High-resolution Photoemission Study Research Articles

A high-resolution photoemission study of confined metal systems on InAs(110)

Metal deposition on semiconductor substrates can give rise to various low-dimensional ordered structures. Their insulating or metallic character can depend on the spatial confinement and on the different atomic geometry. High-resolution and high-luminosity ultraviolet photoelectron spectroscopy is the best suited technique to follow the spectral density evolution of low-dimensional metallic systems deposited on narrow-gap semiconductors, in the energy gap region and close to the Fermi level. Simple metals, like alkali metals (Cs), produce one-dimensional insulating chains on InAs(110), while Bi builds up different symmetry structures with insulating [(1×1)] or metallic [(1×2)] character, and Ag presents an insulator-to-metal transition as a function of coverage. Moreover, high-resolution photoemission brings to light clear two-dimensional quantized eigenstates due to the quantum confinement of accumulated electron charge within the InAs conduction band, induced by InAs surface modifications.

High-resolution temperature-dependent photoemission study of metal–insulator transition of Y 1− xCa xTiO 3

Temperature-dependent high-resolution photoemission spectroscopy has been performed on Y 1− x Ca x TiO 3 ( x=0.37, 0.39, and 0.41) single crystals. Ti 3d photoemission spectra have an incoherent part, indicating electrons in the Ti 3d bands are strongly correlated. Although the temperature dependence of the incoherent part at 150 K for the present samples is continuous and nearly the same, the spectral intensity near E F of the x=0.39 composition clearly shows the metal–insulator transition at ∼150 K, indicating the importance of the carrier density in the Ti 3d bands.

High-resolution resonant photoemission study of CeRu 2

High-resolution Ce 3d–4f resonant photoemission studies have been performed for a valence-fluctuating CeRu 2. The bulk-sensitive Ce 3d–4f resonance spectrum near the Fermi level shows a band character of the 4f state of CeRu 2 beyond a framework of the single impurity model. We also show that the Ru 4d spectral line shape of CeRu 2 is different from that of LaRu 2 due to a strong Ru4d–Ce4f hybridization.

High-resolution photoemission study of ethanol on Si(100)2×1

The adsorption of ethanol on Si(100)2×1 has been investigated at room temperature by high-resolution synchrotron radiation photoemission, and a consistent picture has been obtained in favour of dissociative adsorption, from a comparison of the valence band for pure and adsorbed ethanol, which shows the disappearance of σ OH orbital after adsorption, and from the identification of a SiO-related component in the Si 2p core spectrum. A line-shape analysis of the Si 2p complex envelope corresponding to different ethanol exposures identifies a second component, which grows with the exposure at a different rate, and is assigned to SiH bond. The values for relative quantitative ratios among the various components suggest an exposure-dependent adsorption mechanism for ethanol, characterized by the formation of stable SiO bonds and a high hydrogen surface mobility. The analysis of the C 1s photoemission core-line suggests that no CO bond rupture occurs, at variance with our previous findings for ethanol adsorption on Si(111)7×7.

Femtosecond two-photon photoemission studies of image-potential states

High-resolution two-photon photoemission studies with femtosecond time resolution permit the accurate determination of decay and dephasing processes for image-potential states. The influence of adsorbates on the respective inelastic and quasielastic scattering processes is investigated for Cu on Cu(100) and Cu(111). The results are discussed in relation to previous work for CO on Cu(100).

High-resolution photoemission study of the Ȳ surface state on Ag(110)

We report a high-resolution study of the ‘Shockley-type’ occupied surface state residing in the projected L 2′–L 1 gap around the Ȳ point of the surface Brillouin zone. Along ΓY on Ag(110) this band shows a parabolic dispersion with k ‖, the surface wave vector. The effective mass is m ∗/ m=0.26±0.02 and the bottom of the parabola at Ȳ shows a linear dependence on sample temperature according to E 0=−(106±5)meV+(0.17±0.01 meV/K) T. In consequence, the surface band gets empty above T=624±37 K. These numbers give a quantitative interpretation of strong temperature effects observed earlier by other authors in second-harmonic spectra from Ag(110), where the fundamental light couples the occupied surface state to an unoccupied surface state within the same projected gap. From our data we derive a more precise value of its bottom energy E f=1.66±0.02 eV above E F at Ȳ.

Many-Body Effects in Angle-Resolved Photoemission: Quasiparticle Energy and Lifetime of a Mo(110) Surface State

In a high-resolution photoemission study of a Mo(110) surface state various contributions to the measured width and energy of the quasiparticle peak are investigated. Electron-phonon coupling, electron-electron interactions, and scattering from defects are all identified mechanisms responsible for the finite lifetime of a valence photohole. The electron-phonon induced mass enhancement and rapid change of the photohole lifetime near the Fermi level are observed for the first time.

Temperature-dependent high-resolution photoemission study of the Kondo insulator Ce3Bi4Pt3

Abstract Temperature-dependent high-resolution photoemission spectroscopy was performed on the Kondo insulator Ce3Bi4Pt3. The spectral weight near the Fermi level (EF) is reduced as temperature decreases, especially below ∼100 K. The temperature-dependence of the Ce 4f states was obtained by taking the difference between the He II and He I spectra. The Ce 4f spectrum near EF at 6 K shows a clear dip structure, indicating the opening of a (pseudo)gap at low temperature.

The symmetry of the order parameter in highly overdoped Bi 2Sr 2CaCu 2O 8+ x

We report results of an angle-resolved high-resolution photoemission study of strongly overdoped Bi 2Sr 2CaCu 2O 8+ x single crystals with T c∼60 K. We find a nonzero superconducting (SC) gap along all three high symmetry directions in the Brillouin zone, in contrast with a d-wave scenario of high temperature superconductivity. Our data indicate that both the maximum gap value and the gap anisotropy decrease with overdoping.

High-resolution angle-resolved photoemission study of the heavy-fermion superconductorUPt3

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High-resolution photoemission studies at rough Cu(111) surfaces: The influence of defect scattering and disorder-dependent dephasing processes

We report high-resolution angle-resolved photoelectron spectra for both bulk and surface state emission from disordered Cu(111) surfaces. The surface disorder was induced by homoepitaxy of Cu on Cu(111) at 110 K and subsequent annealing to 290 K. Surface disorder was quantitatively analysed by spot-profile analysis of diffracted low-energy electrons (SPALEED). We are able to correlate emission linewidths and intensities with morphological parameters and present an interpretation in terms of dephasing processes and defect scattering of the photoelectrons.

High-resolution angle-resolved photoemission study of RSb (R=La, Ce, U)

High-resolution angle-resolved photoemission spectroscopy has been performed on isostructural RSbs (R=La, Ce, U) to study the electronic band structure near the Fermi level as well as the Fermi-surface topology. We found that USb has a metallic band structure in contrast with semimetallic LaSb and CeSb.

Cluster-Substrate Interaction on a Femtosecond Time Scale Revealed by a High-Resolution Photoemission Study of the Fermi-Level Onset

We have measured ultraviolet photoemission spectra of quasi-size-selected silver clusters at T ­ 40 K grown in the nanopits of a graphite surface. The Fermi-level onset observed shows distinct deviations from the steplike shape typical for metals. A simple model that takes into account the finite lifetime of the photohole (corresponding to a charged cluster) can explain these deviations by the clustersubstrate interaction on a femtosecond time scale, and hence provide an explanation for the differences between photoemission spectra of free and deposited clusters in general. [S0031-9007(98)07729-1]

High-resolution angle-resolved photoemission study of LaSb

High-resolution angle-resolved photoemission study of LaSb

Doping Dependent Density of States and Pseudogap Behavior inLa2−xSrxCuO4

We have made a high-resolution photoemission study of La2-xSrxCuO4 in a wide hole concentration (x) range from a heavily overdoped metal to an undoped insulator. As x decreases, the spectral density of states at the chemical potential (\mu) is suppressed with an x-dependence similar to the suppression of the electronic specific heat coefficient. In the underdoped region, the spectra show a pseudogap structure on the energy scale of 0.1 eV. The width of the pseudogap increases with decreasing x following the x-dependence of the characteristic temperatures of the magnetic susceptibility and the Hall coefficient.

A high-resolution photoemission study of ethanol adsorption on Si(111)-(7×7)

Ethanol adsorption on Si(111)-(7×7) has been investigated by high-resolution photoemission in the valence band and the Si 2p and C 1s energy regions. The valence band spectra show that, similarly to methanol adsorption on Si(111)-(7×7), ethanol adsorption is dissociative and occurs through O–H bond breakage and Si–O bond formation. However, at variance with a previous study, we find that the adsorption does not proceed selectively on surface rest atoms. The lack of site selectivity is also confirmed by the photoemission spectra of the Si 2p core level line. The possibility of a further fragmentation of the ethoxy species into a methoxy plus a methyl group is discussed.

Valence-band photoemission study of single crystalline CeNiSn

The electronic structure of single crystalline CeNiSn has been investigated using photoemission spectroscopy. The extracted Ce 4f spectrum exhibits three peak structures; the typical Fermi level and 2 eV peaks, and another between them, {approximately}0.9 eV below the Fermi level E{sub F}. The near-E{sub F} peak reflects a substantial Ce 4f-Sn sp hybridization, whereas the 0.9 eV peak arises from the Ce 4f-Ni 3d and Ce 5d-Ni 3d hybridization. A Ni 3d satellite feature is observed about 6 eV below the Ni 3d main band, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The high-resolution photoemission study indicates a finite metallic density of states at E{sub F}, implying a semimetallic ground state. The electronic states near E{sub F} are found to have mixed character from the Sn sp, Ce 5d, Ce 4f, and Ni 3d electrons. Constant-initial-state and constant-final-state yield spectra across the 4d{r_arrow}4f threshold indicate the Ce valence to be close to 3+. {copyright} {ital 1998} {ital The American Physical Society}

Quantum well states in high-quality Cu films deposited on Co (100): A high resolution photoemission study

Quantum well (QW) states of thin Cu films deposited on Co (100) are studied using high resolution photoemission. In order to obtain a smooth Co–Cu interface, Cu films were prepared by evaporating the interfacial layer at 100 K. This allows us to obtain better defined QW features at the valence band. Furthermore, following this preparation method we are able to observe for the first time QW states at the neck of the Cu Fermi surface, which are not observable when the interfacial layer is deposited at 300 K. Using these high-quality films we also study final-state-related oscillations in the intensity of the photoemission spectra as well as the lifetime broadening of the QW states.

High-resolution resonant photoemission study of the 4f states in a typical Kondo system: CePd

We exploited resonant photoemission at the Ce \(4d \to 4f\) absorption edge to investigate the Ce 4f states in3. High resolution spectra reveal, near the Fermi level, the characteristic fine structure of intermediate valence Ce compounds. The spectral lineshape is consistent with the typical “Kondo” character of CePd, but the prominent \(({f^0})\) ionization peak is found at the unusually low binding energy of 1 eV. We briefly discuss the implications of these observations.

High-resolution angle-resolved photoemission study of CeSb and USb

Abstract High-resolution angle-resolved photoemission spectroscopy (HR-ARPES) has been performed on isostructural CeSb and USb to study the electronic structure near the Fermi level (E F ). In CeSb, we observed the hole and electron pockets at the Brillouin-zone (BZ) center and boundary, respectively, as well as the systematic change of the volume upon the temperature-dependent magnetic phase transition ( T N =16 K). The experimental result suggests that the p–f mixing plays an essential role in characterizing the magnetic property of semimetallic CeSb. In USb, on the other hand, we found a large electron pocket at the BZ center consisting of U 6d states and two almost dispersionless U 5f bands just below E F . This illustrates a clear difference in the electronic structure between Ce and U monopnictides as well as the character between 4f and 5f electrons.