Papers by Author: Patrice Raynaud

Abstract: The detection of volatile organic compounds (VOCs), humidity and toxic industrial chemicals is important for various environmental and industrial applications. The design of interdigital capacitor (IDCs) sensor is carried out in such a way that it would be suitable for microelectronic technology. The basic geometry of IDCs is defined by some parameters such as: number of electrodes N, electrode width W, electrode length L and the separation between electrodes G. The interactions between IDCs sensitive coating and analyte induced a change in the sensors capacitance due to the permittivity variation of the sensitive layer and to the change in polymer thickness (swelling). In this work, a fairly new approach of IDCs based sensor in terms of capacitance calculation has been presented. The results have been obtained from the modeling of the sensors geometry 2D and 3D using multi-physics simulation software COMSOL. The effects of some geometry parameters coupled with swelling measurements for polymeric films have been studied.

Abstract: Humidity sensitive layers elaborated from pure HMDSO and TEOS by PECVD technique have been studied. Humidity sensing properties including impedance relative humidity (RH) and current RH characteristics were investigated. TEOS films show higher sensitivity and excellent linearity over the explored range of humidity (20–95% RH). However, HMDSO films exhibits a small response and recovery of about 8 and 34 s for humidification and desiccation, respectively, in addition to very low hysteresis (2%). Structural analyses of sensitive layers were characterized by Fourier transform infrared spectroscopy (FTIR).

Abstract: Hexamethyldisiloxane (HMDSO) thin films coated quartz crystal microbalance (QCM) electrodes have been characterized for the detection of volatile organic compounds (VOCs). The sensitive coatings were plasma polymerized in pure vapor of HMDSO at different flow rates. The QCM based sensors responses were found to be linearly correlated with the concentration of VOCs vapor. It was shown that it is possible to tune the chemical affinity of the sensor by changing the HMDSO flow rate. Contact angle measurements, Fourier transform infrared spectroscopy and scanning electron microscopy were used to study surface wettability, chemical composition and surface morphology of the coated QCM electrodes.

Abstract: A new class of low-k materials thin films, deposited from a DiPhenyleMethylSilane (DPMS) vapors was prepared using PECVD technique. These films are elaborated in microwave excited DECR plasma reactor (Distributed Electron Cyclotron Resonance) from pure DiPhenylMethylSilane (DPMS) using various plasma discharge power (100-400 W) or mixed with 50% of oxygen (O2).The improvements of film properties were investigated by capacitance–frequency (C–f), current–voltage (I–V) techniques and Fourier transform infrared spectroscopy (FTIR). The obtained results show that an increase in plasma discharges power from 100 to 400 watts leads to the decrease in dielectric constant value from 4.4 to 3.7 (measured at 10 kHz). The incorporation of oxygen improves the dielectric properties of the films; the dielectric constant value was reduced to 2.9.

Abstract: The present project is focused on the plasma-deposition of thin films (~150 nm) containing silver nanoparticles embedded in a polymeric matrix, to prevent microbial adhesion to stainless steel. The process originality relies on a dual strategy associating silver target sputtering and plasma polymerization in argon-hexamethyldisiloxane (HMDSO) plasma, using an asymmetrical RF discharge (13.56 MHz). The physico-chemical properties of the obtained films were investigated by transmission FTIR and XPS. To determine the anti-adhesive efficiency, detachment experiments were performed in a shear stress flow chamber with silver-containing and silver-free deposits. The maximal detachment efficiency was achieved with the polymeric matrix alone. Silver antimicrobial effect is assumed to be related to Ag+ ion progressive release from the embedded particles into the surrounding medium. This release was confirmed by ICP-MS measurements. Furthermore, film biocide activity was observed for silver-containing film.

Abstract: Humidity sensors are widely used in industry production, process control, environment monitoring, medical and electrical applications. In this study, water molecule sensitive layers have been elaborated by plasma enhanced chemical vapor deposition PECVD technique, from a mixture of hexamethyldisiloxane (HMDSO) and oxygen (O2) in different proportions. The films were deposited on a comb-shape aluminum electrode evaporated on glass substrate. Electrical and structural characteristics of the elaborated humidity sensors were evaluated by humidity-impedance characteristics, infrared spectroscopy FTIR and ellipsometric analysis. Electrical analysis showed that the elaborated humidity sensor exhibited a detectable response to relative humidity ranging from 35 to 95%. However, increasing O2 concentration in the mixture during deposition, leads to a significant decrease of the sensor sensibility. A sensor elaborated with pure vapor of HMDSO exhibited a better sensibility. FTIR analysis revealed that increasing O2 concentration induces a decrease of methyl groups CH3 and the formation of Si-O groups leading to film densification. Besides, the values of the refractive index deduced from ellipsometric data indicated that the refractive index increases with increasing the O2% in the mixture. This observation may be considered as further evidence to film densification.

Abstract: Thin SiOF films were elaborated in microwave excited DECR plasma reactor (Distributed Electron Cyclotron Resonance) from a mixture of hexamethyldisiloxane (HMDSO) and oxygen (O2) (in 1: 9 proportion) with the presence of various CF4 concentrations. The fluorine contents in the films composition were adjusted by the CF4 gas flow ratio (in the range of 10 - 70%). The refractive index and the deposition rate were estimated from ellipsometric data and the film chemical structure was studied by FTIR analysis technique. The deposition rate increases with increasing CF4 flow and then decreases after reaching a maximum value for 20% of CF4. The decrease in the deposition rate may be attributed to the etching effect by CF4 plasma during the deposition process. As the additive fluorine concentration increases, the intensity of Si–F peak stretching vibrations located at 930 cm-1 increases and the frequency of the Si–O stretching vibration mode centered at 1060 cm-1 shifts towards higher wavenumber.

Abstract: Some investigations on physico-chemical properties of hydrogenated amorphous carbon (a-C:H) thin films deposited from C2H4 precursor have been carried out. The films were elaborated in a Microwave Multipolar Plasma reactor excited at Distributed Electron Cyclotron Resonance (MMP-DECR). The effects of the plasma power on the electrical and structural characteristics of the deposited films have been evaluated. It appeared that for low plasma power ( 400 W), the deposition rate and the hydrogen concentration increases, whereas the Csp2 concentration remains constant. Beyond 400 W, the deposition rate and the hydrogen concentration reach saturation levels and the Csp2 concentration decreases. In contrast, the film density decreased with the increase of the plasma power. Below 400 W, the dielectric constant decreased with the increase of the plasma power, however, beyond 400 W its value remained almost constant. The correlation between film characterization and properties shows that the permittivity is driven by the film density and the film structure.