A semi-Riemannian metric in a n-manifold has n(n − 1)/2 degrees of freedom, i.e., as many as the number of components of a differential 2-form. We prove that any analytic semi-Riemannian metric can be obtained as a deformation of a constant curvature metric, this deformation being parametrized by an analytic 2-form.
Any three-dimensional metric g may be locally obtained from a constant curvature metric, h , by a deformation likewhere σ and s are respectively a scalar and a one-form, the sign ǫ = ±1 and a functional relation between σ and the Riemannian norm of s can be arbitrarily prescribed. The general interest of this result in geometry and physics, and the related open problems, are stressed.
In this paper we present new results on doped c-Si:H thin films deposited by Hot-Wire Chemical Vapour Deposition (HWCVD) in the very low temperature range (125-275 ºC). The doped layers were obtained by the addition of diborane or phosphine in the gas phase during deposition. The incorporation of boron and phosphorus in the films and their influence on the crystalline fraction are studied by Secondary Ion Mass Spectrometry and Raman Spectroscopy respectively. Good electrical transport properties were obtained in this deposition regime, with best dark conductivities of 2.6 S/cm and 9.8 S/cm for the p-and n-doped films respectively. The effect of the hydrogen dilution and the layer thickness on the electrical properties are also studied. Some technological conclusions referred to cross contamination could be deduced from the nominally undoped samples obtained in the same chamber after p-and n-type heavily doped layers.
The possible use of poly(ethylene naphthalate) as substrate for thin silicon solar cells has been studied in this paper. The transparency of this polymer makes it a candidate to be used in both substrate and superstrate configurations. ZnO:Al has been deposited at room temperature on top of PEN. The resulting structure PEN/ZnO:Al presented good optical and electrical properties. PEN has been successfully textured (nanometer and micrometer random roughness) using Hot-Embossing Lithography. Reflector structures have been built depositing Ag and ZnO:Al on top of the stamped polymer. The deposition of these layers did not affect the final roughness of the whole. The reflector structure has been morphologically and optically analysed to verify its suitability to be used in solar cells.
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