Qurashi Ahsanulhaq

University of Toyama Repository

Synthesis and Characterization of Metal Oxide N anostructures for Efficient Gas Sensor Applications 非常勤研究員 Ahsanulhaq Qurashi 1. Introduction Metal oxide nanostructured materials have attracted much attention because of their novel properties that may lead to the basic understanding and novel applications. A large number of nanostructures have been reported in literature using various synthesis methods. Intensive efforts have been directed to the functional metal oxides for possible applications in nanotechnologies. Cost effective and morphology controlled synthesis of metal oxide nanostructures on desired substrates and their shape dependent performance in gas sensors are presently foremost concerns for the researchers. In order to undertake these challenges considerable efforts have been made to accomplish this goal in the present work. 2. Experimental Methodology 2.1 Experimental section Two significant methods have been used for the controlled synthesis of metal oxide (In203 and Ti02) nanostruc旬resfor example, (1) Chemical vapor deposition; and (2) hydrothermal synthesis method. In203 as wide band gap materials is an interesting candidate for the gas sensor applications. However until now various groups reported ID In203 nanostruc印ressynthesized by chemical vapor deposition at high tempera印re( 1100-1500°C) and by carbothermal reduction process. In order to overcome such problems various types of In203 nanostructures were grown on desired silicon substrate by chemical vapor deposition at low temperature (700-900°C) using In metal as source material. By adjusting various important parameters we have effectively synthesized high quality In203 nanowires, nanoneedles, nanopushpins, pyramids and octahedrons on silicon and metal coated silicon substrates. To synthesize metal oxide nanostructures, simple, cost effective and easy hydrothermal method has been employed for the fabrication of high-quality Ti02 nanoparticles and flower-like nanostructures. The common strategy, simple process，日nequality, high yield and clean reaction made hydrothermal synthesis attractive and significant. By optimizing reaction conditions we could successfully grow Ti02 nanoflower like-structures and nanoparticles at low temperature of 180°C. 2.2 Structural characterization The crystalline phase and surface morphology of the metal oxide nanostructures were investigated by X-ray diffraction (XRD), field emission scanning electronic microscope (FESEMふandhigh-resolution transmission electron microscope (HRTEM). The optical properties of In203 nanowires were measured by room tempera制rephotoluminescence (PL). PL spectra were measured by Spex Fluorolog-3 spectrometer using an excitation of 325 nm with a 150-W Xe lamp at room temperature. 2.3 Gas Sensor fabrication In this study metal-oxide nanostructure based hydrogen gas sensors were investigated since hydrogen is a promising potential fuel for the vehicles and can be converted into electricity in the fuel cels. Safety is an important issue while using hydrogen gas. Existing techniques can detect hydrogen gas, however they have numerous drawbacks: limited dynamic range, poor reproducibility and reversibility, subject to false alarms, and tend to be slow, unreliable, and difficult to use. To overcome such intricacies 1 D metal oxide based nanostructures are promising alternative for 92 93 hydrogen gas sensor fabrication. Hydrogen gas sensor devices were fabricated from ID In203 nanostruc印resand Ti02 nanostructures. In order to prepare nanostruc知rebased gas sensor, the Pt interdigitated electrode was used for gas sensor fabrication. The interdigitated Pt electrode was prepared on oxidized silicon substrate by sputtering and patterning Pt film with the help of photolithography and dry etching. A thin film of desired nanostructures is prepared on Pt electrode to measure the gas sensing property. The resistance of the samples was determined by measuring the electric cu町entwhen a specific voltage was applied to the two electrodes. A computerized Agilent multimeter was used for the electrical measurement. 3. Results and discussion Chemical vapor deposition is flourishing technique to synthesize lD metal oxide nanostructures. By regulating various parameters we have effectively fabricated In203 nanostruc印resfor instance nanowires, nanoneedles, nanopushpins, pyramids and octahedrons. Catalyst assisted method was used for the growth of In203 nanowires and nanoneedles. The diameters of In203 nanowires were in between 70-80 nm and their lengths are several micrometers. The diameter of each nanoneedle was about 150・200nm and length about 4-5 μm respectively. Interesting morphologies like In203 nanopushpins, pyramids and octahedrons were also revealed via catalyst-free chemical vapor deposition technique. Gas sensors prepared by nanowires, nanoneedles and nanopushpins showed swift response for hydrogen gas. The nanostruc旬resbased sensor devices are relatively stable. However we will make efforts to investigate the selectivity and also improve the sensitivity in near fu旬re.Ti02 nanoflower and nanoparticles were prepared by hydrothermal synthesis. The flower-like structures and nanoparticles showed excellent reproducibility in synthesis. Ti02 flower皿likestruc旬resconsists of nanorods. Each nanorod has length of 40-50 nm and length about 500-600 nm. The nanoparticles have a size less than 50 nm. Hydrogen based gas sensors were fabricated from the Ti02 nanoflowers and nanoparticles. The sensor showed higher sensitivity at room temperature. The response is quick and devices showed better stability. 4. Conclusion In203 nanostructures prepared by chemical vapor deposition at relatively low temperature. Hydrogen gas sensors were fabricated企omIn203 1 D nanostructures which showed swift response and recovery. Ti02 nanoflowers and nanoparticles were synthesized by hydrothermal synthesis method. Hydrogen sensor prepared企omTi02 nanos仕ucturesshowed high sensitivity and fast response and better stability. 5. Future Plan So far we have successfully prepared In203 nanostruc知resand Ti02 nanostructures from chemical vapor deposition in tube furnace and simple hydrothermal synthesis method. in addition hydrogen gas sensor behavior investigated using In203 and Ti02 nanostructures in terms of stability and swift sensor response. In fu印rework we are looking for the synthesis of other promising metal oxide nanostruc加resby thermal evaporation and hydrothermal synthesis procedure for gas sensor application in terms of selectivity of oxidizing and reducing gases. Our aim is to compare gas sensing property of different metal oxide nanostructures intended for selectivity. We are intensely optimizing parameters to improve the sensitivity. The fabrication of gas sensors based on single nanowire is under the focus. 

Synthesis and Characterization of Metal Oxide Nanostructures for Efficient Gas Sensor Applications

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Synthesis and Characterization of Metal Oxide Nanostructures for Efficient Gas Sensor Applications

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