The substrate plays a key role in chemoresistive gas sensors. It acts as mechanical support for the sensing material, hosts the heating element and, also, aids the sensing material in signal transduction. In recent years, a significant improvement in the substrate production process has been achieved, thanks to the advances in micro- and nanofabrication for micro-electro-mechanical system (MEMS) technologies. In addition, the use of innovative materials and smaller low-power consumption silicon microheaters led to the development of high-performance gas sensors. Various heater layouts were investigated to optimize the temperature distribution on the membrane, and a suspended membrane configuration was exploited to avoid heat loss by conduction through the silicon bulk. However, there is a lack of comprehensive studies focused on predictive models for the optimization of the thermal and mechanical properties of a microheater. In this work, three microheater layouts in three membrane sizes were developed using the microfabrication process. The performance of these devices was evaluated to predict their thermal and mechanical behaviors by using both experimental and theoretical approaches. Finally, a statistical method was employed to cross-correlate the thermal predictive model and the mechanical failure analysis, aiming at microheater design optimization for gas-sensing applications.

Coatings of graphene oxide over two substrates of glass-fibre and polystyrene were obtained by electrophoretic deposition (EPD). A chemical reduction of graphene oxide by exposure to hydrazine hydrate at 100°C significantly changes the interfacial interaction with the substrate as well as the tribology. Spectroscopic techniques like Fourier transform infrared, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction showed that the treatment with hydrazine replaces oxygen functional groups and also induces roughness, a structural disorder and decreases the interlayer separation in the transition from graphene oxide (GO) to reduced graphene oxide (rGO). Treatment with hydrazine reduces adhesion and friction force against diamond like carbon coated Si probe (DLC AFM) at the basal plain of the coatings. Investigation at the edges revealed that the presence of oxygenic functional group leads to higher shear strength with glass-fibre and polystyrene which reduces after treatment with hydrazine.

Recently, several chemical and physical treatments were developed to improve different properties of wood. Such treatments are applicable to many types of cellulose-based materials. Densification leads the group in terms of mechanical results and comprises a chemical treatment followed by a thermo-compression stage. First, chemicals selectively etch the matrix of lignin and hemicellulose. Then, thermo-compression increases the packing density of cellulose microfibrils boosting mechanical performance. In this paper, in comparison with the state-of-the-art for wood treatments we introduce an additional nano-reinforcemeent on densified giant reed to further improve the mechanical performance. The modified nanocomposite materials are stiffer, stronger, tougher and show higher fire resistance. After the addition of nanoparticles, no relevant structural modification is induced as they are located in the gaps between cellulose microfibrils. Their peculiar positioning could increase the interfacial adhesion energy and improve the stress transfer between cellulose microfibrils. The presented process stands as a viable solution to introduce nanoparticles as new functionalities into cellulose-based natural materials.