Unusual disordering processes of oxygen overlayers on Rh(111): A combined diffraction study using thermal He atoms and low-energy electrons

The temperature-dependent behavior of the Rh(111)-(2X2)-1O phase was investigated by He-atom scattering (HAS) and low-energy electron diffraction. The adsorption system undergoes an order-disorder phase transition at Tc=280±5 K, with critical exponents found to be consistent with the four-state Potts model. Beyond the phase transition the HAS specular peak intensity exhibits a strong and reversible increase. This finding points toward a reduction of the surface charge-density corrugation induced by the phase transition itself. Around 160 K, hydrogen adsorbed on the Rh(111)-(2X2)-1O surface reacts with oxygen to form water, and drives the overlayer in an out-of-equilibrium condition which is characterized by a dramatic domain-wall proliferation

Ordering of a prototypical conjugated molecular system during monolayer growth on the (1 x 2)- Au(110) surface

Article on the ordering of a prototypical conjugated molecular system during monolayer growth on the (1x2)-Au(110) surface

NEXAFS experiment and multiple scattering calculations on KO_2: effects on the π resonance in the solid phase

The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum has been measured for in situ prepared potassium superoxide. The experimental data have been analyzed in detail by multiple scattering calculations using self-consistent field potentials. In particular, the so-called π resonance at the rising edge, which presents a double-peak structure, has been totally resolved and reproduced by the calculations. This analysis indicates that the grown material is arranged in a KO_2 structure with an O-O distance between 1.31 and 1.34 Angstrom. Moreover, the calculation demonstrates both a complete ionic character of the bound between the Oˆ(2-) anion and K atoms and a strong interaction between the anion and solid-state matrices

NEXAFS multiple scattering calculations of KO_2

Since many years the oxidation of alkali metals has being attracted much interest due to the catalytic properties of metal promoters and the simple electronic structure of alkali atoms. The alkali-oxides phase diagram indicates that the interaction of oxygen with alkali metals can lead to the formation of different atomic O2- ions and molecular O_2 and O^(2-) ions. Potassium superoxide has been prepared in situ and high resolution O k-edge absorption NEXAFS spectra have been measured at the VUV beam-line at ELETTRA facility. The experimental data have been analyzed by multiple scattering approach deriving many geometrical and electronic details. In particular, we have found that the growth material structure is of the KO_2 type with an O-O distance of about 1.35 Angstrom and that the transition involving single pi molecular empty state of the superoxide O_2^(2-) anion has a fine structure. Multiple Scattering self consistent calculation indicates that the bond between oxygen anion and K atom is totally ionic and that the fine structure is essentially due to solid state effects

Sub-ps pump and probe photoemission from polycrystalline molybdenum

5nonenonePARMIGIANI F.; PELOI M.; BANFI G.; SCHIAVUTA P.; PARMIGIANI F.Parmigiani, Fulvio; Peloi, M.; Banfi, G.; Schiavuta, P.; Parmigiani, F

Nonlinear photoemission from polycristalline molibdenum irradiated by 790 nm -150 fs laser pulses

The total yield photoemission of a polycrystalline molybdenum sample irradiated by 790 nm-150 fs laser pulses is measured in the absence of space charge saturation. The extracted charge versus the laser intensity, measured over three decades of the extracted charge, which represents a significant extension of the previous experiments, gives us the opportunity to test the so-called thermally assisted non-linear photoemission model. The present results show non-linear photoemission behavior that can be explained, as expected, by a thermally assisted 3-photon emission. However a pure 4-photon emission could not be discarded. To take aim at clarifying this question the related non-linear coefficients are calculated and a scaling law for the probability of different multiphoton orders is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved

Disorder-order evolution of InSb(110) studied by He scattering

The evolution of surface defects created by low energy ion bombardment on InSb(110) is studied by He beam scattering experiments. At surface temperatures above 500 K the ion erosion is found to proceed layer-by-layer without changing the stoichiometric composition of the surface. This indicates that the nucleation of surface islands driven by vacancy diffusion is faster than the ion erosion. After different doses of Ar+ ion bombardment, the surface is left in a non-equilibrium state whose time evolution is monitored by measuring the profiles of the He diffraction peaks. It is seen that the coalescence of islands proceeds with anisotropic island size distributions