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.     

Core hole satellites in Ni and Au Ni

The 2p core hole satellite structure in Ni and 5% Ni in Au are compared and discussed in terms of recent theoretical models. The large differences found for these two materials are explained in terms of the large differences in the Ni 3d band, and virtual bound state widths. The satellite structure for Au Ni is found to agree with the multiplet splitting of the free atom in a 2p⁵3d⁹ configuration.     

Proprietes optiques et structure electronique de MnAu2

The optical spectrum of the helical antiferromagnetic compound MnAu₂(t_N = 90°C) has been measured, using a scanning ellipsometric method, in UHV, between 0.47 and 5.7 eV, at temperatures ranging from 88 to 700 K. Below 0.6 eV the experimental data can be fitted to a Drude-like intraband model. The maximum of the interband absorption occurs at 5.1 eV, while the onset of interband absorption may be placed at 0?.4eV as is suggested by the rapid rise of $\text{ε}{}_2\text{(ω)}\text{λ}$. below 0.5 eV. In the absence of theoretical work, the analysis of the optical spectrum leads to a preliminary rough model of the electronic structure; the proposed local density of d states is represented. The 5.1eV peak is attributed to d → E_F transitions (parabolic edge at 2.7 eV similar to Au), originating in the lower part of the band, associated mainly with Au sites. To account for the moment $\text{(}\text{3.6μ}{}_{\mathrm{S}}\text{at Mn}\text{)}$, the upper d band (mainly Mn sites) is split: the d↑ band is below E_F (interband edge at 0.4eV), while the d↓ band contains 1.4 electrons. ESCA measurements tend to confirm this model. An important unusual fact is the sharp anomaly of /~ε(ω) in the infrared, around T_N; attempts to correlate this with magnetic (s-d) interactions have been initiated.     

197Au Mössbauer effect studies on ternary alloys of gold with main-group metals

¹⁹⁷Au Mössbauer effect studies in the ternary gold alloys Li₂AuX (X = Ga, In, Tl; Ge, Sn, Pb; Bi) and Li₂Au_2?xIn_x (1.0 ? x ? 1.75), all of which crystallize in the cubic NaTl structure, have been performed at 4.2 K. The isomer shifts derived from the single-line spectra have been correlated with the average Allred-Rochow electronegativity of the first three coordination spheres around the gold atoms, normalized to the number of outer electrons and corrected for the distance from the gold atom. The isomer shifts have also been correlated with structural data from X-ray diffraction studies. Results of Dirac-Fock atomic structure calculations have been taken into account in discussing the possible valence electron configurations of gold. It is suggested that substantial 5d-6s mixing occurs with nearly matching charge compensation and additional 5d depletion through an interaction of the 5d band of gold with host orbitals of proper symmetry. A net charge flow off the gold sites appears in every case.     

Infrared reflection absorption spectra of Fe(CO)5 adsorbed on Au surfaces

Infrared reflection absorption spectroscopy (IRAS) shows that the CO stretching bands of Fe(CO)₅ adsorbed on Au surfaces are significantly different in band shape as well as in frequency from the bands observed in a transmission mode. This difference has been observed for other metal substrates and explained in terms of the anomalous dispersion of the refractive index in the region of the observed bands. The refractive indices of Fe(CO)₅ are calculated using the Kramers-Kronig relation from the transmission spectra of Fe(CO)₅ adsorbed on a sapphire plate, an SiO₂-coated sapphire plate, and an Au film evaporated on a sapphire plate, and the IRA spectra of Fe(CO)₅ adsorbed on Au are calculated using Fresnel's formula. The results show that the ν₁₀ band of Fe(CO)₅ becomes very sharp and shifts to higher frequencies by more than 10 cm⁻¹, while the ν₆ band becomes a shoulder of the v₁₀ band, in good agreement with the observed IRA spectra. The IRAS calculation also shows that the weak band observed at 2114 cm⁻¹ for the Au film remains unchanged in position, in agreement with the observed IRAS.     

A one parameter model potential for noble metals

A phenomenological one parameter model potential which includes s-d hybridization and core-core exchange contributions is proposed for noble metals. A number of interesting properties like liquid metal resistivities, band gaps, thermoeletric powers and ion-ion interaction potentials are calculated for Cu, Ag and Au. The results obtained are in better agreement with experiment than the ones predicted by the other model potentials in the literature.     

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.     

Densities of states of some f.c.c. noble and transition metals

X-ray photoemission spectra of the d-bands of Cu, Ag, Au, Rh, and Pd are compared with corresponding U.V. photoemission data and with APW band structure calculations. It is found that there is a reasonable correspondence between the two experimental techniques, as well as between theory and experiment.     

Study of energy-band structures,some thermomechanical properties and chemical bonding for a number of refractory metal carbides by the LMTO-ASA method

The energy-band structures of V, Nb, VC, NbC and WC have been calculated with the use of the linearized method of “muffin-tin” orbitals (LMTO-ASA). The calculated band structures are in good agreement with a previous self-consistent APW calculation. The prominent features of the band structures for WC are a particularly wide 5d W, 2p C band, and also the presence of a separate 5d W band below the Fermi level. The values of the lattice constants, bulk moduli, sound velocities, Debye temperatures and melting temperatures have been calculated and are in reasonable agreement with experiment. It is shown that the high values of the bulk moduli of VC and NbC are explained by the hybridization between s- and p-metal states and 2s C, 2p C states, while the extreme value of the modulus for WC is due mainly to the covalency resulting from 5d W, 2s C and 2p C hybridization.     

Structure electronique des oxydes de cobalt CoO et Co3O4

The total density of occupied states in the valence band of CoO and Co₃O₄ is determined by XPS and UPS. From variations of excitation probability of the bands, the 4 e V wide O2_p band is shown to be located around 5 eV for both oxides, while structures obtained from photoionisation of the localized 3d band spread over 10 eV range below the Fermi level overlapping with O2_p band. The 3d peaks located at binding energy <3 eV correspond to the calculated energy of the d_n ?1 manifold final state in the octahedral and tetrahedral crystal field of CoO and Co₃O₄. The 3d levels at higher binding energy are shown to occur from configuration interaction in both final and initial states. These last peaks are higher in intensity for CoO relative to Co₃O₄. A superior limit for the width of the 3d initial band in a one electron energy diagram is given to be <3 eV. This value associated to the Coulomb correlation energy measured equal to ~3 eV. This value associated to the Coulomb correlation energy measured equal to ~3 eV from shake-up and Auger energy confirms the Mott insulator nature of CoO.     

Cells anchored upon a thin organic film with different nano-mechanical properties

By applying dynamic contact module and particular measurement of phase angles, harmonic contact stiffness (S) along with the measured displacement (D) of different self-assembled monolayers (SAMs) adsorbed on Au can be distinguished. The relatively ordered and hydrophobic ODT and DDT molecules adsorbed on Au form high contact stiffness, which are presumably unfavorable substrates for a cell to adhere upon. Short-chain MUA molecules adsorbed on Au provides a hydrophilic characteristic with a relatively low contact stiffness, which may significantly promote cell adhesion. It is, therefore, estimated that the behavior of a cell adhered on SAMs/Au is correlated not only with their outermost chemical species but also with a proper dS/dD matrix acting as a cushion.     

Magnetic order effect on optical absorption and photoconductivity in EuO thin films

The comparison of optical absorption with photoconductivity with left and right circularly polarized light versus temperature, shows similar behaviours. The transition responsible for photoconductivity has been assigned to a 4f-5d transition. Arguments are proposed to explain the relation between absorption which occurs between the 4f correlated levels and the 5d levels more delocalized and photoconductivity which has the same optical cause but whose electron is delocalized in a conduction band.     

Band conduction effects in the ESR spectra of semiconducting Na0.01V2O5

We report on the temperature- and orientation dependence of the ESR linewidth of d-electrons in semiconducting Na_0.01V₂O₅. The observed line narrowing results from hopping of the d-electrons between localized states. At higher temperatures a line broadening occurs which is due to excitation of the d-electrons into a conduction band. The corresponding activation energies, determined from ESR measurements, agree with values derived from electronic conductivity.     

Electron capture decay of 51 min191Hg

The decay¹⁹¹Hg→¹⁹¹Au was investigated by measuring γ-ray spectra, conversion electron spectra, and coincidence spectra, as well as lifetimes in the second region. The parent isotope¹⁹¹Hg was produced by the reaction¹⁹⁷Au (d, 8n) withE _d =80 MeV. About 80 γ-transitions of this decay were observed. Multipolarities of the more intense transitions were determined. An isomeric state of 0.92±0.11 s half-life was found in¹⁹¹Au. A level scheme for¹⁹¹Au is suggested. The measured γ-transitions are attributed to the decay of a 13/2⁺ isomeric state of¹⁹¹Hg; its half-life was found to be 50.8 ±1.5 min. The core excitation model was used to discuss some features of the level structure in¹⁹¹Au.     

Quasielastic transfer reactions in 238U + 197Au and 197Au + 197Au collisions near the Coulomb barrier

Differential cross sections as a function of cm angle were measured for 1n- and 2n-transfer reactions in ²³⁸U + ¹⁹⁷ Au and¹⁹⁷ Au + ¹⁹⁷ Au collisions in the energy range from 0.881 V_c to 1.093 V_c and 0.825 V_c to 0.964 V_c, respectively. For ¹⁹⁸Au and ¹⁹⁹Au from the ²³⁸U + ¹⁹⁷Au collisions, for reduced distances of closest approach d _o 1.55 fm, the angular distributions at all bombarding energies are well described by the semiclassical theory. Equivalently, the transfer probabilities show the expected exponential decrease with increasing d _o over many orders of magnitude. For all other transfer products from ²³⁸U + ¹⁹⁷Au collisions, and for all transfer products from ¹⁹⁷Au + ¹⁹⁷Au collisions, markedly reduced cross sections relative to the semiclassical theory are observed for central collisions at all bombarding energies, even for values of d _o that are well outside the region where absorption is known to set in. Only for the more peripheral collisions, one observes agreement of the angular distributions (transfer probabilities) with the semiclassical expectations. The deviations for central collisions are absent for reactions with positive Q _gg values and scale roughly with increasingly negative values of Q _gg, i.e. with increasing Q-value mismatch. Channel coupling is proposed as the relevant mechanism.     

Revised model for 5d electrons in the heavy rare earth metals

A revised version of a recently published model for 5d electrons in the ferromagnetic state of the heavy rare earth metals is described. The model involves the broadening of local 5d states into overlapping bands with individual widthsW. In the new approach it is assumed that the local 5d wave functions lie at some point between those for atomic 4f _n 5d 6s ² configurations and those calculated for such configurations subject to the restriction that the 4f shell is kept with its moment rigidly fixed in some given direction. The admixture of non-aligned 4f states as in the atom lowers the local energy, but it also lowers the 5d bandwidth due to misfit of the 4f states which occur with and without the presence of a 5d electron. This second effect raises the energy of the low lying states in the band. The best local states are determined by minimising the total electronic energy of the system, using approximations which are most suitable for 4f shells with large excitation energies. Bandwidths are found by fitting the observed saturation magnetic moments in Gd and Tm, and satisfyW?1 eV.     

X-ray photoemission spectra of valence electrons in V3X and Nb3X compounds

The X-ray photoemission spectra (XPS) of the A15 type compounds V₃Au, Nb₃Os, Nb₃Ir, Nb₃Pt and Nb₃Au have been studied. The inner level binding energies of the different components and the valence electron distribution were measured. The Nb4d and the X5d energy bands of the Nb₃X compounds appear to be more and more separate with increasing atomic number of the X component. The comparison between the results from X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) of corresponding V₃X and Nb₃X compounds points out the similarity of their electronic structures.     

Conduction electron distributions in europium and gadolinium by soft x-ray spectroscopy

A study of the 5d6s conduction band in Eu and Gd by soft X-ray spectroscopy is presented. Our observation that the density of occupied d states is lower for Eu than for Gd is supported by band structure calculations. For Gd, the convolution integrals between the 3p_3/2 inner level Lorentzian distribution and the A.P.W. densities of states are compared with our experimental M_m spectra. The position of the occupied 4f states with respect to the Fermi level is determined, compared with X-ray photoemission data and discussed for both metals.     

Electronic structure of PbI2 from photoelectron spectra and the exciton problem

The valence band density of states for PbI₂ is determined from X-ray and u.v. induced photoelectron spectra. It is shown that the band derived from Pb 6s states is at 8 eV binding energy and not at the top of the valence bands as suggested by band structure and charge density calculations. A rigid shift in the predominantly iodine 5p derived bands to lower binding energy brings the band structure calculations into essential agreement with experiment. Pb 5d core level binding energies determined here are used to derive core level exciton energies of 0.7 eV from published reflectivity spectra.