Li/Na-doped CuO nanowires and nanobelts: Enhanced electrical properties and gas detection at room temperature

Oxide semiconductors are promising for gas sensing, but low-concentration gas sensing at room temperature (RT) remains a challenge. In this work, novel Li- and Na-doped CuO single-crystalline nanowires (NWs) and nanobelts (NBs) are synthesized using a low-cost process via stress-assisted growth and in-situ doping. The results show that the dopants induce a morphological transformation from NWs to NBs. Tauc's plots show an increasing redshift in the optical band gap with increasing Li or Na concentration, with a maximum shift of 0.075 eV from 1.2 eV for Li-doped CuO. The devices made of doped one-dimensional (1D) nanostructures (NSs) demonstrate enhanced conductivity and RT gas sensing sensitivity. Li-doped CuO NSs exhibit the greatest improvement in conductivity (104-fold), and enhanced gas sensitivity and selectivity to ethanol at a low concentration of 2 ppm at RT. A Mulliken charge-related mechanism is proposed to explain the excellent sensing performance.