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Two-dimensional transition metal carbides and nitrides (MXenes) are a class of materials that have drawn substantial attention for their diverse application, particularly in the field of energy storage. These materials are commonly derived from layered ternary solids, MAX phases, through etching processes. Efforts have been made to expand the scope of MXene synthesis beyond these top-down approaches to include bottom-up synthesis. Here we demonstrate a general direct synthetic route for scalable and atom-economic synthesis of various MXenes using different organohalide compounds as precursors for both carbon and surface termination groups. By reacting organochlorides (such as C2Cl4, C2Cl6 and CH2Cl2) or organobromides (CBr4 and CH2Br2) with transition metals, we synthesized a variety of MXenes (Ti2CCl2, Ti2CBr2, Zr2CCl2, Zr2CBr2 and Nb2CCl2), including a Nb2CBr2 MXene phase not accessed by other routes. The use of molecular precursors enables precise control of their reactivity, which allows the direct synthesis of MXene nanostructures. We demonstrate that nanometre-scale MXenes show higher surface reactivity compared with MXenes with micrometre-size flakes. 

Hybrid organic–inorganic MXenes (h-MXenes) are a novel class of two-dimensional materials with tuneable structural and chemical properties, making them promising candidates for electronic and structural applications as well as platforms for exploring novel physical phenomena [1]. In this study, we employ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) at both room and cryogenic temperatures to investigate the formation and behaviour of ripplocations—localized ripple-like distortions—in h-MXenes. Our findings reveal that ripplocations are abundant in these materials and can be induced in situ with high precision under controlled electron beam exposure. 

Inorganic–organic hybrid MXenes (h‐MXenes) are a family of 2D transition metal carbides and nitrides functionalized with alkylimido and alkylamido surface groups. Using cryogenic and room temperature scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS), it is shown that ripplocations, a form of a fundamental defect in 2D and layered structures, are abundant in this family of materials. Furthermore, detailed studies of electron probe sample interactions, focusing on structural deformations caused by the electron beam are presented. The findings indicate that at cryogenic temperatures (≈100 K) and below a specific dose threshold, the structure of h‐MXenes remains largely intact. However, exceeding this threshold leads to electron beam‐induced deformation through ripplocations. Interestingly, the deformation behavior, required dose, and resultant structure are highly dependent on temperature. At 100 K, it is demonstrated that the electron beam can induce ripplocations in situ with a high degree of precision. 

Abstract Surface chemistry of MXenes is of great interest as the terminations can define the intrinsic properties of this family of materials. The diverse and tunable terminations also distinguish MXenes from many other 2D materials. Conventional fluoride‐containing reagents etching approaches resulted in MXenes with mixed fluoro‐, oxo‐, and hydroxyl surface groups. The relatively strong chemical bonding of MXenes’ surface metal atoms with oxygen and fluorine makes post‐synthetic covalent surface modifications of such MXenes unfavorable. In this minireview, we focus on the recent advances in MXenes with uniform surface terminations. Unconventional methods, including Lewis acidic molten salt etching (LAMS) and bottom‐up direct synthesis, have been proven successful in producing halide‐terminated MXenes. These synthetic strategies have opened new possibilities for MXenes because weaker surface chemical bonds in halide‐terminated MXenes facilitate post‐synthetic covalent surface modifications. Both computational and experimental results on surface termination‐dependent properties are summarized and discussed. Finally, we offer our perspective on the opportunities and challenges in this exciting research field. 

Solid-state reactions formed vertical carpets of 2D metal carbides and nitrides on metal substrates.