Transport and Gas Sensing Properties of One Dimensional Metal Oxide Nanostructures and Graphene Oxide Based Composites

Abstract

One dimensional (1D) metal oxides nanostructures are considered to be a promising material for solar cells, biosensors, electrochemical detection, and photocathode applications, as they are economically cheaper and highly suitable for large scale production. Therefore it is imperative to study these nanostructures in detail so that a cost effective technology for various field effect and sensing application using metal oxides can be realized. This thesis is an attempt to contribute in the direction of establishing a highly reliable technique for synthesizing 1D metal oxide nanostructures and reduced graphene oxide based composites and study their electrical transport characteristics as well as gas sensing properties. First, the effect of reduced graphene oxide (RGO) thin film on the transport characteristics of vertically aligned zinc oxide nanorods (ZnO NRs) grown on ITO substrate were studied. We showed that GO uniformly drop casted on ZnO NRs can be easily converted to RGO at 600C. Thermally excited electrons from Zni interstitial sites (~30 meV) of ZnO nanorods aided this low temperature reduction. From the current-voltage (I-V) measurements of RGO ZnO NRs, we demonstrated that the RGO layer not only acts as a short circuiting inhibitor but also reduces the height of the potential barrier for electron tunneling. We further probed the presence of trap and defect states in ZnO nanorods by carrying out temperature dependent I-V characteristics. From the activation energies we found that there are different traps and defect states which are active in different temperature regimes. From the results we have concluded that Zn interstitial states can be a possible source of inherent n-type conductivity of ZnO. The other important metal oxide we focused in this thesis was copper oxide (Cu2O). Growth of free standing Cu2O nanopillars (on gold substrate) were carried out by template (AAO) assisted electrodeposition technique. We optimized the experimental procedure for the removal of AAO template to obtain free standing