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Hennemann J.,Institute of Applied PhysicsJustus Liebig University GiessenHeinrich Buff Ring 1635392GiessenGermany | Kohl C.-D.,Institute of Applied PhysicsJustus Liebig University GiessenHeinrich Buff Ring 1635392GiessenGermany | Smarsly B.M.,Institute of Physical ChemistryJustus Liebig University GiessenHeinrich Buff Ring 5835392GiessenGermany | Sauerwald T.,Laboratory of Measurement TechnologySaarland UniversityCampus A566123SaarbruckenGermany | And 2 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2015

We present a new concept for the detection of hydrogen sulfide (H2S) doses based on percolation effects in semiconducting (p-type) copper (II) oxide (CuO) thin films. Under H2S exposure at 180°C CuO undergoes a chemical reaction to metallic conducting copper (II) sulfide (CuS). Reaching a certain dose of H2S (concentration×exposure time) the conductance increases rapidly by two orders of magnitude which is attributed to the formation of CuS percolation paths. This study focuses on the reproducibility of this effect as well as on theoretical modeling of the assumed underlying percolation mechanism. Analysis of conductance data reveals a behavior that is qualitatively very similar to standard scaling theory, but with a lower conductance exponent of μ≈0.85 (instead of 1.3 for 2D systems). The deviation can be explained by a superimposing diffusion process and by deviations of the experimental systems from standard percolation systems. Nevertheless, the CuO thin films exhibit intrinsic structure controlled thresholds for H2S doses, which allows the utilization as H2S dosimeter. Conductance behavior of a CuO thin film exposed to 20ppm H2S at 180°C. The percolation threshold pc is reached 1054s after start of the measurement. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Beu M.,Institute of Applied PhysicsJustus Liebig University GiessenHeinrich Buff Ring 1635392GiessenGermany | Klinkmuller K.,Institute of Applied PhysicsJustus Liebig University GiessenHeinrich Buff Ring 1635392GiessenGermany | Schlettwein D.,Institute of Applied PhysicsJustus Liebig University GiessenHeinrich Buff Ring 1635392GiessenGermany
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

Kelvin probe force microscopy at air in the dark and under illumination by visible light was performed for electrodeposited porous ZnO films, which were sensitized by the indoline dye D149. A contact potential difference was measured that confirmed electron injection into the semiconductor matrix and their subsequent stabilization in trap states. A locally widely homogenous signal was observed speaking in favor of a well-crystallized sample. The rise and decay times of the photovoltage in the ms to s timescale could be analyzed by use of individual scan lines or scanned images, respectively. The results are discussed in the context of recent pump-probe spectroscopy results as well as such from photoelectrochemical experiments with such electrodes and implications will be deduced for their use in dye-sensitized solar cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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