Papers by Keyword: Platelets

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Authors: Frank Kern, Rainer Gadow
Abstract: Zirconia-alumina composites are structural ceramics which due to their high strength and toughness are interesting in biomedical and engineering applications. Reinforcement of such materials with in situ formed platelets can improve fracture toughness and reliability, the mechanisms are however not yet fully understood. In this study alumina and zirconia based composites (ZTA and ATZ) reinforced with various hexaaluminates were investigated. In ZTA materials the main effect of platelets is the improvement of toughness as the the grain size distribution of the microstructure is broadened and transformability of the zirconia dispersion is improved. Crack deflection by platelets is unimportant, toughening is commonly achieved at the expense of strength and hardness. In case of zirconia based composites results are strongly depending on the type of stabilizer (Y-TZP or Ce-TZP) used and the type of hexaaluminates formed in situ. Here platelets can cause crack deflection and crack bridging. By variation of the composite recipes a multitude of compositions can be produced which have mechanical properties tailored for individual applications.
Authors: Marie-Laure David, Frédéric Pailloux, Michèl Drouet, Marie France Beaufort, Jean François Barbot, Eddy Simoen, Cor Claeys
Abstract: (001) n-type Ge has been implanted at given fluence and intermediate temperature with hydrogen ions using two processes: conventional in-line implantation and plasma based ion implantation. The as-created microstructure has been compared using transmission electron microscopy. In particular, it has been shown that the major differences observed are due to the implantation temperature, much higher during the PBII process. This suggests that plasma based ion implantation could be used for layer transfer in spite of a higher surface roughness observed after the PBII process.
Authors: Reinhart Job, Yue Ma, Yue Long Huang, Alexander G. Ulyashin, Wolfgang R. Fahrner, Marie France Beaufort, Jean François Barbot
Authors: Nikolay Cherkashin, Francois Xavier Darras, Alain Claverie
Abstract: Hydrogen implantation at room temperature into monocrystalline silicon leads to the formation of complex defects and also to the appearance of in-plane compressive stress. During annealing hydrogen atoms and vacancies co-precipitate into platelets lying on two types of habit planes. These platelets play a decisive role in the fracture of the material that can occur during further annealing and which is used for the manufacture of SOI wafers. Thus, their stress assisted nucleation mechanism has to be well understood. Here, we develop a formalism based on the Volmer’s model which allows calculating the variation of the free Gibbs energy of the system following the nucleation of a platelet. In an unstressed crystal, this energy only relies on the habit plane of the platelet. When the system is under stress, this energy also depends on a term coupling this stress and the strain field generated by the platelet. Because those energies control the nucleation rate of the platelets variants, we could calibrate our model using the transmission electron microscopy observations of the platelets occurrences as a function of depth and, thus, as a function of the magnitude of the intrinsic stress and the angles between the stress direction and Burgers vectors of the considered platelets. These experimental distributions allowed us adjusting the parameters describing the Gibbs free energy of platelets.
Authors: Filipe J. Oliveira, Rui F. Silva, Joaquim M. Vieira
Authors: T. Nakamura, Y. Kato, Yoshimi Watanabe
Authors: N. Martsinovich, A.L. Rosa, M.I. Heggie, Patrick R. Briddon
Abstract: We use DFT calculations to investigate the problem of hydrogen aggregation in silicon. We study atomic structures of finite hydrogen aggregates containing four or more hydrogen atoms. Beyond four hydrogen atoms, complexes consisting of Si-H bonds are likely to form, rather than aggregates of H2 molecules, which are the most stable diatomic hydrogen complex. Our calculations show that the basic structural unit of such complexes is a hydrogenated dislocation loop, which is formed spontaneously by a structural transformation of two H∗2 complexes. Hydrogen-induced formation of dislocation loops may account for the experimental observations of dislocation loops in proton-implanted or hydrogen plasma-treated silicon. We indicate the routes leading from H∗2 aggregates and hydrogenated dislocation loops to twodimensional hydrogen-induced platelets. We discuss the effect of hydrogen-catalysed formation of dislocation loops on the plasticity of silicon.
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