Silicon
Silicon Powder
Michael Frenklach, Larry Ting, Hai Wang, and Martin J. Rabinowitz,
'Silicon Particle Formation in Pyrolysis of Silane and Disilane',
submitted for publication.
ABSTRACT
Silane and disilane diluted in argon and hydrogen mixtures were pyrolyzed behind
incident shock waves at temperatures from 900 to 2000 K, pressures from 0.2 to
0.7 atm, and total concentration from 3e+16 to 1e+17 silicon atoms per cm^3.
Formation of silicon particles was monitored by the attenuation of laser beams of
two different wavelengths, thereby determining particle size, number density, and
fractional yield. The conversion of silane and disilane into silicon particles
exhibited a pronounced maximum at about 1150 K, which was found to be affected by
reaction pressure, initial reactant concentration, and addition of hydrogen.
Selected silicon particle samples were examined by electron diffraction,
transmission electron microscopy, and secondary ion mass spectrometry. The
results indicated that the produced particles were spherical, ranging from 100 to
400 A in diameter, loosely agglomerated, and contained about 15 % hydrogen on an
atomic basis. A detailed chemical kinetic model was developed that describes
gas-phase pyrolysis of the parent molecule and homogeneous nucleation of silicon
particles by 117 elementary reactions of 42 chemical species, and coagulation of
the forming particles and their growth by gas-surface deposition reactions with a
method of moments. The model predictions were found to be extremely sensitive to
the values of optical constants assigned to the silicon particle material.
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