High Dynamic Range Methanol Sensor Based on Aligned ZnO Nanorods

A resistive methanol sensor based on ZnO hexagonal nanorods having average diameter (60-70 nm) and average length of ~ 500 nm, is reported in this paper. A low temperature chemical bath deposition technique is employed to deposit vertically aligned ZnO hexagonal nanorods using zinc acetate dihydrate and hexamethylenetetramine (HMT) precursors at 100°C on a SiO₂ substrate having Sol-Gel grown ZnO seed layer. After structural (XRD, FESEM) and electrical (Hall effect) characterizations, four types of sensors structures incorporating the effect of catalytic metal electrode (Pd-Ag) and Pd nanoparticle sensitization, are fabricated and tested for sensing methanol vapor in the temperature range of 27°C -300°C. The as deposited ZnO nanorods with Pd-Ag catalytic contact offered appreciably high dynamic range (190-3040 ppm) at moderately lower temperature (200°C) compared to the sensors with noncatalytic electrode (Au). Surface modification of nanorods by Pd nanoparticles offered faster response and recovery with increased response magnitude for both type of electrodes, but at the cost of lower dynamic range (190-950 ppm). The possible sensing mechanism has also been discussed briefly.