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The sensing material plays a very important role in determining the sensing properties of a gas sensor. In order to synthesise the sensing material, the precursors have a large effect on the properties of the sensing material. In this study, three types of γ-Fe2O3 nanoparticles were prepared with different ferric ion concentrations of [Fe3+] and [Fe2+] as precursors, by a typical facile chemical precipitation process and a following annealing treatment. A mass-type gas sensor was fabricated by using a quartz crystal microbalance (QCM) coated with various γ-Fe2O3 nanoparticles. The morphology, crystallisation, and gas adsorption characteristics of the γ-Fe2O3 nanoparticles were investigated. The effect of ferric ion concentrations of [Fe3+] and [Fe2+] on sensing properties is discussed in detail. Interestingly, the sensor based on γ-Fe2O3 nanoparticles synthesised with ferric ion [Fe3+] showed excellent sensing properties for the detection of SO2 gas, with high sensitivity and repeatability at room temperature. The experimental results clearly demonstrate that the γ-Fe2O3 nanoparticle is an excellent sensing material which may be suitable for practical sensing applications.

Aluminum (3 at%)-doped ZnO (AZO)/Au/AZO multilayer films with low resistivity and high transmittance are in situ deposited at room temperature via facing-target sputtering for AZO and direct current (DC) sputtering for Au. The optical and electrical properties of multilayer films are compared with conventionally ( on -axis) sputtered and facing-target sputtered (FTS) AZO films. The FTS samples show better crystallinity than that of on -axis sputtered samples, and the lowest value for resistivity is 7.9×10 −5 Ω-cm at an Au layer thickness of 8 nm, which is compared with that of a conventional FTO electrode. The photo-conversion efficiencies (PCE) of the perovskite solar cells based on the AZO multilayer electrodes deposited via FTS and on -axis sputtering are 9.5% and 8.2%, respectively. Although the PCE of AZO multilayer-based-solar cells exhibit a lower efficiency than that of the FTO based-devices (~12.3%), the perovskite solar cell performance based on the FTS AZO multilayer electrodes is very attractive for applications to flexible planar-structured solar cells.

The TECCO protection system consists of the high strength components such as the high tensile steel (HTS) wire mesh and the high strength thread bar. This system is used in the construction for slope stabilization, ground support, landslide protection, especially rock-fall protection. The purpose of this study was to predict the behavior of the wire mesh under impact loading of rock-fall. A finite element has been constructed in order to model the impact between a rock of 0.5 tons and a rectangular wire mesh with high velocity. The mechanical response of the HTS material is assumed as elastic-plastic-isotropic material. Further, the contact behavior within the steel wire mesh and rock-fall are also considered in the model using the Coulomb friction model. Thanks to ABAQUS/Explicit based on finite element method, the impact phenomenon will be clarified. The model may help to reduce the number of experiments with high cost.

Graphene oxide (GO) is an excellent suitable material as a gas-sensing layer due to its adsorption ability towards toxic gas molecules. In this work, GO nanosheets (GO-NSs) were employed in a mass-type toxic gas sensor using a quartz crystal microbalance (QCM) transducer. The sensor was prepared by spraying the GO-NS suspension on the working electrode surface of the QCM. The gas-sensing properties of the sensor were examined with various concentrations of toxic gases, including NO2, SO2, CO, and NH3. The results demonstrated that the adsorption potential of the prepared GO-NSs makes them a promising candidate for the sensing layer of mass-type gas sensors to detect toxic gases.

CH3NH3PbI3 (MAPbI3) perovskite thin films were applied to fluorine-doped SnO2 (FTO)/glass and Au/Ti/polyethylene terephthalate (PET) substrates via a two-step process, which involved depositing a CH3NH3I (MAI) solution onto PbI2 films via spin-coating followed by crystallization at temperatures of 100 °C. The 500 nm-thick crystallized MAPbI3 perovskite thin films showed a Curie temperature of ∼328 K, a dielectric permittivity of ∼52, a dielectric loss of ∼0.02 at 1 MHz, and a low leakage current density of ∼10−7 A cm−2 at ±3 V. The polarization–electric field (P–E) hysteresis loop and piezoresponse force microscopy (PFM) results showed that the films had well-developed ferroelectric properties and switchable polarization. Poling at an electrical field of 80 kV cm−1 enhanced the power density of the generator. The values for output voltage and current density of the poled films reached 2.7 V and 140 nA cm−2, respectively, which were 2.7-fold higher than those of the non-poled samples.

In this study, we demonstrated long-term stability in the resistive switching (RS) properties of MAPbI3 films, coated via a one-step chemical vapor deposition (CVD) method using no additives or polymers. The RS behavior of the CVD-fabricated memory devices compares favorably to that of spin-coated films; these devices exhibited reliably stable bipolar resistive switching properties for 30 days under ambient conditions, while spin-coated devices were stable for only 10 days. For further enhancement of air stability, a 20 nm-thick ZnO passivation layer was deposited on MAPbI3 via on-axis and facing-target sputtered (FTS) techniques. The resistive random-access memory (ReRAM) devices with a ZnO passivation layer deposited via FTS technique exhibited extended air stability for 3 months under ambient conditions, whereas in the case of memory devices fabricated with an on-axis sputtered passivation layer, air stability was limited to 60 days. This extended air stability can be attributed to excellent step coverage and free of plasma damage during deposition. Memory devices fabricated via the CVD and FTS methods showed no significant variations at either set or reset levels of voltage and showed favorable levels in terms of both data retention and endurance performance with storage time.

Monitoring toxic chlorine (Cl2) at the parts-per-billion (ppb) level is crucial for safe usage of this gas. Herein, ZnO, WO3, and SnO2 nanowire sensors were fabricated using an on-chip growth technique with chemical vapor deposition. The Cl2 gas-sensing characteristics of the fabricated sensors were systematically investigated. Results demonstrated that SnO2 nanowires exhibited higher sensitivity to Cl2 gas than ZnO and WO3 nanowires. The response (RCl2/Rair) of the SnO2 nanowire sensor to 50 ppb Cl2 at 50 °C was about 57. Hence, SnO2 nanowires can be an excellent sensing material for detecting Cl2 gas at the ppb level under low temperatures. Abnormal sensing characteristics were observed in the WO3 and SnO2 nanowire sensors at certain temperatures; in particular, the response level of these sensors to 5 ppm of Cl2 was lower than that to 2.5 ppm of Cl2. The sensing mechanism of the SnO2 nanowire sensor was also elucidated by determining Cl2 responses under N2 and dry air as carrier gases. We proved that the Cl2 molecule was first directly adsorbed on the metal oxide surface and was then substituted for pre-adsorbed oxygen, followed by lattice oxygen.

Nowadays, adhesively reconstituted products made of beech timber appear to be of increasing interest for structural purposes due to its high strength/stiffness properties as compared to the most soft-wood species. Furthermore, beech timber is not recognized by most standards for structural uses and restricted to service class 1 and only the furniture, interior joinery and do-it-yourself sectors are still the major users. The French market shows great increasing imports of adhesively reconstituted structural products from Germany and Austria. Moreover, the use of local species, like beech, for the production of reconstituted structural elements could be better for the carbon balance, since it reduces import transportation. However, despite the high mechanical performance of beech timber, adhesively reconstituted products need to meet some requirements, such as the performance of finger-joints. This thesis presents experimental and numerical approaches to deal with the mechanical behaviour of adhesively reconstituted beech beams, for structural purposes. Two-layer and three-layer beams with or without finger-joints have been considered and successfully studied. In addition, a parametrical study has been undertaken to study the influence of several parameters on the mechanical resistance of finger-joints. We, finally, proposed an optimization of the finger-jointing geometry in order to increase the resistance of finger-joints, Les produits structuraux (poutres, poteaux…etc) en bois de hêtre reconstitué par collage, notamment le Bois Massif Reconstitué (BMR) présentent un fort potentiel tant au niveau de la performance mécanique que de la ressource disponible par comparaison aux essences résineuses. Par ailleurs, les normes européennes actuelles sont rédigées pour les essences résineuses et l’usage du bois de hêtre en structures est limité à la classe de service 1 et aux produits d’intérieur et d’ameublement. Le marché français montre une forte augmentation de l’importation de produits structuraux en bois reconstitué par collage, principalement d’Allemagne et d’Autriche. Au-delà du potentiel de résistance mécanique du hêtre, son utilisation comme bois d’œuvre contribuera positivement au bilan carbone pour l’environnement, par la réduction des transports des bois d’importation. Cependant, pour un usage structural, les produits en hêtre reconstitué par collage nécessitent de passer par une évaluation de leur performance, notamment la fiabilité des aboutages. Cette thèse présente une méthodologie expérimentale et numérique permettant l’analyse du comportement mécanique des poutres en BMR. La démarche a été appliquée avec succès dans le cadre de poutres constituées de 2 à 3 lamelles avec ou sans aboutages. Dans ce contexte, nous avons également réalisé une étude paramétrique pour étudier l’influence de plusieurs paramètres sur la résistance des aboutages. En fin, nous avons formulé le problème d’optimisation de la géométrie de l’enture multiple afin d’augmenter la résistance des aboutages et donc la résistance globale des poutres en BMR