Regensburg 2010 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 6: Poster Session I
DY 6.28: Poster
Montag, 22. März 2010, 16:00–18:00, Poster B2
Gas sensitivity in nanoporous crystalline metal oxide: a site-bond percolation approach — •Julia Dräger1, Stefanie Russ2, Claus-Dieter Kohl3, and Armin Bunde1 — 1Institut für Theoretische Physik III, 35392 Giessen — 2Freie Universität Berlin, 14195 Berlin — 3Institut für Angewandte Physik, 35392 Gießen
By means of a site-bond percolation model we study numerically and analytically the gas-induced metal-insulator transition of thin films of nanoporous crystalline metal oxides. We model the layers by a network of intergranular contacts where the conductances of the grains (sites) and of the bonds depend on the amount of adsorbed gas molecules that extract electrons from the inner part of the grains, leaving a depletion zone. While below a critical gas concentration Nc the nanoporous structure is insulating due to the absence of a conducting percolating cluster, above Nc the conductance increases rapidly. Depending on the parameters of the system (layer thickness, average grain size, coordination number) we find two different scenarios: for systems of small grains and high porosity (i.e low coordination number) the transition from a conducting towards an insulating phase arises from the disappearance of conducting grains due to the lack of charge carriers. For systems of large grains and lower porosity, on the other hand, the transition is governed by the bond percolation effect, which reflects the influence of the depletion zone on the grain necks and thus on the bonds. Furthermore, we explore which details of the shape of the characteristic curve are due to percolation effects and which properties arise from the variation of the bonds.