Sol-gel deposition of nanostructured low refractive index materials on solar collector glazing

Nanoporous SiO2 and nanocomposite MgF2:SiO2 coatings have been deposited by sol gel dip-coating in a particle-free atmosphere. The refractive index of the prepared nanostructured thin films is determined from spectrophotometric data. In both cases, significantly lower values than for compact SiO2 have been achieved. Highly transparent samples have been produced in a single dip-coating step followed by simple thermal annealing in air. Broad spectral transmittance maxima are observed exceeding values of 98.5% (nanoporous SiO2) and 99.5% (quaternary Mg:F:Si:O films). MgF2:SiO2 nanocomposite thin films can be expected to exhibit a higher aging stability than porous SiO2 films with respect to pore-filling by hydrocarbons and are therefore a promising alternative as well for single-layered anti reflection coatings as for multilayered coulored coatings on solar collector glazing

Aluminum-induced in situ crystallization of HWCVD a-Si : H films

Aluminum-induced in situ crystallization (AIC) of amorphous silicon films deposited by hot wire chemical vapor deposition (HWCVD) on glass is demonstrated. Aluminum was deposited at temperatures varying from room temperature to 300 degrees C on HWCVD a-Si:H films. The AIC was observed to take place in situ during the deposition of Al films, when the glass/a-Si:H temperature is kept 300 degrees C. A 20-nm Al film was effective in inducing crystallization of about 63% in the a-Si:H film. Thus, separate post-deposition annealing step can be avoided. For an Al film thickness comparable to the amorphous silicon film deposited at an optimum deposition rate, crystallization at temperature as low as 200 degrees C is observed. It was also observed that the growth pattern of c-Si in case of AIC without post-deposition annealing was identical to AIC with annealing step. (c) 2007 Elsevier B.V. All rights reserved