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Papers by Julien El Sabahy

La détection de gaz est un enjeu de plus en plus important, aussi bien dans le domaine de la surv... more La détection de gaz est un enjeu de plus en plus important, aussi bien dans le domaine de la surveillance de la qualité de l’air -intérieur et extérieur- que dans le suivi de procédés. Cet enjeu est d’autant plus critique dans le cas des composés organiques volatiles (COVs) que leur impact sur la santé publique est avéré. Détecter et quantifier leur présence devient une problématique majeure et différentes solutions existent. L’une d’elles, basée sur le couplage d’une nano-poutre résonnante et d’une micro colonne de chromatographie, s’avère être une solution prometteuse. Ces deux dispositifs alliant sélectivité et grande sensibilité nécessitent cependant une fonctionnalisation à l’aide d’une couche sensible. Ces travaux se sont focalisés sur le développement de matériaux sensibles de la famille des SiOCH déposés en couche mince par dépôt chimique en phase vapeur assisté par plasma (PECVD). L’étude de la réponse sous gaz des différents matériaux synthétisés au cours de cette thèse a ...

Dans le cas de la détection de gaz, ces systèmes électromécaniques de dimensions nanométriques (N... more Dans le cas de la détection de gaz, ces systèmes électromécaniques de dimensions nanométriques (NEMS pour Nano-ElectroMechanical Systems) nécessitent d'être rendus sensibles au gaz d'une part et sélectifs d'autre part. En effet, une molécule de gaz a peu de probabilité de se fixer à la surface de la nano-poutre et d'être par conséquent détectée. Une couche sensible doit y être déposée afin d'augmenter les probabilités d'interaction avec les gaz. En piégeant ces analytes d'intérêt { la surface du NEMS, cette fonctionnalisation rend ainsi sensible la nano-poutre. La problématique de la sélectivité

Microporous and Mesoporous Materials, 2021

Sensors and Actuators B: Chemical, 2018

 Several SiOCH thin films deposited by PECVD has been studied for gas detection.  A compromise ... more  Several SiOCH thin films deposited by PECVD has been studied for gas detection.  A compromise between hydrophobicity and methyl content is necessary.  The optimized film presents a K > 15000 (for toluene) and rapid temporal response.  This material is a good candidate for the functionalization of NEMS gas sensors.

Volatile organic compounds (VOCs) such as benzene or toluene are increasingly present in our envi... more Volatile organic compounds (VOCs) such as benzene or toluene are increasingly present in our environment and represent a significant risk for human healthcare. In order to detect such gases, sensors with sensitive layers are being developed to capture and concentrate these species selectively and in a reversible manner. To develop such sensors, an experimental setup was set up to study the affinity towards toluene of hybrid organic-inorganic layers coated on QCM (Quartz Crystal Microresonator) , in different experimental conditions. These chemically active layers deposited by PECVD present K factors higher than those reported in the literature. A model based on the Langmuir approach is proposed and numerical simulations are performed to provide an interpretation of the high K factor values and their relation with injected gas concentration.

Sensors and Actuators B: Chemical, 2014

A poly(neopentyl methacrylate) (p(npMA)) layer was deposited using initiated chemical vapor depos... more A poly(neopentyl methacrylate) (p(npMA)) layer was deposited using initiated chemical vapor deposition and its affinity toward gaseous toluene was characterized by Quartz crystal microbalance. High partition coefficients were measured and showed dependence with toluene concentration. In order to better understand these partition coefficient values and evolution, Langmuir adsorption theory was used. Analytical expressions were first compared to experimental data to provide interpretation of the thin film affinity and time response toward toluene. Numerical simulations were realized to take into account toluene mass transport and verify assumptions leading to analytical expressions. Finally, these simulations were used to refine interpretation of p(npMA)-toluene interaction. Analytical and numerical solutions showed good agreement with experimental data, providing an interpretation of toluene with an organic polymer in terms of affinity and also time response.

Microelectronic Engineering, 2017

Significant advances have been made in the realization of porous SiOCH by chemical vapor depositi... more Significant advances have been made in the realization of porous SiOCH by chemical vapor deposition processes. In this paper, the different approaches developed to introduce porosity in an organosilicate thin films are described with a specific focus on the new concepts to obtain highly porous SiOCH by CVD and to simplify the existing processes. A second part of the paper is dedicated to the application of these porous SiOCH thin films in nanotechnologies: from low-κ dielectrics to chemical and biochemical sensors. Highlights  Different approaches to deposit porous SiOCH thin films by CVD are described.  For low-κ applications, Si-CH x-Si bonds can be introduced in order to improve the mechanical properties and resistance to plasma-induced damage of porous SiOCH.  Highly porous SiOCH can be obtained by using a foaming technique.  A simple process using UV curing of a dense SiOCH leads to porous thin films.  These porous materials are promising as sensitive layer in chemical and biochemical sensors.

There is an increasing need for on-site and real-time analyses of complex gas mixtures in many ap... more There is an increasing need for on-site and real-time analyses of complex gas mixtures in many application fields such as industry, air quality, security and medicine. One challenge consists in developing complete and portable multi-gas analysis systems allowing in situ and real-time quantitative analysis of complex gas mixtures. A promising approach is based on the integration of resonating devices on silicon chips by using “standard” microelectronic technologies. The fabrication of these gravimetric gas sensors based on Nano Electro Mechanical System (NEMS) requires the use of a chemical sensitive layer to ensure a better collection and concentration of the target molecules. This enhances the sensitivity in conjunction with the limit of detection. The integration of a chemical sensitive layer on to NEMS fabricated on Si wafers leads to specific material requirements. The use of solvent is prohibited in order to avoid the degradation of the Si nanocantilevers due to capillarity forces, Very thin film thickness (less than few hundred of nanometers) should be deposited on the Si beam in order to avoid filling the gap between the resonant cantilever and the electrodes, The deposition technique should provide good uniformity over a large surface (typically on 200 mm Si wafers) for a collective sensor fabrication. And the material should be optimized to absorb the highest level of targeted gas for a given thickness, reversibly and quickly. In this work, the objective was to develop materials deposited using microelectronic compatible techniques in order to detect light alkanes and aromatic volatile organic compounds such as BTEX (for Benzene, Toluene Ethylbenzene and Xylene). Organosilicate materials are potentially good candidates for this application especially because they are nonpolar or weakly polar materials. In order to better understand the impact of the material chemistry on the detection of hydrocarbon gas and optimize the sensitivity of the chemical layer, a large panel of organosilicate thin films were deposited by different chemical vapor deposition (CVD) techniques. First, SiOCH were deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD), this technique being the most used in the microelectronic industry for dielectric thin-film deposition. Several precursors (diethoxymethylsilane, trimethylsilane or octamethyltrisiloxane) and deposition conditions were used in order to vary their chemical composition and their physical properties. In these SiOCH, the carbon content is mainly under the form of methyl groups bonded to silicon. At the same time, to allow a better flexibility in term of chemical functions, filament assisted chemical vapor deposition (FACVD) was used for the deposition of organosilicate thin films. Indeed, FACVD allow a better control over the precursor fragmentation pathway in comparison to plasma-based techniques. Then, it is possible to add polar groups (such as ethoxy to in case of FACVD of methyltriethoxysilane) or to introduce siloxane rings in the materials (in case of initiated CVD of cyclosiloxane). Finally, the introduction of additional porosity was investigated as another way to potentially improve the sensitivity of the chemical sensitive layers. By using a porogen approach, it is possible to introduce up to 40 % porosity in a PECVD SiOCH. Using a foaming approach, we can go even further (> 50 %). Film properties after deposition and after potential annealing were investigated using multiple characterization techniques (ellipsometry, FTIR and Tof-SIMS). Porosity was characterized by ellipsometric porosimetry and grazing incidence small angle X-ray Scattering. In these material, pores (if any) are nanometrics and porosity is mainly open and interconnected. Thin film response under toluene or pentane exposures was studied using Quartz Crystal Microbalance functionalized with the different SiOCH. Through the synthesis and characterization of these various SiOCH thin films, the role of hydrophobicity, carbon content and specific chemical bonding can be highlighted. It is shown that the hydrophobic nature of SiOCH materials composed of a Si-O-Si backbone with methyl groups bonded to silicon, combined with the presence nanoporosity, lead to very high sensibility. The presence of isolated polar bonds such as ethoxy groups seems beneficial especially for BTEX detection. High partition coefficients toward toluene and pentane can be obtained, at least ten time higher than those measured on more classical polymers such as PDMS. Both deposition techniques (PECVD or FACVD) are able to produce good chemical sensitive layers for the detection of light alkanes and aromatics VOCs and these organosilicates constitute promising solution for the functionalization of NEMS-based gas sensors. Acknowledgment: Developments on FACVD were performed in the frame of a collaboration with TEL, US-Technology Development Center, America.

Volatile Organic Compounds are a cause of concern for human health. It is particularly the case f... more Volatile Organic Compounds are a cause of concern for human health. It is particularly the case for BTEX compounds (Benzene, Toluene, Ethylbenzene and Xylenes). Gravimetric sensors are good candidates for their detection but they have to be functionalized by a sensitive film to become active. In this work, organosilicate thin films (SiOCH) deposited by plasma enhanced chemical vapor deposition are investigated. This work aims at understanding the role of their chemical composition on gas adsorption and to propose an optimized material for BTEX detection. Through the synthesis and characterization of various SiOCH thin films, the role of hydrophobicity, carbon content and specific chemical bonding is highlighted. This led to an optimized film presenting both high affinity (partition coefficient toward toluene higher than 15000) and rapid temporal response.

The Journal of Physical Chemistry C, 2016

Sensors and Actuators B: Chemical, 2014

Patents by Julien El Sabahy

Co-authors: Vincent Jousseaume and Florence Ricoul

Conferences by Julien El Sabahy

Co-authors: Vincent Jousseaume and Florence Ricoul.

Thesis Chapters by Julien El Sabahy

Gas detection is a growing field, both for indoor and outdoor air quality monitoring and for proc... more Gas detection is a growing field, both for indoor and outdoor air quality monitoring and for process monitoring. It is indeed particularly critical in the case of volatile organic compounds (VOC) whose impact on public health is proven. Detecting and quantifying their presence becomes a major problem and various solutions are available. One of them, based on the coupling of a resonant beam and a chromatography micro column, appears to be a promising solution. Those two devices combine selectivity and high sensitivity; however, they require functionalization with a sensitive layer. This work focused on SiOCH thin films deposited by PECVD. The gas interaction of the sensitive layers deposited during this work was studied using quartz crystal microbalances (QCM). The obtained measurements were then correlated to a simple model, providing an interpretation of the interaction – for steady-state but also kinetic regime - between the SiOCH and the gas of interest. The first part of the study shows the impact of the chemical composition of those materials on their affinity for toluene, representative for aromatic VOCs. Relying on physico-chemical characterization techniques, the role of various chemical bonds on the solid/gas interaction was investigated. This work shows that a compromise between chemical composition and hydrophobicity has to be reached to preserve SiOCH affinity and temporal response. The influence of porosity was then explored in a second step to further increase the sensitivity of those materials. Original deposition processes were developed in order to propose new porous materials with higher toluene affinity. The limits of the subtractive approach generally used for these PECVD materials (i.e. the porogen approach) were then overcome in terms of porosity and pore size. Concerning gas detection, it is difficult to decorrelate between the impact of chemistry and porosity. Whatever, increasing porosity does not appear to be the only relevant parameter in order to increase these materials affinity at low concentrations.

Microporous and Mesoporous Materials, 2021

Sensors and Actuators B: Chemical, 2018

Sensors and Actuators B: Chemical, 2014

Microelectronic Engineering, 2017

The Journal of Physical Chemistry C, 2016

Sensors and Actuators B: Chemical, 2014

Co-authors: Vincent Jousseaume and Florence Ricoul

Co-authors: Vincent Jousseaume and Florence Ricoul.