Enhancement of CO and NO2 sensing in n-SnO2-p-Cu2O core-shell nanofibers by shell optimization.

SnO2-Cu2O core-shell nanofibers (C-S NFs) with various shell thicknesses (15-80 nm) were fabricated for gas (CO and NO2) sensing applications. SnO2 NFs were produced by electrospinning and then coated with Cu2O by atomic layer deposition, which allows control of the shell thickness. The role of the Cu2O shell thickness on the sensing characteristics was investigated systematically. The sensor responses to both CO and NO2 gases exhibited bell-shaped curves in the range of 15-80 nm, which was related to the radial modulation of the hole-accumulation layer (HAL) in the Cu2O and blocking of the expansion of the HAL because of the existence of the n-p heterojunction. In addition, the volume fraction of the shell relative to the total volume of C-S has a direct effect on the total degree of resistance modulation. Furthermore, the effects of SnO2 surface-Cu2O heterojunctions and Cu2O grain boundaries on the sensing behavior are explained. This study revealed an important aspect of C-S nanostructures for sensing studies, which is needed to optimize the shell thickness and obtain the strongest response towards specific hazardous gases.