RESUMO
Smith-Purcell (SP) radiation produced by interaction of fast electron beams running parallel to strings of nanoparticles is investigated. Results for the radiation emission probability and electron energy loss spectra using finite and infinite strings of Al and silica spheres are presented. Both of these quantities are obtained by solving Maxwell's equations exactly using a multipole expansion approach. The response of the spheres is described in terms of their local frequency-dependent dielectric functions. In silica, the emission probability is seen to coincide with the energy loss probability within the gap region, where the solid cannot absorb any energy. Large emission rates are predicted for Al, suggesting its possible application in tunable soft uv light generation. The dependence of the emission on the size of the spheres, the string period, and the electron energy is discussed in detail. Finite size effects are also studied for strings of 1-15 Al spheres.
RESUMO
Measurements and theoretical calculations are reported for an interatomic multi-atom resonant photoemission (MARPE) effect that permits direct determination of near-neighbor atomic identities (atomic numbers). MARPE occurs when the photon energy is tuned to a core-level absorption edge of an atom neighboring the emitting atom, with the emitting level having a lower binding energy than the resonant level. Large peak-intensity enhancements of 33 to 105 percent and energy-integrated effects of 11 to 29 percent were seen in three metal oxides. MARPE should also be sensitive to bond distance, bonding type, and magnetic order, and be observable via the secondary processes of x-ray fluorescence and Auger decay.