Function Of Impact Electron Energy Research Articles

BEAMDB and MolD – databases for atomic and molecular collisional and radiative processes: Belgrade nodes of VAMDC

We present two atomic and molecular (A&M) databases, MolD and BEAMDB, hosted by the SerVO – the Serbian virtual observatory ( http://servo.aob.rs ). These databases and web applications have been implemented in accordance to the standards developed by Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu ). The MolD database contains photo-dissociation cross-sections for individual rovibrational states of the diatomic molecular ions and rate coefficients for the atom-Rydberg atom chemi-ionisation and inverse electron-ion-atom chemi-recombination processes. The Belgrade electron/atom(molecule) database (BEAMDB) provides collisional data for electron interactions with atoms and molecules. Differential cross sections (DCS) are presented for both elastic and inelastic (excitation) cross sections in tabulated data tables. These DCS data are integrated over a full range of scattering angles in order to achieve integral, momentum transfer and viscosity cross sections as functions of impact electron energy. Beside these tables, energy loss spectra are presented in the graphical form.

Electron stimulated desorption from the 316 L stainless steel as a function of impact electron energy

The electron stimulated desorption (ESD) yields of vacuum chamber wall materials are required as one of the important input parameters in the design of vacuum systems for particle accelerators and many other vacuum systems where energetic electrons hit vacuum chamber walls. In the present study, the ESD yields were measured and analyzed (a) as a function of accumulated electron dose, (b) as a function of the total amount of desorbed gas, and (c) as a function of the energy of electrons bombarding. In this study, three separate 316 L stainless steel samples were bombarded with electrons up to an accumulated electron dose of ∼2 × 1023 e−/m2 at three different corresponding electron energies: 50 eV, 500 eV, and 5 keV. Once the required dose was reached, the ESD yield as a function of electron energy was measured between 10 eV and 6.5 keV. The results obtained by both methods were in agreement showing that ESD yield increases with electron energy. Experimental difficulties and problems with interpretation of data relating to such a study are described and discussed in the paper.

Resonantlike desorption of negative ions by core-level excitation under electron bombardment.

Electron-stimulated desorption of positive and negative hydrogen ions from hydrogenated GaAs surfaces has been studied as a function of impact electron energy. Well-defined peaks in the negative ion yield are observed at incident electron energies close to Ga and As core-level binding energies, suggesting that resonantlike core-level electronic transitions involving matrix atoms are most likely responsible for such behavior. We propose that the formation and subsequent breakup of superexcited molecular complexes containing a core hole can lead directly to the ejection of negative ions. {copyright} {ital 1996 The American Physical Society.}

Desorption of positive and negative fluorine ions from BaF2 surfaces by core level excitation under electron bombardment

Electron stimulated desorption of negative and positive fluorine ions from BaF2 surfaces has been studied as a function of impact electron energy. Thresholds observed for F+ and F− are correlated with core‐level binding energies of Ba atoms. We propose that core level ionization of Ba ions, followed by an interatomic Auger decay involving halogen ions, can initiate F+ desorption, while the formation and subsequent breakup of superexcited molecular complexes containing a core hole can lead directly to the ejection of negative ions.

Desorption of positive and negative ions from SiO2/Si surfaces by electron excitation of core levels.

Electron-stimulated desorption of positive and negative oxygen ions and positive, multiply charged silicon ions from thin ${\mathrm{SiO}}_{2}$/Si films has been studied as a function of impact electron energy. Thresholds observed for ${\mathrm{O}}^{+}$ are correlated with core-level binding energies of substrate atoms. Desorption of negative ions closely follows threshold behavior of positive ions; it is explained in terms of a charge-exchange process in which the outgoing positive ions (or neutrals) capture electrons in the surface region and desorb as negative ions. Desorption of multiply charged silicon ions is also related to creation of core holes, but requires some additional, multielectron excitations.

Polarisation of radiation from H2excited by electron impact Lyman and Werner emissions and Lyman-α

The polarisation of selected Lyman and Werner bands and also of Lyman- alpha radiation are measured as a function of impact electron energy in the range from threshold to 300 eV. Polarisations in excess of 0.2 are obtained in certain instances. The results for Lyman- alpha confirm and extend those of Ott et al. (1970). Extrapolations of the results to the thresholds are compared with estimates based on angular-momentum conservation and symmetry arguments. For the Werner emission a further comparison is made with a 'pseudo'-threshold polarisation measurement using the scattered-electron-delayed-photon coincidence technique. The apparent excitation functions for the two molecular emissions are derived from the measurements of polarisation. In both cases good agreement is obtained with the semi-empirical data of Gerhart (1975). Comparison is made with the results of other workers wherever possible.