Experimental characterization of a random metallic rough surface by spectrophotometric measurements in the visible range

Back-reflected light from a random rough surface is studied with the purpose of characterising the surface statistical properties. A new goniospectrophotometer with optic fibres is presented and a random rough copper surface is analysed. The probability density of the surface normal and the h/l ratio (r.m.s. roughness/autocorrelation length) are so obtained. Optical results are compared with mechanical ones, performed with a profilometer. For the first time, Abel's transform method is used to connect the two-dimensional statistical information deduced from optical measurements and the one-dimensional profiles.     

Three-phase contact line energetics from nanoscale liquid surface topographies

We observed light-induced alignment of the nematic liquid crystal, 4, 4(')-n-pentylcyanobiphenyl (5CB), on a fused quartz. Irradiation of the adsorbed layer with polarized ultraviolet light produced homogeneous alignment in a 5CB-filled liquid crystal cell with the easy orientation axis perpendicular to the polarization direction. The measured anchoring energy increases with illumination up to 10(-4) erg/cm (2). Phase retardation and pretilt measurements confirmed near homogeneous alignment of the LC in a cell, while the polarization dependence of second harmonic generation suggested a near normal alignment of the adsorbed layer. We believe that light-induced rearrangement or phototransformation of the adsorbed layer causes the observed phenomenon.     

Chemisorption energetics and surface reactivity: UBI-QEP versus DFT projections

The wealth of information accumulated recently by ab initio/DFT calculations of adsorption energetics and reactivity on metal surfaces makes it possible to systematically compare projections of the DFT and UBI-QEP approaches. We make such comparisons covering both qualitative regularities in and the quantitative accuracy of binding energies and activation barriers. We focus on the following areas: (1) DFT verification of the UBI-QEP assumptions and rigorous projections concerning atomic and molecular binding energies at low coverage; (2) coverage effects revealing in the M-A bond energy competition (metal sharing A-M-A) under atomic co-adsorption; (3) reactivity patterns including both qualitative (periodic dependence of the activation barriers, barrier vs. reaction enthalpy relationships, geometry of the transition state, etc.) and quantitative aspects. We demonstrate the broad agreement between the DFT and UBI-QEP projections and point out the areas where further testing by the ab initio/DFT techniques might be necessary and illuminating. In particular, while discussing the ab initio/DFT absolute values of the atomic binding energies Q _A and their periodic trends, we revised our previous assumptions about monotonic changes of the Q _A values with the changing atom A valence and along the VIII and IB group metals, where the periodic trends appear to be complicated. Accordingly, we make corrections to the original UBI-QEP parameters, summarizing the current recommended values of Q _A.     

The use of surface photovoltage measurements for the surface characterisation of photoconductors

Measurements of the surface photovoltage as a function of wavelength of the exciting radiation show a number of features which change with variations in the surface conditions. In the case of photoconducting cadmium sulphide, it is shown that the changing spectral features, rather than being directly associated with surface states, are due to bulk transitions which give rise to changes in the bulk carrier concentrations and (indirectly) to changes in the surface potential as a result of redistribution of charge between bulk and surface states.     

Experimental measurements of atmospheric neutrinos

This talk reports the latest indications of an anomaly in the measurements of atmospheric neutrinos. New results from Soudan-2 and Super-Kamiokande provide evidence that the ratio of ν_μ to ν_e interactions is not as expected. High energy Super-Kamiokande data indicates the cause is a deficit of upward-going ν_μ, and the zenith angle dependence of the effect is consistent with neutrino oscillations. Upward-going muon measurements by several detectors are discussed, but in total they provide inconclusive evidence for the anomaly.     

Self-diffusion measurements in In_2O_3 isotopic heterostructures:Oxygen vacancy energetics

正As a prototypical transparent conducting oxide (TCO), In2O3after heavily doped with Sn exhibits a priority in optoelectronic applications involving organic light emitting diodes(OLED) and organic photovoltaics (OPVs)[1,2]. Mean-     

Ab-initio calculation of the electronic structure and energetics of the unreconstructed Au(001) surface

The electronic structure, surface and relaxation energies, and the electric field gradient for the unreconstructed Au(001) surface were calculated by means of the ab-initio all-electron full-potential linearized augmented plane wave slab method. The valence states were calculated within the standard semi-relativistic approach whereas the core states are treated in a fully relativistic way. The Au(001) surface was modelled by free slabs of 5, 7, and 9 layers. From the 9-layer calculation a work function of 5.39 eV was obtained. For the surface energy a value of 1.30 J/m² for the unrelaxed geometry was derived from the total energies of the 7- and the 9-layer slabs. From total energy minimization of the 7-layer slab, a negative, inward relaxation of −2.6% and a relaxation energy of 14.3 × 10⁻³ J/m² were derived. To discuss a mechanism of reconstruction, particular surface states were analyzed in detail in terms of the band structure, layer-dependent density of states and the charge density distribution. Differences of surface and central-layer charge densities show a gain of charge in z-direction localised below and also, to a smaller extent, above the surface atoms. We find a very small gain of delocalised charge in the surface plane between the nearest neighbour positions at the expense of more localised s-d hybridised states. The electric field gradient component Φ_zz was obtained in a two energy window calculation for which the Au5p states were also treated as band states. The resulting Φ_zz values are −16.50 × 10¹⁷ V/cm² surface layer, and −3.3 × 10¹⁷ V/cm² for the subsurface layer.     

Non-adiabaticity in surface chemical reactions

Chemical reactions at surface may dissipate energy exciting electron-hole pairs in the metal substrate. Direct detection of the chemically induced hot charge carriers may be achieved by measuring the tunnel current in Ta–TaOx–Au tunnel junctions when the Au top electrode is exposed to an atomic hydrogen beam. A current of 1 nA cm^?2 was observed during a hydrogen exposure with a flux of 0.1 ML s^?1. The transient is related to the reaction kinetics and allows us to identify the elementary reaction steps causing the electronic excitations which are monitored by the observed current. Using Pt as top electrode material a markedly different transient is observed. Applying a bias voltage to the sensor allows spectroscopy of the electronic excitations. The experiments provide detailed insights into the non-adiabaticity of various reaction steps at a surface.     

Compatibility of field emitter studies of oscillating surface reactions with single crystal measurements: catalytic CO oxidation on Pt

Kinetic oscillations in catalytic CO oxidation on Pt have been studied on large (millimeter size) single crystal planes of Pt as well as on a Pt field emitter tip that exposes different crystal facets of nanometer size. In order to examine the compatibility of results from the two types of experiments, the regions of different dynamical behavior (bifurcation diagram) have been mapped out in p_CO,T-parameter space using a field electron microscope (FEM) and a field ion microscope (FIM). The comparison with the results of single crystal measurements shows that in the case of applied electrostatic fields less than 5 V nm⁻¹ (FEM), the field-induced effects are negligible, but they are significant for fields exceeding 12 V nm⁻¹ (FIM). The field-induced shift of the bifurcation diagram toward lower p_CO values, observed with FIM, is explained in terms of a field-modified interaction of CO and O₂ with Pt studied here with field ion appearance energy spectroscopy. With coadsorbed lithium (submonolayer coverage), the existence range for rate oscillations is shifted toward higher p_CO values. This shift is attributed to a redistribution of the electron density at the surface induced by alkali metal co-adsorption.     

Model-independent analysis of density-matrix element measurements in multiparticle reactions

We present a general study of polarization measurement in multiparticle production processes, including a definition of experimentally observable quantities, the splitting into natural- and unnatural parity exchanges and a study of their relative phase, and information concerning the quantum numbers of a packet of particles. When only one single particle is detected in the final state (inclusive reactions for instance) we prove that the usual formalism for two-body reactions is applicable. Very interesting new information on multi-particle production can be reached when it can be asserted that another particle has been emitted above or below a given plane, parallel or perpendicular to the scattering plane.     

Fermi surface measurements on UPd3

The Fermi surface of the DO24 compound UPd₃ has been investigated by the de Haas-van Alphen effect in magnetic fields up to 46 Tesla. Two sheets are detected, one with a high frequency, about 4 10³ Tesla, and one having low frequencies, about 4 10² Tesla. Values of the effectives mass obtained are in accordance with a non-f character of the electron wave function on the orbits investigated.     

The energetics of NH3 adsorption at the MgO(001) surface

Ab initio quantum-mechanical calculations based on density-functional theory and the pseudopotential method have been used to study the adsorption of the NH₃ molecule at the MgO(001) surface. The calculations employ slab geometry and periodic boundary conditions, with the occupied orbitals expanded in plane waves. The reliability of the theoretical methods has been verified by calculations on the bare surface and the isolated molecule. Four different adsorption geometries have been studied, and in each case the equilibrium configuration has been determined by full relaxation of the system. The two most stable configurations have about the same adsorption energy, and this energy agrees well with the results of recent thermal desorption measurements. Intermolecular repulsion is found to be a dominant effect at monolayer coverage, but becomes small at coverages below 25%. It is shown that chemical effects are not significant, and that the adsorption mechanism is predominantly physisorption.     

Experimental investigation of pion reactions with the lightest nuclei

The dynamics of the N-system in the lightest nuclei, its effects, and properties are reviewed and discussed.Invited talk to the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia, September 5–10, 1988.