E. Figueras

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

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.

Detection of volatile organic compounds using flexible gas sensing devices based on tungsten oxide nanostructures functionalized with Au and Pt nanoparticles

Flexible gas sensor devices are fabricated and optimized by integrating directly, via a single-step vapor-phase deposition method, highly crystalline tungsten oxide nanostructures functionalized with either gold or platinum nanoparticles. Gas tests of these devices show significant improvements with respect to flexible gas sensors based on non-functionalized structures, including greater responses to various volatile organic compounds (ethanol, acetone, methanol and toluene) and better selectivity towards ethanol and methanol, as demonstrate results for the sensors based on platinum-functionalized structures. The method presented here, which includes the fabrication of the whole flexible gas sensing device and the integration of functional nanostructures without the use of transfer methods, provides a simpler, faster and inexpensive method for the fabrication of highly functional flexible microsystems for gas sensing.

Catalyst-Free vapor-phase method for direct integration of gas sensing nanostructures with polymeric transducing platforms

Tungsten oxide nanoneedles (NNs) are grown and integrated directly with polymeric transducing platforms for gas sensors via aerosol-assisted chemical vapor deposition (AACVD) method. Material analysis shows the feasibility to grow highly crystalline nanomaterials in the form of NNs with aspect ratios between 80 and 200 and with high concentration of oxygen vacancies at the surface, whereas gas testing demonstrates moderate sensing responses to hydrogen at concentrations between 10 ppm and 50 ppm, which are comparable with results for tungsten oxide NNs grown on silicon transducing platforms. This method is demonstrated to be an attractive route to fabricate next generation of gas sensors devices, provided with flexibility and functionality, with great potential in a cost effective production for large-scale applications.

Micro-cantilevers for gas sensing

Cantilevers fabricated from a SOI wafers using bulk micromachining are used in combination with polymer deposition to detect down to 25 ppm of toluene concentration in synthetic air. The cantilevers proposed are thermoelectrically actuated and the movement detection is done by piezoresistance in a Wheatstone bridge configuration.

Dimension-Scaling of Microcantilevers Resonators

In order to analyze the influence of the dimension-scaling on the sensitivity of a cantilever, a set of microcantilevers resonators were designed, fabricated and subsequently scaled. The cantilevers proposed are piezoelectrically actuated and the movement detection is done by four piezoresistors in a Wheatstone bridge configuration. As expected the experimental results show improvement of the resonance frequency and quality factor with the dimension-scaling. For example, an structure with dimensions in the range of 400x300mum2 show the first mode of resonance frequency about 98 kHz and the quality factor around 680 and for this structure scaled with dimensions in the range of 200x150mum2 the resonance frequency and the quality factor was 354 kHz and 950 respectively.

Micro and nanotechnologies for the development of an integrated chromatographic system

The development of an integrated gas chromatographic system using micro and nanotechnologies is presented in this paper. For this purpose, the different components of the chromatographic system, namely the preconcentrator, the chromatographic column and the gas sensors are being investigated and developed, and the actual state of this investigation is presented. The proposed target application comes from the agrofood industry, in particular the determination of the fish freshness. The structure of the preconcentrator has been fabricated using deep reactive ion etching (DRIE). The same fabrication technique has been employed for the patterning of the silicon microcolumns, which have been sealed with Pyrex glass. Inlet and outlets have been connected and initial experiments of functionalization have been performed. Gas sensors have been obtained by microdeposition of doped WO3 or SnO2 nanomaterials on microhotplates and their responses to the gases of interest have been measured, proving that the target gas concentrations can be detected.

Microsystems for the agrofood field

Microsystems will play an important role in the agrofood field as many different safety and quality assurance procedures may benefit from the inherent advantages of small, fast and reliable devices. An example is proposed for the detection of gases of interest in the control of fruit with a microsystem that combines optical and semiconductor gas sensors. A simple process step is also introduced that allows to improve the performances of such devices.

Micromachined sensors based on ZnO structures and their thermo- and photo-activated response to reducing gases

ZnO rods were grown via aerosol-assisted chemical vapor deposition on Si-based micromachined platforms. The photo- and thermo-activated sensor characteristics were evaluated towards carbon monoxide, ethanol and toluene. Results proved photo-activated response at room temperature with improved response and selectivity compared to the thermo-activated response at 250 °C. This property becomes significantly advantageous as it allows for the sensor to operate without heating.

Improving Sensitivity of a Chemoresistive Hydrogen Sensor by Combining ZIF-8 and ZIF-67 Nanocrystals

In the present work, nanostructures of zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) were combined to obtain a novel chemoresistive sensor, improving the sensitivity of ZIF-67 and facilitating measurement of ZIF-8 by decreasing the resistivity. The sensor detected concentrations as low as 10 ppm of hydrogen increasing its resistivity about 4.5 times. The response of the sensor was compared with a similar chemoresistive sensor based exclusively on ZIF-67, and the sensitivity was around three times higher in the case of the sensor with ZIFs combination.

Flexible gas sensing devices with directly grown tungsten oxide nanoneedles via AACVD

Flexible gas sensing devices have been fabricated by directly integrating multilayer polymer-based platforms and highly crystalline tungsten oxide nanoneedles grown via aerosol-assisted chemical vapor deposition (AACVD). Thermal simulations and characterization of the heating element demonstrate these devices provide uniform temperature distribution at the sensing active area and gas sensing tests show repeatable and satisfactory responses towards hydrogen and ethanol. These devices go beyond traditional gas sensors, offering flexibility and functionality, with a fabrication method that provides great advantages for the integration of nanomaterials and flexible platforms and that can be used in a cost effective production for large-scale applications.