Enhancement of CO and NO sensing in n-SnO-p-CuO core-shell nanofibers by shell optimization.

SnO-CuO core-shell nanofibers (C-S NFs) with various shell thicknesses (15-80 nm) were fabricated for gas (CO and NO) sensing applications. SnO NFs were produced by electrospinning and then coated with CuO by atomic layer deposition, which allows control of the shell thickness. The role of the CuO shell thickness on the sensing characteristics was investigated systematically. The sensor responses to both CO and NO 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 CuO 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 SnO surface-CuO heterojunctions and CuO 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.