Journal Article borophene 2D materials 2D polar metal Au‐template‐assisted mechanical exfoliation Dirac cone angle-resolved photoemission spectroscopy angle‐resolved photoemission spectroscopy anisotropic buckled honeycomb binary lattice dirac nodal lines/points dry‐transfer techniques first-principles calculations first‐principles calculations interlayer excitons long-range order mixed phases moiré superlattices molecular beam epitaxy phase separation quasi-1D chains