Nearly free electron states in MXenes

Abstract

Using a set of first-principles calculations, we studied the electronic\nstructures of two-dimensional transition metal carbides and nitrides, so called\nMXenes, functionalized with F, O, and OH. Our projected band structures and\nelectron localization function analyses reveal the existence of nearly free\nelectron (NFE) states in variety of MXenes. The NFE states are spatially\nlocated just outside the atomic structure of MXenes and are extended parallel\nto the surfaces. Moreover, we found that the OH-terminated MXenes offer the NFE\nstates energetically close to the Fermi level. In particular, the NFE states in\nsome of the OH-terminated MXenes, such as Ti2C(OH)2, Zr2C(OH)2, Zr2N(OH)2,\nHf2C(OH)2, Hf2N(OH)2, Nb2C(OH)2, and Ta2C(OH)2, are partially occupied. This is\nin remarkable contrast to graphene, graphane, and MoS2, in which their NFE\nstates are located far above the Fermi level and thus they are unoccupied. As a\nprototype of such systems, we investigated the electron transport properties of\nHf2C(OH)2 and found that the NFE states in Hf2C(OH)2 provide almost perfect\ntransmission channels without nuclear scattering for electron transport. Our\nresults indicate that these systems might find applications in nanoelectronic\ndevices. Our findings provide new insights into the unique electronic band\nstructures of MXenes.\n

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Affiliated Institutions

• RIKEN Center for Computational Science JP
• RIKEN Center for Emergent Matter Science JP
• RIKEN JP
• University of Cambridge GB
• Tohoku University JP
• National Institute for Materials Science JP

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