Cu-doped p-type ZnO nanostructures as unique acetone sensor at room temperature (~25 °C)

We demonstrate prominent specificity on acetone gas sensing at room temperature (~25 °C) enabled solely by rendering ZnO nanostructures p-type via Cu doping of 0.8–3.7 at%, synthesized by chemical vapor deposition at 575 °C. Structural and chemical bonding analysis confirmed the successful substitution of Cu⁺¹ for Zn⁺² lattice sites leading to the conversion of n-type ZnO to p-type. Besides, Cu doping caused significant change in the morphology of the resulting ZnO nanostructures from highly aligned ZnO nanowires to randomly-aligned nanobelts, nanoribbons, and needle-like nanowires with length of 15–20 μm. The electrical measurement based on field-effect transistors comprising of individual nanowires revealed the transition of n- to p-type at a doping concentration of 1.1 at. %. The same devices were then exposed to acetone to monitor the gas sensing properties through chemiresistive responses as gas sensors. Both the un-doped and the Cu-doped n-type ZnO nanowires did not respond toward acetone exposure at room temperature. Exclusively, only the p-type Cu-doped ZnO nanostructures (>1.1 at% Cu) exhibited striking responses toward the exposure of acetone at even 1 ppm with supreme specificity over various gas species (acetone, ammonia, oxygen and alcohols) at room temperature. These results promise the unique implementation of the devices into wearable gadgets for early diagnosis of diabetes.