O. Casals

Portable microsensors based on individual SnO2 nanowires

Individual SnO(2) nanowires were integrated in suspended micromembrane-based bottom-up devices. Electrical contacts between the nanowires and the electrodes were achieved with the help of electron- and ion-beam-assisted direct-write nanolithography processes. The stability of these nanomaterials was evaluated as function of time and applied current, showing that stable and reliable devices were obtained. Furthermore, the possibility of modulating their temperature using the integrated microheater placed in the membrane was also demonstrated, enabling these devices to be used in gas sensing procedures. We present a methodology and general strategy for the fabrication and characterization of portable and reliable nanowire-based devices.

A Highly Selective and Self‐Powered Gas Sensor Via Organic Surface Functionalization of p‐Si/n‐ZnO Diodes

Selectivity and low power consumption are major challenges in the development of sophisticated gas sensor devices. A sensor system is presented that unifies selective sensor-gas interactions and energy-harvesting properties, using defined organic-inorganic hybrid materials. Simulations of chemical-binding interactions and the consequent electronic surface modulation give more insight into the complex sensing mechanism of selective gas detection.

Site-selectively grown SnO2 NWs networks on micromembranes for efficient ammonia sensing in humid conditions

SnO2 NWs networks on heated micromembranes have been characterized as ammonia sensors. The approach allows achieving reproducible growth and stable and long-lasting ammonia sensors with site-specific grown SnO2 NWs. The devices have been tested both in dry and humid conditions showing response time down to two minutes. Sensors have been tested up to 1 month, only presenting variation of the base resistance with full retention of the response towards the gaseous analytes. Different concurrent sensing mechanisms have been identified relating the determined sensing kinetics with previous theoretical calculations. Specifically, oxygen dissociation seems to play a key role in the overall ammonia sensing sequence. In humid conditions, moisture reduces the response to ammonia but also lowers the activation energy of the reaction process.

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.

Colorimetric sensor for bad odor detection using automated color correction

Colorimetric sensors based on color-changing dyes offer a convenient approach for the quantitative measurement of gases. An integrated, mobile colorimetric sensor can be particularly helpful for occasional gas measurements, such as informal air quality checks for bad odors. In these situations, the main requirement is high availability, easy usage, and high specificity towards one single chemical compound, combined with cost-efficient production. In this contribution, we show how a well stablished colorimetric method can be adapted for easy operation and readout, making it suitable for the untrained end user. As an example, we present the use of pH indicators for the selective and reversible detection of NH3 in air (one relevant gas contributing to bad odors) using gas-sensitive layers dip coated on glass substrates. Our results show that the method can be adapted to detect NH3 concentrations lower than 1 ppm, with measure-to-result times in the range of a few minutes. We demonstrate that the color measurements can be carried out with the optical signals of RGB sensors, without losing quantitative performance.

NO2 Measurements with RGB Sensors for Easy In-Field Test

We present a simple an inexpensive method to implement a Griess-Saltzman-type reaction that combines the advantages of the liquid phase method (high specificity, fast response time) with the benefits of a solid implementation (easy to handle). We demonstrate that the measurements can be carried out using conventional RGB sensors; circumventing all the limitations around the measurement of the samples with spectrometers. We also present a method to optimize the measurement protocol and target a specific range of NO2 concentrations. We demonstrate that it is possible to measure the concentration of NO2 from 50 ppb to 300 ppm with high specificity and without modifying the sensing elements.

Highly Specific and Wide Range NO2 Sensor with Color Readout

We present a simple and inexpensive method to implement a Griess-Saltzman-type reaction that combines the advantages of the liquid phase method (high specificity and fast response time) with the benefits of a solid implementation (easy to handle). We demonstrate that the measurements can be carried out using conventional RGB sensors; circumventing all the limitations around the measurement of the samples with spectrometers. We also present a method to optimize the measurement protocol and target a specific range of NO2 concentrations. We demonstrate that it is possible to measure the concentration of NO2 from 50 ppb to 300 ppm with high specificity and without modifying the Griess-Saltzman reagent.

1.1.4 SiC-based MIS gas sensor for CO detection in very high water vapor environments

Due to their feasibility to operate at high temperature in environments with extremely high concentrations of water vapor (up to 45% by volume ratio to nitrogen), SiC-based MIS (MetalInsulator-Semiconductor) capacitors are good candidates to monitor the presence of CO in the exhaust gases of hydrogenor hydrocarbon-based fuel cells. In this work, we show that these devices are able to detect down to 2 ppm of CO and that their response is hardly affected by the presence of high concentrations of CO2 or by extremely high water vapor concentrations in pure nitrogen.

Fabrication of bottom-up gas sensors based on individual SnO 2 nanowires and suspended microhotplates

In this work, bottom-up devices based on individual monocrystalline SnO2 nanowires (NWs) were fabricated using FIB nanolithography on top of suspended microhotplates, with integrated heater and interdigitated microelectrodes. The electrical characterisation of such devices in the presence of different gases show that devices with improved gas sensing properties can be fabricated.

Bottom-up Fabrication of Individual SnO 2 Nanowires-based Gas Sensors on Suspended Micromembranes

Bottom – up techniques were used to obtain gas sensors based on individual SnO2 nanowires placed over microhotplates with integrated heaters. These nanowires were electrically contacted to pre-patterned microelectrodes by means of Focused Ion Beam (FIB) nanofabrication methodologies. The performance of these sensors, which exhibit reproducible and stable responses, was evaluated as function of different gas atmospheres and dissipated power by the heater, demonstrating that this technological approach could be used to develop functional devices based on nanomaterials.