Publications by authors named "Stella Vallejos"

13 Publications

  • Page 1 of 1

VOCs Sensing by Metal Oxides, Conductive Polymers, and Carbon-Based Materials.

Nanomaterials (Basel) 2021 Feb 22;11(2). Epub 2021 Feb 22.

Institute of Microelectronics of Barcelona (IMB-CNM, CSIC), Campus UAB, 08193 Cerdanyola del Vallès, Barcelona, Spain.

This review summarizes the recent research efforts and developments in nanomaterials for sensing volatile organic compounds (VOCs). The discussion focuses on key materials such as metal oxides (e.g., ZnO, SnO, TiO WO), conductive polymers (e.g., polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene)), and carbon-based materials (e.g., graphene, graphene oxide, carbon nanotubes), and their mutual combination due to their representativeness in VOCs sensing. Moreover, it delves into the main characteristics and tuning of these materials to achieve enhanced functionality (sensitivity, selectivity, speed of response, and stability). The usual synthesis methods and their advantages towards their integration with microsystems for practical applications are also remarked on. The literature survey shows the most successful systems include structured morphologies, particularly hierarchical structures at the nanometric scale, with intentionally introduced tunable "decorative impurities" or well-defined interfaces forming bilayer structures. These groups of modified or functionalized structures, in which metal oxides are still the main protagonists either as host or guest elements, have proved improvements in VOCs sensing. The work also identifies the need to explore new hybrid material combinations, as well as the convenience of incorporating other transducing principles further than resistive that allow the exploitation of mixed output concepts (e.g., electric, optic, mechanic).
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http://dx.doi.org/10.3390/nano11020552DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7926866PMC
February 2021

Influence of Mg Doping Levels on the Sensing Properties of SnO Films.

Sensors (Basel) 2020 Apr 10;20(7). Epub 2020 Apr 10.

Electronic Materials Study for Medical Applications (LEMEAMED) Laboratory, Electronic Department, Science and Technology Faculty, Frères Mentouri University, 25000 Constantine, Algeria.

This work presents the effect of magnesium (Mg) doping on the sensing properties of tin dioxide (SnO) thin films. Mg-doped SnO films were prepared via a spray pyrolysis method using three doping concentrations (0.8 at.%, 1.2 at.%, and 1.6 at.%) and the sensing responses were obtained at a comparatively low operating temperature (160 °C) compared to other gas sensitive materials in the literature. The morphological, structural and chemical composition analysis of the doped films show local lattice disorders and a proportional decrease in the average crystallite size as the Mg-doping level increases. These results also indicate an excess of Mg (in the samples prepared with 1.6 at.% of magnesium) which causes the formation of a secondary magnesium oxide phase. The films are tested towards three volatile organic compounds (VOCs), including ethanol, acetone, and toluene. The gas sensing tests show an enhancement of the sensing properties to these vapors as the Mg-doping level rises. This improvement is particularly observed for ethanol and, thus, the gas sensing analysis is focused on this analyte. Results to 80 ppm of ethanol, for instance, show that the response of the 1.6 at.% Mg-doped SnO film is four times higher and 90 s faster than that of the 0.8 at.% Mg-doped SnO film. This enhancement is attributed to the Mg-incorporation into the SnO cell and to the formation of MgO within the film. These two factors maximize the electrical resistance change in the gas adsorption stage, and thus, raise ethanol sensitivity.
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http://dx.doi.org/10.3390/s20072158DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7180774PMC
April 2020

Love Wave Sensors with Silver Modified Polypyrrole Nanoparticles for VOCs Monitoring.

Sensors (Basel) 2020 Mar 6;20(5). Epub 2020 Mar 6.

CEITEC-Central European Institute of Technology, Brno University of Technology, 61200 Brno, Czech Republic.

Love wave sensors with silver-modified polypyrrole nanoparticles are developed in this work. These systems prove functional at room temperature with enhanced response, sensitivity and response time, as compared to other state-of-the-art surface acoustic wave (SAW) sensors, towards volatile organic compounds (VOCs). Results demonstrate the monitoring of hundreds of ppb of compounds such as acetone, ethanol and toluene with low estimated limits of detection (~3 ppb for acetone). These results are attributed to the use of silver-modified polypyrrole as a second guiding/sensitive layer in the Love wave sensor structure, which provides further chemically active sites for the gas-solid interactions. The sensing of low VOCs concentrations by micro sensing elements as those presented here could be beneficial in future systems for air quality control, food quality control or disease diagnosis via exhaled breath as the limits of detection obtained are within those required in these applications.
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http://dx.doi.org/10.3390/s20051432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7085531PMC
March 2020

AACVD Synthesis and Characterization of Iron and Copper Oxides Modified ZnO Structured Films.

Nanomaterials (Basel) 2020 Mar 5;10(3). Epub 2020 Mar 5.

CEITEC-Central European Institute of Technology, Brno University of Technology, 61200 Brno, Czech Republic.

Non-modified (ZnO) and modified (FeO@ZnO and CuO@ZnO) structured films are deposited via aerosol assisted chemical vapor deposition. The surface modification of ZnO with iron or copper oxides is achieved in a second aerosol assisted chemical vapor deposition step and the characterization of morphology, structure, and surface of these new structured films is discussed. X-ray photoelectron spectrometry and X-ray diffraction corroborate the formation of ZnO, FeO, and CuO and the electron microscopy images show the morphological and crystalline characteristics of these structured films. Static water contact angle measurements for these structured films indicate hydrophobic behavior with the modified structures showing higher contact angles compared to the non-modified films. Overall, results show that the modification of ZnO with iron or copper oxides enhances the hydrophobic behavior of the surface, increasing the contact angle of the water drops at the non-modified ZnO structures from 122 to 135 and 145 for FeO@ZnO and CuO@ZnO, respectively. This is attributed to the different surface properties of the films including the morphology and chemical composition.
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http://dx.doi.org/10.3390/nano10030471DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7153246PMC
March 2020

Raman and XPS studies of ammonia sensitive polypyrrole nanorods and nanoparticles.

Sci Rep 2019 06 11;9(1):8465. Epub 2019 Jun 11.

Central European Institute of Technology, Brno University of Technology, Purkyňova 123, 612 00, Brno, Czech Republic.

Polypyrrole (PPy) nanorods (NRs) and nanoparticles (NPs) are synthesized via electrochemical and chemical methods, respectively, and tested upon ammonia exposure using Raman and X-ray photoelectron spectroscopy (XPS). Characterization of both nanomaterials via Raman spectroscopy demonstrates the formation of PPy, displaying vibration bands consistent with the literature. Additionally, XPS reveals the presence of neutral PPy species as major components in PPy NRs and PPy NPs, and other species including polarons and bipolarons. Raman and XPS analysis after ammonia exposure show changes in the physical/chemical properties of PPy, confirming the potential of both samples for ammonia sensing. Results demonstrate that the electrochemically synthesized NRs involve both proton and electron transfer mechanisms during ammonia exposure, as opposed to the chemically synthesized NPs, which show a mechanism dominated by electron transfer. Thus, the different detection mechanisms in PPy NRs and PPy NPs appear to be connected to the particular morphological and chemical composition of each film. These results contribute to elucidate the mechanisms involved in ammonia detection and the influence of the synthesis routes and the physical/chemical characteristics of PPy.
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http://dx.doi.org/10.1038/s41598-019-44900-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6559985PMC
June 2019

Cerium Oxide-Tungsten Oxide Core-Shell Nanowire-Based Microsensors Sensitive to Acetone.

Biosensors (Basel) 2018 Nov 23;8(4). Epub 2018 Nov 23.

Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC), Campus UAB, 08193 Bellaterra, Spain.

Gas sensitive cerium oxide-tungsten oxide core-shell nanowires are synthesized and integrated directly into micromachined platforms via aerosol assisted chemical vapor deposition. Tests to various volatile organic compounds (acetone, ethanol, and toluene) involved in early disease diagnosis demonstrate enhanced sensitivity to acetone for the core-shell structures in contrast to the non-modified materials (i.e., only tungsten oxide or cerium oxide). This is attributed to the high density of oxygen vacancy defects at the shell, as well as the formation of heterojunctions at the core-shell interface, which provide the modified nanowires with 'extra' chemical and electronic sensitization as compared to the non-modified materials.
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http://dx.doi.org/10.3390/bios8040116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316039PMC
November 2018

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods.

J Vis Exp 2017 09 14(127). Epub 2017 Sep 14.

Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC).

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 °C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 °C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.
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http://dx.doi.org/10.3791/56127DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5752247PMC
September 2017

ZnO Rods with Exposed {100} Facets Grown via a Self-Catalyzed Vapor-Solid Mechanism and Their Photocatalytic and Gas Sensing Properties.

ACS Appl Mater Interfaces 2016 Dec 28;8(48):33335-33342. Epub 2016 Nov 28.

Instituto de Microelectrónica de Barcelona, Consejo Superior de Investigaciones Científica , Campus UAB, 08193 Bellaterra-Barcelona, Spain.

We present a new method for vapor deposition of columnar ZnO structures in the form of rods on various substrates without the need for substrate modification with catalyst seed particles and at relatively low temperatures compared to other vapor deposition methods. These structures are used for the photodegradation of stearic acid (CHO) and the photoactivated detection of gases such as carbon monoxide (CO), ethanol (CHO), toluene (CH), and nitrogen dioxide (NO) at room temperature, showing improved selectivity compared to tests performed in themoactivated mode.
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http://dx.doi.org/10.1021/acsami.6b12992DOI Listing
December 2016

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

Sci Rep 2016 06 23;6:28464. Epub 2016 Jun 23.

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

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.
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http://dx.doi.org/10.1038/srep28464DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4917840PMC
June 2016

Nanoscale Heterostructures Based on Fe2O3@WO3-x Nanoneedles and Their Direct Integration into Flexible Transducing Platforms for Toluene Sensing.

ACS Appl Mater Interfaces 2015 Aug 14;7(33):18638-49. Epub 2015 Aug 14.

Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC) , 08193 Cerdanyola, Barcelona, Spain.

Nanoscale heterostructures based on WO3-x nanoneedles functionalized with Fe2O3 nanoparticles are integrated directly into flexible polymer-based transducing platforms via aerosol-assisted chemical vapor deposition. Results demonstrate that the incorporation of Fe2O3 nanoparticles at the surface of WO3-x nanoneedles enhances the electronic and sensing properties of WO3-x, providing a 6-fold increase in sensitivity to toluene and low cross-sensitivity to hydrogen and ethanol. These enhanced-sensing properties are comparable to those obtained via functionalization with precious metal (Pt) nanoparticles, which are commonly used to enhance sensor performance.
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http://dx.doi.org/10.1021/acsami.5b05081DOI Listing
August 2015

Aerosol-assisted CVD-grown WO₃ nanoneedles decorated with copper oxide nanoparticles for the selective and humidity-resilient detection of H₂S.

ACS Appl Mater Interfaces 2015 Apr 23;7(12):6842-51. Epub 2015 Mar 23.

†Research Centre on the Engineering of Materials and micro/nano Systems, Universitat Rovira i Virgili Països Catalans 26, 43007 Tarragona, Spain.

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.
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http://dx.doi.org/10.1021/acsami.5b00411DOI Listing
April 2015

Single-step co-deposition of nanostructured tungsten oxide supported gold nanoparticles using a gold-phosphine cluster complex as the gold precursor.

Sci Technol Adv Mater 2014 Dec 9;15(6):065004. Epub 2014 Dec 9.

Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, UK.

The use of a molecular gold organometallic cluster in chemical vapour deposition is reported, and it is utilized, together with a tungsten oxide precursor, for the single-step co-deposition of (nanostructured) tungsten oxide supported gold nanoparticles (NPs). The deposited gold-NP and tungsten oxide supported gold-NP are highly active catalysts for benzyl alcohol oxidation; both show higher activity than SiO supported gold-NP synthesized via a solution-phase method, and tungsten oxide supported gold-NP show excellent selectivity for conversion to benzaldehyde.
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http://dx.doi.org/10.1088/1468-6996/15/6/065004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090393PMC
December 2014

Au nanoparticle-functionalised WO3 nanoneedles and their application in high sensitivity gas sensor devices.

Chem Commun (Camb) 2011 Jan 19;47(1):565-7. Epub 2010 Nov 19.

Departament d'Enginyeria Electrònica, Universitat Rovira i Virgili, Països Catalans 26, 43007 Tarragona, Spain.

A new method of synthesising nanoparticle-functionalised nanostructured materials via Aerosol Assisted Chemical Vapour Deposition (AACVD) has been developed. Co-deposition of Au nanoparticles with WO(3) nanoneedles has been used to deposit a sensing layer directly onto gas sensor substrates providing devices with a six-fold increase in response to low concentrations of a test analyte (ethanol).
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http://dx.doi.org/10.1039/c0cc02398aDOI Listing
January 2011