Facile Synthesis of ZnO Nanofoam on ZnO Nanowire for Hydrogen Gas Detection

Abstract

Background: ZnO nanofoam cluster was deposited on ZnO nanowires using SiO2/Si substrate. Nanocrystalline ZnO nanofoam cluster was grown on Chemical Bath Deposition (CBD) grown ZnO nanowires by consecutive immersion (50 times) of the sample into Sodium Zincate (Na2ZnO2) bath (0.125M) kept at room temperature and into the de-ionized (DI) water maintained at 80oC. Methods: Sodium Zincate was prepared by reacting Zinc Sulphate (ZnSO4) and excess Sodium Hydroxide (NaOH) in aqueous solution. By simple Chemical Bath Deposition (CBD) technique ZnO nanowires of length of 1-1.5 µm with diameter 2-3 nm were deposited on SiO2 coated <100> p-Si substrate. The ZnO nanofoam cluster area was found to be ~(0.5 x 0.5) µm2. After structural and morphological characterizations by FESEM, EDX and AFM, the sensor was tested for three different H2 concentrations (0.1, 0.5 and 1%) taking N2 as carrier gas at four different operating temperatures (50ºC, 75ºC, 100ºC and 125ºC). Results: The sensor offered ~98% response magnitude at very low operating temperature 100ºC at 1000 ppm H2 gas with very fast response time (16 sec) and recovery time (52 sec). The unique structure of nanofoam covers multidimensional area having more molecular surface interactions thus permitting better response in gas sensing. The I-V characteristics was studied to indicate ohmic nature of the silver contacts for four operating temperatures with 1% hydrogen in N2 and it was also observed that amplitude of current is higher with the presence of H2. Conclusion: Finally the stability study of the H2 sensor was also done in presence of carrier gas (N2) over a span of 24 hours (6 hr daily).