Thin Cu films on manganese: aes and photoemission,by synchrotron radiation,investigations

The initial growth of Cu on polycrystalline manganese at room temperature has been investigated by Auger Spectroscopy and UV-synchrotron radiation photoemission spectroscopy, for copper coverages ranging from 1 to 18 Å. By monitoring the changes of the Cu3d level, a strong intermixing at the interface has been observed. The simultaneous growth of a copper phase which is lying on top of the intermixed region has also been detected. Analysis of the Auger data indicates that copper is most probably growing in a layer-by-layer mode, with a simultaneous diffusion into the substrate. Calculations for a layer-by-layer growth model are compared with the experimental data. They support our analysis.     

Silicon L2,3VV Auger lineshape and oxygen chemisorption study of Pd4Si

The SiL_2,3VV Auger Lineshape for Pd₄Si was measured and found to be in good agreement with the self-fold of the Si partial density of states model calculated by Riley et al. Oxygen chemisorption altered both the Auger lineshape and the HeI photoemission spectrum, especially near the Fermi energy.     

A resonant photoemission model for nickel metal

We present a model for the resonance near the 3p threshold in the photoemission associated with a static 3d pair-hole bound state in paramagnetic nickel. We show that, following Auger processes, the strong intra-atomic screening of the pair hole by the 4s?4p conduction band electrons is essential to explain experimental photoemission data not only in copper but also in nickel. From the energy relaxation of the conduction band states we estimate the bare Coulomb interaction between two d-holes in nickel.     

Experimental determination of the internal photoemission contribution to KLM Auger spectra of Na,Mg and Al

Photoemission from the 2p levels of the light metals excited by internally generated K_α1,2 X-rays has been observed, and the intensities compared with valence band to 2p intensity ratios obtained from X-ray photoemission spectroscopy. It is found that internal photoemission from the valence band contributes 0.5% of the intensity of the KL_2,3M Auger peak.     

Observation of resonance recombination lines in electron excited auger spectra of Gd

Combined measurements of electron excited N_4,5 Auger spectra and photoelectron emission on clean and oxidized Gd lead to a distinction between Auger lines originating from 4d → continuum and 4d → 4? resonance excitations. Several Auger structures are identified as due to the direct recombination of 4d⁹4?⁸ states with the 4f and valence electrons. The shape of the most prominent Auger line for oxidized Gd agrees perfectly with the Fano profile of the 4? photoemission intensity.     

Auger spectroscopy of polyethylene and poly (ethylene oxide)

The X-ray excited Auger spectra of polyethylene and poly(ethylene oxide) have been corrected for Auger electron energy losses due to interactions with the solid and compared to the corresponding spectra of gas phase molecular analogs. The corrected polyethylene spectrum is an extrapolation of trends observed in the spectra of gas phase alkanes from CH₄ through C₆H₁₄. The O(KVV) spectrum of poly(ethylene oxide) is similar to that of methyl ether, consistent with similar nearest neighbor environments for the oxygen atoms in the two materials. In contrast, the C(KVV) spectrum of poly(ethylene oxide), a material which contains C-C bonds, is better approximated by the spectrum of ethane (H₃C-CH₃). A comparison of the polyethylene Auger spectrum with the spectra of the normal alkanes and with a self-fold of its X-ray excited valence band photoemission (single hole) spectrum indicates the presence of correlated two-hole final states in the case of polyethylene.     

Strongly Z-dependent Auger and photoelectron diffraction in MgO(001)

We have measured angular distributions of Mg KL_2,3L_2,3 Auger and O 1s core-level photoemission intensities at high angular resolution for MgO(001). We find substantial differences in the two types of scans over many regions of k space, despite the very similar local structure of Mg and O in the rocksalt lattice. These diffraction scans are quantitatively predicted by spherical-wave, single-scattering theory, assuming an s wave for the Mg KL_2,3L_2,3 Auger transition. The differences that are observed between Mg KL_2,3L_2,3 Auger and O 1s diffraction scans are shown to be due purely to differences in the elastic scattering phase shifts for Mg and O atoms in the solid.     

Electron spectrometer calibration. consistency between magnesium- and aluminum-excited spectra

Analysis of a variety of Auger and photoemission spectra leads to the conclusion that the value given by Bearden for the MgKα_1,2 X-ray energy is not the best value for use in photoemission spectroscopy. The reported value is the energy at the maximum of the X-ray spectrum. Use of this can lead to inconsistencies in measured energies. These are removed if one uses the centroid of the magnesium X-ray spectrum (1253.53 eV). Use of this value also resolves a disagreement between values reported by different laboratories for the Nels ionization energy.     

The electronic structure of the [CuO5]8− unit: A photoemission study of Y2BaCuO5

A photoemission study of the green phase Y₂BaCuO₅, including core level spectra of the elements, CuL ₃VV Auger, and XPS and UPS valence band spectra has been performed. The crystal structure of Y₂BaCuO₅ contains discrete [CuO₅]^8– units with divalent copper. The surface status of the Y₂BaCuO₅ samples is discussed with respect to the problems encountered in photoemission studies of the YBaCuO superconductors. The photoemission data are analysed within a simple cluster configuration interaction model by considering in addition previously reported optical spectra. Y₂BaCuO₅ is a charge transfer insulator with the charge transfer energy 0.5 eV being much smaller than thed–d Coulomb interaction energyU6eV. Cluster model parameters and valence band shapes of Y₂BaCuO₅ are compared with those of Nd₂CuO₄ the structure of which contains divalent copper within an extended copper-oxygen network. More detailed cluster and impurity models for cuprates described in literature are discussed in view of the present results.     

Experimental evidence for molecular ultrafast dissociation in O<Subscript>2</Subscript> clusters

Resonant Auger spectra of O₂ clusters excited at the O1s edge are reported. After excitation to the repulsive 1s^-13σ^* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular ultrafast dissociation processes within the clusters or on their surface.     

Radiation-induced decomposition of the metal-organic molecule Bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II)

The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)₂), (C₂₄H₃₆N₂O₄Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)₂, adsorbed on Co(1 1 1), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)₂ and this decomposition is initially dominated by loss of peripheral hydrogen.     

Surface electronic structure of α-Mo2C(0 0 0 1)

The electronic structure of α-Mo₂C(0 0 0 1) has been investigated by angle-resolved photoemission spectroscopy utilizing synchrotron radiation. A sharp peak is observed at 3.3 eV in normal-emission spectra. Since the peak shows no dispersion as a function of photon energy and is sensitively attenuated by oxygen adsorption, the initial state of the peak is attributed to a surface state. Resonant photoemission study shows that the state includes substantial contribution of 4d orbitals of the Mo atoms in the second layer. The emissions with constant kinetic energies of 22 and 31 eV above the Fermi level (E_F) are found in normal-emission spectra, and these emissions are interpreted as originating from the Mo N₁N₂₃V and N₂₃VV Auger transitions, respectively.     

Interatomic internal photoemission peaks in (Auger) electron spectra

Internal photoemission (IPE) features appearing in (Auger) electron spectra have two distinguishing properties: (1) they obey optical selection rules and (2) IPE intensities increase rapidly with incident excitation electron energy. IPE and Auger electrons from elemental materials have similar energies, giving complicated mixed spectra; however, core-level interatomic IPE peaks (from compounds) can appear by themselves, as shown here using SiO ₂. The IPE process has high photon utilization efficiency, and core interatomic IPE shows promise for certain specialized applications discussed in the text.     

High resolution Auger electron spectroscopy of metallic copper

Part of the LMM Auger spectrum from metallic copper has been studied in a high resolution X-ray photoelectron spectrometer. Fine structure not earlier reported has been observed. The main L₃M_4,5M_4,5 peak is very narrow, 1.0 eV, although the valence band is involved in the transition. The agreement between experimental and calculated Auger electron energies is very good. Since fine structure is found to be an intrinsic property in Auger spectra the interpretation of “satellite” peaks as due to electron—plasmon interactions should be used with care. The L₃M_4,5M_4,5 peak is very sensitive to the copper surface conditions. Surface oxygen affects the peak in a characteristic way.     

Investigation of the chemical state of copper in Cu/SiO2 composite films by x-ray photoelectron spectroscopy

The concentration and chemical state of copper in the subsurface region of Cu/SiO₂ composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO₂) 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 SiO₂ 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.     

Photoemission studies of core exciton decay in KI

The decay of K⁺ 3p-core excitons in KI was studied by using new methods for obtaining photoemission spectroscopy data with synchrotron radiation. The Auger and non-radiative direct-recombination decay processes are separately identified in the data and a measure for the Auger energy distribution is obtained.     

Photoemission spectra of ion implanted amorphous Si and Fe84B16 metal glass

Ultraviolet photoemission spectra of Si and Fe₈₄B₁₆ were measured in amorphous and crystalline states at 10.2 eV photon energy. The surface compositions were determined by Auger electron spectroscopy. The samples were prepared by ion implantation, evaporation and by splat-cooling. The photoelectron spectra of amorphous phases are found to be different from those of the crystalline for both materials and all preparation methods. The UPS of amorphous Si and Fe₈₄B₁₆ metal glass have some common characteristics.     

Electron beam-induced fullerite structure transformation

Auger spectra of thin fullerite (C₆₀) films have been measured under the conditions precluding their electrostatic charging and destruction. The Auger line of these subjects, E _f=268.3±0.2 eV, turned out to lie considerably lower in energy than that of the ion-beam amorphized graphite (E _AG=272.3±0.2 eV) and of pyrographite (E _PG=271.8±0.5 eV). Fullerite was found to convert to a graphitic form under irradiation by low-intensity electron beams used customarily in AES, reflection EELS, and inverse photoemission spectroscopy. It has been established that such beams produce noticeable changes in the fullerite structure already in a few minutes of irradiation. Fiz. Tverd. Tela (St. Petersburg) 39, 187–190 (January 1997)     

Resonance effects in the non-radiative de-excitation of silicon in porous silicon

Resonant silicon Auger KLL and 2s and 2p photoemission spectra of a porous silicon sample have been studied when excited by photons in the energy domain of the 1s edge in pure silicon and silicon oxide. Characteristic features of a resonant process could be detected. In particular, the constant initial state spectrum of the 2p state of silica behaves similarly to that encountered in systems which present a well-defined atomic level. This is due to the existence of a well-localized molecular orbital built in the SiO₄ unit. The use of high-energy photons, which generate high-energy electrons, allows these photoemission experiments to be quite bulk sensitive.     

Line shape analysis and relaxation energies in the MVV Auger spectra of zinc and zinc oxide

The oxidation of polycrystalline zinc has been studied by recording the evolution of the line shape of the corresponding Auger spectra. The fine structure of the surface-sensitive low energy M₁ VV and M₂₃VV (V = 4s ? 3d valence band) lines in pure zinc has been analyzed and a new feature involving the 4s band tentatively identified. In the course of oxidation the main peaks broaden and shift to lower energies. This behaviour is explained in terms of increase of the 3d band width and decrease in the extraatomic relaxation energies. The extraatomic relaxation is found to decrease in the oxide by ~3.8 eV. A derivation of Auger intra and Extraatomic energies involving basically experimental data is presented. These values are compared to theoretical evaluations and their connection with photoemission dynamical relaxation data is discussed.