Gas Sensing on Oxidized Bronze

We perform oxidation and phase segregation of bronze (an alloy of Cu: Sn = 95: 5) and demonstrate that the heterogeneous oxide formed is suitable for oxygen sensing. Tin oxide (SnO₂) is an n-type semiconductor whereas, cupric oxide (CuO) is a p-type semiconductor. Both oxides have shown sensitivity to detecting gas molecules. Therefore, the presence of both n and p-type oxide on the same substrate can lead to a sensory platform with a wide array of gas sensing capabilities.

Thermally oxidized bronze forms a CuO layer on top, underneath which exists a mixed, CuO-SnO₂ layer. It is found that Sn segregates to the grain boundaries whereas Cu exists mostly on grain surfaces. This happens due to the differences in the diffusion constants of the Cu and Sn atoms. Further, the oxidation process creates a variety of nanostructures including CuO nanowires and SnO₂ plates. Supporting characterization data is provided via SEM, HRTEM, Raman and x-ray diffraction.

The oxidized samples are then prepared as conductometric sensors for testing various gasses. As an example, on the introduction of dry air into a vacuum chamber (maintained at 2 mTorr), the devices showed a 10% resistance change at 400 K and a 6% resistance change at 373 K. This indicates that facile thermal oxidation of low-cost alloy substrates can lead to the formation of effective, ‘on-skin’ sensors.