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Answer by Paul Kolk for Are there any 2D materials whose bonding can be best described as metallic rather than covalent?

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Yes, there are many of them.

Some examples from Wikipedia:

The presence of the Fermi level and electrons in the conduction bandof h-MBenes (MBenes in hexagonal conformation ), cause the intrinsicmetallic character of MBenes 7 . Thanks to this metallic character andtherefore a significant delocalization of electrons, MBenes haveexcellent electrical conductivity , an interesting character for thedifferent applications cited in the next major part 5 , 7 , 8 .

With a high electron density at the Fermi level, MXene monolayers arepredicted to be metallic.[1][53][54][55][56] In MAX phases, N(EF) ismostly M 3d orbitals, and the valence states below EF are composed oftwo sub-bands. One, sub-band A, made of hybridized Ti 3d-Al 3porbitals, is near EF, and another, sub-band B, −10 to −3 eV below EFwhich is due to hybridized Ti 3d-C 2p and Ti 3d-Al 3s orbitals. Saiddifferently, sub-band A is the source of Ti-Al bonds, while sub-band Bis the source of Ti-C bond. Removing A layers causes the Ti 3d statesto be redistributed from missing Ti-Al bonds to delocalized Ti-Timetallic bond states near the Fermi energy in Ti2, therefore N(EF) is2.5–4.5 times higher for MXenes than MAX phases.[1]

https://en.wikipedia.org/wiki/MXenes#

https://fr.wikipedia.org/wiki/MBenes

Note that all of them, including graphene, also have covalent bonds.

The bonding in a monolayer of metallic element is possibly described as only metallic, but those need additional support from a substrate.


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