Photoemission Spectroscopy Spectra Research Articles

Arsenic doping for synthesis of nanocrystalline p-type ZnO thin films

Nanocrystalline p-type arsenic-doped ZnO (ZnO:As) films have been synthesized on (0001) sapphire substrates by pulsed laser deposition using a ZnO target mixed with 6.6wt% As2O3. The process of synthesizing p-type ZnO:As films was performed in an ambient gas of ultrapure (<99.99%) oxygen. The ambient gas pressure was 5Pa with the substrate temperature in the range of 350–500°C. The ZnO:As films grown at 500°C are p type, and the acceptor concentration in ZnO:As films is about 1.9×1018at.∕cm3 as determined by Hall effect measurements. The concentration of As in ZnO:As films is estimated to be about 1.7% from the x-ray photoemission spectroscopy (XPS) spectrum. Guided by the XPS analysis and a model for large-sized-mismatched group-V dopant in ZnO, an AsZn–2VZn complex was thought to be the most possible acceptor.

Electronic nature of layered oxysulfide Sr2−xCaxCu2CoO2S2 with CoO2 planes

We have studied the electronic nature of the layered oxysulfide Sr2−xCaxCu2CoO2S2 which has strongly correlated CoO2 square planes. These materials exhibit narrow-gap semiconducting behavior and the conduction mechanism depends on the temperature. Valence band x-ray photoemission spectroscopy spectra show that Ca doping and the production of Sr defects cause the generation of a quasiparticle band near the Fermi level. These phenomena suggest that the materials are changing from correlated semiconductors to bad metals.

Soft X-ray angle-resolved photoemission spectroscopy of heavily boron-doped superconducting diamond films

We have performed soft X-ray angle-resolved photoemission spectroscopy (SXARPES) of microwave plasma-assisted chemical vapor deposition diamond films with different B concentrations in order to study the origin of the metallic behaviorof superconducting diamond. SXARPES results clearly show valence band dispersions with a bandwidth of ~ 23 eV and with a top of the valence band at gamma point in the Brillouin zone, which are consistent with the calculated valenceband dispersions of pure diamond. Boron concentration-dependent band dispersions near the Fermi level (Ef) exhibit asystematic shift of Ef, indicating depopulation of electrons due to hole doping. These SXARPES results indicate that diamond bands retain for heavy boron doping and holes in the diamond band are responsible for the metallic states leading to superconductivity at low temperature. A high-resolution photoemission spectroscopy spectrum near Ef of a heavily boron-doped diamond superconductor is also presented.

Characterization of the photo-irradiation effects on polystyrene ultrathin films with ultraviolet photoemission spectroscopy

The synchrotron-radiation-induced structural degradation in polystyrene thin films was analyzed by comparing measured ultraviolet photoemission spectroscopy (UPS) spectra with model molecular orbital calculations. The analysis confirms degradation of the phenyl pendant groups and the generation of conjugated double-bonds in the degraded polymer. The observed degradation in polystyrene is found to be very similar to one from polyethylene previously investigated.

Quantitative analysis ofSr2RuO4angle-resolved photoemission spectra: Many-body interactions in a model Fermi liquid

Angle-resolved photoemission spectroscopy (ARPES) spectra hold a wealth of information about the many-body interactions in a correlated material. However, the quantitative analysis of ARPES spectra to extract the various coupling parameters in a consistent manner is extremely challenging, even for a model Fermi liquid system. We propose a fitting procedure which allows quantitative access to the intrinsic line shape, deconvolved of energy and momentum resolution effects, of the correlated two-dimensional material ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. In correlated two-dimensional materials, we find an ARPES linewidth that is narrower than its binding energy, a key property of quasiparticles within Fermi liquid theory. We also find that when the electron-electron scattering component is separated from the electron-phonon and impurity scattering terms, it decreases with a functional form compatible with Fermi liquid theory as the Fermi energy is approached. In combination with the previously determined Fermi surface, these results give a complete picture of a Fermi liquid system via ARPES. Furthermore, we show that the magnitude of the extracted imaginary part of the self-energy is in remarkable agreement with DC transport measurements.

Core-level spectroscopic study of FeO andFeS2

The electronic structures of iron oxide and iron disulfide (FeO and $\mathrm{Fe}{\mathrm{S}}_{2}$) have been examined using x-ray emission spectroscopy and other core-level spectroscopies. We compare the excitation spectra for charge neutral excitation (x-ray emission) and ionization (photoelectron spectroscopy) at the $2p$ edge and with final-state $3s$ holes. At the Fe ${L}_{2}$-edge, the branching ratio of $L\ensuremath{\beta}$ to $L\ensuremath{\alpha}$ emission is much higher for high spin FeO than for low spin $\mathrm{Fe}{\mathrm{S}}_{2}$, similar to previous observations of Heusler alloys. We suggest that there is a general trend toward high branching ratios for magnetic $3d$ materials and low branching ratios for nonmagnetic materials. Resonant inelastic x-ray spectra of FeO with $3s$ final-state holes show a smaller exchange splitting than the corresponding x-ray photoemission spectroscopy spectra with $3s$ hole states.

Electronic structure and magnetic properties of CePdSb andCe1−xLaxPdSb

Using the various full-potential linear augmented plane wave (LAPW) methods we have studied the band structure of CePdSb and ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Pd}\mathrm{Sb}$ series of compounds. In the band calculations, CePdSb is half-metallic, i.e., metallic for majority spin while semiconducting for minority spin bands. The spin-polarized linearized muffin-tin orbital method also shows a half-metallic behavior of the ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Pd}\mathrm{Sb}$ compounds. The magnetic investigations and the electrical resistivity data indicate the existence of a ferromagnetic state in ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Pd}\mathrm{Sb}$ for $x\ensuremath{\leqslant}0.7$. The sample ${\mathrm{Ce}}_{0.1}{\mathrm{La}}_{0.9}\mathrm{Pd}\mathrm{Sb}$ is nonmagnetic and shows the power-law exponents in its susceptibility $\ensuremath{\Delta}\ensuremath{\chi}$, resistivity $\ensuremath{\Delta}\ensuremath{\rho}$, and specific heat $\ensuremath{\Delta}C∕T$ temperature dependences indicative of the non-Fermi liquid behavior. The $3d$ x-ray photoemission spectroscopy (XPS) spectra indicate the occupation number of the $f$-shell, ${n}_{f}=1$, in CePdSb and ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Pd}\mathrm{Sb}$ compounds. Analysis of the $3{d}^{9}{f}^{2}$ weight in the $3d$ XPS spectra using Gunnarsson\char21{}Sch\onhammer theory suggests the $f$-states and conduction electron-states hybridization interaction $\ensuremath{\Delta}$ of about $80\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ for different configurations $x$ of the system. We interpret the XPS data in terms of the band-structure calculations.

Electronic structure and angle-resolved photoemission spectra of vicinalCu(111)surfaces via the one-step model

The electronic structure of the $\mathrm{Cu}(332)$ and $\mathrm{Cu}(221)$ surfaces is obtained by the self-consistent screened Korringa-Kohn-Rostocker method. Angle-resolved photoemission spectroscopy (ARPES) spectra for the Shockley-type surface states at binding energies $\ensuremath{\leqslant}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ are calculated within the one-step formalism and found to be in good agreement with experimental data. There is a parabolic band, asymmetrically displaced to the boundary of the surface Brillouin zone. We show that the asymmetry occurs only in the ARPES spectra, whereas the underlying surface band structure is symmetric and explain the asymmetry of the ARPES spectra by analyzing the surface state wave function.

Resonant photoemission spectroscopy study of UTSn (T=Ni,Pd)

Abstract The electronic structures of the localized 5f system UTSn (T=Ni, Pd) have been investigated using photoemission spectroscopy (PES). The U 5f PES spectra of UTSn exhibit a broad peak centered at ≈0.3 eV below E F with rather small spectral weight near E F ( N f (E F )) . The small N f ( E F ) in UTSn is found to be correlated with the T d PES spectra that have a very low DOS near E F .

PES and XAS studies of Mn12-Ac molecular magnet

Abstract The electronic structure of Mn12-Ac has been investigated using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The PES spectrum indicates that Mn 3d states are located near the top of the valence band, and the Mn 2p XAS spectrum provides clear evidence for the Mn3+–Mn4+ mixed-valent states.

High-resolution soft X-ray photoemission spectroscopy of spinel-type compound CuIr2S4

Abstract The electronic structure of spinel-type chalcogenide CuIr 2 S 4 , which exhibits a metal–insulator transition, has been studied by photoemission spectroscopy (PES). The valence-band PES spectra indicate a gap formation below the transition temperature T MI . The line shape of the Ir 4f core-level PES spectra shows a dramatic change across T MI , which may be associated with the variation of the Ir 5d electron states.

Spatially resolved valence band study of nanostructured carbon films containing transition metal nanocrystals

We studied the electronic structure of nanostructured C films produced by ultrasonic cluster beam deposition with the intention to find out the bonding configuration of the C network and to determine the modification induced by transition metal cluster inclusion in the film. Exploiting the energy and spatial resolution of the Spectromicroscopy beamline at Elettra Synchrotron, we were able to follow the valence band features depicted in 95.0 eV-excited photoemission spectra with a 0.5 μm lateral resolution. The spectroscopic results allowed to conclude that nanostructured C films have a mixed sp 2/sp 3 bond configuration and an amorphous-like structure and that those features are uniformly distributed in the film. The inclusion of metal cluster (Ni, Ti and Mo) in the film strongly modifies the valence band spectra. The surface stoichiometry of the embedded metal clusters and the keeping of their metallic nature are determined by a detailed analysis of the spatial dependence of the ultraviolet photoemission spectroscopy (UPS) spectra and by a comparison with previous studies on metal-carbide and -oxide surfaces.

Electronic Structure of Delafossite-Type Oxide PtCoO2 by Resonant-Photoemission Spectroscopy

The electronic structure of delafossite-type oxide PtCoO2 has been studied by resonant-photoemission spectroscopy (RPES). The density of state (DOS) at the Fermi level (EF) is not observed in the O 1s- and Co 2p-RPES spectra, and the photoemission spectroscopy (PES) spectrum measured at hv=190 eV, which corresponds to the cooper minimum of Pt 5d. The finite DOS at EF is observed in the PES spectra at lower photon energies, at which the ionization cross section of Pt 5d increases. These findings indicate that the Pt 5d is closely related with the low electrical resistivity of PtCoO2.

Electronic states and superconductivity in multilayer high-Tccuprates

We study electronic states of multilayer cuprates in the normal phases as functions of the number of ${\mathrm{CuO}}_{2}$ planes and the doping rate. The resonating valence bond wave function and the Gutzwiller approximation are used for a two-dimensional multilayer $t\ensuremath{-}{t}^{\ensuremath{'}}\ensuremath{-}{t}^{\ensuremath{''}}\ensuremath{-}J$ model. We calculate the electron-removal spectral functions at $(\ensuremath{\pi},0)$ in the ${\mathrm{CuO}}_{2}$ plane next to the surface to understand the angle-resolved photoemission spectroscopy (ARPES) spectra. We find that the trilayer spectrum is narrower than the bilayer spectrum but is wider than the monolayer spectrum. In the tri- and tetralayer systems, the outer ${\mathrm{CuO}}_{2}$ plane has different superconducting amplitude from the inner ${\mathrm{CuO}}_{2}$ plane, while each layer in the bilayer systems has same amplitude. The recent ARPES and NMR experiments are discussed in the light of the present theory.

Quasiparticle excitations in multi-layer cuprate superconductors

Quasiparticle excitations of multi-layer cuprates are studied in the normal phases. The electron-removal spectral functions at (π,0) in the CuO 2 planes nearest and second neighbor to the surface are calculated to understand the angle-resolved photoemission spectroscopy (ARPES) spectra. The resonating valence bond wave function and the Gutzwiller approximation are used for a two-dimensional multi-layer t– t ′– t″– J model. We find that the tri-layer spectrum is narrower than the bi-layer spectrum but is wider than the mono-layer spectrum. The recent ARPES experiments are discussed from the theoretical viewpoint.

Electronic structure studies of CeRhSb with Rh substituted by Pd and Ni

We have investigated the influence of the valence of Ce ions on the gap formation in CeRhSb-type Kondo insulators. We present the $3d$ x-ray photoemission spectroscopy (XPS) spectra for CeRhSb, ${\mathrm{CeRh}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}\mathrm{Sb},$ and ${\mathrm{CeRh}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{Sb}$ compounds. From the experimental Ce $3d$ XPS spectra we extracted the spectral weight of the different ${3d}^{9}{f}^{0},$ ${3d}^{9}{f}^{1},$ and ${3d}^{9}{f}^{2}$ final states. We used the Doniach-\ifmmode \check{S}\else \v{S}\fi{}unji\ifmmode \acute{c}\else \'{c}\fi{} method to separate the overlapping peaks in the $3d$ XPS spectra. Analysis of the ${3d}^{9}{f}^{2}$ weight using Gunnarsson-Sch\"onhammer theory suggests a hybridization interaction $\ensuremath{\Delta}$ of about 150 meV for CeRhSb. The hybridization energy $\ensuremath{\Delta}$ obtained for CeNiSb and CePdSb is $\ensuremath{\sim}3$ times smaller than that of the Kondo insulating compound CeRhSb. Analysis of the ${3d}^{9}{f}^{0}$ component indicates a mixed valence of Ce in CeRhSb, and a stable configuration of Ce in the Ni or Pd alloys. The experimental results indicate the influence of atomic disorder on the magnetic behavior of CePdSb and CeNiSb.

Magnetic and electronic nature of layered manganese oxysulfide Sr2CuMnO3S

We have synthesized and investigated the magnetic and electronic nature of layered manganese oxysulfide Sr2CuMnO3S which crystallizes in an unusual intergrowth structure with Cu2S2 and pyramidal MnO5 layers separated by Sr ions. A Cu 2p x-ray photoemission spectroscopy (XPS) spectrum of Sr2CuMnO3S indicates that the Cu ion is in the monovalent state, or Cu+. This feature of the Mn 2p XPS spectrum of Sr2CuMnO3S is similar to that of the parent compound La3+Mn3+O3 of colossal magnetoresistance materials. The MnO5 cluster model analysis suggests that the electronic nature of the pyramidal MnO5 layers belongs to a strongly correlated electron system, and the system is the so-called Mott insulator resulting from the strongly correlated electron nature. Magnetic susceptibility (χ) exhibits low-dimensional antiferromagnetic ordering of Mn3+ in pyramidal MnO5 layers. Fitting the χ data to Curie–Weiss law provides evidence of strong second neighbor Mn–Mn interaction.

Analysis of the electronic structure of zirconium hydride

The electronic structure of zirconium hydride was analyzed by a discrete-variational (DV)-Xα molecular orbital method. The density of states of zirconium hydride estimated by DV-Xα calculation agreed with X-ray photoemission spectroscopy spectra of zirconium hydride. The net charges of Zr atom and H atom were found to be small and independent of the hydrogen content. While the Zr–Zr bond order decreased with the hydrogen content, the Zr–H bond order was hardly affected by the hydrogen content. The mechanical properties such as elastic modulus were qualitatively discussed on the basis of the results for the molecular orbital calculation.

Electronic structure of thiophenes and phtalocyanines

The results of x-ray fluorescence measurements of thiophenes [regioregular poly 3-hexylthiophene (P3HT) and {alpha},{omega}-dihexylquaterthiophene (DH{alpha}4T)] and phtalocyanines [copper phtalocyanine (CuPc) and copper hexadecafluorophtalocyanine (F{sub 16}CuPc)] are presented. Experimental carbon, nitrogen, fluorine K{alpha} and sulphur, copper L{sub 2,3} x-ray emission spectra are compared with ultraviolet photoemission spectroscopy spectra and deMon density-functional theory calculations of model molecules. We find that the carbon K{alpha} emission is almost identical for P3HT and DH{alpha}4T. This indicates that the electronic structure of the {pi} system is not affected by the presence of the side group. The ratio of emission intensities of the Cu L{sub 2} to Cu L{sub 3} intensities is found to be smaller by a factor of 2 for CuPc and F{sub 16}CuPc than it is for pure metal. This demonstrates the strong covalency in phalocyanines.

Experimental and theoretical study of the electronic structures of Ni 3Al, Ni 3Ga, Ni 3In, and NiGa

The electronic structures of Ni 3Al, Ni 3Ga, Ni 3In, and NiGa are studied by resonant photoemission spectroscopy (RESPES) and X-ray absorption near-edge spectra (XANES) at the Ni L 2,3-edges. The RESPES spectra are explained with atomic multiplet model, and the XANES data are compared with those calculated with multiple-scattering theory. The number of 3d holes per Ni atom is calculated for Ni 3Al, Ni 3Ga, and Ni 3In.