Light scattering spectroscopy of the liquid-glass transition : comparison with idealized and extended mode coupling theory
Light scattering experiments were performed on several fragile glass-forming materials at temperatures ranging from above the melting temperature T, to below the calorimetric glass transition temperature T, in the frequency range 0.2 GHz to 4000 GHz. The experimental susceptibility spectra x”(o) exhibit both the form and the scaling properties predicted by the idealized mode coupling theory. In particular, the scaling frequency o, was found to obey the power law w, a 1 T T,_jzO for three different materials, confirming the predicted “critical slowing down” as T+ Tc from either above or below. At low frequencies and temperatures the spectra deviate from the predictions due to the neglect of ergodicity-restoring activated transport (hopping) processes. We have therefore reanalyzed the data using the extended version of the theory, including activated transport.
Light scattering spectroscopy of the liquid-glass transition
Supercooled liquids approaching the liquid-glass transition exhibit unusual properties associated with structural relaxation. The mode-coupling theory (MCT) of supercooled liquid dynamics shows that non-linear interactions among density fluctuation modes can produce effects resembling these observations. MCT produces detailed predictions for the dynamics of density fluctuations in supercooled liquids, including a crossover from liquid to glassy dynamics at a critical temperature Tc. Recent light scattering studies of supercooled CaKNO3 are described that have provided detailed tests of MCT both above and below Tc, including a cusp in the scaling time at Tc=105+or-5 degrees C. These experiments are reviewed, and comparisons with both the idealized and extended versions of MCT are described.
Anomalous Annealing Behavior of Arsenic Implanted Silicon as a Function of Dose and Energy
Anomalous annealing behavior of damage in As implanted Si has been investigated by channeling effect measurements. Room temperature As implants with doses from 1014 to 2 × 1016cm-2 at energies ranging from 50 to 250 keV into Si were annealed over the range of 600°C to 1100°C. Anneal temperatures ≥ 950°C reduce the disorder for ion doses of 0.5 to 1 × 1016 cm-2 at energies between 50 and 250 keV. Anomalously high residual disorder was found for the intermediate doses of 2 × 1014 to 2 × 10/cm2 implanted above 100 keV. For this intermediate dose, annealing of implants performed at liquid nitrogen temperatures did not show significant reduction in this damage. However implants at 200° to 300°C indicate a lower amount of damage compared to the room temperature implants.