SEMINAIRE LMGP - 14.04.2020 - Athanasios GKOUNTARAS

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Athanasios GKOUNTARAS
PhD student of LMGP & Institute NEEL

Abstract

MXenes are usually obtained by chemically etching the aluminum layers intercalated between the 2D M_n+1C_n transition metal-carbon layers of Al-based MAX phases. Although MAX phases are not van der Waals solids, we show that single crystals can also be mechanically exfoliated in order to produce flakes whose thickness can be reduced down to half a unit cell of the starting crystal with few tens of microns lateral dimensions. The process can be applied to all phases already known for leading to stable MXenes (such as V₂AlC). Besides, it can be applied to MAX phases that do not resist chemical etching (such as Cr₂AlC), to phases where the A element is not Al (such as Ti₂SnC), or to phases where it is important to keep an intercalating A layer in order to preserve, e.g., magnetic properties (such as Mo₄Ce₄Al₇C₃). Using electric force microscopy, we analyse the exfoliated flakes transferred onto SiO₂/Si and we find no appreciably variation with flake thickness. Using an appropriate surface preparation, the measurements reveal a contribution from both contact surface potential and the local capacitance, which can be used to confirm the metallic character of the flakes.