  Boron forms compounds with nearly all metals, with notable exception of
copper and other group IB and IIB elements. Here, we report an unexpected
discovery of ordered copper boride grown epitaxially on Cu(111) under ultrahigh
vacuum. Scanning tunneling microscopy experiments combined with ab initio
evolutionary structure prediction reveal a remarkably complex structure of
2D-Cu8B14. Strong intra-layer p-d hybridization and a large amount of charge
transfer between Cu and B atoms are the key factors for the emergence of copper
boride. This makes the discovered material unique and opens up the possibility
of synthesizing ordered low-dimensional structures in similar immiscible
systems.
