Papers by Author: Y. Segui

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: Amorphous hydrogenated carbon (a-C:H) films have been deposited in Microwave Multipolar plasma reactor (MMP) using pure acetylene as precursor with controlling substrate temperature. Investigations on the optical properties of deposited films according to the substrate temperature have been reported. It has been observed that the optical band gap decreases and the Csp2 concentration increases when cooling down the substrate temperature. On the other hand, it has been revealed elsewhere that cooling down the substrate temperature during the deposition process, leads to the increase of particles trapped density in the deposited films due to a phenomenon of thermophoresis. Therefore, the optical properties evolution is linked to the increases of particles trapped density in the deposited films.

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.