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« Wednesday May 27, 2009 »
Wed
Hypergratings: nanophotonics in planar anisotropic metamaterials Start: 2009-05-27 16:00 End: 2009-05-27 16:30 We present a technique capable of producing subwavelength focal spots in planar nonresonant structures not limited to the near-field of the source. The approach combines the diffraction gratings that generate the high-wave-vector-number modes and planar slabs of homogeneous anisotropic metamaterials that propagate these waves and combine them at the subwavelength focal spots. On the origin of p-type conductivity in BaCuChF (Ch = S, Se Te) Start: 2009-05-27 16:30 End: 2009-05-27 17:00 Density functional calculations have been performed to elucidate the source of unintentional p-type conductivity in nominally stoichiometric BaCuChF (Ch = S, Se, Te) wide bandgap semiconductors. Formation enthalpies and transition levels (activation energies) were found for all vacancies and antisites, and for some interstitials. Results of this initial study suggest that of all hole-producing point defects, copper vacancies are the easiest to form. The formation energy of copper vacancies decreases with increasing