Prof. Christophe COUPEAU: A new insight on atomic scale crystal surfaces under strain/stress using the original Nanoplast experimental equipment (2025/03/21)

Title	A new insight on atomic scale crystal surfaces under strain/stress using the original Nanoplast experimental equipment
Speaker	Prof. Christophe COUPEAU University of Poitiers, France
Time	3：00pm, March 21, 2025
Place	Material Science and Research Building B902
Brief Bio of the Speaker	Christophe COUPEAU is Professor in Materials Science at University of Poitiers, France. His research activity is related to a variety of problems in materials science concerned with plasticity, mechanical properties and stability, and failure phenomena in engineered-material systems. Our approach is based on the development of scanning probe microscopy enabling nano-scale surface features to be routinely analyzed, even under in situ deformation conditions. The investigation of the surface evolution under stress and the characterization at a nanometre scale of the surface effects allow a better understanding of basic deformation mechanisms controlling deformation kinetics and may establish the foundation to propose and/or develop more reliable models for describing the elastic or plastic response of crystalline materials under stress. The works extend from the mechanical properties of thin films and coatings to the study of variable temperature deformation of advanced bulk materials.
Abstract	A new experimental equipment called NANOPLAST was developed few years ago. It consists in three UHV chambers interconnected together and allows to investigate by scanning tunnelling microscopy the evolution at the atomic scale of crystalline surfaces submitted to compressive strains (or stresses). For details, see nanoplast.pprime.fr/en/. The strain/strain curve can be acquired simultaneously and the temperature can be tuned from approximately 50 to 650 K for in situ (i.e. scanning STM tip always in contact with the surface) investigations or up to 1200 K for ex situ observations. Two current fields of research pay our attention. (1) The first one is related to understand the elementary plastic mechanisms taking place in crystals. When plastically strained, interesting signatures appear at the free surface of crystals, called slip traces, those height is only about a few hundreds of picometers. The slip traces allow to investigate at the atomic scale the pathway of single dislocations (the structural defaults that are responsible of plasticity) gliding in their slip planes. These experimental results are of great interest to compare with what can be routinely obtained at the same scale by atomistic simulations such as molecular dynamics or functional density theory^1,2. (2) The second one concerns the stress- induced evolution of surface atomic structures to reach some surface patterns that could be of great interest for specific functional properties in the future. It can be for instance how does the chevron-like Au(111) reconstruction evolve depending on the intensity and direction of stress in the elastic regime^3,4 or how vicinal surfaces characterized by successive elementary atomic steps are destabilized by the gliding dislocations^5,6. In this case, the dislocations are using as nano-engineering tools to put the surface out of equilibrium. ¹Douat et al., Scripta Materialia 183 (2020) 81 ²Bonneville et al., Modelling Simul. Mater. Sci. Eng. 32 (2024) 065021 ³Chauraud et al., Surface Science 714 (2021) 121908. ⁴Chauraud et al., Phys. Rev. B 99 (2019) 195404. ⁵Coupeau et al., Phys. Review B 93 (2016) 041405. ⁶Coupeau et al., Acta Materialia 175 (2019) 206.


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