Abstract
Abstract. Copper oxides, such as CuO and Cu2O, are promising materials for H2S detection because of the reversible reaction with H2S to copper sulfides (CuS, Cu2S). Along with the phase change, the electrical conductance increases by several orders of magnitude. On CuOx films the H2S reaction causes the formation of statistically distributed CuxS islands. Continuous exposition to H2S leads to island growth and eventually to the formation of an electrical highly conductive path traversing the entire system: the so-called percolation path. The associated CuOx ∕ CuxS conversion ratio is referred to as the percolation threshold. This pronounced threshold causes a gas concentration dependent switch-like behaviour of the film conductance. However, to utilize this effect for the preparation of CuO-based H2S sensors, a profound understanding of the operational and morphological parameters influencing the CuS path evolution is needed.Thus, this article is focused on basic features of H2S detection by copper oxide films and the influence of structural parameters on the percolation threshold and switching behaviour. In particular, two important factors, namely the stoichiometry of copper oxides (CuO, Cu2O and Cu4O3) and surface morphology, are investigated in detail. CuOx thin films were synthesized by a radio frequency magnetron sputtering process which allows modification of these parameters. It could be shown that, for instance, the impact on the switching behaviour is dominated by morphology rather than stoichiometry of copper oxide.
Highlights
Hydrogen sulfide (H2S) exhibits a characteristic odour of rotten eggs and is released, for example, during the generation of biogas
Aside from the conductance measurements, the materials were carefully characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD)
In order to identify the relevant factors for manipulation of the percolation threshold, Cu thin films were oxidized by different thermal programs; the resulting changes in the oxide growth causes changes in the surface morphology of the samples
Summary
Hydrogen sulfide (H2S) exhibits a characteristic odour of rotten eggs and is released, for example, during the generation of biogas. The dosimetric behaviour of the copper-oxide-based sensors allows the detection of very small concentrations to, for example, predict filter breakthrough. Sharma (1980) noted that the reactivity of Cu2O towards H2S can strongly depend on the humidity (Sharma, 1980) As another potentially important factor, the morphology of copper oxides (surface area, roughness, grain boundaries, etc.) is expected to exert a significant impact on the conductance increase and percolation effect. Since a precise determination of the conductance is inevitable for such comparison, films prepared by RF sputtering are ideal with respect to their overall homogeneity For these measurements, a H2S concentration range between 1 and 10 ppm was used, being similar to typical applications. Aside from the conductance measurements, the materials were carefully characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD)
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