Fabien Josse

Phthalocyanines as Sensitive Materials for Chemical Sensors

This paper provides a review of phthalocyan- ines suitable for the development of chemical sensors. Phthalocyanines may be utilized for different types of chemical sensors, including in particular electronic conductance sensors [such as semiconductive, field-effect transistor (FET), solid-state ionic and capacitance sensors], mass-sensitive sensors utilizing a quartz crystal microbalance (QCM) and surface acoustic-wave (SAW) sensors, and optical sensors. The phthalocyanines used are discussed in terms of their physical and chemical properties, as well as their sensitivity, selectivity and reversibility towards the detection of NO2 and organic solvent vapours. The interaction mechanism between phthalocyanine films and analyte molecules is also discussed.

Thermal Excitation and Piezoresistive Detection of Cantilever In-Plane Resonance Modes for Sensing Applications

Thermally excited and piezoresistively detected bulk-micromachined cantilevers vibrating in their in-plane flexural resonance mode are presented. By shearing the surrounding fluid rather than exerting normal stress on it, the in-plane mode cantilevers exhibit reduced added fluid mass effects and improved quality factors in a fluid environment. In this letter, different cantilever geometries with in-plane resonance frequencies from 50 kHz to 2.2 MHz have been tested, with quality factors as high as 4200 in air and 67 in water.

Analysis of piezoelectric bulk-acoustic-wave resonators as detectors in viscous conductive liquids

An analytical solution for the resonance condition of a piezoelectric quartz resonator with one surface in contact with a viscous conductive liquid is presented. The characteristic equation that describes the resonance condition and accounts for all interactions including acoustoelectric interactions with ions and dipoles in the solution is obtained in terms of the crystal and liquid parameters. A simple expression for the change in the resonance frequency is obtained. For viscous nonconductive solutions, the frequency change is reduced to a relationship in terms of the liquid density and viscosity. For dilute conductive liquid, the change in frequency is derived in terms of the solution conductivity and dielectric constant. The boundary conditions for the problem are defined with and without the electrical effects of electrodes. Experiments were conducted with various viscous and conductive chemical liquids using a fabricated miniature liquid flow cell containing an AT-cut quartz crystal resonator. The results, which show good agreement with the theory, on the use of quartz crystal resonators as conductivity and/or viscosity sensors are reported.<<ETX>>

Theory and application of a quartz resonator as a sensor for viscous liquids

Abstract A comprehensive analysis of the interaction between an AT-cut quartz crystal resonator and a viscous fluid is presented. The analysis, which includes peizoelectric effects, assumes a liquid of finite extent and therefore could also be used to study thin film of viscous liquids. A novel continuous flow cell system was designed and fabricated to monitor viscosity using an 11-MHz quartz crystal resonator. Measured data for frequency shifts of aqueous solutions of alcohols and sugars are in excellent agreement with theory.

Characteristics of laterally vibrating resonant microcantilevers in viscous liquid media

The characteristics of microcantilevers vibrating laterally in viscous liquid media are investigated and compared to those of similar microcantilevers vibrating in the out-of-plane direction. The hydrodynamic loading on the vibrating beam is first determined using a numerical model. A semi-analytical expression for the hydrodynamic forces in terms of the Reynolds number and the aspect ratio (beam thickness over beam width) is obtained by introducing a correction factor to Stokes’ solution for a vibrating plate of infinite area to account for the effects of the thickness. The results enable the effects of fluid damping and effective fluid mass on the resonant frequency and the quality factor (Q) to be investigated as a function of both the beam’s geometry and liquid medium’s properties and compared to experimentally determined values given in the literature. The resonant frequency and Q are found to be higher for laterally vibrating microcantilevers compared to those of similar geometry experiencing transv...

On the use of ZX-LiNbO3 acoustic plate mode devices as detectors for dilute electrolytes

Abstract Acoustic plate mode (APM) devices on Z-cut, X-propagating LiNbO3, a high piezoelectric coupling material, are investigated as detectors in dilute electrolyte or metal-ion solutions. The sensing wave is an APM, a slow shear wave coupled to the interdigital transducer, which results in a relatively strong acoustic-ionic interaction. The resulting electrical loading leads to a measurable perturbation in the wave-propagation characteristics, which can then be related to the liquid electrical properties. Experiments conducted at different frequencies with various solutions that compare well with theoretical results show a detector that is at least two orders of magnitude more sensitive than similar APM sensors on quartz. These promising results have also led to the investigation of the detection of aqueous transition-metal ions (Fe3+, Cu2+, etc.) using solution conductivity changes rather than the commonly used mass sensitivity. The method involves the bonding of metal ions in soluiton to a ligand-coated silica or LiNbO3 support, placed adjacent to the APM device and in the path of the liquid flow. The resulting frequency increase is then interpreted in terms of the concentration of the metal ions. X-ray photoelectron spectroscopy analysis of the coated surface is performed to confirm the binding.

AC-impedance-based chemical sensors for organic solvent vapors

Abstract A type of chemical sensor based on impedance spectroscopy (IS) measurements utilizing an interdigital transducer structure on a glass substrate is investigated for the detection of organic solvent molecules, such as chloronated hydrocarbons, in the gas phase. The IDT structures were coated with sensitive material such as soluble tetrakis-t-butyl phthalocyaninatonickel(II), ethylcellulose, poly(ethyl acrylate), and poly(etherurethane). The target organic solvent molecules are dichloromethane, chloroform, trichloroethene, tetrachloroethene, toluene, and ethanol. The sensor responses were monitored by measuring changes in the transducer/coating composite properties upon exposure to the organic solvent molecules. The sensor parameters of interest include the electrostatic capacitance, the resistance of the composite and the relaxation time, which will lead to the implementation of a multi-information sensor. Results are presented and compared for selected samples with completely reversible sensor signals at room temperature. Based on the measurements, use of metal complexes can improve sensitivity and increase the signal-to-noise ratio.

Liquid-Phase Chemical Sensing Using Lateral Mode Resonant Cantilevers

Liquid-phase operation of resonant cantilevers vibrating in an out-of-plane flexural mode has to date been limited by the considerable fluid damping and the resulting low quality factors (Q factors). To reduce fluid damping in liquids and to improve the detection limit for liquid-phase sensing applications, resonant cantilever transducers vibrating in their in-plane rather than their out-of-plane flexural resonant mode have been fabricated and shown to have Q factors up to 67 in water (up to 4300 in air). In the present work, resonant cantilevers, thermally excited in an in-plane flexural mode, are investigated and applied as sensors for volatile organic compounds in water. The cantilevers are fabricated using a complementary metal oxide semiconductor (CMOS) compatible fabrication process based on bulk micromachining. The devices were coated with chemically sensitive polymers allowing for analyte sorption into the polymer. Poly(isobutylene) (PIB) and poly(ethylene-co-propylene) (EPCO) were investigated as sensitive layers with seven different analytes screened with PIB and 12 analytes tested with EPCO. Analyte concentrations in the range of 1-100 ppm have been measured in the present experiments, and detection limits in the parts per billion concentration range have been estimated for the polymer-coated cantilevers exposed to volatile organics in water. These results demonstrate significantly improved sensing properties in liquids and indicate the potential of cantilever-type mass-sensitive chemical sensors operating in their in-plane rather than out-of-plane flexural modes.

Electrical surface perturbation of a piezoelectric acoustic plate mode by a conductive liquid loading

Surface loading of a piezoelectric crystal supporting acoustic plate modes (APMs) by a dilute conductive liquid is analyzed using a perturbation theory. The formulation of the problem is such that only the electrical loading is relevant, and the mass loading and viscous entrainment caused by the solute are ignored. The perturbation in the propagation characteristics is then obtained relative to the solvent and is described in terms of the coupling coefficient, the capacitive loading, and the conductivity of the liquid. The results are compared to measurements made on Z-cut X-propagating LiNbO/sub 3/ APM device loaded with various conductive liquids of different concentrations. While an interpretation of the results can be given on the use of the APM device as a detector of the liquid properties, it is shown that a conductive liquid loading of the piezoelectric surface can be used as a means of assessing the electromechanical coupling coefficient of APMs.<<ETX>>

Analysis of shear horizontal surface waves at the boundary between a piezoelectric crystal and a viscous fluid medium

Surface shear horizontal wave propagation at the boundary of a piezoelectric substrate with a viscous fluid is theoretically analyzed. The analytical solution clearly shows the dependence of the velocity change, the wave propagation loss, and the wave amplitude profile (thus the energy confinement near the surface), in terms of the liquid viscosity and density, the layer thickness, and the wave frequency. It is shown that the viscous fluid loading produces some guidance near the surface but also some damping of the wave. The propagation loss is due only to viscous coupling and not to a mode conversion and viscous coupling as is the case with Rayleigh surface acoustic waves (SAWs). Closed‐form expressions are derived for the attenuation coefficient and the fractional velocity change (thus the frequency change) in terms of the piezoelectric crystal and viscous liquid parameters. The theory, applicable to both a Bleustein–Gulyaev (BG) wave and a surface skimming bulk wave (SSBW), indicates that surface shear...