Browsing by Author "Ngqondo, Sipho Tumi"

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    Hydrothermally grown Pb2+ doped ZnOnanorods for hydrogen and acetylene gas sensing
    (2008) Ngqondo, Sipho Tumi; Ndwandwe, O.M.
    Randomly orientated ZnO nanorods were deposited hydrothermally on Si <100> wafers. The precursor solutions used for ZnO nanorods deposition were zinc chloride + aqueous ammonia and Zinc nitrate + HMT. ZnO nanorods were deposited on Si<100> wafers to establish the optimal PH and concentration which yield the best substrate coverage for each precursor solution. ZnO thin films were deposited on glass substrates using pulsed laser deposition. These thin films were used for both gas sensing and as seed for orientated ZnO nanorods deposition. Rutherford Backscattering was used to measure the thickness and stochiometry of the deposited ZnO films. Orientated ZnO nanorods were then deposited on glass slides with ZnO thin films using the optimal PH and concentration for reagents established when Si<100> wafers were used as substrates. Pb doped ZnO nanorods were prepared by adding Lead (II) Nitrate as the Lead source into Zinc nitrate + HMT precursor solution. These Pb doped ZnO nanorods were then deposited on glass substrates with a ZnO thin film. The crystal structure and preferred plane orientation of all samples was studied using X-ray diffraction. Morphological and elemental analysis of samples was investigated using Scanning Electron Microscopy equipped with EDX. All samples showed good ZnO stochiometry with no foreign atoms except the samples with Pd doped ZnO nanorods. Ag contacts were deposited on the samples using EDWARDS vacuum coater. The gas sensing characteristics were investigated on all samples using 20% hydrogen and acetylene as test gases while 80% nitrogen was used as a carrier gas. ZnO thin films were found be at optimum for hydrogen gas sensing in the range 300-350oC, the minimum temperature for acetylene sensing was 400oC. Orientated ZnO nanorods also operated at their optimum in the 300- 350oC range like thin-films, however they exhibited better sensitivity in this range than thin films. ZnO nanorods started sensing acetylene at 350oC, slightly lower than ZnO thin films. Pb doped ZnO nanorods were able to sense hydrogen with 67% sensitivity at 250oC. These Pb doped ZnO nanorods were also found to be cable of sensing acetylene in the whole temperature range.