Hydrogensulfide threshold sensors
Hydrogensulfide gas (H2S) is an important key gas for the control of biogas plants and must therefore be measured to protect people and machines. For this purpose, threshold sensors for H2S detection based on percolation effects in nanostructured copper oxide materials are to be researched.
When offering hydrogensulfide gas, copper oxide films (CuO, p-type semiconductors) show an abrupt increase in the conductance by several orders of magnitude, which can be described with the help of percolation theory. Chemical reactions of the H2S with the CuO produce coppersulfide islands (CuS, degenerate p-type semiconductors, metallic conductivity) on its surface, which cross-link to form highly conductive paths from a certain gas dose (gas concentration x time). This effect can be used for dose measurement.
The dose at which the switching of the film takes place is determined by the geometry and can only be controlled within certain limits by the operating temperature. In addition, the film sensors cannot be regenerated, since there are morphological changes in the film during the phase change.
As part of the project, the CuO geometry is modified with the help of various nanostructuring processes and the switching thresholds are varied (see Figure 1). The use of suitable nanocomposite materials also enables the structures to be stabilized (e.g. by preventing migration effects) and thus enables the production of regenerable sensors. In addition to experimentally researching the underlying percolation effects, the results are analyzed using theoretical model systems.