Philippe Menini

A computational chemist approach to gas sensors: Modeling the response of SnO2 to CO, O2, and H2O Gases

A general bottom‐up modeling strategy for gas sensor response to CO, O2, H2O, and related mixtures exposure is demonstrated. In a first stage, we present first principles calculations that aimed at giving an unprecedented review of basic chemical mechanisms taking place at the sensor surface. Then, simulations of an operating gas sensor are performed via a mesoscopic model derived from calculated density functional theory data into a set of differential equations. Significant presence of catalytic oxidation reaction is highlighted.

Wireless sensing and identification based on radar cross section variability measurement of passive electromagnetic sensors

In this paper, we present the wireless measurement of various physical quantities from the analysis of the radar cross section variability of passive electromagnetic sensors. The technique uses a millimeter frequency-modulated continuous-wave radar for both remote sensing and wireless identification of sensors. Long reading ranges (up to some decameters) are reached at the expense of poor measurement resolution (typically 10xa0%). A review of recent experimental results is reported for illustration purposes.

Wireless sensing and identification of passive electromagnetic sensors based on millimetre-wave FMCW RADAR

The wireless measurement of various physical quantities from the analysis of the RADAR Cross Sections variability of passive electromagnetic sensors is presented. A millimetre-wave Frequency-Modulated Continuous-Wave RADAR is used for both remote sensing and wireless identification of sensors. Long reading ranges (up to some decameters) may be reached at the expense of poor measurement resolution (typically 10%).

Organometallic approach for platinum and palladium doping of tin and tin oxide nanoparticles: structural characterisation and gas sensor investigations

Platinum and palladium surface doped tin nanoparticles have been obtained by decomposition of [Pt2(dba)3] and [Pd(dba)2] organometallic precursors, respectively, in a colloidal suspension of tin/tin oxide core–shell nanoparticles of uniform size (≈13 nm), in anisole under 1 bar of carbon monoxide at room temperature. The particles can be isolated as pure solids and present effective doping ratios [Pt]/[Sn] and [Pd]/[Sn] of 2.5 and 3.1%, respectively. These nanomaterials have been characterized by means of transmission electron and high-resolution transmission electron microscopies (TEM and HRTEM), Energy Dispersive X-ray spectroscopy (EDX), photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS and XANES). The TEM micrographs show spherical nanoparticles whose size and size distribution are essentially similar to those of the initial Sn/SnOx material. HRTEM, EDX, XPS and X-ray absorption spectroscopy (XAS) studies at the Pd and/or Sn-K edge show the conservation of the composite nature of the particles that consist of a tin(0) core covered with a layer of tin oxides on which the doping element is deposited under the form of crystalline metallic platelets of size near 2 nm. The thermal oxidation of these Pt- or Pd-doped tin materials yields nanoparticles of crystallized SnO2 covered with crystallites of Pt or Pd oxides, as demonstrated by XRD, XPS and XAS experiments, without coalescence or size change. In the oxidised Pd-doped material, EXAFS analysis combined with HRTEM, point towards the formation of two main Pd disordered oxide phases: a rather pure oxopalladate Pd3.5O4-type phase at the surface of the particle and a mixed Pd/Sn phase having a PdO structure-type at the interface Pd oxide/Sn oxide. The thermal oxidation process can be easily achieved onto the silicon platform of a micro-machined device after integration of the Pt- or Pd-doped Sn/SnOx colloidal suspension by drop deposition. The first electrical measurements indicate remarkable behaviours of the as-obtained microsensors when exposed to traces of carbon monoxide. In addition to the expected large increase of sensitivity of the doped relatively to the undoped sensitive layer measured in humid atmosphere, a surprising and unprecedented inversion of sensitivity from undoped to Pt- and Pd-doped sensors has been observed in dry atmosphere.

Novel millimeter-wave gas sensor using dielectric resonator with sensitive layer on TiO 2

A new generation of gas sensors that operates in millimeter-wave frequency range is presented. The sensor uses a dielectric resonator operating with whispering-gallery modes. Here the dielectric resonator is covered by TiO2 thin film as sensitive layer. A gas or humidity adsorption makes the TiO2 dielectric permittivity changing and such changing modifies the resonant frequencies of high-Q whispering-gallery modes within the dielectric resonator. From the measurement of these resonant frequencies the humidity concentration is derived. Here, the proof of concept is demonstrated through full wave electromagnetic simulations. This humidity (gas) sensor can be remotely interrogated and has great potential for wireless sensors network applications.

Feasibility of wireless gas detection with an FMCW RADAR interrogation of passive RF gas sensor

The feasibility of the remote measurement of gas detection from an RF gas sensor has been experimentally investigated. It consists of a Frequency-Modulated Continuous-Wave (FMCW) RADAR interrogation of an antenna loaded by the passive sensor. The frequency band of the RADAR [28.8–31GHz] allows the detection of the resonant frequencies of Whispering Gallery Modes that are sensitive to gas concentration. Reported experimental results provide the proof-of-concept of remote measurement of gas concentration fluctuation from RADAR interrogation of this new generation of passive gas sensors.

SnO2 "Russian Doll" Octahedra Prepared by Metalorganic Synthesis: A New Structure for Sub-ppm CO Detection.

Micrometer-sized hierarchical Sn3 O2 (OH)2 octahedra, which are self-assembled one inside the other, resembling Russian doll organization, have been obtained by a metalorganic approach. This synthesis is based on the controlled hydrolysis of [Sn(NMe2 )2 ]2 in the presence of an alkylamine ligand in an organic solvent (THF). The water content of the medium proved to be a key parameter for the formation of these multi-walled octahedra. The resultant structures have been used as gas-sensitive layers on micromachined silicon devices. During in situ heating, Sn3 O2 (OH)2 is oxidized to SnO2 while retaining the initial morphology. The sensors present outstanding dynamic responses at very low CO concentrations (7u2009% and 67u2009% resistance variation to 0.25 and 20u2005ppm CO, respectively, at an operating temperature of 500u2009°C). This superior gas-sensing performance is closely related to the unique microstructure of the SnO2 multi-walled octahedra.

Ultra-sensitive SnO 2 gas sensors based on hierarchical octahedra

The controlled hydrolysis of Sn11 precursor ([Sn(NMe)2]2) yields micrometric Sn3O2(OH)2 octahedra, formed by a self-assembly process. The water content and alkylamine surfactants are major parameters for the growth process. These structures have been employed to prepare highly sensitive gas sensors, which present 7% variation of their resistance at only 0.25 ppm CO.

Miniaturized 3D gas sensors based on silicon nanowires for ppb range detection

Here, we reported 3D devices implemented on silicon nanowires (SiNW) for chemical gas sensing, working at room temperature and in presence of moisture or interfering gas. This sensor combines for the first time high sensibility, selectivity, reversibility, low-power consumption and reliability in real condition. In addition the sensors are miniaturized and develop through a cost effective and large scale approach.