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

Gas-Sensing Properties of Thermally-Oxidized Metal Oxide Nanowires

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Niobium and Tungsten Oxide Nanowires for Chemical Sensor

AbstractThin films of tungsten and niobium (WNb) were the starting point for the growth of metal oxide nanowires. RF Magnetron sputtering was used to deposit a layer of 100nm on 2 · 2 mm2 alumina substrates. Prepared samples were thermally oxidized to obtain the growth of nanostructures whose morphology was investigated by a scanning electron microscope (SEM). Structural properties of these nanostructures were investigated by RAMAN spectroscopy. Functional characterization was carried out using a homemade test chamber. Interdigitated contacts and heating elements were deposited by DC Magnetron sputtering, and samples were bonded to TO packages thanks to gold wires. The gas sensing properties of samples were analyzed in a wide range of working temperatures for different target gases in order to verify the best working condition

SnO2-SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

SnO2 is one of the most employed n-type semiconducting metal oxide in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, the authors introduce 1D SnO2-SiO2 core-shell nanowires (CSNWs). The amorphous SiO2-shell layer with varying thicknesses (1.8–10.5 nm) is grown onto the SnO2 nanowires (NWs) by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response is strongly correlated to the thickness of the SiO2-shell and the working temperature. The SnO2-SiO2 CSNWs sensor with a 4.8-nm SiO2 shell thickness exhibits the best selectivity and sensitivity, having ca. 7-fold higher response toward hydrogen compared to bare-SnO2 NWs. The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increase in the width of the electron-depletion-layer due to a strong electronic coupling between the SnO2 core and SiO2 coating, respectively.Peer Reviewe

Influence of Nb-doping on hydrogen sensing performance of WO3 nanowires

Tungsten oxide nanowires were synthetized by thermal oxidation in vacuum, using a custom tubular furnace, adding niobium in the growth process to evaluate the influence of niobium in the conductometric response towards hydrogen gas. Samples were characterized by XRD and Raman spectroscopy, to confirm the crystalline structure of the material. The conductometric response of fabricated sensors was evaluated towards hydrogen gas. The addition of small percentage of niobium during the synthesis enhance the hydrogen sensing performance of the devices. (C) 2016 The Authors. Published by Elsevier Ltd

Titanium dioxide nanostructures chemical sensor

Titanium dioxide (TiO2) nanostructures were grown directly on the sensitive area of the transducer. A titanium thin film was deposited on 2 . 2 mm(2) alumina substrates by RF magnetron sputtering and hydrothermal method was used to achieve TiO2. This method is characterized by the use of different solutions (KOH, NaOH), a not stirred pressure reactor and a heating system. As-prepared samples require an acid treatment followed by a calcination step to obtain pure TiO2 nanostructures. The nanostructured morphology was confirmed by a scanning electron microscope (SEM) and their structural properties were investigated by RAMAN spectroscopy. Obtained samples were used as gas sensors, and their behaviour towards several gaseous species was analysed in a wide range of working temperatures. Measurements were carried out in a test chamber, investigating the change in the electrical conductance due to the surrounding atmosphere

NiO/ZnO nanowire-heterostructures by vapor phase growth for gas sensing

Physical interface between p and n-types semiconducting materials known as p-n junction or heterojunction represents the key technology in many electronic and optoelectronic devices such as gas sensors. In this work we are presenting a novel method for the growth of NiO/ZnO (NWs) based heterostructures with vapor phase mechanism and their preliminary sensing study for acetone. To fabricate the NiO/ZnO NWs heterostructures, firstly NiO nanowires were grown on alumina substrates with VaporLiquid- Solid (VLS) method and then Vapor-Solid (VS) method was used for the growth of ZnO nanowires on as grown NiO nanowires. The surface morphology of NiO nanowires and NiO/ZnO heterostructures were investigated with scanning electron microscopy (FE-SEM). Raman spectroscopy has also been used for the structural characterization of heterostructures. A set of conductromertric sensing devices based on NiO/ZnO heterostructures have been prepared. The preliminary sensing performance of NiO/ZnO NWs heterostructure devices towards acetone at temperature of 400 degrees C is reported in this work. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

Niobium Oxide Nanostructures for Chemical Sensing

AbstractNiobium oxide nanostructures were synthesized by hydrothermal method starting from niobium films deposited by RF magnetron sputtering on 2 × 2 mm2 alumina substrates. The samples were firstly treated with a KOH solution and with HNO3, and then annealed to obtain the Nb2O5 nanostructures. A scanning electron microscope (SEM) was used to investigate the morphology of the samples, while RAMAN spectroscopy was used to analyse their structural properties. In order to study the functional properties of the material, electrical contacts and heating elements were deposited over the substrates by DC magnetron sputtering. The as-prepared samples were mounted on TO packages using gold wires. Afterwards, functional tests were performed in a test chamber to investigate their electrical conductance variation as a function of the surrounding atmosphere and thus the sensitivity to different gaseous species

Bottle-brush-shaped heterostructures of NiO-ZnO nanowires: growth study and sensing properties

We present here heterostructured ZnO-NiO nanowires, constituted by a core of single crystalline ZnO nanowires, covered by poly-crystalline NiO nanorods. The bottle-brush shape was investigated by SEM and TEM, confirming that a columnar growth of NiO occurred over the ZnO core, with a preferred orientation of NiO over ZnO nanowires. The heterostructured devices are proposed for gas sensing application. Bare ZnO nanowires and heterostructured sensors with two different thicknesses of NiO poly-crystalline nanorods were analysed for acetone, ethanol, NO2 and H2 detection. All sensors maintained n-type sensing mechanism, with improved sensing performance for lower thickness of NiO, due to high catalytic activity of NiO. The sensing dynamic is also strongly modified by the presence of heterojunction of NiO/ZnO, with a reduction of response and recovery times towards ethanol and acetone at 400°C.