F.E. Annanouch

Aerosol-Assisted CVD-Grown WO3 Nanoneedles Decorated with Copper Oxide Nanoparticles for the Selective and Humidity-Resilient Detection of H2S

A gas-sensitive hybrid material consisting of Cu2O nanoparticle-decorated WO3 nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO3 nanoneedles decorated with p-type Cu2O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO3 nanoneedles) and a low detection limit (below 300 ppb of H2S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p-n heterojunctions created at the nanoscale in our hybrid nanomaterial.

Aerosol-Assisted CVD-Grown PdO Nanoparticle-Decorated Tungsten Oxide Nanoneedles Extremely Sensitive and Selective to Hydrogen

We report for the first time the successful synthesis of palladium (Pd) nanoparticle (NP)-decorated tungsten trioxide (WO3) nanoneedles (NNs) via a two-step aerosol-assisted chemical vapor deposition approach. Morphological, structural, and elemental composition analysis revealed that a Pd(acac)2 precursor was very suitable to decorate WO3 NNs with uniform and well-dispersed PdO NPs. Gas-sensing results revealed that decoration with PdO NPs led to an ultrasensitive and selective hydrogen (H2) gas sensor (sensor response peaks at 1670 at 500 ppm of H2) with low operating temperature (150 °C). The response of decorated NNs is 755 times higher than that of bare WO3 NNs. Additionally, at a temperature near that of the ambient temperature (50 °C), the response of this sensor toward the same concentration of H2 was 23, which is higher than that of some promising sensors reported in the literature. Finally, humidity measurements showed that PdO/WO3 sensors displayed low-cross-sensitivity toward water vapor, compared to bare WO3 sensors. The addition of PdO NPs helps to minimize the effect of ambient humidity on the sensor response.

Nanostructure Initiator Mass Spectrometry for tissue imaging in metabolomics: Future prospects and perspectives ☆

Mass spectrometry-based metabolomics provides a new approach to interrogate mechanistic biochemistry related to natural processes such as health and disease. Physiological and pathological conditions, however, are characterized not only by the identities and concentrations of metabolites present, but also by the location of metabolites within a tissue. Unfortunately, most relevant MS platforms in metabolomics can only measure samples in solution, therefore metabolites are typically extracted by tissue homogenization. Recent developments of imaging-MS technologies, however, have allowed particular metabolites to be spatially localized within biological tissues. In this context, Nanostructure-Initiator Mass Spectrometry (NIMS), a matrix-free technique for surface-based analysis, has proven an alternative approach for tissue imaging of metabolites. Here we review the basic principles of NIMS for tissue imaging and show applications that can complement LC/MS and GC/MS-based metabolomic studies investigating the mechanisms of fundamental biological processes. In addition, the new surface modifications and nanostructured materials herein presented demonstrate the versatility of NIMS surface to expand the range of detectable metabolites.

New approaches for improving selectivity and sensitivity of resistive gas sensors: a review

Purpose – This paper aims to present the methods of improving selectivity and sensitivity of resistance gas sensors. Design/methodology/approach – This paper compares various methods of improving gas sensing by temperature modulation, UV irradiation or fluctuation-enhanced sensing. The authors analyze low-frequency resistance fluctuations in commercial Taguchi gas sensors and the recently developed tungsten trioxide (WO3) gas-sensing layers, exhibiting a photo-catalytic effect. Findings – The efficiency of using low-frequency fluctuations to improve gas detection selectivity and sensitivity was confirmed by numerous experimental studies in commercial and prototype gas sensors. Research limitations/implications – A more advanced measurement setup is required to record noise data but it will reduce the number of gas sensors necessary for identifying the investigated gas mixtures. Practical implications – Fluctuation-enhanced sensing can reduce the energy consumption of gas detection systems and assures bett...

Microsensors based on Pt–nanoparticle functionalised tungsten oxide nanoneedles for monitoring hydrogen sulfide

Gas microsensors based on non-functionalised and functionalised tungsten oxide nanoneedles with platinum nanoparticles, synthesised and integrated directly onto transducing microsensor platforms via Aerosol Assisted Chemical Vapour Deposition, are fabricated and tested towards various concentrations of hydrogen sulfide and some interfering gases (CO, H2, NH3, EtOH). Results show improved sensing characteristics in functionalised microsensors as a result of the incorporation of platinum nanoparticles of reduced size (<4 nm) with even distribution onto highly crystalline tungsten oxide nanoneedles. An arrangement of both non-functionalised and functionalised sensing films in an array of sensors shows the potential of these devices to selectively monitor hydrogen sulfide.

Aerosol assisted chemical vapour deposition of gas sensitive SnO2 and Au-functionalised SnO2 nanorods via a non-catalysed vapour solid (VS) mechanism.

Tin oxide nanorods (NRs) are vapour synthesised at relatively lower temperatures than previously reported and without the need for substrate pre-treatment, via a vapour-solid mechanism enabled using an aerosol-assisted chemical vapour deposition method. Results demonstrate that the growth of SnO2 NRs is promoted by a compression of the nucleation rate parallel to the substrate and a decrease of the energy barrier for growth perpendicular to the substrate, which are controlled via the deposition conditions. This method provides both single-step formation of the SnO2 NRs and their integration with silicon micromachined platforms, but also allows for in-situ functionalization of the NRs with gold nanoparticles via co-deposition with a gold precursor. The functional properties are demonstrated for gas sensing, with microsensors using functionalised NRs demonstrating enhanced sensing properties towards H2 compared to those based on non-functionalised NRs.

UV-Light-Induced Fluctuation Enhanced Sensing by WO 3 -Based Gas Sensors

WO3-based gas sensors were investigated under UV-light irradiation and at different working temperatures with the object of achieving superior sensitivity and selectivity. Resistance fluctuations in the WO3 layer were studied together with dc resistance measurements. The data were taken in synthetic air, ethanol, nitrogen dioxide, and mixtures of these gases. We conclude that UV irradiation can easily be applied to enhance the gas sensing properties of a WO3 layer.

AA-CVD growth and ethanol sensing properties of pure and metal decorated WO3 nanoneedles

This paper reports the co–deposition, in a single step, of metal nanoparticles and tungsten oxide nanoneedles by aerosol–assisted chemical vapour deposition. The method leads to the growth of WO3 nanoneedles decorated with copper, gold or platinum metal nanoparticles, respectively. Scanning electron microscopy, transmission electron microscopy and energy–dispersive X–ray analysis have been used to investigate the morphology and composition of the different nanostructures grown on Al2O3 substrates. Gas sensors employing the different nanostructures have been fabricated and a preliminary characterisation of their sensing properties to ethanol vapours is shown. Our nanomaterials behave as n–type semiconductors in the presence of ethanol, and those decorated with metal nanoparticles show high stability, high reproducibility, high response and rapid detection of ethanol vapours at moderate operating temperatures (i.e. 250°C).

Pt/WO 3 microsensor grown by cold wall reactor Aerosol Assisted Chemical Vapor Deposition for C 6 H 6 and NO 2 detection

Aerosol Assisted Chemical Vapor Deposition (AACVD) induced via localized heating of the gas sensor shows high flexibility, low cost and capability for the direct synthesis of low-dimensional metal oxide nanostructures in a wide scale of substrates. In this work, we report for the first time the successful co-deposition of tungsten trioxide nanowires decorated with Pt nanoparticles (Pt/WO3) in a single step, via AACVD method employing the self-heating capability of MEMS transducer platforms. E-SEM and XRD analysis have been used to investigate the morphology and the composition of the nanostructures grown. The fabricated gas microsensors have been tested toward different concentration of NO2 and C6H6. In comparison with our previous work, these new results show a clear improvement in the synthesis of the nanostructures, a highly enhanced sensitivity towards small concentrations of benzene, and good sensitivity and selectivity toward NO2.

Tungsten oxide nanowire sensors grown by cold wall reactor aerosol assisted chemical vapour deposition

This paper reports on a new method for the growth of single-crystalline WO3 nanoneedles (NN) on sensor substrates using a horizontal aerosol assisted CVD cold wall reactor. The heating element of the sensors is used to keep the appropriate growth temperature. The morphology and the crystalline structure of the films were characterized by using scanning electron microscopy, X-ray diffraction and Raman spectroscopy, and the results proved the synthesis of thin layers of monoclinic WO3 NN with preferred orientation in the [002] direction. The gas sensing properties of the films were also evaluated by exposing our sensors to different analytes: EtOH, H2, and CO and we have compared their responses to those obtained from WO3 sensors fabricated by a hot AA-CVD wall reactor. The new growth method is able to highly improve sensor stability and sensitivity in comparison to the conventional hot wall reactor. Additionally, it could be more easily adapted to rigid and flexible sensor substrates.