Elaboration d’un capteur pour la détection des composés organiques volatils à base d’une microbalance à quartz

Abstract

The work presented in this thesis concerns the study of the effects of the low frequency plasma discharge parameters (discharge time, monomer total pressure, and the proportion of oxygen with the monomer) on the essential characteristics of the elaborated chemical sensor such as: sensitivity, selectivity, linearity, reversibility,response time and ageing. The analysis of sensor response in adsorption mode and desorption mode show a good reproducibility and reversibility. The study of the response and recovery time showed that these latter appeared extremely short compared to those usually obtained with the chemical sensors base on the QCM. The study of the variation of the sensitivity with deposited layer thickness showed an increase in the sensitivity with increasing film thickness followed by a decrease for a thicker film. Physical and chemical analysis of the deposited films revealed that the increase in the film thickness induces a densification of the elaborate layers. In the case of elaborate sensitive layers with TEOS in mixture with oxygen, the characteristic curves of the sensor response showed a significant increase in the sensor sensitivity with the increase of oxygen content in the mixture, followed by a reduction for a film elaborated with a high proportion of oxygen. Beyond 50% of O2 in the mixture, the films deposited have an inorganic character with a composition of SiOx type, close to thermal silica structure (dense, more rigid and less permeable). The study of the reliability of the sensor shows that the sensors elaborated from organosilicon films have a reasonable stability. The theoretical study of the diffusion phenomenon of the organic molecules inside the deposited films revealed that the molecular weight and the molar volume of the molecules influence significantly the diffusion phenomenon of COV. The results also show that all types of VOC have diffusion coefficients of about D > 1.90 X 10-11 cm ² /s and their diffusion kinetics follow a Fickienne evolution.