Two-dimensional Phase Transformation Materials – 2DTransformers

Structural phase transitions are ubiquitous in everyday's life and have given rise to various applications in information technologies and energy storage for instance. They exploit functional materials, whose properties change significantly upon a structural change, induced by a control parameter. These materials have so far been considered in a bulk form or as thin films. Works on structural phase transitions in two dimensions (2D), initiated in the 1970's, have focused on lattices of atoms or molecules in weak interaction, which are little suited to the design of functional materials of relevance for applications. Two-dimensional crystals, which are more cohesive, offer new opportunities in this respect, first in reason of their unique properties differing from those of thicker materials, second in reason of their reduced dimensionality. We expect the latter to ease the structural phase transitions, a desirable characteristics in view of faster and less energy-costly applications. In our project, we will explore compounds whose potential for structural phase transitions and applications based on them has only be skimmed over. These compounds, unlike carbon which is little prone to transform once in the graphene phase, exhibit considerable polymorphism in the bulk. They are the 2D transition metal dichalcogenides and crystalline silica, which were recently reported to experience structural phase transitions but without clear evidence of control. Based on our recent unpublished results, we plan to achieve a full understanding at the thermodynamics and kinetics level, down to elementary processes, of the phase transition in 2D, to demonstrate changes of properties (electronic, vibrational, optical, reactivity) occurring due to the phase transition, and to build advanced architecture combining two 2D crystals. Our work will exploit surface science approaches coupled with state-of-the-­art atomistic simulations to develop advanced materials on demand, to achieve proof-of-concepts and to allow insightful understanding of the underlying mechanisms. Our work will also address phase transitions beyond the stringent conditions typical of surface science experiments, with the ambition to broaden the potential of phase change materials based on 2D crystals. Potential applications of such materials could include flexible rewritable memories, reconfigurable photonic devices, and controllable catalytic systems. The project will involve three partners with complementary expertise, Institut Néel (Grenoble), Institut Nanosciences et Cryogénie (Grenoble), and Institut Jean Lamour (Nancy).