Two-Dimensional Transition Metal Honeycomb Realized: Hf on Ir(111)

Two-dimensional (2D) honeycomb systems made of elements with d elections are rare. Here, we report the fabrication of a transition metal (TM) 2D layer, namely, hafnium crystalline layers on In 111). Experimental characterization reveals that the Hf layer has its own honeycomb lattice, morphologically identical to graphene. First-principles calculations provide evidence for directional bonding between adjacent Hf atoms, analogous to carbon atoms in graphene. The realization and investigation of TM honeycomb layers extend the scope of 2D structures and could bring about novel properties for technological applications.