Control of Electronic Properties of Organic-Inorganic MXenes via Surface Functionalization.

Abstract

Surface terminations critically affect the electronic structure of two-dimensional (2D) transition metal carbides and nitrides (MXenes), yet the synthetic exploration has been hindered by the lack of predictive factors. Here, we establish that the number of lone-pair electrons (LPEs) on an organic ligand serves as a key factor governing the synthesis of organic-inorganic hybrid MXenes. Experimentally, successful surface functionalization is strongly dominated by 3-LPE ligands, enabling the synthesis of a broad library of over 20 distinct organically terminated MXenes (OT-MXenes). DFT calculations on representative experimentally realized terminations further show that the investigated 3-LPE ligands preferentially stabilize highly coordinated FCC configurations, providing a microscopic connection between LPE availability, surface coordination, and the experimentally observed functionalization behavior. Remarkably, organic surface termination enables the intrinsic carrier density of MXenes to be tuned over 7-8 orders of magnitude. This unprecedented level of control provides access to the intrinsically high carrier mobility in the low-carrier-density regime. In particular, hexanamide-terminated Ti3C2 exhibits an electron mobility of ∼48 cm2 V-1 s-1, representing an improvement of more than two orders of magnitude compared to metallic Ti3C2Tx. Our work clarifies a fundamental design principle for MXene surface engineering, which may guide the precise synthesis of organic-inorganic hybrid MXenes with tailored terminations and properties, thereby promoting MXene device applications and advancing the development of organic-inorganic 2D materials.

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