  Note this is a rather coarse version of our manuscript since uploading tex
files are necessary (we are not willing to upload all tex files).
  The existence of BiXenes, a new family of 2D monolayers is here predicted.
Theoretically, BiXenes have 1H symmetry (P-6m2) and can be formed from the
4d/5d binary carbides. As the name suggests, they are close relatives of
MXenes, which instead have 1T symmetry (P-3m1). The newly found BiXenes, as
well as some new MXenes, are shown to have formation energies close to that of
germanene, which suggests that these materials should be possible to be
synthesised. Among them, we illustrate that 1H-Tc2C and 1T-Mo2C are dynamically
stable at 0 K, while 1H-Mo2C, 1TTc2C, 1H-Tc2C, and 1T-Rh2C are likely to be
stabilised via strain or temperature. In addition, the nature of the chemical
bonding is analysed, emphasizing that the covalency between the transition
metal ions and carbon is much stronger in BiXenes than in MXenes. The emergence
of BiXenes can not only open up a new era of conducting 2D monolayers, but also
provide good candidates for carrier materials aimed at energy storage and
spintronic devices that have already been unveiled in MXenes.
