Photoemission and the electronic structure of PuCoGa5

The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.     

Photoemission study of the electronic structure of Mn in Ag

The electronic structure of the (001) surfaces of Ag and two Ag–Mn alloys (5 and 10 at.% Mn) was studied using angle-resolved photoelectron spectroscopy with unpolarised HeI, NeI and ArI radiations. Compared to pure Ag, the alloy spectra are found to be broadened and the main features slightly (0.1 eV) shifted to higher binding energy as a result of adding Mn into Ag. In addition, there is an increase in intensity between Fermi level and top of the Ag 4d-band and significant changes in thed-band region. However, a well-defined Mn spin-up feature clearly separated from the top of Ag 4d-band is not seen in the alloy photoemission spectra. It is suggested that this is due to the strong hybridisation between the Mnd-states and Agd- andsp-states. Our results do not support the virtual bound state model for Mn in Ag for concentration range5 at.% Mn.     

Photoemission studies of the electronic structure of III–V semiconductor surfaces

The photoemission technique using synchroton radiation in the photon energy range 5–450 eV has been applied to the study of the electronic structure of some III–V semiconductor surfaces, prepared by cleavage in situ under ultrahigh vacuum conditions, ? 10^?11 Torr. For p-type GaAs(110), the Fermi level is pinned at the top of the valence band and thus no filled surface states extend into the band-gap. The situation is more complicated for n-type GaAs(110), where band bending easily can be introduced by extrinsic effects (impurities, cleavage quality, etc.) and push the Fermi level down to about midgap. Chemical shifts of inner core levels (3d for Ga and As) are used to obtain information on the bonding site of oxygen on the (110) surface. GaAs(110) can be exposed to atmospheric pressure of molecular oxygen without breaking the bonds between the surface atoms and the bulk. Oxygen is predominantly bonded to the As atoms on the surface. The oxidation behavior is strikingly different for GaSb(110) with formation of gallium and antimony oxides on the surface directly upon oxygen exposure. Heavier oxidation of GaAs(110) and breaking of the surface bonds will also be reported.     

Photoemission spectroscopy and electronic energy levels of CoS

Photoemission (XPS and UPS) and inverse photoemission spectra (BIS) of CoS have been measured. From these data the occupied and empty density of states of this material are deduced. The metallic nature of CoS is not caused by a breakdown of Mott-insulation but rather because of Co(d) - S(p) hybridization.     

Photoemission study of electronic structure evolution across the metal-insulator transition of heavily B-doped diamond

We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E_F) up to ∼5k_BT can be observed (k_B is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E_F. Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E_F, can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT.     

Photoemission from laser excited semiconductors: Dynamic response of the electronic structure in Si

Using angle-resolved photoemission in coincidence with a pulsed Nd:Yag laser beam (hν_L = 2.33 eV), we have studied the dynamic rearrangement of the electronic states in Si in the presence of a large number of electron hole pairs created by laser photon excitation. We observed considerable changes in the valence band structure, a renormalization of the bandgap, and a satellite peak in the 2p core level emission due to more effective core hole screening.     

The decay of93g Ru,93m Ru,91g Mo,91m Mo,91g Tc and91m Tc

Decay studies on a number of short-lived odd nuclei in theN=50 region are described. The 59.6-s ⁹³Ru ground state decay was studied in detail for the first time; in these experiments the 10.8-s activity^93m Ru was discovered. The⁹¹Tc activities were also observed for the first time. The ground state and an isomeric state of this nucleus decay with nearby equal half-lives (3.14 and 3.3-min). The activities^91g Mo (16.6-min) and^95m Mo (65.1-s) have been reinvestigated. A number ofγ-rays, previously erroneously assigned to the⁹¹Mo activities, could be eliminated. A strong similarity is noted for the decay schemes of theN=49 isotones^91m Mo and^93m Ru. The energy of the 1/2^? isomeric state in⁹³Ru and theB(M4)-value of the isomeric transition fit well into the systematics of the previously knownN=49 isotones.     

The geometrical structure, electronic structure and magnetism of bimetallic Au_nM_2 (n=1, 2; M=Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd) clusters

The geometrical structure, stability, magnetism, and electronic structure of bimetallic clusters AuM2 and Au2M2, where M are 4d transition metal elements, are investigated systematically by using the first-principles method based on density functional theory. The calculation results show that there is a large amount of low-energy isomers with the very similar structure. AuM2 and Au2M2 clusters display dramatic magnetism. The magnetic moment of the 4d element is either enhanced or weakened with respect to th...     

Photoemission spectroscopy investigation of the electronic structure of carbidic and graphitic carbon on Ni (111)

Photoemission measurements have been carried out on different forms of carbon deposits of catalytic importance on the (111) face of nickel, and give a picture of the electronic structure of “carbidic” and “graphitic” carbon.The photoemission spectra of graphitic overlayers strongly resemble spectra taken on graphite bulk samples but show an (almost) rigid shift of the levels with respect to the Fermi level.The results we obtain for carbidic carbon can be understood on the basis of recent surface electronic structure calculations. In particular a p-like state has been observed very near the Fermi level, which is probably responsible for the high chemical reactivity of carbidic carbon.     

The electronic structure of Cs adsorbed on Mo(111)

The main loss observed in an ELS study of Cs adsorbed on Mo(100) is described as an interband transition with initial and final states in the adsorbate. This interpretation is preferred to that involving the plasmon excitation mechanism observed for Cs on Cu(111) in the coverage range where the Cs has a metallic nature. The occurence of this transition is assumed to be related to the substrate effect.     

Photoemission and electronic structure of crystalline Co3B and amorphous Co - P - B

We present an XPS and UPS study of crystalline Co, Co₃B and Co₇₈P₁₄B₈ glassy metal. For Co₃B the electronic distribution curves (EDC) of the valence band and the previous specific heat and magnetic results are interpreted in a qualitative model where : i) the s-p cobalt-boron bonding states lie in the low part of the band, the upper levels being mainly cobalt d states and ii) a large density of states of the majority spin band is present at the Fermi level. For amorphous Co₇₈P₁₄B₈ the EDC shows that E_F is located in a high density of states region, it is suggested that the phosphorus p states ae centred at 7.5 eV. The photoemission and the magnetic results can be also interpreted in the framework of the previous model.     

Photoemission study of the electronic and chemical structure of amorphous CuxY100-x films

Valence band and core level photoelectron spectra are reported for clean Cu_xY_100-x amorphous thin films grown in situ by sputtering of targets with different stoichiometry. The density of occupied states of these amorphous metallic alloys is shown not to be a simple linear superposition of the constituent densities of states. Experimental evidence shows overlap of Cu and Y d bands with significant electron transfer from Y to Cu atoms which induce large bonding shifts, narrowing and intensity modifications of the valence band. The same conclusion is reached from the Cu core level shift and asymmetry. An estimation of the effective Coulomb interaction on Cu sites from Auger results is attempted.     

Increased rigidly triaxial deformations in neutron-rich Mo,Ru isotopes

Pairing-deformation-frequency self-consistent crankingWoods-Saxon model is employed to investigate the triaxiality in the ground states of the neutron-rich even-even Mo, Ru isotopes. Deformation evolutions and transition probabilities have been studied, giving the triaxial shapes in their ground states. The kinematic moments of inertia have been calculated to illustrate the gradually rigid deformation. To understand the origin of the asymmetry shape in this region, we analyze the evolution of single-particle orbits with changing γ deformation. The present calculations reveal the importance of the triaxial deformation in describing not only static property, but also rotational behaviors in this mass region, providing significant probes into the shell structure around.     

First-principles study of the electronic structure and magnetism of SrFe0.5Ru0.5O2

We study the electronic structures and magnetism of SrFe_0.5Ru_0.5O₂ by first-principles calculations in the framework of density functional theory (DFT) with generalized gradient approximation plus on site repulsion (GGA+U). The DFT calculations were carried out with ten kinds of Fe-site doping form. Calculations show that the d-orbital electronic configurations of Fe²⁺ and Ru²⁺ ions are (d_z²)²(d_yzd_xz)²(d_xy)²(d_x²_−y²)¹ and (d_z²)²(d_yzd_xz)³(d_xy)¹(d_x²_−y²) , respectively, which are independent of the doping form. The degenerated (d_xzd_yz) orbitals of Ru²⁺ ions are occupied by three electrons, so it gives rise to the Jahn–Teller distortion. The calculated magnetic moments of Fe²⁺ and Ru²⁺ ions are 3.7 μ_B and 1.6 μ_B, respectively. The exchange parameters including nearest neighbor (NN) ions and next nearest neighbor (NNN) ions are calculated by using Heisenberg model and the magnetic frustration in the ordered structure is explained by the competition of the exchange parameters. We also study the external pressure effect on the compound. A pressure-induced orthorhombic to tetragonal structure transition accompanied by an insulator to half-metal transition and an antiferromagnetic (or spin glass) to ferromagnetic state transition is observed.     

Hyperfine structure and nuclear moments of99Ru and101Ru

The atomic-beam magnetic-resonance method in combination with the triple resonance technique has been used to determine the nuclear magnetic dipole moments of⁹⁹Ru and¹⁰¹Ru. The moments are deduced fromrf transition measurements in the⁵F₅ and⁵F₄ states at magnetic fields between 770 and 2400 Oe. In order to reduce the part of the uncertainty of the moments which arises from the uncertainty of the hyperfine structure constants more precise values of the constants than those available up to now were determined from low field measurements. After making corrections for hyperfine and Zeeman interactions with neighbouring atomic states we obtain the following values for the magnetic dipole moments:μ ₉₉=?0.6381 (51)μ _N andμ ₁₀₁=?0.7152 (60)μ _N (uncorrected for diamagnetic shielding). The results of the present work combined with the results of an earlier hyperfine structure investigation in the⁵F multiplet are analysed with respect to the effective-operator formalism. From this analysis we obtain the following values for the electric quadrupole moments:Q ₉₉=0.076 (7) b andQ ₁₀₁=0.44 (4) b (uncorrected for Sternheimer shielding or antishielding).