Inelastic life-time of the conduction electrons in some noble metal films

Magneto-conductance measurements of thin films of Cu, Ag and Au are reported. The measurements are evaluated with the theory of weak localization and yield for the noble metals a very good agreement with the theory in the whole field range up to 5T. No adjustment of the theoretical prefactor is necessary. The magneto-conductance curves show a pronounced structure caused by spin-orbit coupling. The measurements yield the inelastic life-time and the spin-orbit coupling of the conduction electrons for Cu, Ag and Au. _i obeys a 1/T ^p law withp=1.65.     

Evaluation of positron annihilation angular correlation curves and line profiles of compton scattering in noble metals

Angular correlation curveN () as well as the Compton line profile I() of Cu, Ag, Au and Pt have been calculated by the assumption, that the coincidence counting rate and Compton line shift intensity are proportional to the area of cuts through the body defined by the Fermi surface. Parametrical expression of the Fermi surface were employed and the results were used to fit some measured curves on Cu, Ag and Au.The authors are indebted to Prof. P.Ry and Dr. I.Volf for enabling the work, Dr. A. íek for supplying the experimental data for Au, Ag and Cu and J. Sedláek for assistance by programming of numerical evaluations.     

High reflective p-GaN/Ni/Ag/Ti/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) applications

The fabrication of high reflective Ni/Ag/(Ti, Mo)/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) are proposed and considered, Ni/Ag/Au Ohmic contacts are also fabricated to compare their resulting reflectivities. From secondary ion mass spectrometry (SIMS) depth profiles, it indicates that the Au in-diffusion occurs in Ni/Ag/Au contacts after annealing. It is considered that Au in-diffusion, which is intermixed with Ag, Ni and GaN in Ni/Ag/Au contacts after annealing, is responsible for the resulting low reflectance (63% at the wavelength of 465 nm). To avoid Au in-diffusion and enhance the reflectivity, a diffusion barrier metal (Ti or Mo) between Ni/Ag and Au is fabricated and examined. It is demonstrated and found that an insertion of diffusion barrier metal of Ti enables to block Au diffusion effectively and also improve the reflectivity significantly, up to 93%.     

The total virtual photoabsorption cross section,deeply virtual Compton scattering and vector-meson production

Based on the generic two-gluon-exchange dynamical mechanism for deeply inelastic scattering at low , we stress the intimate direct connection between the total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson electroproduction. A simple expression for the cross section for deeply virtual Compton scattering is derived. Parameter-free predictions are obtained for deeply virtual Compton forward scattering and vector-meson forward production, once the parameters in the total virtual photoabsorption cross section are determined in a fit to the experimental data on deeply inelastic scattering. Our predictions are compared with the experimental data from HERA. Received: 16 February 2004, Revised: 16 July 2004, Published online: 2 September 2004 Supported by Deutsche Forschungsgemeinschaft, contract number schi 189/6-2. An erratum to this article is available at .     

Compton mechanism of γ-quanta emission in the extremely inelastic scattering of electrons by hadrons

The Compton mechanism at the emission of -quanta, in the extremely inelastic scattering of charged leptons by hadrons is investigated using the quark-parton model. The cross section of the e^– + qe^– + q + (q-quark) process, in which two particles are recorded in the final state corresponding to the Compton mechanism, is calculated. The structural functions of the extremely inelastic scattering of electrons by nucleons are obtained for this mechanism. A violation of the gauge invariance of extremely inelastic scattering due to consideration of the radiational corrections is pointed out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 9–13, January, 1982.     

Effect of bcc-fcc phase transition on the compton profiles of iron

The effect of the- or bcc-fcc phase transition on the electron momentum distribution and Compton profiles of iron has been theoretically examined by a band structure calculation in the two phases. The calculated band Compton profile for the bcc phase shows a good agreement with the experimental results by Phillips and Weiss. The calculated directional Compton profiles show significant changes while going from the bcc to the fcc phase.     

Theoretical study of polymeric metal clad optical waveguide polarizer

Planar optical waveguides consisting of thin dielectric films and buffer layers with metal cladding have been investigated theoretically. A computer program was written to calculate the exact zeroes of complex eigenvalue equation for TE and TM modes in multilayer metal clad waveguide polarizer. Numerical results and illustrations are given for Polycarbonate waveguide with other polymers as buffer and Al, Ag and Au as cladding metals at . It is also shown that, using thin (finite) films of metal produce more efficient polarizers as compared to semi-infinite metal films. Effect of low index buffer layer on attenuation of TM/TE modes is also investigated.     

Analytical model of oscillating size dependence of energy and force characteristics of subatomic metal films

For a wide thin film of thickness L, the expansion of energy characteristics in powers of 1/L is constructed using the free-electron approximation and a model of a potential well of finite depth. The errors in each order of the expansion are analyzed. Using the exact formulas, the thickness dependences of the work function and of the electronic contribution to the elastic force for Al, Au, Ag, and Na films are calculated. It is concluded that the work function of a low-dimensional metal structure is always smaller than that of the corresponding semi-infinite metal.     

Hartree-Fock investigation of the electron momentum distribution in metallic beryllium

The wave function resulting from an accurate Hartree-Fock computation has been used to describe the electron momentum distribution in beryllium metal. Appreciable discrepancies are found with respect to a simple model that amounts to filling with plane waves the first plus second Brillouin zone. In comparing the calculated with the experimental directional Compton profiles, very close agreement is found in particular with a recent set of accurate -ray profiles. The differential Compton profiles are also semiquantitatively reproduced, better on average than with all previous calculations. Concerning the Fourier transforms of the Compton profiles, all the features of the experimental curves are accurately reproduced, in particular the position of the zero passages, which is a powerful test of the adequacy of a theoretical model to account for the metallic nature of the solid. The possible influence of the correlation correction is discussed, and it is shown that such a correction would substantially improve the overall agreement with the experiment.     

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.     

Interfacial segregation in Ag-Au,Au-Pd,and Cu-Ni alloys: I. (100) surfaces

Atomistic simulations of segregation to (100) free surface in Ag–Au, Au–Pd, and Cu–Ni alloy systems have been performed for a wide range of temperatures and compositions within the solid solution region of these alloy phase diagrams. In addition to the surface segregation profiles, surface free energies, enthalpies, and entropies were determined. These simulations were performed within the framework of the free energy simulation method, in which an approximate free energy functional is minimized with respect to atomic coordinates and atomic site occupation. The effects of the relaxation with respect to either the atomic positions or the atomic concentrations are discussed. For all alloy bulk compositions (0.05 C 0.95) and temperatures (400 T(K) 1,100) examined, Ag, Au, and Cu segregates to the surface in the Ag–Au, Au–Pd, and Cu–Ni alloy systems, respectively. The present results are compared with several theories for segregation. The resultant segregation profiles in Au–Pd and Ag–Au alloys are shown to be in good agreement with an empirical segregation theory, while in Cu–Ni alloys the disagreement in Ni-rich alloys is substantial. The width of the segregation profile is limited to approximately three to four atomic planes. The surface thermodynamic properties depend sensitively on the magnitude of the surface segregation, and some of them are shown to vary linearly with the magnitude of the surface segregation.     

Effect of interfacial alloying on the surface plasmon resonance of nanocrystalline Au-Ag multilayer thin films

Nanocrystalline Au and Ag in multilayer thin film form with Au/Ag/Au structure were prepared by high pressure (∼40 Pa) d.c. sputtering techniques. The Ag concentrations in Ag_xAu_1-x films were changed from x = 0 to 1. These multilayer films with varying Ag concentration showed significant changes in microstructures obtained from TEM and XRD analyses. The optical absorption spectra of these multilayer films showed a single plasmon band confirming the formation of Au-Ag alloy. We ascribe this alloying to the interfacial reactions in nanophase limited at the Au-Ag interface. The red-shift and broadening of the plasmon bands with the increase in silver concentration could be associated to the increase in size of the nanoparticles and its distribution. The observed red shift in the plasmon band may be associated with the change in electronic structure at the Au-Ag interface due to configuration mixing of the atomic energy levels of Au and Ag. Received 17 October 2002 / Received in final form 26 February 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: msakp@mahendra.iacs.res.in     

Analysis of the 3-dimensional electron distribution in silicon using directional Compton profile measurements

A method of reconstructing the electron momentum density (p), and its Fourier transform,B(t), from a series of directional Compton profiles is described. It is based on a double Fourier inversion technique and an expansion in lattice harmonic functions. The effect of random errors has been analysed, and the implications for the data collection discussed. We have used the reconstruction technique to obtain (p) andB(t) for silicon from six directional Compton profiles measured with 412 KeV gamma-radiation. The experimental result is in good agreement with earlier measurements and with available solid state theories. A recent Wannier function calculation for silicon using orthogonalised bond orbitals provides a useful tool for identifying the physical origins of the observed anisotropies. A comparison between the information presented in position and momentum space shows that the ease of interpretation depends upon the degree to which the various interactions give rise to localised features in each representation.     

Generalized stacking fault energy in FCC metals with MEAM

The second nearest-neighbor modified embedded atom method (2NN-MEAM) is used to investigate the generalized stacking fault (GSF) energy surfaces of eight FCC metals Cu, Ag, Au, Ni, Pd, Pt, Al and Pb. An offset is observed in all the metals for the displacement δ_us of unstable stacking fault energy from the geometrically symmetric displacement point . The offset value is the greatest for Al and the smallest for Ag. By analyzing the stable stacking fault energy γ_sf and unstable stacking fault energy γ_usf, it can be predicted that stacking fault is more favorable in Cu, Ag, Au, and especially in Pd than the other metals, while it is most preferred to create partial dislocation for Ag and to create full dislocation for Al.     

Experimental and theoretical studies on the role of silver in gold nanorods growth

Gold nanorods (AuNRs) have attracted high attention because of their multifunctions and potential applications in optical, electronic, catalytic and biomedical areas. This study demonstrates a key role of silver (Ag) atoms/clusters, experimentally and theoretically, in the formation and growth of AuNRs. It was found that the addition of silver salt (silver nitrate) can preferably deposit on certain Au crystalline {100} and/or {110} facets to affect the stacking of Au atoms when form and grow to AuNRs in the reported reaction system, resulting in slower atomic stacking on these two {100} and {110} facets but regular growth on the {111} facets. If no use of silver salt(s), gold nanospheres rather than nanorods were obtained in such a reaction system. It was found, by theoretical simulations (molecular dynamic method, MD), that Ag atoms can be oxidized to Ag⁺ ions by AuCl₄ ^? ions and exist in a short lifetime, which finally diffuses out from the Au crystal structure. The findings would be useful for better understanding the role of Ag in the formation and growth of AuNRs with crystal facet control, which will be beneficial for catalytic and gas sensing applications that often require highly exposed crystalline facets.

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Graphical abstract Silver-assisted synthesis of gold nanorods in the presence of CTAB in aqueous solution has been confirmed by both experimental method and molecular dynamic simulations.

     

Suppressing the background process to QED Compton scatteringfor delineating the photon content of the proton

We investigate the QED Compton process (QEDCS) in and , together with the major background coming from virtual Compton scattering (VCS), where the photon is emitted from the hadronic vertex. We suggest new kinematical constraints which suppress the VCS background and are furthermore suitable for the extraction of the equivalent photon content of the proton at the HERA collider. We show that the cross section, commonly expressed in terms of the proton structure functions, is reasonably well described by the equivalent photon approximation of the proton, also in the inelastic channel in the proposed kinematical region.Received: 5 February 2004, Revised: 8 March 2004, Published online: 9 June 2004     

Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 < d < 20 nm in size are applied on InGaN/GaN multiple quantum well structures with surface morphology less nonuniform than that of ZnO films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.     

Inelastic effect in low energy ion-surface collisions: He+Au,Ag

Energy distributions of He⁺ ions scattered by Au and Ag surfaces are measured by an ISS system with high energy resolution, at a scattering angle of 90° and at incident ion energies ranging from 277 to 977 eV. It is found that the observed peak energies deviate toward the low energy side by several electron-volts with respect to the calculated elastic single collision energies. Both the deviation Q' and the inelastic loss energy Q are plotted as a function of incident ion energy for the Au surface.     

Interactions of oxygen and CO with AgAu bimetallic nanoparticles on sputtered highly ordered pyrolytic graphite (HOPG) surfaces

Oxidation of AgAu bimetallic nanoparticles on sputtered HOPG by atomic oxygen and reduction of the oxidized surface by CO at room temperature were studied using X-ray photoelectron spectroscopy (XPS). For 2 nm-sized nanoparticles, prepared by postdeposition of Ag on Au-core, atomic oxygen exposure mostly leads to the formation of chemically inert oxygen species. This result is analogous to that of pure Ag and Au nanoparticles of similar sizes on the same substrate. In contrast, “Au on Ag-core” nanoparticles form chemically active oxygen species, suggesting that depending on detailed structures of bimetallic nanoparticles, diverse chemical properties can be obtained.