Highly sensitive and selective trimethylamine sensor using one-dimensional ZnO-Cr ₂O ₃ hetero-nanostructures

Highly selective and sensitive detection of trimethylamine (TMA) was achieved by the decoration of discrete p-type Cr ₂O ₃ nanoparticles on n-type ZnO nanowire (NW) networks. Semielliptical Cr ₂O ₃ nanoparticles with lateral widths of 38nm were deposited on ZnO NWs by the thermal evaporation of CrCl ₂ at 630°C, while a continuous Cr ₂O ₃ shell layer with a thickness of 3040nm was uniformly coated on ZnO NWs at 670°C. The response (R _a/R _g: R _a, resistance in air; R _g, resistance in gas) to 5ppm TMA of Cr ₂O ₃-decorated ZnO NWs was 17.8 at 400°C, which was 2.4 times higher than that to 5ppm C ₂H ₅OH and 4.38.4 times higher than those to 5ppm p-xylene, NH ₃, benzene, C ₃H ₈, toluene, CO, and H ₂. In contrast, both pristine ZnO and ZnO (core)Cr ₂O ₃ (shell) nanocables (NCs) showed comparable responses to the different gases. The highly selective and sensitive detection of TMA that was achieved by the deposition of semielliptical Cr ₂O ₃ nanoparticles on ZnO NW networks was explained by the catalytic effect of Cr ₂O ₃ and the extension of the electron depletion layer via the formation of pn junctions.