On the electronic density of states of the transition metals

XIS measurements of the elements Ir, Pt and Au are reported. High precision and reproducibility is obtained by the application of a “π/2-method” which approximates a Bragg angle of 90° at the dispersing crystal. Theoretical densities of states exist for Pt and Au. The agreement with the measured isochromats is good. A rigid-band model for Ir, Pt, and Au is ruled out by the measurements. Rather they suggest (combined with results of photoemission experiments) a narrowing of thed-bands from Ir through Pt to Au. Moreover, thed-band of Ir lies relative to thesp-band at a lower energy than thed-bands of Pt and Au. A fitting parameter concerning the experimental resolution is explained and considered as a possible indication of localization for XIS.     

Effect of pressure on superconductivity in transition metal alloys

Measurements on twelve alloys of the series Zr-Nb-Mo show a close correlation ofdT _c /dp with thed-band structure of these alloys and suggest that thed-band is virtually rigid with respect to pressure. The results are not compatible with an empirical observation of McMillan thatT _c is governed only by a phonon factor Mω ².     

Trends in the density of states of hydrogen chemisorbed on the transition metal series

Extensive many-body calculations of the ground state properties of hydrogen chemisorbed on all 3d, 4d and 5d transition metal surfaces are performed. The trends of the location E_p of the discrete level under the bottom of the d-band are presented. It is found that, on going to the right of the series, E_p approaches the bottom of the d-band, eventually merges in it and detaches again from it for the last elements of the series.     

Hydrogen-induced states in VHx and VDx observed by soft X-ray emission spectroscopy

From measurements of soft X-ray emission spectra (V-L₃) of VH_x and VD_x, a gradual change of d-band of V metal with addition of H(D), and an appearance of H(D)-induced states immediately below the d-band, are clearly demonstrated. The states, located at 7 eV below the Fermi energy for all compositions, are interpreted as being bonding states formed by H(D)-1s and V-3d orbitals. No isotope effects were detected within the accuracy of the experiment.     

Optische Messung der Elektronenstoß-Anregung von Xenon und molekularem Stickstoff im Schwellenbereich mit hoher Energieauflösung

Relative optical excitation functions of Xe and N₂ have been measured in the threshold region. The inciting electron beam had a FWHM of 50 meV. The threshold behaviour of the excitation functions ofp-levels of Xenon is strongly influenced by resonances. The onset is step-like, in some cases resonance structure is to be seen just above threshold. In some excitation functions resonance structure is found immediatly above the ionization limit. This is believed to be caused by two compound states the parent states of which could be the 6d′ and the 8s′ autoionizing state of Xenon. In nitrogen, the excitation functions of two bands of the second positive group have been measured (3371 and 3755 Å), the upper levels of which are thev=0 and thev=1 levels of theC ³Π _u state. The excitation raises linear from threshold. In the 3371 Å excitation function a resonance maximum at 11.50 eV is observed, where the cross section is increased due to resonance population by about 100%, as measured with a FWHM of 50meV of the electron beam. The broad absolute maximums of the excitation functions are found to lie at 14.0±0.1 eV in the case of the 3371 Å- and at 14.3±0.1 eV in the 3755 Å-band.     

Surface photoemission in the 4d band from polycrystalline silver surfaces

Surface induced local d-band states in the upper 4d band between ～ 4 and ～ 5.2 eV below E_Fermi have been identified for polycrystalline silver films in photoemission experiments using synchroton radiation. A thin over-coat (10 å) by an Al film leads to a depression of these surface induced local states whereas a change from s- to p-polarized excitation leads to an enhancement. Deposition of additional silver (～ 3 Å) at 120 K induces additional emission 4.2 eV below E_F with a FWHM of only ～ 0.4 eV.     

A conceptual model for surface states and catalysis ond-band perovskites

This paper proposes a conceptual model to describe symmetry factors believed to be most important in catalyzing a reaction on a transition metal oxide. An hypothetical situation is constructed from a model reaction, the dimerization of ethylene to form cyclobutane, and a model perovskite, SrTiO₃. A detailed review is given of the symmetry imposed energy barrier for the gas phase reaction. Then it is shown how thed _xy, d_xz, d_yz atomic orbitals have the symmetry required to reduce this energy barrier when a transition metal atom is included in the reaction. It is also shown how the evergy barrier reduction depends upon the electronic occupation of thed orbitals and upon the relative energies of thed orbitals involved in the reaction. Using SrTiO₃ as an example, it is shown that the perovskites possess highly localized, atomic-liked surface states of the required symmetry. Two semiquantitative examples are developed for the catalyzed dimerization of ethylene on the (100) surface of SrTiO₃. A preliminary discussion is given of the role played by surface potentials in promoting the reaction.     

Optical absorption and electronic structure of intermetallic compound RuIn3

The optical properties of intermetallide RuIn₃ are investigated by ellipsometry in the spectral range of 0.22–10 μm. The experimental data point to the existence of an energy gap of about 0.5 eV in the electronic spectrum of the compound. The density of the electron states and interband optical conductivity are calculated in terms of the density functional theory. The experimental and theoretical spectra of the optical conductivity are compared. It is found that the formation of basic absorption bands is caused by interband transitions of electrons of the d-band of Ru and p-band of In.     

First principles investigations of hydrazine adsorption conformations on Ni(111) surface

Theoretical investigation on hydrazine (N₂H₄) adsorption on Ni(111) was done by using density functional theory. Stability and mechanism of hydrazine adsorption in anti, gauche and cis conformation on nickel surface were studied. Charge transfer between lone-pair orbital and d-band was found to stabilize the anti-conformation as the most stable conformation, in contrast with hydrazine in the gas-phase where gauche conformation is more favored. However, the derived anti-bonding state between adsorbate and substrate is partially occupied due to the spin-polarization in the local states near the Fermi level and thus contributes in weakening the bonding. The stable adsorption structure was further verified by comparing the calculated vibrational frequencies with HREELS measurement results. The results were found to be in agreement with experimental results. It was also found that the adsorption in cis-conformation is a transition state as evident from the existence of imaginary frequency on its lowest vibrational mode which belongs to NH₂ torsional movement around N–N axis.     

Stark effect,hyperfine structure and isotope shifts in highly excited states of BaI and CaI

The electric dipole polarizabilities of 9 even-parity barium states (6s8s ¹ S ₀,³ S ₁; 6s7d ¹ D ₂,³ D _1,2; 5d7s ¹ D ₂ and 6p ^{2 3} P _0,1,2) in the interval 33,800–35,800 cm^?1 have been measured with high resolution laser-atomic-beam spectroscopy. Simultaneously, values of isotope shifts and hyperfine coupling constants for theJ=1 states have been obtained. Comparison of the experimental polarizabilities with calculated values as well as inspection of the data on isotope shifts and hyperfine structure from the present and earlier work strongly suggests erroneous assignments of theJ=2 states, with an exception for the 5d 7s ¹ D ₂ state. The influence of an electric field on the 3d ^{2 3} P _0,1,2 states of calcium has also been studied. A marked departure from a quadratic Stark effect has been observed at relatively small field strengths. This can be attributed to the large polarizabilities of neighbouring Rydberg states. The low field data allow the determination of admixtures of Rydberg states into the 3d ^{2 3} P-states as small as 0.02%.     

Application of X-ray photoelectron spectroscopy to characterization of Au nanoparticles formed by ion implantation into SiO2

In X-ray photoelectron spectroscopy (XPS) of Au nanoparticles, the width of 5d valence band changes with Au particle size. This enables us to estimate the size of Au nanoparticles by using XPS. In this work, the 5d-band width has been measured for Au nanoparticles formed by ion implantation into SiO₂. The 5d-band width is found to be correlated strongly with the Au concentration. As the Au concentration increases, the 5d-band width becomes larger, indicating that the Au nanoparticles with the larger size tend to be formed in the vicinity of the projected range of Au ions. This correlation agrees very well with the results from transmission electron microscopy.     

Appearance potential spectroscopy of CuZr and CuTi metallic glasses

The local density of empty electronic states at the Cu sites in CuZr and CuTi has been derived from soft X-ray appearance potential spectroscopy (SXAPS) on glassy Cu₆₀Zr₄₀ and Cu₄₀Ti₆₀ samples. An energetically narrow d-like density of states is found just above the Fermi level. Results are discussed in terms of d-band hybridization.     

Surface enhanced covalency and its effect on the surface states ofd-band metal oxides

The effect of electron-electron interactions on the surface states of ionicd-band oxides is reported. The local density of states of surface cations in the valence band region is significantly increased when surface states occur in the band gap. Coulomb repulsion associated with thissurface enhanced covalency tends to force surface states out of the band gap. These results suggest an explanation of recent experiments on SrTiO₃ and TiO₂.     

Surface effects in the valence band XPS spectrum of copper

Comparison of valence band XPS spectra of Cu samples with theoretical density of states shows a high intensity near the upper edge of the d-band. This is a feature common for most d-band metals. However, if the difference in the density of states of the first two atomic layers with respect to the bulk is taken into account, good agreement between theory and experiment is found.     

Virtual bound states of Pd in Cu,Ag and Au and of Pt in Ag

The positions and widths of the virtual bound states of 5 and 10% Pd in Cu, Ag and Au and of 5 and 10% Pt in Ag have been measured by XPS. The spin—orbit splitting of the Pt state in Ag is reduced from the theoretical value, but comparable to the spectroscopic atomic value. The host lattice d-band structure is perturbed in the alloys.     

Rotational band crossings in the actinides

In the actinides bothi _13/2 protons andj _15/2 neutrons are close to the Fermi surface. At rapid rotation these high-j particles will unpair and align their orbital angular momentum along the axis of rotation giving rise tos-bands that cross the ground-state band. Coulomb excitation of the odd nuclei ₂₃₇ ⁹³ Np (established up to the 45/2⁺ state) and ₂₃₅ ⁹² U (established up to the 51/2^? state) provides specific information about these band crossings: From the saturating alignment of the odd high-j particle in both nuclei at intermediate rotational frequencies we find the aligned angular momentum of thei _13/2 protons-band to be 6.6? while the corresponding value for thej _15/2 neutrons-band is 5.5?. At more rapid rotation above ?ω=0.18 MeV we observe additional alignment in²³⁵U. This is ascribed to the interaction of the protons-band. From the gradual onset of the additional alignment we deduce that forZ=92 the protons-band interacts strongly with the ground-state band and from a comparison of the actual amount of alignment with the full value of 6.6? we estimate the crossing to occur around ?gw _c ^p =0.25 MeV.     

The deformation of the ground and excited states in the Ag and Sn nuclei

The microscopic calculation of the potential energies in the ground and excited states of Ag and Sn nuclei has been performed. The single particle Nilsson potential and the shell correction Strutinski method have been used. The weak sensitivness to nonaxial deformation has been found for even neighbours of these nuclei. The small tendency towards prolate deformation of the ground and excited one-quasiparticle states originating from theg _9/2 proton subshell in^101–105Ag odd isotopes has been noticed. The behaviour with quadrupole e and hexadecapole ε₄ deformation of the ground and two-quasiparticle excited 0⁺ states originating from thed _5/2,g _9/2 andg _7/2 proton subshells andh _11/2 neutron subshell in^112–118Sn has been investigated. The small quadrupole deformation of the excited 0⁺ states has been found what is in agreement with the experimental data concerning the rotational bands build on the first excited 0⁺ states in Sn isotopes.     

Oxygen chemisorbed on Cu(001): The Cu3d−O2p interaction studied by angular-resolved photoemission using synchrotron radiation

Angular-resolved photoemission measurements have been performed on a Cu(001) surface with and without a c(2 × 2) oxygen overlayer in the photon-energy range 40–170 eV. The relative peak positions in spectra obtained from the clean surface at various emission parameters as to direction and energy are well predicted by a simple direct-transition model, with different spectra thus corresponding to specific high-symmetry points in the 3D Brillouin zone. Photoelectron emission from the Cu3d-derived states near some of these high symmetry points, especially those near W and K, are strongly affected by the chemisorption. The results further show an oxygen-induced structure in the d-band region near X not previously observed.     

Magnetic dipole moments of excited states of105Pd and other spectroscopic investigations in the decay of105g Ag

The IPAC-method has been used with the external magnetic field of 9.0 T of a split coil superconducting magnet and with the internal field of PdFe for a measurement of magnetic moments of¹⁰⁵Pd states populated in the decay of 41.29d¹⁰⁵Ag. The results are:μ _7/2 (645 keV)=?1.49(9) nmμ _5/2 (319 keV)=+0.95(20) nmμ _3/2 (280keV)=?0.074(13) nm. The half-life of the 645 keV state has been redetermined by use of cooled thallium free Nal detectors asT _1/2 (645 keV)=126(2) ps. γ-γ directional correlations were measured with a system of three large Ge planar diodes for the cascades 443–645 keV, 332–319 keV, 393–280 keV, and 64–280 keV and analyzed in terms of dipole quadrupole mixing ratios of theγ-lines involved. The spin of the 673 keV state was derived as l/2⁺.     

New aspects of the rotational model in25Mg

Spin assignments have been made to the²⁵Mg levels in theE _x=5–6 MeV region fromγ-ray angular distributions measured in the²²Ne(α, n y) reaction atE _α=8.0 and 8.8 MeV and fromp-γ angular correlations measured in the²⁴Mg(d, p γ) reaction atE _d=6 MeV. Unique spin assignments ofJ=7/2, 5/2, 5/2, and 9/2 could be made to the levels atE _x=5005, 5511, 5851, and 5967 keV, respectively. Ambigious assignments have been made to the levels atE _x=5245, 5524, 5785, 6032 keV (J=11/2, 7/2), 5455 keVJ=13/2, 9/2), and 5738 keV (J=3/2, 5/2). The present data confirm previous assignments ofJ=1/2 to the levels atE _x=5108 and 5466 keV, respectively. Lifetime estimates have been obtained, using the Doppler-shift attenuation method, for the levels atE _x=5245 keV (τ=30–60 fs), 5785 keV (τ=50–100 fs), 5967 keV (τ=50–100 fs), and 5455 keV (τ>1ps). All other levels in theE _x=5–6 MeV region haveτ<60 fs. A breakdown of theK-selection rule has been observed in theγ-decay of some high spin states, indicating a deviation from the strong coupling model.