1,721,114 research outputs found
Estimate of image-potential perturbation on the normal inverse and direct photoemission yelds
No full textThe effect of the image-potential perturbation on the direct and inverse angle-resolved normal photoemission is evaluated for semiconductor surfaces, from the effective-mass equation using a classical dielectric picture. For the Si(1, 1, 1) and GaAs(1, 1, 0) surfaces, in inverse photoemission, shifts of the order of tens of meV are evaluated for the first peak in the final photon yields
Estimate of image-potential effect in normal direct and inverse and photoemission
No full textEstimate of image-potential effect in normal direct and inverse and photoemissio
Geometric structure and optical properties of the GaAs(001)-c(4 X 4) surface
No full textWe consider the electronic structure and optical properties for several geometries of the GaAs(001)-c(4x4) surface using first-principles calculations. We find strong evidence that the best agreement with photoemission and reflectance anisotropy spectroscopy experiments carried out on surfaces prepared under As-4 flux is obtained for a structure containing three Ga-As dimers per unit cell. The standard As-As dimer model yields similar, but distinguishable results, while an asymmetric dimer model is found to yield completely incompatible surface spectra
Calculation of optical properties within the local density approximation to density functional theory: application to palladium
No full textWe calculate the optical functions of Pd using the ab initio, all-electron Full Potential Linear Muffin Tin Orbital
method within the framework of the Density Functional Theory in the Local Density approximation.
We test, in the case of Pd, the convergence of the dielectric function and energy loss function in different energy ranges
vs. the completeness of the basis and give a quantitative estimate of the accuracy.
The present approach opens the possibility of extending the energy range where the optical functions can be calculated with good
accuracy without increasing the computational effort
Synthesis of photoswitchable submicroparticles and their evaluation as ion-imprinted polymers for Pd(II) uptake
No full textThe idea of developing a system that enables modulation of the amount of Pd(II) ions bonded to a substrate upon exposure to external stimuli could open interesting prospects for application in various research fields such as sensors, catalysis, gas storage, and separation. In this context, in the present work, a photoresponsive compound was used as a functional monomer in the preparation, for the first time, of a photoresponsive ion-imprinted polymer (PIIP) for metal ion uptake. The Pd(II) template was used as a metal ion model, and the binding behavior of PIIP was evaluated under different experimental conditions. The adopted precipitation polymerization technique allowed us to obtain dispersed submicroparticles, as confirmed by the dynamic light scattering and Langmuir isotherm results. The photoisomerization capability of PIIP, with conformational changes of the polymer, was demonstrated, and an improved binding capacity for Pd(II) was observed after UV exposure of the polymer, with a maximum binding capacity approaching 22 mg g−1. Moreover, from the kinetic studies, the equilibrium binding capacity was reached within almost 3 h either in the dark or under UV irradiation. Finally, the reusability of the polymer over three cycles was demonstrated, and the ion selectivity of Pd(II)-PIIP was confirmed when other metal ions such as Ni(II) and Pb(II) were tested
Ab initio characterization of surface states at the S/Cu(100) interface
No full textS headgroups are present in many organic molecules and realize their adsorption on metallic surfaces. We calculate ab initio the electronic structure of S/Cu(100) adopting the same geometry as that of the S atom in the C7H5NOS molecule on the same surface. The interface, represented by the S overlayer and by the Cu subsurface layer, is characterized quantitatively by the surface state dispersion of the S-Cu hybrids (bonding and antibonding). The role of the S atom as “hook” for the whole molecule is strongly supported by our calculations. Our results are in quantitative agreement with the photoemission results of C7H5NOS on Cu and also in qualitative agreement with more complicated biological adsorbates on different metallic surface
Excitons in semiconductor confined systems
No full textExciton quantization and oscillator strength are studied for three different geometries of confinements, namely: quantum wells, quantum well wires and quantum dots, as a function of sample dimension. Numerical results for CdS samples are discussed and the importance of non-adiabatic effects in the intermediate range of dimensions are pointed out
Exciton wave functions and optical properties in a grating of quantum-well wires
No full textA variational wave function for excitons in quantum-well wires is obtained. The reflectivity of a grating of quantum-well wires is computed by use of a Green's-function formalism for s- and p-polarized light, with the spatial dispersion and the electromagnetic coupling between the wires taken into account. The resulting energy shift between the s- and p-polarized spectra is discussed
Exact solution of the Schrodinger equation for Wannier excitons on a microsphere
No full textThe effective-mass Schrodinger equation for an electron and a hole, confined to the surface of a sphere and interacting via the Coulomb potential, is studied. The exact energies and wavefunctions of the optically allowed exciton states are presented. Wavefunctions are expanded as series of polynomials which satisfy an equation of the same order but with a smaller number of singularities
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