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An energetic electron beam has been used to stimulate crystallization of spatially isolated amorphous regions in Si, Ge, GaP, and GaAs at 30 and 300 K. In the four materials it was found that crystallization was induced even when the energy of the electron beam was less than that required to create point defects in the crystalline structure. The rate of crystallization depended on the material and on the electron energy. In all materials, the rate decreases as the electron energy increases from 50 keV (the lowest electron energy used), reaching a minimum value at an electron energy slightly below the displacement threshold voltage. Above the displacement threshold, the regrowth rate again increases with increasing electron energy. The possible role of electron-beam heating was studied both theoretically and experimentally. Calculations suggested heating effects were negligible and this was confirmed by in situ ion implantations and electron irradiations performed at 30 K, where subthreshold electrons stimulated crystallization. The subthreshold and low-temperature results are consistent with the model that the crystallization process is dependent on the creation of defects (dangling bonds and kinks) at the crystalline-amorphous (c-a) interface. The crystallization stimulated by the subthreshold electron beams suggests that electronic excitation of the bonds along the c-a interface can induce the amorphous to crystalline transition.

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The aggregation in dilute aqueous solutions of several ω-substituted single-chain quaternary ammonium surfactants has been studied by Krafft temperature and critical aggregation/micelle concentration measurements and by cryo-transmission electron microscopy:  (16-carboxyhexadecyl)trimethylammonium bromide (1a); (16-methoxycarbonylhexadecyl)trimethylammonium bromide (1b); (17,18-dihydroxyoctadecyl)trimethylammonium bromide (1c). Octadecyltrimethylammonium bromide (2) was included for comparison. The aggregation of 1a was also studied by Raman spectroscopy. Surfactant 1a at pH 6.8 forms ribbonlike fibers with lengths of up to 1.2 μm and cross sections of 3−4 nm × 12−16 nm; at pH 2.2, ribbon to rodlike fibers; and at pH 11.5, wormlike aggregates. Surfactants 1b and 1c at pH 6.8 form rod-shaped aggregates. The Raman spectroscopy results indicated that 1a is not in a fully extended conformation within its fibers at pH 6.8. Tentative structural models have been proposed for the aggregates of surfactants 1.

The damage produced in GaAs by implantation with low energy heavy ions has been studied as a function of ion mass and implantation temperature (30 and 300 K). The experiments were performed in situ in the microscope-accelerator facility at Argonne National Laboratory. In samples implanted and examined at 30 K, spatially isolated amorphous regions were produced by the direct impact of 50 keV Ar, Kr, and Xe ions. The probability that the impact of an individual ion formed an amorphous zone increased as the ion mass increased from Ar to Kr but not from Kr to Xe. The average dimension of the amorphous zones also increased with ion mass, being greater for the Xe than for the Kr ion implantation. On warming to room temperature, the amorphous zones decreased in size and density as the sample temperature was increased above 200 K. In samples implanted and examined at 300 K, the probability of forming an amorphous zone by direct impact increased as the ion mass increased from Kr to Xe, although the probability was always less than at 30 K. The density of amorphous zones produced at 300 K was similar to that remaining in a sample implanted at 30 K and then warmed to room temperature. With time at 300 K the amorphous zones decreased in size and eventually crystallized completely, leaving no trace of their prior existence.

Nanophase powders of Si, C, and SiC with narrow size distributions are synthesized by dissociating reactants in a dc are plasma and quenching the hot gases in a subsonic nozzle expansion. The plasma is characterized by calorimetric energy balances and the powders by on-line aerosol measurcment techniques and conventional materials analysis. The measured nozzle quench rate is about 5 × 106 K/s. The generated particles have number mean diameters of about 10 nm or less, with Si forming relatively dense, coalesced particles, while SiC forms highly aggregated particles. Our data suggest that SiC particle formation is initiated by the nucleation of small silicon particles.

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The response of AlxGa1−xAs/GaAs samples to bombardment with heavy ions (50 keV Kr+, 50 keV and 1.5 MeV Xe+) was studied as a function of ion dose at temperatures of 30 and 300 K using transmission electron microscopy. Samples with x=0.2 and 0.85 were used. Under all irradiation temperature and ion combinations, the AlGaAs was more resistant to amorphization than GaAs. The resistance increased with increasing Al content and decreased with decreasing irradiation temperature. This difference in the response may be attributed to differences either in the mechanisms by which a region is rendered amorphous (i.e., by direct impact amorphization or by the buildup of point defects) or to differences in the inherent stability (recrystallization temperature and rate) of individual amorphous zones in AlGaAs and GaAs.