Céline Zimmermann

A love-wave gas sensor coated with functionalized polysiloxane for sensing organophosphorus compounds

Love-wave devices based on quartz piezoelectric substrate and SiO2 guiding layer coated with a specific polysiloxane polymer are used to detect organophosphorus compounds. This allows to study affinities of the polysiloxane polymer coating towards organophosphorus compounds, and to demonstrate the high sensitivity of love-wave devices for gas detection. We also present a theoretical model which describe wave propagation in love devices and allow to design optimized structures. Then, we discuss experimental results, in terms of interactions between sensor and vapor and in comparison to SAW results.

Love-waves to improve chemical sensors sensitivity: theoretical and experimental comparison of acoustic modes

Both a theoretical and experimental comparison of the sensitivities of various acoustic wave sensors is presented. From a theoretical point of view, several methods to calculate the sensors mass loading sensitivity are reviewed. Particular attention is turned on Love-wave devices which present a high sensitivity, and are very promising chemical sensors. Experimental tests of gas detection are presented for SAW, SH-APM and Love-wave sensors. The results are discussed. Experimental sensitivities are compared. Some hypotheses are given to explain the discrepancy between theoretical and experimental results.

Coupled determination of gravimetric and elastic effects on two resonant chemical sensors: love wave and microcantilever platforms

The field of chemical microsensors for both gas and liquid sensing has been widely investigated in recent years. Several technologies have been utilized which include love-wave acoustic sensors and silicon microcantilevers. Those structures are both used as chemical sensors by adding a sensitive coating to the device surface. Perturbations of the sensitive coating properties induce frequency drift in both devices, thus making chemical detection possible. Microcantilevers are essentially sensitive to the coating mass changes which modify the resonant frequency of the structure. However, the acoustic wave device is sensitive to all types of propagation perturbations which include mass loading and mechanical properties changes of the coating. One of the difficulties in acoustic sensor field is to separate each contribution from the induced frequency shifts. The aim of this paper is to couple experimental results from microcantilevers and love-wave devices in order to identify and separate the two effects. At last, this coupled study is also interesting for gas and liquid phase detection applications, as it will permit to determine the elasticity evolution during the detection process, i.e. the analyte sorption.

A theoretical study of Love wave sensors mass loading and viscoelastic sensitivity in gas and liquid environments

The sensitivity of Love wave (also known as guided shear horizontal surface acoustic wave (SH-SAW)) sensors to mass loading and/or to viscoelastic change, in gas and liquid environments, is theoretically investigated. The objective is to present effective design parameters for Love wave sensors. The investigated sensor platform consists of a ST and AT-cut quartz substrate, a guiding layer, and a thin (poly)methylmetacrylate (PMMA) coating, used to simulate the chemically sensitive layer. The investigation process consists of computing optimal guiding layer thickness (resulting in the largest perturbation, hence the highest sensitivity), for increasing layer density and shear modulus that includes all available materials. It is demonstrated that the device sensitivity, in general, increases as the difference in bulk shear wave velocities between the substrate and the guiding layer. The relative importance of mass loading and viscoelasticity are discussed. First experiments to confirm this theoretical study lead us to bring up a material characterization technique which shows that literature material parameters are not usable for film materials.

Detection of organophosphorus vapors (GB and DMMP) using polysiloxane coated Love-wave sensors: sensitivity and interaction mechanisms analysis

In this paper, polysiloxane-coated Love-wave sensors are used to detect organophosphorus compounds (GB and DMMP). A coating system to improve sensitive layer deposition for Love-wave sensors is presented. A comparison between theoretical calculations and experimental results brings to light that a pure mass loading effect cannot explain the sensor response.

Coupled determination of gravimetric and elastic effects on two resonant chemical sensors: Love wave and microcantilever platforms

The objective of this paper is to couple theoretical and experimental results from microcantilevers and Love-wave acoustic devices in order to identify and separate mass loading effects from elastic effects. This is important in the perspective of sensing applications. For that, a thin-film polymer is deposited on both resonant platforms. It is demonstrated that microcantilevers are essentially mass sensitive. They allow one to determine the polymer layer thickness, which is validated by optical profilometry measurements. Then, taking into account this thickness, theoretical modeling and experimental measurements with Love-wave devices permit one to estimate an equivalent elastic shear modulus of the thin-film polymer at high frequency. Results are interesting if one is to fully understand and optimize (bio)chemical sensor responses.

Dynamic analysis of Love waves sensors responses: application to organophosphorus compounds in dry and wet air

The Love wave sensor, made of quartz substrate with SiO2 as guiding layer and a polysiloxane sensitive coating, was put in the retroaction loop of an oscillator, in order to access the wave phase velocity thanks to the oscillator frequency. Experiments were done with two organophosphorus compounds: GB and dimethylmethylphosphonate (DMMP), with dry and wet air as gas vector. The purpose of this paper is to extract unexploited aspects of the sensors responses that allow measurements analysis, and even quantification, without waiting for steady state. Four transient parameters have been selected for a principal component analysis. As expected a plot regroups measurements by concentrations, then it is explained how this method can be a calibration for a later functional sensor.

Evaluation of Love waves chemical sensors to detect organophosphorus compounds: Comparison to SAW and SH-APM devices

We report on the application of Love-wave devices for organophosphorus detection. First, we propose a theoretical modelling of Love devices. Experimental results on organophosphorus detection are then exposed. Finally, we compare theses results to theoretical results and to SAW and SH-APM experimental results, and we present some conclusions.

Vapor detection with polysiloxane coated Love-wave devices. Influence of thin film viscoelastic properties: sensitivity analysis

In this paper, polysiloxane coated Love-wave devices are used to detect organophosphorus compounds. Theoretical calculation (analytical and numerical) has been undertaken taking into account sensitive coating shear modulus and viscosity on the Love-wave device sensitivity. A comparison with experimental results under gas (DMMP compounds) brings to light that a pure mass loading effect cannot explain the sensor response. According to several assumptions about polymer properties, an analysis of the detection mechanism is proposed and shows the influence of the coating viscoelastic properties.

P2J-1 Love-Wave Characterization Platform for Micro and Nano Processed Thin Films

Acoustic wave sensors uses more and more often micro and nano-structured thin film new materials (e.g. as sensitive layer). This lead to an increasing need for materials viscoelastic properties characterization. A new characterization method is proposed here using Love-wave platforms and allowing the material properties characterization directly with the sensor platform. A Love-wave device consists in a multilayer structure with a piezoelectric substrate, a guiding layer and, for chemical detections, a sensitive layer able to trap chemical species. Sensitive and guiding layers involve thin films organic and inorganic materials in which a 100 MHz Love-wave propagates during sensor operation. Materials are then excited at high frequency and mechanical properties are affected by the wave propagation. The characterization method determines material layer density and shear modulus by fitting simulation results to experimental measurements. First results concern the characterization of Love-wave SiO2 guiding layer and demonstrate that using characterized SiO2 density and shear modulus allows to simulate accurately the wave phase velocity of Love-wave devices with different SiO2 guiding layer thicknesses