- Matrix Reactions of SiH4 and GeH4 with F2. Infrared Spectra of Several HF Product Complexes
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Silane and germane were condensed with F2 at high dilution in argon on a 13 +/- 1 K substrate.Weak product complexes produced on condensation and increased by ultraviolet photolysis are assigned to SiH3F..HF, SiH2..HF or SiH2..(HF)2, and HSiF..HF.Annealing produced new bands due to F atom reactions that are attributed to SiH3..HF.The GeH3F molecule was observed in the similar GeH3F..HF complex.H-F vibrations in these complexes suggest that F is more basic in GeH3F than in SiH3F owing to the more electropositive nature of germanium as compared to silicon.
- McInnis, Thomas C.,Andrews, Lester
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p. 5276 - 5284
(2007/10/02)
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- THERMAL REACTIONS OF F2 AND NF3 WITH SILICON(110) STUDIED BY LASER IONIZATION MASS SPECTROMETRY
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The techniques of laser and electron ionization mass spectrometry have been employed to study the thermal etching of Si(110) by F2 and NF3 at substrate temperatures between 300 and 1200 K.By two-photon resonance-enhenced ionization of SiF2 via the B1B2 state, the apparent activation energy for gaseous silicon difluoride production was found to be 8.9+/-0.3 and 22.1+/-1.7 kcal/mol for F2 and NF3, respectively.SiF was not detected.An extensive search for SiF3 during etching by F2 at 1000 K, by means of resonance ionization from 320 to 325 and from 416 to 510 nm, also showed no signs of the species.Both SiF and SiF3 are thermochemically unimportant etch products under the conditions employed.In F2 etching, SiF4 and total silicon fluoride ΣSiFx+ signals as measured by electron ionization rose rapidly at lower temperatures and stabilized between 700 and 900 K before rising again.No such behavior was observed for SiF2 production from F2 or for the products formed in NF3 etching.Apparent activation energies for total silicon fluoride and SiF4 production are similar.For F2, they were found to be abaut 9 kcal/mol in the low-temperature region, and for NF3 both were measured to be abaut 21 kcal/mol.A proposed reaction mechanism explaining these and related results is discussed.
- Squire, D. W.,Dagata, J. A.,Hsu, D. S. Y.,Dulcey, C. S.,Lin, M. C.
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p. 2827 - 2834
(2007/10/02)
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- Energetics and dynamics in the reaction of Si+ with SiF4. Thermochemistry of SiFx and SiF+x (x=1, 2, 3)
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The title reaction is studied using guided ion beam mass spectrometry.Absolute reaction cross sections are measured as a function of kinetic energy from thermal to 40 eV, and three endothermic product channels are observed.The dominant SiF+ + SiF3 channel is only slightly endothermic, while the SiF3+ + SiF and SiF2+ + SiF2+ channels have much higher thresholds.The SiF3+ cross section magnitude is about half that of SiF+, while the SiF2+ cross section is an order of magnitude smaller than that of SiF+.A second feature which appears in the SiF2+ cross section is due to dissociation of SiF3+ .There is evidence that SiF+ and SiF3+ are produced via a direct mechanism.Competition between these two channels is interpreted in terms of molecular orbital correlations and qualitative potential energy surfaces.One surface is found to correlate only with the SiF3+ + SiF channel, while another correlates diabatically with this channel and adiabatically with the SiF+ + SiF3 channel.Competition on this latter surface has an energy dependence which is consistent with the Landau-Zener model.Reaction thresholds are analyzed to yield 298 K heats of formation for SiFx and SiFx+ species.From an evaluation of these and literature values, we recommend the following values:.
- Weber, M. E.,Armentrout, P. B.
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p. 6898 - 6910
(2007/10/02)
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