Absolute cross section for the formation of Si(~1S) atoms following electron impact dissociation of SiH_4

摘要

A combination of elatmn scattering and laser-induced fluorescence ~LJF) techniques was used in the experimental determination of the absolute cross section for the formation of Si( 15) ground-state atoms following the neutral molecular dissociation of SiH4 by electron impact for energies from 20 eV ~ 100 eV. Electron impact on SiH4 produces—among other species—Sit ground-state arwus which are detected by pumping the Si(3p)2 ‘S—*(3p)(4s)’P transition at 390 nm with a tunable dye laser and recording the subsequent Si( 3p)(4s)1 P—4 ( 3p)2 ‘D fluorescence at 288 nm. We found a peak cross section for the formation of SiO 5) atoms from SiH4 of 4.5 ~ ~o- r cm2 at an impact energy of 60 eV. When compared to the previously determined total SiH4 neutral dissociation cross section obtained from measurements in a constant-flow plasma reactor Pen-in et aL, Chem. Phys. 73. 383 (1982)1, we find a branching ratio of about 0.037 for the formation of (‘S) atoms in the electron-impact induced neutral dissociation of SiH4. The absolute calibratiwi of our measured dissociation cross section was made relative to the cross section for the formation of N~(X) ground-state ions produced by electron impact- on N2 which was previously measured in. the same apparatus using the same experimental technique. This cross section is known to within 10 and can serve as a benchmark for the calibration of neutral dissociation cross sections as discussed previously Abramzon et al., I. Phys. B 32. L247 (1999)3.