Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.
The formation of the ͕12 10͖ stacking fault, which has two atomic configurations in wurtzite ͑Ga,Al,In͒N, has been investigated by high-resolution electron microscopy and energetic calculations. It originates from steps at the SiC surface and it can form on a flat ͑0001͒ sapphire surface. A modified Stillinger-Weber potential is used in order to investigate the relative stability of the two atomic configurations which have comparable energy in AIN, whereas the 1 2 ͗101 1͕͘12 10͖ atomic configuration should be more stable in GaN and InN.Experimental evidence is shown in the case of AIN and GaN from high-resolution electron microscopy. Observations carried out in plan-view show the 1 2 ͗101 1͕͘12 10͖ atomic configuration in GaN layers. The 1 6 ͗202 3͘ configuration was found in small areas inside the AIN buffer layer in cross-section observations. It folds rapidly to the basal plane, and when back in the prismatic plane it bears the 1 2
The infrared modes of annealed Si1−yCy alloys were studied experimentally and theoretically. The alloys were grown on Si(100) substrates by solid-source molecular beam epitaxy and were characterized by Fourier transform infrared spectroscopy. At annealing temperatures above 850 °C, the localized vibrational mode of substitutional C around 605 cm−1 diminished in intensity while another mode due to incoherent silicon carbide precipitates appeared at 810 cm−1. For lower processing temperatures, a peak around 725 cm−1 has been tentatively attributed to a C-rich phase, which is a precursor to SiC precipitation. Theoretical calculations based on the anharmonic Keating model predict that small (1 nm) 3C–SiC coherent precipitates may actually produce a mode at 725 cm−1. This mode occurs if the bonds gradually vary in length between the C-rich region and the host lattice. On the other hand, if the bonds are abruptly distorted at the edges of the precipitate, it becomes elastically isolated from the host lattice, and the 810 cm−1 mode appears. This study yields a picture of the thermal stability of dilute SiC alloys, which is important for the high-temperature processing steps necessary for device applications. Moreover, the coherent precipitation may provide a controllable way to form self-assembled 3C–SiC quantum dots into silicon germanium carbon alloys.
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