Gas Detection Applications of Vertically Aligned Metal Oxide Nanowire Arrays

To build novel electronic noses for mimicking biological olfactory systems that consist of olfactory receptor arrays with large surface area and massively-diversified chemical reactivity, three dimensional (3D) vertical aligned ZnO nanowire arrays were employed as active materials for gas detection. ZnO nanowire arrays share 3D structures similar to mammalian olfactory receptor arrays, with thousands of vertical nanowires providing a high reception area which can significantly enhance the sensors’ sensitivity. Meanwhile, with different material decorations (such as SnO2, In2O3, WO3 and polymers), each array of nanowires can produce a distinguishable response for each separate analyte, which would provide a promising way to improve the selectivity. Both patterned grown well-aligned and wafer size random-distributed 3D nanowire array sensing devices are investigated. Several different types of gas sensors have been investigated in this dissertation. Metal oxide semiconductor gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have detected NO2 and H2S down to ppb level, and five gases of NO2, H2S, H2, NH3, and CO have been discriminated. Active self-powered gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have been successfully fabricated and worked well for H2S and NO2 detection. With the decoration by mixture of PEDOT polymer with metal oxide nanoparticles, ZnO vertical nanowire array gas sensors have fast response and recovery time as well as good sensitivity to volatile organic gases of acetone, methanol and ethanol. A novel ionization sensor also has been built by ZnO vertical nannowire arrays, and this device could be able to ionize air under safety operation voltage

Gas Detection Applications of Vertically Aligned Metal Oxide Nanowire Arrays

To build novel electronic noses for mimicking biological olfactory systems that consist of olfactory receptor arrays with large surface area and massively-diversified chemical reactivity, three dimensional (3D) vertical aligned ZnO nanowire arrays were employed as active materials for gas detection. ZnO nanowire arrays share 3D structures similar to mammalian olfactory receptor arrays, with thousands of vertical nanowires providing a high reception area which can significantly enhance the sensors’ sensitivity. Meanwhile, with different material decorations (such as SnO2, In2O3, WO3 and polymers), each array of nanowires can produce a distinguishable response for each separate analyte, which would provide a promising way to improve the selectivity. Both patterned grown well-aligned and wafer size random-distributed 3D nanowire array sensing devices are investigated. Several different types of gas sensors have been investigated in this dissertation. Metal oxide semiconductor gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have detected NO2 and H2S down to ppb level, and five gases of NO2, H2S, H2, NH3, and CO have been discriminated. Active self-powered gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have been successfully fabricated and worked well for H2S and NO2 detection. With the decoration by mixture of PEDOT polymer with metal oxide nanoparticles, ZnO vertical nanowire array gas sensors have fast response and recovery time as well as good sensitivity to volatile organic gases of acetone, methanol and ethanol. A novel ionization sensor also has been built by ZnO vertical nannowire arrays, and this device could be able to ionize air under safety operation voltage

Design and Simulation of a Refractive Index Sensor Based on SPR and LSPR using Gold Nanostructures

In the last two decades, the unusual optical and physical properties of novel metallic nanostructures (such as gold, silver, and aluminum) has been the subject of intense research efforts. Surface plasmon resonance and localized surface plasmon resonance are two of the unique phenomena in novel metals which can be used to create different kinds of sensitive sensors and biosensors. In this work, a refractive index sensor based on surface plasmon resonance is designed and analytically investigated by a finite element method via COMSOL Multiphysics to detect chemicals. The intensity, spectral width and sensitivity of the plasmonic signals are highly affected by the shape, size, and configuration of the metallic nanostructures. Patterning the planar metallic thin film with cavities or protrusion can result in obtaining a tunable sensitivity for the sensor. The architecture of the nanohole/nanowire arrays leads to a nanostructure having multiple plasmonics properties. The simulation results show that the co-excitation of surface plasmon resonance and localized surface plasmon resonance modes can enhance the sensitivity of the SPR-based sensors significantly. To obtain this result, several cut lines through the metallic thin film were considered and the variation of the electric field intensity along those cut lines is studied. To determine the SPR and LSPR modes, the penetration depth of the plasmon field is characterized at metal/dielectric interfaces. After investigation of three models for the metallic layer (planar thin film, nanohole patterned thin film, and protrusive thin film), it was concluded that the device made of 20 nm cylindrical nanowire supported by a 40 nm thin film can result in the best performance parameters (in terms of sensitivity, absorption, and accuracy). Eight substances with refractive indices ranging from 1.333 to 1.38 were used to obtain the calibration data of the optimum sensor. The linear characteristic of the calibration curve shows that the sensor is able to detect unknown materials as a function of resonance wavelength. This study is proposing a new way to show the duality nature of patterned thin films to support both propagating and localized surface plasmon modes

Metal oxide nanowire chemical sensors: innovation and quality of life

Metal oxides are emerging as important active materials for applications such as sensors. Recent advances in the preparation of metal oxide materials offer unique possibilities for their integration into devices with new capabilities, for example, wearable/flexible devices, smart textiles for well-being and health monitoring in everyday life, or with innovative sensing architectures such as work function, surface ionization, magnetic, self-heating, and Schottky-based devices. This review presents the author's opinion on innovations and challenges in the field of metal oxide nanowire chemical sensors

An enhanced gas ionization sensor from Y-doped vertically aligned conductive ZnO nanorods

A stable and highly sensitive gas ionization sensor (GIS) constructed from vertically aligned, conductive yttrium–doped ZnO nanorod (YZO NR) arrays is demonstrated. The conductive YZO NRs are synthesized using a facile one-pot hydrothermal method. At higher Y/Zn molar ratio, the aspect ratio of the YZO NRs is increased from 11 to 25. Doping with yttrium atoms decreases the electrical resistivity of ZnO NRs more than 100 fold. GIS measurements reveal a 6-fold enhancement in the sensitivity accompanied with a significant reduction in breakdown voltage from the highly conductive YZO NRs. Direct correlations between the resistivity of the NRs and GIS characteristics are established

Localized Charge Transfer Process and Surface Band Bending in Methane Sensing by GaN Nanowires

The physicochemical processes at the surfaces of semiconductor nanostructures involved in electrochemical and sensing devices are strongly influenced by the presence of intrinsic or extrinsic defects. To reveal the surface controlled sensing mechanism, intentional lattice oxygen defects are created on the surfaces of GaN nanowires for the elucidation of charge transfer process in methane (CH4) sensing. Experimental and simulation results of electron energy loss spectroscopy (EELS) studies on oxygen rich GaN nanowires confirmed the possible presence of 2(ON) and VGa-3ON defect complexes. A global resistive response for sensor devices of ensemble nanowires and a localized charge transfer process in single GaN nanowires are studied in situ scanning by Kelvin probe microscopy (SKPM). A localized charge transfer process, involving the VGa-3ON defect complex on nanowire surface is attributed in controlling the global gas sensing behavior of the oxygen rich ensemble GaN nanowires.Comment: 42 pages, 6 figures, Journa

Gas-Sensing Properties of Thermally-Oxidized Metal Oxide Nanowires

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