating the Ge 3d core level, demonstrates that the favorite adsorption sites are the Bi-terminated terraces, where the Ge–Bi site exchange takes place. At larger Ge coverage, in addition to the previous process, the occurrence of a pure Ge epitaxy on the bare fraction of the substrate is indicated by the presence of the 2×1 surface components in the Ge 3d core level. In the case of Sb/Si(001)2×1 interface, the Ge 3d shows a complete lack of surface components, which indicates the absence of dimerized Ge atoms at the top layer, and demonstrates that the Ge–Sb site exchange process has taken place on the whole Si(001) surface.

We report x-ray photoelectron spectroscopy experimental results on band offsets at Ge/Si(100)2 x 1 interfaces grown by hydrogen and Sb-surfactant mediated epitaxy. For Ge deposited at 400 degrees C in Si(100)2 x 1, the valence band discontinuity was of 0.72 +/- 0.07 eV. Using atomic hydrogen and a Sb-monolayer mediated growth, we obtained values of 0.75 +/- 0.07 and 0.69 +/- 0.07 eV. Our data show that the surfactant Ge layer strain induced effects on the modification of band offsets are surprisingly negligible.

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.

We investigate the evolution of the electronic structure across the insulator-metal transition in NiS 2−x Se x with changing composition, but in the absence of any structural or magnetic changes. A comparison of the inverse photoemission spectra with band-structure calculations establishes the importance of correlation effects in these systems. Systematic changes in the spectral distribution establish the persistence of the upper Hubbard band well into the metallic regime, with the insulator-to-metal transition being driven by a transfer of spectral weight from the Hubbard band to states close to the Fermi energy.

By mapping the low-energy electronic dynamics using angle resolved photoemission spectroscopy (ARPES), we have shed light on essential electronic characteristics of the (3 × 3) silicene phase on Ag(111) surfaces. In particular, our results show a silicene-derived band with a clear gap and linear energy-momentum dispersion near the Fermi level at the Γ symmetry point of the (3 × 3) phase at several distinctive Brillouin zones. Moreover, we have confirmed that the large buckling of ~0.7 A of this silicene structure induces the opening of a gap close to the Fermi level higher than at least 0.3 eV, in agreement with recent reported photoemission results. The two-dimensional character of the charge carriers has also been revealed by the photon energy invariance of the gapped silicene band, suggesting a limited silicene-silver hybridization, in disagreement with recent density-functional theory (DFT) predictions.

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.}

Synchrotron radiation ultraviolet photoemission spectroscopy (UPS) of O(2s) core levels, valence band (VB) and Sn(4d) spectroscopy was used to monitor the effect of Ar + sputtering on SnO 2 films. The decrease of the O(2s) peak intensity and the increase of the Sn 2+ component in the Sn(4d) peak could be satisfactorily correlated with the enhancement of the band gap feature, occurring at 2.9 eV in the VB spectrum, never been due to the formation of Sn(5s–5p) states.

The Sn on the Si(100) system constitutes an epitaxial interface of Group-IV elements. Its phase diagram presents several surface reconstructions, whose structure depends on the Sn adlayer coverage and the annealing temperature. The interfaces of Sn grown at room temperature on Si(100)(2 × 1) and the superstructures obtained after annealing have been studied by means of inverse photoemission (IPES), and Auger and LEED spectroscopy, to characterize the electronic empty states of the different overlayer phases and relate them with other electronic properties. Sn/Si(100) systems, both at room temperature deposition and after thermal treatment, present the onset of a metallic overlayer for tin coverages above 1 ML. For the interfaces grown at room temperature the IPES spectra with Sn thicknesses below 1 ML show a peak at about 1.0 eV above the Fermi level. At the E F level no emission is present. The IPES spectra of Sn/Si(100) after annealing clearly show that the empty states evolution can be related to the kind of reconstruction observed by LEED. These results indicate the formation of interfaces with peculiar properties. In particular in the Sn/Si(100)c(8 × 4) system the phase is semiconducting and the gap is reduced; a new prominent state appears at 1.1 eV above E F . The role played at the interface by the Sn-Sn dimers, related to the dimensionality, is discussed.

We performed a photoemission study on the (α-Si)/Si(111) homojunction with a thin intralayer of calcium fluoride (one monolayer). The intralayer and the amorphous silicon were grown in situ on cleaved Si(111) single crystals. From the core-level analysis we found a valence-band discontinuity of 0.35 eV due to the electrostatic dipole induced by the intralayer ionic bonds. Our results show that the intralayer forms an abrupt interface with Si and that the overlayer valence band has a lower binding energy than the substrate one. This implies that the most probable interface configuration is Si(111)-Ca-F-(α-Si), confirming the results of previous works on the CaF 2 /Si(111) interface

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.

Thermotransmission measurements have been carried out on thin, self-supported, semitransparent gold films in the 1.8–3.5-eV energy region. The results compare very favorably with the spectra of Rosei et al., taken on quartz-backed samples, showing the feasibility of extending the techniques of modulation spectroscopy into the soft x-ray region. Moreover, it is shown that the widths of the spectral features are a factor of two smaller than those obtained on films evaporated on a quartz substrate. The thermal time constant is in the range of a few milliseconds, so that a very high modulation efficiency can be obtained, even when operating at several hundred hertz.

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 present synchrotron-radiation photoemission studies of the electronic structure of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$S alloys, together with results for the parent binary compound CdS. Analysis of the partial photoionization cross section at the Mn 3p-3d resonance was conducted to investigate the Mn 3d contribution to the valence bands. We use ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$S as a test case to examine different methods of data reduction. A comparative analysis of constant-initial-state (CIS) spectra, ternary-binary difference curves, as well as resonance-antiresonance difference curves identifies a major Mn 3d density of states feature 3.12\ifmmode\pm\else\textpm\fi{}0.05 eV below the CdS valence-band maximum, together with relevant Mn 3d contribution to the electron states near the valence-band maximum and a broad satellite in the 4--8-eV range. A quantitative analysis of the Fano parameters derived from a least-squares fit of the CIS spectra allowed us to characterize the varying amount of Te p--Mn 3d hybridization in the valence states.

We investigated the structural and magnetic properties of MnxGe1x, with 0.02 6 x 6 0.1. The MnxGe1x samples were grown on Ge(001)2 · 1 by molecular beam epitaxy, at a substrate temperature of 520 K. The samples were characterized in situ by reflection high-energy electron diffraction and ex situ by high-resolution transmission electron microscopy, energy dispersive X-ray reflectivity and magneto-optical Kerr effect. From microscopy images we evidenced on all samples the presence of Mn5Ge3 nanocrystallites in addition to the MnxGe1x diluted magnetic semiconductor with an estimated Mn concentration x 1.5%. The size and the density of the Mn5Ge3 precipitates were found to increase with increasing the Mn concentration x. Magnetic analysis showed ferromagnetism with a Curie temperature of 280 K for all samples.

We studied morphological and magnetic properties of Ge/MnxGe1-x/Ge(0 0 1)2 x 1, x = 0.02-0.04. Several MnxGe1-x alloys were grown on Ge(0 0 1)2 x I by molecular beam epitaxy, as a function of substrate temperature and Mn concentration. The samples were characterized in situ by RHEED, and ex situ by energy dispersive X-ray reflectivity (EDXR) and magneto-optical Kerr effect, (MOKE). From RHEED analysis we found an optimal growth temperature T-epi = 523 K to achieve 2D epitaxial MnxGe1-x (x = 0.02-0.04) alloy on a Ge(001) substrate. X-ray reflectivity measurements provided: the film roughness, the MnxGe1-x scattering length density, and the average thickness for all samples. MOKE analysis showed ferromagnetism with Curie temperature T-C = 270 K for samples grown at T-epi = 523 K. (c) 2006 Elsevier B.V. All rights reserved.

In this paper we investigated the effect of the direction of an external magnetic field, applied during electrodeposition, on the magnetic properties and morphology of Co–Ni–P layers.

Structural and magnetic properties of Ge 1-x mn x alloys, epitaxially grown on a Ge(001)2 x 1 surface have been investigated. We prepared Ge 1-x mn x films by MBE as a function of substrate temperature and Mn concentration x. In-situ RHEED was used to monitor the streaks of the Ge 1-x mn x epitaxial films. The optimal temperature, to obtain a very well-ordered epitaxial Ge 1-x mn x alloy, for Mn concentrations of x = 0.02, and x = 0.04, was found to be 525 K. Ex-situ magneto-optical Kerr effect and XMCD at the L 2/3 Mn2p absorption edges on Ge 1-x Mn x films, show isotropic magnetic properties. The Curie temperature of about 270 K was found on most of the ordered samples.

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.

Highly ordered array of quantum stripes are obtained on In-terminated InAs(001) reconstructed surface. We report the investigation of clean In-terminated InAs(OO1)(4x2)-c(8x2), and InAs(001)-(4x4) surfaces by low electron energy diffraction (LEED) and by high-resolution angle-resolved photoemission spectroscopy (ARPES). Monitoring the InAs(001) surface by LEED as a function of the substrate temperature, the -(4x4) and the -4x2(8x2) reconstructions were observed. ARPES measurements on both reconstructions show electronic states belonging to the In-stripes, which appear on the surface after the annealing treatment. These states are non-dispersive as a function of photon energy and in the case of 4x2-c(8x2) reconstruction the k-dispersion exists only along the [011] stripes direction, at variance on c(4x4s) surface the states have a fix energy.

New photoemission data are presented for a series of Ce-doped or undoped, reduced or nonreduced, Nd cuprates. The data, taken with high signal-to-noise level in the constant-initial-state mode, demonstrate the presence of Cu+, in contrast with previous photoemission and electron-energy-loss studies.

We present expressions for the resonant magnetic X-ray scattering (XRMS) by surfaces possessing roughness and analyze both the structural and magnetic roughness of a surface, as well as their correlation. We demonstrate that the leading contribution to the difference (DI) in the diffuse scattering between left- and right-circularly polarized light for a rough surface vanishes unless the structural and magnetic roughnesses are correlated, to leading order in the magnetization. The effects of magnetic domain structure and magnetic dead layers on the surface scattering are also discussed.

Note: Univ wisconsin,dept phys,madison,wi 53706. ist struttura mat,i-00044 frascati,italy. Evangelisti, f, univ la sapienza,dipartimento fis,i-00185 roma,italy.ISI Document Delivery No.: TW959 Reference LSE-ARTICLE-1984-007doi:10.1103/PhysRevLett.53.2504 Record created on 2006-10-03, modified on 2017-05-12

We report on Low-Energy-Electron-Loss-Spectroscopy studies on the Ge-Au interfaces obtained by gold deposition on cleaved Ge(111) 2×1 substrates. A disruption mechanism of the Ge surface arises after 1.6 A of Au coverage and a new Ge-Au stoichiometric compound is formed. This compound shows LEELS features completely different from those of pure germanium and gold substrates. The new structures are explained using previously reported photoemission EDC's (1) and are in very good agreement with theoretical predictions in the Au 3 -Ge stoichiometric compound (2) .