Abstract
Time-resolved optical emission spectroscopy, with a resolution of ≂10 ns, was used to investigate the formation of excited photofragments during pulsed ArF excimer-laser irradiation of gaseous aluminum bromide. The solid Al2Br6 source was maintained at 50 °C and Ar used as a carrier gas to provide an aluminum bromide partial pressure of ≂3×10−6 Torr (4×10−4 Pa). The total pressure in the reactor was typically 300 mTorr (40 Pa). Following the laser pulse, emission was observed from the Al 4s 2S1/2→3p 2P1/2 and 4s 2S1/2→3p 2P3/2 transitions at 394 and 396 nm, respectively. The decay of the Al emission intensity IAl was convoluted with the temporal shape of the excitation pulse since the radiative lifetime of the Al 2S state, 6.8 ns, was less than the laser pulse width, ≂20 ns. The rise time of IAl, on the other hand, was <10 ns, indicating that Al was formed photolytically rather than through subsequent collisions involving photofragments. IAl varied with the ArF laser intensity Ihν as IAl∝I2hν for Ihν≲4.5 MW cm−2 and IAl∝Ihν at higher laser fluences. Raising the source gas temperature to increase the AlBr3 to Al2Br6 ratio in the feed gas, at constant total pressure, dramatically increased IAl.
Published Version
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