Single‐Step Deposition of Au‐ and Pt‐Nanoparticle‐Functionalized Tungsten Oxide Nanoneedles Synthesized Via Aerosol‐Assisted CVD, and Used for Fabrication of Selective Gas Microsensor Arrays

Abstract

Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C2H5OH, H2, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H2, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment.

Gas Sensing Characterization of Single-Nanowire Sensor Array Systems Based on Non-Functionalized and Pt-Functionalized Tungsten Oxide

“…Thus, non-functionalized nanosensors displayed up to 40% higher response to nitrogen dioxide than Pt-functionalized nanonsensors, whereas Pt-functionalized nanosensors showed up to 60% higher response to ethanol compared to the non-functionalized nanosensors. These results are consistent with our previous observations on non-functionalized and Pt-functionalized multiple-nanowire based sensors [2]. Figure 3a,b show the typical electrical resistance changes when exposing the sensors to different concentrations of nitrogen dioxide and ethanol, respectively.…”

“…1D MOx, such as SnO2, WO3−x or ZnO, have been used previously to monitor various toxic gases, including CO and NO2. In particular, WO3−x has been found to be highly sensitive to NO2, and recently the functionalization of WO3−x with platinum nanoparticles (NPs) has shown to enhance the sensitivity of WO3−x to other analytes, including ethanol and hydrogen [2], attributed to the chemical and electronic sensitization of WO3−x when functionalized with platinum NPs. These studies also proved that arrays of multiple-nanowire films based on nonfunctionalized and Pt-functionalized tungsten oxide nanowires could be used to enhance the selectivity of the gas sensor device.…”

Smart control of chemical gas sensors for the reduction of their time response

“…The average diameter of gold nanoparticles is 7 nm. More details on the morphology and composition of the film can be found elsewhere, [15]. The morphology of the sensing layer is shown in Figure 3. …”

Gas Sensing Approaches Based on WO3 Nanowire-Back Gated Devices

“…Pt-nanoparticle decorated WO3 nanowires were co-deposited directly onto the electrode area in a single step aerosol assisted-CVD (AA-CVD). Prior to the deposition of the nanowires, the substrate was heated to a temperature of 380 °C, and followed by the transfer of ultrafine aerosols to the heated substrate by N2 carrier gas at a flow rate of 0.5 L/min [5,7]. Surface morphology images were taken using Scanning Electron Microscopy (ESEM) with FEI Quanta 60 and Tunneling Electron Microscopy with JOEL model 1011 equipment.…”