CuO thin films for the detection of H₂S doses: Investigation and application

Abstract

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 20 ppm H2S at 180 °C. The percolation threshold pc is reached 1054 s after start of the measurement.

H<sub>2</sub>S dosimeter with controllable percolation threshold based on semi-conducting copper oxide thin films

“…For the sake of ease of the experiment, it was decided to only apply DC pulses. Reproducibility of the experimental method was already shown by Hennemann et al (2015b) utilizing the same setup; a couple of different samples of one batch measured under same conditions exhibited variations in switching time of ±5 %. Comparison of this earlier work with the actual results also reveals high reproducibility of the chosen methodology.…”

Gas Responsive Nanoswitch: Copper Oxide Composite for Highly Selective H2S Detection

“…Opposed to effect (i), this cannot be explained by a catalytic surface process. As it is known for film type structures, this is rather caused by the formation of CuS, which is a strongly degenerated p‐type semiconductor with close to metallic conductivity (0.37 S cm −1 ) . The number of CuS particles increases as a function of the absolute absorbed amount of H 2 S. It is assumed, that at a certain threshold concentration, conducting pathways of CuS particles throughout the pore structure of the composite material are responsible for the observed conductance increase.…”

“…In summary, it could be shown, that the new composite material offers major advantages in terms of long‐term stability over current CuO based materials …”

“…The large conductivity variation accompanied by the formation of CuS was already utilized to build CuO thick film sensing layers . The described (localized) chemical transformation leads to a distinct switching transition in the generated electrical signal; significantly different from the signal shape observed for adsorption type sensors.…”

Copper oxide nanofibres for detection of hydrogen peroxide vapour at high concentrations

“…Subsequently, the fibres were calcinated for 24 h in ambient air at 600 °C in order to remove the polymer and convert the Cu(NO 3 ) 2 to CuO. In this way, CuO fibres with a mean diameter of 483 ± 143 nm are formed .…”