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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 SiO 2 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 PdAg 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.

Abstract-Capacitive mode methanol sensing performance of ZnO hexagonal nanorods based MIS devices having diameters of 40-60 nm and lengths of 460-480 nm, is reported in this paper. ZnO nanorods were synthesized on p-Si substrate by chemical bath deposition method (CBD) using 50 ml aqueous solution of Zinc acetate dihydrate and HMT. The as deposited sensor with Pd catalytic contact in metal-insulator-metal (MIS) configuration offered 99% response magnitude (RM) in the temperature range of (300-325) º C towards 700 ppm methanol concentration. The response time (Rs:140s) and recovery time (Rc:110s) of the methanol sensor at 325º C were also obtained. The sensor was able to detect methanol even down to 10 ppm.Index Terms-Capacitive sensor, CBD, ZnO hexagonal nanorods, methanol sensing. I. INTRODUCTIONRecent advances in nanomaterials provide the opportunity to dramatically increase the response of these materials, as their performance is directly related to exposed surface volume. Detection of toxic and flammable gases is a subject of growing significance in both domestic and industrial environments [1]. Various air pollutants coming from industrial plants, households or automobiles should be controlled in order to keep them below a safe level. This has motivated the researchers to develop various types of gas sensors based on different principles. The conductometric semiconducting metal oxide gas sensors currently constitute one of the most investigated groups of gas sensors. Metal-insulator-semiconductor (MIS) structure attracts the interests as its capacitance (based on surface space charge of semiconductor) is delicately influenced by effective voltage applied on metal electrode for detecting combustible, reducing, or oxidizing gases by conductive measurements [2] The gas sensors used noble metal electrode as a sensing material. The following oxides show a gas response in their conductivity: Capacitive-type sensors have good prospects given that the capacitor structure is so simple enabling miniaturization and achieving high reliability and low cost. In addition, amplification of capacitance is easily performed by oscillator Manuscript

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