Tsofar Maniv

The interaction between an oscillating dipole and a metal surface described by a jellium model and the random phase approximation

Abstract The electric field acting on an oscillating dipole located near a metal surface is computed. The latter is described by a jellium model and the random phase approximation. The aim is ascertaining to what extent spatial dispersion and variation of the dielectric properties across the interface modify the image dipole. Implications for surface Raman and fluorescence spectroscopy are discussed.

Electrodynamics at metal surfaces. IV. The electric fields caused by the polarization of a metal surface by an oscillating dipole

We compute the electromagnetic field generated by an oscillating dipole located near a metal surface. The dielectric response of the metal is obtained by using the random phase approximation for a jellium model with a surface represented by an infinite barrier. The model includes the role of spatial dispersion (nonlocal response) and of the fact that the dielectric response varies continuously across the interface. These two effects remove the divergence given by the phenomenological electrodynamics (image formula).

Electron gas effects in the spectroscopy of molecules chemisorbed at a metal surface. I. Theory

It is known that the spectroscopic properties of a chemisorbed molecule are affected by the interaction between the molecular charge density and the free electrons in the metal. Such effects have been previously discussed by using a model in which the molecule is represented by a point dipole and its interaction with the metal is treated by using macroscopic electrodynamics. We examine critically this model and remove some of its shortcomings by developing a microscopic theory in which the interaction between the molecule and the metal is treated within the random phase approximation. We discuss applications to infrared, electron energy loss and Raman spectroscopy, as well as to the computation of dispersion forces between chemisorbed molecules.

Electrodynamics at a metal surface. II. Fresnel formulas for the electromagnetic field at the interface for a jellium model within the random phase approximation

We compute the electromagnetic fields generated at a vacuum–metal interface by incident radiation. We use a jellium model and the random phase approximation. The validity of the Fresnel equations at small distances from the surface is discussed. Numerical values for the continuous variation of the electric field vector through the interface are presented. Our main concern here is to illustrate the effects of the nonlocality of the dielectric response and of the continuous variation of the response function across the interface on the electrodynamic properties of the system.

A comparative reflection electron energy loss study of C60 and graphite

Abstract Electronic excitations of solid C60 have been studied using the reflection EELS technique with a 0.2 eV energy resolution. A comparison with graphite revealed an overall similarity of the spectral gross features, while significant differences were observed in the fine details, mainly at low loss energies. A similar dominant plasmon was observed in C60 at a slightly shifted energy of 23.2 eV. For C60, in contrast to graphite, a clear energy loss onset was found at 1.7 eV and up to 6 eV six loss peaks were clearly observed. It was found that minima in the loss spectrum fit well with reported optical transitions. This observation supports an interpretation which attributes a significant collective character to the loss peaks.

A study of O2 adsorption on α-CuAl(100) surfaces of different Al concentrations by means of AES and XPS

Abstract The adsorption of O 2 on α-CuAl(100) for small concentrations of aluminum has been studied at room temperature by means of AES and XPS. A strong long range influence of aluminum on the adsorption processes as compared to pure Cu(100) has been found, the surface composition of the alloys has been studied and different aspects of adsorption processes have been addressed. The enhanced rate of oxygen adsorption on the alloy is explained on the basis of a long range influence of aluminum atoms on copper sites.

Application of the complex rotation method to the study of resonance states of atoms at a corrugated surface

The complex rotation method is applied to the calculation of complex poles of the scattering matrix for atoms selectively trapped at a corrugated, static surface. The method is found to be extremely efficient and accurate even for highly corrugated surfaces, for which the use of more conventional methods is known to be in trouble. The method also provides insight into the trapping processes, revealing that for a simple harmonic corrugation there is a critical value of the corrugation amplitude, below which the trapping process is dominated by the coupling between adjacent diffraction channels, while above this critical value the coupling between more distant channels dominates.

Electrodynamics at a metal surface. III. Reflectance and the photoelectron yield of a thin slab

We use a jellium model with an infinite barrier to minic the dielectric bahavior of a thin slab of a free electron metal. The model includes spatial dispersion (nonlocality) and allows the dielectric response to vary continuously across the interface. We compute the reflectance and the photoelectron yield as functions of frequency, film thickness, and electron mean free path.

A theory of He diffraction and resonance scattering from Cu(115) by the complex coordinate method

Our method for computing specular elastic scattering intensities of atomic beams from a periodically corrugated solid surface, is generalized to include nonspecular diffraction intensities, and is applied to the scattering of a helium beam from the Cu(115) surface for resonance as well as off‐resonance incident angles. Using a simple corrugated Morse potential with a one‐dimensional corrugation function and reasonable values of its parameters, a remarkable agreement with the experimental resonance line shapes over the entire angular range is obtained for both the specular and a nonspecular diffraction channel. The line shapes are found to be extremely sensitive to the corrugation strength parameter, but quite insensitive to the shape of the surface corrugation.

Raman reflection, a possible mechanism for enhancement of Raman scattering by an adsorbed molecule

Abstract Calculations illustrate a new physical process, Raman reflection, which contributes to Raman scattering by adsorbed molecules. It is induced by the interaction between the vibrating ion-core charges of adsorbed molecules and the electrons of the metal; this interaction causes energy transfer from the electron-hole pair to the oscillating molecule. Since the energy transferred equals the vibrational energy, the photon emitted by subsequent electron-hole recombination is Raman shifted, augmenting the Raman intensity.