In the present work,we challenge the conventional wisdom that honeycomb structure can exist only in elements that bear great chemical similarity to carbon.We report that honeycomb structure of transition metal(TM)elements can also be fabricated with totally uncharted physics and chemistry,in particular for Hf on Ir substrate.Low energy electron diffraction(LEED)and scanning tunneling microscopy(STM)measurements reveal that,despite the triangular planar structure of the substrate,Hf forms its own honeycomb lattice,morphologically identical to graphene.Electronic structure calculation reveals direct bonding of covalent character between the nearest neighbor Hf atoms,as refected in the calculated total charge density.Calculations further suggest that the freestanding Hf honeycomb could be ferromagnetic with magnetic moment μ/Hf = 1.46μB.The realization and investigation of TM honeycomb layers extend the scope of 2D structures and could bring about novel properties for technological applications.