Enhanced ammonia sensing characteristics of Cr doped CuO nanoboats

• Undoped and Cr doped (2 and 6 at.%) CuO nanorods and nanoboats were synthesized by hydrothermal method.
• Green emission in doped samples validates the presence of oxygen vacancies which is absent in undoped CuO.
• Correlation between nanostructure and properties (e.g., electrical, optical) was established.
• Enhancement of ammonia sensing was observed for 6 at.% Cr doped CuO nanoboats due to relatively low activation energy.

Here, we report a room temperature NH3 sensing prototype with an enhanced sensitivity utilizing undoped CuO nanorods (NRs) and Cr doped (2 at.% and 6 at.%) CuO nanoboats (NBs) synthesized by a simple hydrothermal method. Deep level emissions were observed in the range of 350–610 nm by photoluminescence analysis. The observed green emission in Cr doped samples indicates the presence of oxygen vacancies which are induced by doping. Electrical measurements confirmed the ohmic contact of the samples with Ag electrode. The temperature and gas concentration dependence on the sensing properties demonstrated that the addition of Cr significantly enhanced the sensing performance towards NH3 in the 100–600 ppm concentration range at room temperature. In the case of 6 at.% Cr doped CuO NBs, a 2.5 fold increase in sensor response was observed at room temperature and a maximum sensitivity of 180% at 75 °C for 600 ppm of NH3. The enhanced sensing response is attributed to the increase in surface area, surface charge and oxygen vacancies in CuO nanostructures by Cr doping.

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