Newly developed SnO2:F films having “double–texture (W-texture)” were evaluated in terms of optical and electrical properties and compared with Asahi type-U substrate. “W-textured” transparent conductive oxide (TCO) film was composed of a combination of 300-500nm large hills and small pyramidal texture covering them. “W-textured” TCO could show a large haze value exceeding 80% even at 800nm. Microcrystalline Si (μc-Si:H) thin film solar cells were fabricated on these TCOs and characterized. The result showed that a quantum efficiency of μc-Si:H solar cells was improved with “W-textured” TCOs significantly in longer wavelength region.

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We construct boundary states for supertubes in the flat spacetime. The T-dual objects of supertubes are moving spiral D1-branes (D-helices). Since we can obtain these D-helices from the usual D1-branes via null deformation, we can construct the boundary states for these moving D-helices in the covariant formalism. Using these boundary states, we calculate the vacuum amplitude between two supertubes in the closed string channel and read the open string spectrum via the open closed duality. We find there are critical values of the energy for on-shell open strings on the supertubes due to the non-trivial stringy correction. We also consider supertubes in the type IIA Gödel universe in order to use them as probes of closed timelike curves. This universe is the T-dual of the maximally supersymmetric type IIB PP-wave background. Since the null deformations of D-branes are also allowed in this PP-wave, we can construct the boundary states for supertubes in the type IIA Gödel universe in the same way. We obtain the open string spectrum on the supertube from the vacuum amplitude between supertubes. As a consequence, we find that the tachyonic instability of open strings on the supertube, which is the signal of closed time like curves, disappears due to the stringy correction.

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