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Abstract: The morphological changes induced in (RuPc)2 gas sensing thin films by hydration and de-hydration processes were investigated. Prior to this study a preliminary characterization was performed by conductivity measurements upon exposure to NO2 gas fluxes, to verify the electrical sensing response of the films. This response was correlated to the bulk morphological modification of the films. Subsequently, the effect of external moisture on the morphological stability of the films was addressed. This morphological characterization of the films was performed by using the energy dispersive X-ray reflectivity (EDXR) and atomic force microscopy (AFM) techniques, both ex situ and in situ, i.e. under operating conditions, during exposure of these films to 100% of relative humidity. The measurements allowed an accurate observation of both the surface morphology (i.e. its roughness obtained independently by EDXR and AFM). Moreover bulk evolution of the films was obtained by in situ EDXR and the morphological changes allowed to retrieve information on the water uptake dynamics. Moreover, the reversibility of the water/film interaction was studied and correlated to the sensing properties of the (RuPc)2. [Copyright &y& Elsevier]

Abstract: The present study investigates the response of NO2 gas sensing devices, based on bis(phthalocyaninato)titanium thin films, by combined electrical and time-resolved energy-dispersive X-ray reflectometry (EDXR) analysis. Samples of various thicknesses were exposed to a NO2 gas flux and their electrical response was recorded, during interaction with the oxidising molecules. At the same time, the changes induced in the film thickness and roughness, produced by the “breathing like” mechanism, which characterized the diffusion of the gas in the film bulk, were monitored by EDXR. Comparing the two results, the first direct correspondence between the morphological changes and the electrical response of the sensor was found. This also demonstrates that the morphological characteristics of the films are actually related to their sensing behaviour and can therefore be used, as an alternative to the electrical response, to follow the gas–film interaction process. [Copyright &y& Elsevier]