Low-energy-electron collision cross-sections in silane

Abstract

A Monte-Carlo procedure has been used to evaluate elastic and vibrationally inelastic momentum transfer cross-sections which are consistent with measured electron swarm transport coefficients in SiH₄ and SiD₄ at low E/N(ratio of applied electric field to gas number density). In each molecule the elastic cross-section has a Townsend minimum between 0.3 and 0.4 eV electron energy. The form and magnitude of the derived vibrational excitation functions are consistent with direct (electron-vibrating dipole) excitation of the i.r.-active vibrations at energies close to vibrational threshold. Scattered electron spectra recorded in a trapped electron spectrometer confirm that vibrational excitation cross-sections in silane rise very steeply from threshold and also reveal a broad shape resonance at ca. 1.8 eV which enhances the vibrational excitation cross-sections. This is compatible with the electron swarm analysis.