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Ab initio quantum chemical methods were used to study ground-state energies and geometrical configurations of boron and boron hydrogen chains. The ground-state energies of the boron chain were found to be comparable with those of boron clusters. The structure of chains can be obtained by unfolding the two rings of boron nanotubes. The ab initio ground-state energies of the dimerized (BH)n chain were fitted into the SSH model, in order to determine the corresponding parameters for the ground-state energy. According to the SSH model, this dimerization induces a band gap of around 0.6 eV.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 AbstractThe effects of the addition of small amounts of Zr and Hf (0.5 -3 %) on the atomic structure of Al 88 Y 7 Fe 5 metallic glass were examined from extended x-ray absorption fine structure (EXAFS) experiments to better understand the influence of these microadditions on the glass forming ability of this alloy. Measurements at the Zr K and Hf LIII absorption edges have allowed the local structures around Zr and Hf atoms to be determined. The same Al environment was found for the different concentrations, consisting of a small cluster extending up to 4.5 Å around the Zr atoms and up to 6 Å around the Hf ones. Although the clustering effect is smaller in the Zr neighbourhood, a drastic shortening of the nearest Zr-Al distance is shown, providing evidence for some covalent character to the bonding, in line with the increased glass-forming ability found in the alloys made with the Zr microaddition.

The electric field effect on the carrier capture cross section of deep traps has been studied. The experimental results on the H4F and H5 hole traps in p-type InP show an enhancement of the capture cross section with the increase in the applied electric field. This enhancement depends on the nature of the deep traps and its peak temperature. Increasing the electric field from 4.1×106 to 2.4×107 V/m leads to an increase in the H4F capture cross section by a factor of 3 to 20. While in the case of H5 it increases by a factor of 2 to 5 by increasing the applied electric field from 8.0×106 to 2.4×107 V/m. A theoretical model has been suggested to explain the electric field effect on the capture cross section. This model deals with the cascade and multiphonon processes semiclassically. Applying this model to the above deep traps, we have found that H4F is negatively charged complex and H5 is positively charged complex.

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