Plasma radiation from sodium films induced by slow electrons

The radiation emitted by sodium films in the 2.5–5 eV photon energy range as a result of bombardment by 300-eV electrons is measured. It is shown that the feature observed in the region of 4 eV is associated with the radiative decay of surface plasmons, while the radiation emitted at 4.6 and 4.68 eV is due to the radiative decay of multipole plasmons.     

Radiation from silver films bombarded by low-energy electrons

Emission spectra from Ag films irradiated by low energy electrons (20–1500 eV) have been measured, and the results compared with theory. For relatively smooth films, two peaks in the spectra are resolved. One at 3.73 eV, the volume plasmon energy, is attributed to transition radiation and/or bremsstrahlung. The second, at about 3.60 eV, is very sensitive to surface roughness in both position and magnitude and is produced by roughness-coupled radiation from surface plasmons. For rough films, the roughness-coupled radiation dominates the emission. In addition to spectral shapes, the polarization of the radiation and its intensity as a function of electron energy were measured. The experimental results are compared with new calculations of roughness-coupled emission which account for most of our observations. They indicate that high wavevector roughness components play the dominant role in the emission process.     

Emission of circularly polarized recombination radiation from p-doped GaAsP bombarded with longitudinally polarized electrons

We report measurements of circularly polarized recombination radiation from a GaAs_0.6P_0.4 crystal bombarded with longitudinally spin polarized electrons of 10 eV energy. Qualitatively, this process can be considered as the inverse of the photoemission utilized in GaAs and GaAsP polarized-electron sources. The measured degree of circular polarization is 0.29%±0.06% if the crystal is cooled with liquid nitrogen and the incident electrons are 15%±3% polarized.     

Microscopy with slow electrons

Low energy microscopy is treated as the low energy limit of electron microscopy as a whole in all its basic branches, i.e. the emission, transmission and scanning microscopies. The instrumental and methodological aspects are briefly discussed. These include the interaction of electrons with a solid, the contrast formation mechanisms, the instrumentation problems and actual progress achieved in all three microscopies, from the point of view of lowering the energy of electrons, impacting or leaving the specimen, down to the low energy range below 5 keV and the very low energy range below 50 eV.Invited lecture presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September 1993.     

Inelastic scattering of slow electrons from adsorbed molecules

The inelastic scattering of slow electrons from molecules adsorbed on a metal surface is studied. Previous calculations are improved by including the Coulomb interaction between the incident electrons and the induced charge density that they give rise to in the surface region of the metal.     

Inelastic scattering of slow electrons from adsorbed CO

We have investigated how the cross section for vibrational excitation of adsorbed CO by slow electrons varies with the angle of incidence. Experimental results for the NiCO and CO stretching vibrational modes are presented and compared with a recently developed dipole scattering theory. Good agreement between theory and experiment is obtained.     

A comparative study between slow electrons and positrons transport in solid thin films

In this work, we have conducted a comparative study between the transport of electrons and positrons in aluminum and gold solid thin films, in the examined primary energy range (0-4 keV), by using the Monte Carlo method. This comparative study has been used for three transport phenomena: transmission, absorption and backscattering and it will be useful for experimenters to choose between electron or positron beams for thin film characterizations. Here, we have calculated quantities such as absorption probability, mean penetration depth, transmission probability, transmission energy distributions and backscattering coefficient, for both electron and positron. The agreement between our results and the available experimental data is found to be good within the limits of the statistical accuracy.     

Elastic and inelastic backscattering of slow electrons from silicon

The elastic and inelastic backscattering from Si(111) surfaces and evaporated amorphous silicon were measured as a function of the primary energyE _p (30eVE _p 200eV). A detailed evaluation of the amplitude of the volume plasmon lossA _vp was carried out in the loss spectra. In contrast to single crystals amorphous silicon produces a smooth curve as function of the energy, both for the elastic backscattered electron current and forA _vp (E).To interpret the measured curves for the amorphous Si calculations were made for the elastic scattering and for the excitation probability of the volume plasmon in a randium-jellium-model. In the case of elastic scattering a random distribution of atoms is assumed. In the case of inelastic scattering the free electron model is used. Double scattering processes are included. The comparison between theory and experiment shows satisfactory agreement for elastic scattering. The energy dependent excitation probability of the volume plasmon is excellently represented by this model.     

Phase formation in ion bombarded metallic films

The interplay of several events, ranging from production, migration and interaction of defects, to irradiation enhanced atomic diffusion and chemical mixing, is responsible for phase formation in surface layers of ion bombarded metallic alloys. The problem is so complicated that even the interpretation and the prediction of extreme cases such as the attainment of a crystalline, or a glassy product are presently beyond the possibilities of first principle approaches, and empirical criteria have been proposed to this end. In this work we limit ourselves to the very beginning of phase formation, i.e. thenucleation stage, in the frame of an atomistic model. In a binary alloy, after formation of collision cascades, the relaxation to metastable equilibrium of the locally altered compositional profile due to preferential migration to the cascade-matrix interface of one alloy component, is schematized by charge transfer events As a result, dimers of an effective alloy are formed. Conditions specific of glass and respectively crystal formation are extracted from an analysis of surface and thermochemical properties of starting and effective alloys.     

Three-body recombination of atomic ions with slow electrons

Using the time-dependent wave-packets method, we have quantum mechanically investigated the three-body recombination process for electron energies varying from 10 to 0.01 eV. The classical "bottleneck" prediction on the probable population was confirmed by our S-wave quantum calculations for electron kinetic energies (K(E)) as low as 0.1 eV. But for K(E)<0.1 eV, the quantum three-body recombination tends to populate lower n levels than the classical theory predicted. We also find that, in the same n level, the recombination tends to populate higher angular-momentum states with K(E) decreasing. These results may shed light on the intrinsic dynamics of both ultracold plasmas and frozen Rydberg gases.     

VUV resonant transition radiation from relativistic electrons

The modified radiator for generation of the resonant transition radiation from relativistic electrons is presented. This radiator consists of a set of small thin foils inclined with respect to the trajectory of an emitting electron. It is shown that the photoabsorption of the emitted photons is almost completely suppressed in the considered scheme. Therefore, the possibility of generating intense beams of quasimonochromatic vacuum ultraviolet (VUV) quanta by the proposed method appears.     

Inelastic collisions of slow electrons with yttrium trichloride molecules

Inelastic collisions of electrons with YCl₃ molecules are investigated by the method of extended crossing beams. As in the case of LaCl₃ molecules, only the spectral lines of singly charged metal ions are found, with the lines of yttrium atoms and the spectral bands of yttrium monochloride being absent. The excitation cross sections of the energy levels of Y(II) and the contribution of the cascade population are calculated using the results obtained. Possible reaction channels upon dissociative excitation are discussed.     

Scattering of slow electrons by Si

The close coupling method is applied to e-Si scattering using Hartree-Fock target wavefunctions. Scattering cross-sections are found to be free from the effects of shape resonances and large elastic cross-sections are obtained at low energies.     

Number of electrons active in slow collisions of and with

Resonant excitation or resonant electron scattering is a two step process in which Auger rates are involved in both steps. First an electron is captured into a bound state and a bound electron is excited (inverse Auger effect). Then an Auger transition leads to the emission of the electron from the ion. The corresponding cross-sections are very sensitive to the Auger rates and allow a detailed study of the Breit interaction which is a current-current contribution to the static electron-electron interaction. The contribution of the Breit interaction to the cross-section of resonant excitation on hydrogen-like uranium ions is discussed and shown that it is roughly twice as large as in the case of dielectronic recombination. Received 4 August 1999 and Received in final form 29 September 1999     

Thermal emission of electrons from highly excited sodium clusters

Positively charged sodium clusters can be easily ionized by a fs laser pulse of relatively low intensity (<10¹⁰ W/cm²), if the laser is in resonance with the plasmon excitation of the cluster. This ionization process was investigated in detail by measuring the kinetic energy distribution of electrons emitted from a size-selected Na₉₃ ⁺ as a function of the fs laser intensity. In all cases pure Boltzmann-like energy distributions were observed. A comparison with statistical theory shows that the emission is a purely thermal process. It is different to normal thermionic emission insofar as the electrons are emitted from a hot electron system which is only weakly coupled to a cold ionic background. The results demonstrate purely statistical behaviour of a small fermionic system even for very high excitation energy. Received: 25 May 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

Inelastic scattering of slow electrons in solids

A theory of the inelastic scattering of slow electrons in solids due to excitation of interband transitions is developed. It is shown that both nondirect and direct transitions occur which can be described by a generalization of the formalism used in solid state optics. Experiments with 30–200 eV electrons scattered from Si (111) surfaces with well defined surface structures as determined by low energy electron diffraction confirm the theoretical predictions. They indicate that the inelastic scattering of slow electrons can be understood in terms of the three-dimensional band structure of solids and suggest the use of inelastic low energy electron scattering as a tool for band structure analysis.     

Excitation of adenine molecules by slow electrons

The excitation of adenine molecules in the gas phase by slow electrons is studied by optical spectroscopy. The emission spectra of the molecule in the region of 250–500 nm upon excitation by slow electrons in the energy range of 15–120 eV, as well as the optical excitation functions of the most intense emission bands, are presented.