Dual Functional Sensing Mechanism in SnO2-ZnO Core-Shell Nanowires

We report a dual functional sensing mechanism for ultrasensitive chemoresistive sensors based on SnO2-ZnO core shell nanowires (C-S NWs) for detection of trace amounts of reducing gases. C S NWs were synthesized by a two-step process, in which core SnO2 nanowires were first prepared by vapor liquid solid growth and ZnO shell layers were subsequently deposited by atomic layer deposition. The radial modulation of the electron-depleted shell layer was accomplished by controlling its thickness. The sensing capabilities of C S NWs were investigated in terms of CO, which is a typical reducing gas. At an optimized shell thickness, C S NWs showed the best CO sensing ability, which was quite superior to that of pure SnO2 nanowires without a shell. The dual functional sensing mechanism is proposed as the sensing mechanism in these nanowires and is based on the combination of the radial modulation effect of the electron-depleted shell and the electric field smearing effect.