Stress-corrosion mechanisms in silicate glasses

The present review is intended to revisit the advances and debates in the comprehension of the mechanisms of subcritical crack propagation in silicate glasses almost a century after its initial developments. Glass has inspired the initial insights of Griffith into the origin of brittleness and the ensuing development of modern fracture mechanics. Yet, through the decades the real nature of the fundamental mechanisms of crack propagation in glass has escaped a clear comprehension which could gather general agreement on subtle problems such as the role of plasticity, the role of the glass composition, the environmental condition at the crack tip and its relation to the complex mechanisms of corrosion and leaching. The different processes are analysed here with a special focus on their relevant space and time scales in order to question their domain of action and their contribution in both the kinetic laws and the energetic aspects.Comment: Invited review article - 34 pages Accepted for publication in J. Phys. D: Appl. Phy

Variable stiffness biological and bio-inspired materials

This article reviews the main mechanisms of stiffness variation typically found in nature. The temporal changes in stiffness may be fully or partially reversible, or completely irreversible, and can be very slow or fast in time depending on the strategy adopted to alter the mechanical properties. It is also possible to observe changes in the stiffness in order to recover the original mechanical properties in damaged natural materials by means of self-healing mechanisms. In addition to stiffness variations in time, natural materials can also exhibit stiffness changes in space. These variations can be represented by alterations in the spatial distribution of the microscopic constituents across multiple hierarchical scales, from very small physical scales to large macroscopic dimensions. In order to optimise the strength and multifunctionality of these materials, spatial changes can also occur over larger areas at one single scale. In addition, several examples are provided to illustrate how natural materials have been exploited further in order to develop new bio-inspired materials. © 2012 The Author(s)

4H-SiC VJFETs with Self-Aligned Contacts

International audienceTrenched-implanted-gate 4H–SiC vertical-channel JFET (TI-VJFET) have been fabricated with self-aligned nickel silicide source and gate contacts using a process sequence that greatly reduces process complexity as it includes only four lithography steps. The effect of the channel geometry on the electrical characteristics has been studied by varying its length (0.3 and 1.2μm) and its width (1.5-5μm). The transistors exhibited high current handling capabilities (Direct Current density 330A/cm2). The output current reduces with the increase of the measurements temperature due to the decrease of the electron mobility value. The voltage breakdown exhibits a triode shape, which is typical for a static-induction transistor operation