On the primary process in the plasma‐chemical and photochemical vapor deposition from silane. Mechanism of the radiative species SiH*(A 2Δ) formation

Experimental scaling of plane-Born cross sections and ab initio assignments for electron-impact excitation and dissociation of XF4 (X = C, Si, and Ge) molecules

Electron energy loss spectra of carbon tetrafluoride, silicon tetrafluoride, and germanium tetrafluoride molecules (CF₄, SiF₄, and GeF₄) have been measured for incident electron energies of 50-360 eV at 1.5°-15.5° and for 30 eV and 30° scattering angle, while sweeping the energy loss over the range 9.0-20.0 eV. Low-lying valence excited triplet and singlet states are investigated by quantum chemical ab initio calculations. The Rydberg series converging to the (lowest) ionisation energy limits of XF₄ (X = C, Si, Ge) are also identified and classified using the systematic behaviour according to the magnitude of the quantum defects. A generalized oscillator strength analysis is employed to derive oscillator strength f₀ value and the apparent Born integral cross sections from the corresponding differential cross sections by using the Vriens formula for the optically allowed transitions. The f₀ value is compared with the optical oscillator strength of the photoabsorption, pseudo-photon measurements, and theoretical values. The binary-encounter and f-scaled Born cross sections of the most intense optically allowed transitions have been also derived from the excitation threshold to the high energy region where the Born approximation is valid. Potential energy curves were obtained along the XF₃ + F coordinate with two different basis sets to lend support on electron impact dissociation processes yielding radical formation. We found that in CF₄, the lowest-lying dissociative character is due to intramolecular conversion from Rydberg 3s to valence character (σ*(C-F)), whereas in SiF₄ and GeF₄, an antibonding behaviour prevails.

Matrix isolation infrared observation of HxSi(N2)y (x = 0, 1, 2 and y = 1, 2) transient species using a 121-nm vacuum ultraviolet photolysis source

Vacuum ultraviolet photolysis (121.6 nm) of silane in a nitrogen matrix at 12 K leads to the observation of several transient species, which have been characterized using Fourier transform infrared spectroscopy. Four transient species containing silicon and nitrogen have been observed (SiN2, Si(N2)2, HSiN2, and H2SiN2), and one transient species containing only silicon and hydrogen has been observed. The assignment of the infrared bands due to each of these species is accomplished by performing isotopic substitution experiments (SiD4, 15N2, and mixtures with SiH4 and 14N2), matrix annealing experiments, UV-visible photolysis experiments, by comparison with previous experimental matrix isolation frequencies, where available, and for HSiN2 and H2SiN2 by comparison to B3LYP/aug-cc-pVTZ-calculated vibrational frequencies. The observation and infrared assignment of the HSiN2 and H2SiN2 molecules in these experiments is significant in that HSiN2 has not been previously reported in the matrix isolation literature, and H2SiN2 has only been reported once previously by a different route of formation. The energetics of the overall formation pathways for the molecules observed in these experiments is discussed using B3LYP/aug-cc-pVTZ calculations.