Photoelectric emission from the negative electron affinity (100) diamond surface — exciton effects

Investigation of the photoelectric yield characteristics of the negative electron affinity NEA (100) diamond surface (produced by hydrogen plasma exposure) finds a striking similarity to the emission from NEA (111) diamond surfaces. Work on NEA diamond (111) surfaces has revealed the important role (sometimes dominant) of photoexcited excitons in the photoelectric yield. Comparison of the electron emission properties among surfaces with different crystallographic orientations can give further insight into electron emission mechanisms. We find that the kinetic energy distribution, the photon energy dependence of photoelectric yield, and the photon energy dependence of constant final state measurements of NEA (100) diamond are characteristically similar to the emission from NEA (111) diamond surfaces. Observed differences appear related to the change in band bending at the surface.     

Momentum conservation in the luminescence of modulation-doped Ga x In1−x As−Al y In1−y As quantum wells

Summary Thek-conserving selection rule in the electron-hole recombination is investigated by intensity-dependent photoluminescence measurements inn-type modulation-doped Ga _x In_1−x As−Al _y In_1−y As single quantum wells intentionally doped with Be acceptors in the well centre. Thek-non-conserving recombination process involves electrons with momentum up to the Fermi edge and holes localized on the Be acceptors. The transition from a one-component electron plasma to a two-component electron-hole plasma is studied by comparing the experimental results with theoretical line shape models. The density-dependent band gap renormalization is determined for the one-component and the two-component electron-hole plasma. The obtained results are found to agree well with recent theoretical calculations.     

Sum of squares manifolds: The expressibility of the Laplace-Beltrami operator on pseudo-Riemannian manifolds as a sum of squares of vector fields

In this paper, we investigate under what circumstances the Laplace-Beltrami operator on a pseudo-Riemannian manifold can be written as a sum of squares of vector fields, as is naturally the case in Euclidean space.

We show that such an expression exists globally on one-dimensional manifolds and can be found at least locally on any analytic pseudo-Riemannian manifold of dimension greater than two. For two-dimensional manifolds this is possible if and only if the manifold is flat.

These results are achieved by formulating the problem as an exterior differential system and applying the Cartan-Kähler theorem to it.

     

Experimental evaluation of reflectance of surface plasmon polaritons at metal step barrier

We have proposed a way to evaluate the reflectance of surface plasmon polaritons (SPP) at a Ag step barrier from an experiment using the attenuated total reflection structure consisting of ultra-thin metal films sandwiched by dielectrics with nearly identical refractive index. At a wavelength of 632.8 nm, for a long-range SPP (L-SPP) excited in a Ag film of 5.7 nm in thickness, the reflectance at Ag step barriers of 766 nm in height was evaluated to be 7.9 × 10⁻².     

An alternative method of using combined-space method: high index surfaces

This paper presents an alternative method for calculating I(E)-spectra for a high index crystal surface using the SATLEED (symmetrized automated tensor-LEED) program. Two test structures, Cu{2 1 1} and Cu{2 1 1}-c(2 × 2)-Cs, have been analyzed. The SATLEED results are compared with results from earlier published CHANGE analyses for the same systems. Relaxations for the first three interlayer spacings of Cu{2 1 1} are −0.09 ± 0.01, −0.05 ± 0.02 and +0.05 ± 0.02 Å, respectively. The corresponding values for the Cs adsorption system are −0.09 ± 0.01, −0.04 ± 0.01 and +0.06 ± 0.01 Å. The adsorption site and effective radius of Cs determined by SATLEED are slightly different from the earlier CHANGE study. Computational and theoretical issues related to the use of these two programs are also discussed.     

Characterisation of the interaction of glycine with Cu(1 0 0) and Cu(1 1 1)

Reflection-absorption infrared spectroscopy (RAIRS) has been used to characterise the interaction of standard and fully deuterated glycine with Cu(1 0 0) and Cu(1 1 1). RAIRS shows clearly that the surface interaction leads to formation of the adsorbed deprotonated glycinate (NH₂CH₂COO-) species, with some evidence for changes in orientation with coverage previously seen on Cu(1 1 0). Qualitative low energy electron diffraction observations were also conducted to characterise the long-range ordering, although effects of electron-beam-induced radiation damage limited the information obtained. Nevertheless, the results do suggest some subtle isotopic-mass-related structural variations. The results are discussed in the context of previously published scanning tunnelling microscopy and photoelectron diffraction measurements.     

Temperature-programmed surface reactions (TPSR) on heterogeneous surfaces

On the basis of calculations using a simple model of the energetic heterogeneity of a solid surface (assuming linear dependence of activation energy of desorption of the reactant on the degree of coverage), it is shown that both the degree of conversion and the course of desorption of the reactants are strongly influenced by the degree of heterogeneity assuming non-isothermal conditions. In contrast to a homogeneous solid surface, the degree of conversion for a heterogeneous surface depends strongly on the initial coverage of a catalyst by reactant. Possibilities for kinetic evaluation are indicated from the modelling calculations.     

Quantitative Methods for the Characterization of Complex Surface Structures

Attempting to model the processes resulting in complex pattern formation and small-scale roughness of surfaces and to compare with experimental measurements calls for numerical methods which allow a quantitative characterization being as complete as possible. New methods incorporating wavelets and stochastic approaches based on the theory of Markov processes allow a stepwise characterization of increasing completeness and unambiguousness. In this paper we demonstrate the underlying numerical approaches taking electropolished and laser-jet etched surfaces for demonstration.     

Steps and facets on annealed LaAlO3{100} and {110} surfaces

Lanthanum-aluminate (LaAlO₃) is one of the optimum substrates for epitaxic growth of thin oxide films. In this paper, the structures of the {100} and {110} surfaces of annealed LaAlO₃ are studied using reflection electron microscopy (REM). 010 steps have been observed on {100}, these are the lowest energy steps. The {100} surface is atomically flat, but the {110} surfaces exhibit high-density fine structures distributed on large surface terraces. These fine structures correspond to the formation of small width (100) and (010) facets on the (110) surface. A growth model is given to interpret the formation of large steps and large terraces on the {110} surfaces.