Hamburg 2001 – scientific programme

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DS: Dünne Schichten

DS 31: Postersitzung

DS 31.47: Poster

Tuesday, March 27, 2001, 16:30–17:30, Foyer Saal 4

GASOCHROMIC TUNGSTEN OXIDE FILMS (WO₃): A CORRELATION BETWEEN FILM PROPERTIES AND COLORATION KINETICS — •Chr. Salinga, H. Weis, and M. Wuttig — I. Physikalisches Institut A, RWTH Aachen, 52062 Aachen

Optically switchable coatings based on tungsten oxide offer a wide variety of promising applications, such as the variation of transmission in smart windows. This allows a control of solar energy flux into the room. For this purpose large area coatings are needed, which are usually realized by reactive-dc-magnetron-sputtering. Fast switching is desirable and hence the understanding of the influence of deposition parameters on switching kinetics is essential. We have examined the influence of deposition pressure and target age. Our research focusses on gasochromic switching of WO₃-films with a Pd catalyst cap layer, colored by a gas atmosphere with diluted hydrogen and bleached by an oxygen containing gas. The samples showed a lateral inhomogeneous switching behaviour, where the coloration speed varied over more than one order of magnitude. To understand this phenomenom the samples were laterally analyzed by optical spectroscopy and subsequent simulations of their dielectric function. Switching kinetics of the films could be correlated to the index of refraction n: regions with high n did not switch, regions with lower n showed fast switching behaviour. Since n is linked via the Lorentz-Lorenz equation to the film density, this implies that films with a low density switch much faster than high density films. Finally a model to explain the observed lateral inhomogeneous deposition and switching behaviour is presented.