Events, articles, or annoncements from the laboratory.
Journées Verre 2022
PhD defenses 2022/2023
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By combining the well-known grid reflection method with a digital image correlation algorithm and a geometrical optics model, a new method is proposed for measuring the change of curvature of a smooth reflecting substrate, a common reporter of stress state of deposited layers. This tool, called Pattern Reflection for Mapping of Curvature (PReMC), can be easily implemented for the analysis of the residual stress during deposition processes and is sufficiently accurate to follow the compressive-tensile-compressive stress transition during the sputtering growth of a Ag film on a Si substrate. Unprecedented resolution below 10−5 m−1 can be reached when measuring a homogeneous curvature. A comparison with the conventional laser-based tool is also provided in terms of dynamical range and resolution. In addition, the method is capable of mapping local variations in the case of a non-uniform curvature as illustrated by the case of a Mo film of non-uniform film thickness under high compressive stress. PReMC offers interesting perspectives for in situ accurate stress monitoring in the field of thin film growth.
The post-growth stress relaxation in thin polycrystalline Ag films, deposited by direct-current magnetron sputtering under different growth conditions, was explored through wafer curvature measurements. It exhibits exponential behaviour with three distinct characteristic time components . The slowest one, namely s, is ascribed to thermal stress inherent to the deposition method. In fact, the performed temperature measurements match perfectly with an exponential stress variation with heating or cooling, as predicted by a thermal exchange model detailed in this work. Based on a comparison between different deposition co0nditions (continuous/interrupted sputter deposition and evaporation), the case of Mo deposition and stress relaxation modelling, the remaining components are assigned to the out-diffusion of atoms from grain boundaries and to changes in the grain surface shape induced by grain boundary grooving. The relaxation amplitude of the first mechanism varies linearly with the steady-state stress at the end of growth in agreement with theoretical expectations. Yet, that of the second one does not. However, clues point to a kinetic limitation of atomic diffusion mechanism along grain boundaries. This study provides proofs of the simultaneous occurrence of several mechanisms of stress relaxation in thin metallic films.
3 positions on mixing or melting granular media
Waterglass exhibits intumescent behavior on thermal treatment, a property being utilized extensively for fire-resistant glass applications. Here, we report on the fundamental understanding of the macro and microscopic structural changes related to foaming.
Congratulations to Barbara BOUTEILLE, former PhD student of SVI lab, whose outstanding achievements during PhD thesis ‘Phase separation in glass thin films for surface nanostructuration’ were rewarded by USTV (‘Union pour la science et technologie verrieres’, french for ‘Glass science and technology union’).
Van der Waals forces modify the fluctuations of the surface of a liquid film and this effect has been measured in collaboration between SVI, SIMM (ESPCI, Paris) and LOMA (Univ. Bordeaux)
Micrometric, electrically irreversible smectic A liquid crystal defect patterns can be used as active films for smart windows with voltage-adjustable and reversible haze levels.