Application of the Lucy-Richardson deconvolution procedure to high resolution photoemission spectra

Angle-resolved photoemission has developed into one of the leading probes of the electronic structure and associated dynamics of condensed matter systems. As with any experimental technique the ability to resolve features in the spectra is ultimately limited by the resolution of the instrumentation used in the measurement. Previously developed for sharpening astronomical images, the Lucy-Richardson deconvolution technique proves to be a useful tool for improving the photoemission spectra obtained in modern hemispherical electron spectrometers where the photoelectron spectrum is displayed as a 2D image in energy and momentum space.     

The surface electronic structure of Ag8Au4 superlattice

We present the calculations of electronic structure and photoemission spectra for a lattice-matched Ag-Au(111) superlattice. The selfconsistent band structure exhibits a superlattice gap at about 1 eV below the Fermi level. A surface state is found in this gap and its dispersion properties are investigated. Its energy location is varied with location of surface terminating plane within the superlattice period. The calculated normal photoemission spectra explain well available experimental data.     

Unoccupied band dispersion of Si(1 1 1):√3 × √3-Ag surface studied by time- and angle-resolved two-photon photoemission spectroscopy

Band dispersion and transient population of unoccupied electronic states on Si(1 1 1):√3 × √3-Ag surface have been studied by time-resolved (TR) and angle-resolved (AR) two-photon photoemission (2PPE) spectroscopy. The band dispersions originating from unoccupied electronic states have been identified from the comparison between AR-2PPE spectra and angle-resolved one-photon photoemission spectra with synchrotron radiation. A lifetime of unoccupied surface state has been determined from the TR-2PPE spectra.     

Self-consistent electronic structure calculation for nitrogen chemisorbed on copper (100)

A fully self-consistent calculation of the electronic structure of a N covered Cu slab is reported. The density of states shows changes relative to a clean Cu slab that reproduce the changes observed in photoemission spectra when N is chemisorbed on Cu(100). Thus initial state information is correctly mirrored in the photoemission spectra in this case. The changes are due to the presence of the N 2p-bands, and to significant alteration of the surface Cu 3d-bands by the chemisorption of N. The localization in space of the chemisorption bond and the importance of self-consistency are demonstrated.     

Angle-resolved photoemission study of Ag nanofilms grown on fcc transition-metal (111) substrates

A comparative study of the electronic structures of Ag nanofilms on the pseudomorphic metastable fcc Fe(111) and bulk-like fcc Co(111) substrates has been carried out to investigate their quantized electronic structures. The photoemission spectra of both Ag nanofilms exhibit the fine structures derived from the quantized sates of Ag sp valence electron. The nanofilm-thickness dependences of the binding energy of the quantized states are reproduced by the calculated results based on the phase accumulation model. From the angle-resolved photoemission measurements, the effective masses of the quantized electronic states along the direction parallel to the nanofilm surface were directly determined. We discuss the electronic hybridization effect between quantized states in Ag nanofilm and 3d-derived electronic states in transition-metal substrates.     

Novel photoemission studies of the PtCu alloys

The photoemission spectra of PtCu alloys of a number of different compositions has been measured. A new method of sample preparation by an interdiffusion technique allowed rapid measurement as a function of composition. The results are in general agreement with the coherent potential approximation to the electronic structures of alloys.     

Manganese silicide single crystal and films deposited on Si(1 1 1): A comparative spectroscopic study

A comparative experimental study is presented of the electronic properties of MnSi films grown on Si(1 1 1) and of MnSi single crystals, using X-ray absorption spectroscopy (XAS), and core level and valence band photoemission spectroscopy (PES). No significant differences in the electronic structure of the two systems can be found.Absorption measurements on the Mn 2p threshold show a mixed valence ground state, where the multiplet structure is washed out by the hybridisation of the Mn 3d states with the Si sp states. These results are also confirmed by photoemission (PE) spectra from the valence band and the Mn 3s, 3p and 2p core levels.Strong attention has been paid to the effect of contamination. The occurrence of multiplet effects in the absorption spectra indicates unambiguously the localisation of the Mn 3d electrons in Mn-O bonds, which strongly influences the electronic properties of these systems.     

Spectral function of ferromagnetic 3d metals: a self-consistent LSDA+DMFT approach combined with the one-step model of photoemission

The electronic structure of ferromagnetic 3d-transition metals in the vicinity of the Fermi level is dominated by the spin-polarized d bands. Experimentally, this energy region can be probed in detail by means of angle-resolved ultraviolet photoemission and inverse photoemission. In several earlier studies the measured spectra were described either within a single-particle approach based on the local spin-density approximation including matrix-element effects within the so-called one-step model or by sophisticated many-body approaches neglecting these effects. In our analysis we combine for the first time correlation with matrix-element effects to achieve an improved interpretation of photoemission data from ferromagnetic nickel.     

Surface electronic structure of the organic superconductor κ-(ET)2Cu(NCS)2 studied via photoemission microscopy

The surface electronic structure of cleaved single crystals of the organic superconductor κ-(ET)₂Cu(NCS)₂ has been studied using photoemission microscopy. Two types of cleaved surfaces were observed, displaying different valence band photoemission spectra and different spectral behavior near the Fermi level, E_F. In particular, spectra from one surface type display relatively broad spectral features in the valence band and finite spectral intensity at E_F, while spectra from the other surface type show well-defined valence band emission features and zero photoemission intensity at E_F. We propose that the spectral differences are due to a very short electron mean free path in this material, and our results are used to explain the differences between previously published photoemission spectra from this superconductor. We also report the results of an investigation of the electronic structure of defects in this material.     

The electronic structure of from high energy spectroscopy

We report the results of a detailed study of the occupied and unoccupied electronic structure of dimers of the new heterofullerene by means of photoemission and electron energy-loss spectroscopy. A close similarity is found between the electronic structures of pristine and with an additional broadening of the spectra in the former due to the distortion of the fullerene cage caused both by dimerization and the chemical substitution. Both the occupied and unoccupied electronic states, as well as the interband transitions between them, attest to the high degree of molecular character retained in the solid state. Comparison of the shake-up structures in the and X-ray photoemission spectra confirm that the highest lying occupied states in the heterofullerene have a strong degree of N character, whereas the lowest lying unoccupied states have mainly C character. We also present the optical conductivity of the heterofullerene (derived from the loss function), which shows an optical gap of 1.4 eV, some 0.4 eV smaller than that of . Received: 25 August 1997 / Revised: 22 September 1997 / Accepted: 16 October 1997     

Electronic structure of dendrimer-encapsulated Au nanocluster

We have carried out optical and X-ray photoemission studies of the dendrimer-encapsulated Au nanoclusters. The dendrimer-encapsulated Au nanoclusters are prepared by the chemical reduction of Au ions loaded within the dendrimer templates. Photoluminescence spectrum of the dendrimer-encapsulated Au nanoclusters with diameter of about 1.0 nm shows the visible luminescence centered at about 2.8 eV. In addition, we have measured the nanocluster-size dependent photoemission spectra in the valence-band region. From line shape analysis of Au 4f X-ray photoemission spectra, Au 4f core-level spectra of the dendrimer-encapsulated Au nanoclusters reflect the size dependent chemical-states. From these results, we discuss electronic structures and chemical states of the dendrimer-encapsulated Au nanoclusters.     

The electronic structure of RbTiOPO(4) and the effects of the A-site cation substitution in KTiOPO(4)-family crystals

The electronic structure of RbTiOPO(4) has been investigated with x-ray photoemission spectroscopy. Detailed photoemission spectra of the element core levels have been recorded under excitation by nonmonochromatic Al Kα radiation (1486.6?eV). The chemical bonding parameters are compared to those reported for complex titanates and phosphates. The band structures of KTiOPO(4), RbTiOPO(4), K(0.535)R(0.465)TiOPO(4) and TlTiOPO(4) have been calculated by ab?initio methods and compared to available experimental results. It is found that the band structure of KTP-type phosphate crystals is weakly dependent on the nature of the A-site (A=K, Rb, Tl) element.     

Chalcogen adsorption on Ni(100)

The successive stages of the oxidation of Ni(100) have been investigated by angle-resolved uv photoemission. The adsorption spectra are very similar to that measured previously for the same surface saturated with sulphur. Results are interpreted using recent theoretical calculations. It is found that this interpretation can be extended to the other chalcogens adsorbed on Ni(100). When increasing oxygen exposures, photoemission spectra have shown a continuity of the electronic character in the oxidation process.     

Angle resolved photoemission study and calculation of the electronic structure of the Pt(111) surface

Angle resolved photoemission spectra of Pt(111) were measured along the direction of the surface Brillouin zone (SBZ). The electronic structure of a semi-infinite Pt(111) crystal was calculated applying the LMTO-TB approximation to aid interpretation of the spectra. The experimental spectra are well described by the calculated bulk band structure. Both the experiment and calculation reveal a surface state near the Fermi level in the neighborhood of the point of the SBZ.     

Photoemission from InAs/GaAs quantum dots decorated with cesium adatoms

An array of non-overgrown InAs/GaAs quantum dots has been decorated with adsorbed metal atoms in situ in ultrahigh vacuum. Their electron and photoemission properties have been studied. The radical modification of the spectra of the threshold emission from the quantum dots with increasing cesium coating has been found. Two photoemission channels have been established; they are characterized by considerably different intensities, spectral locations, and widths of the selective bands. It has been shown that the decoration of the quantum dots makes it possible to control the electronic structure and quantum yield of photoemission, the nature of which is related to the excitation of the electronic states of the GaAs substrate and InAs/GaAs quantum dots.     

Revelation of the role of impurities and conduction electron density in the high resolution photoemission study of ferromagnetic hexaborides

We investigate the temperature evolution of the electronic structure of ferromagnetic CaB6 using ultrahigh resolution photoemission spectroscopy; the electronic structure of paramagnetic LaB6 is used as a reference. High resolution spectra of CaB6 reveal a finite density of states at the Fermi level E(F) at all the temperatures and evidence of impurity induced localized features in the vicinity of E(F), which are absent in the spectra of LaB6. Analysis of the high resolution spectra suggests that disorder in the B sublattice inducing partial localization in the mobile electrons and low electron density at E(F) is important to achieve ferromagnetism in these systems.     

Inverse photoemission from solids: Theoretical aspects and applications

The current status of inverse photoemission from clean crystals is reviewed with special emphasis on theoretical aspects and applications. The article focuses on general photoemission theory, the effective barrier potential at metal surfaces and the calculation of inverse photoemission spectra for both bulk and surface electronic states. In particular the information originating from inverse photoemission on Shockley and image-potential surface states, effective masses of mage-potential states and spin-split surface states at ferromagnets is discussed.     

Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface

The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.     

Charge accumulation nanolayer: A 2D electronic channel in Cs/n-InGaN ultrathin interfaces

This paper reports on the formation of a 2D electronic channel, i.e., a charge accumulation layer on the n-InGaN(0001) surface observed under adsorption of submonolayer Cs coatings. It is found that photoemission from the accumulation layer is excited by light in the InGaN transparency region. It is established that the potential well depth and the density of electronic states in the accumulation layer can be controlled by properly varying the Cs coverage. It is shown that the accumulation layer exhibits quantum-well effects. The photoemission matrix element is calculated, and the energy parameters of the accumulation layer are obtained. An oscillatory structure originating from the Fabry-Perot interference is revealed in the spectra of photoemission from the accumulation layer.     

Ultrahigh-resolution laser photoemission study of URu2Si2 across the hidden-order transition

We have studied the electronic structures of URu₂Si₂ employing ultrahigh-resolution laser angle-resolved photoemission spectroscopy. The change of photoemission spectra is investigated across the hidden-order transition, and the emergence of a narrow band is clearly observed near the Fermi level for both (π,0) and (π,π) directions. In addition, it is shown that tuning of light's polarization allows the signal of a hole-like dispersive feature to enhance. These observations prove that laser angle-resolved photoemission spectroscopy is an effective tool for studying the evolution of electronic structures across the hidden-order transition in URu₂Si₂.