Large-scale formation of ordered one-third-hydrogenated graphene on Ru(0001)*

It is generally thought that hydrogen atoms can chemisorb on graphene in a perfect periodic manner, forming new crystalline two-dimensional (2D) materials that exhibit unique electronic properties beyond pristine graphene, such as graphane, graphone and 2D CxHy. So far, samples with small patches of ordered hydrogen adatoms can only be produced. Here, we present atomically resolved scanning tunneling microscope (STM) images that demonstrate the fabrication of one-third hydrogenated graphene that is perfectly ordered over hundreds of nanometers. Moreover, we show that, this crystalline one-third-hydrogenated graphene is decoupled from the substrate and structurally anisotropic. Calculations show that the structural anisotropy of one-third hydrogenation results in an anisotropic electronic structure. The present work directly provides atomic-scale evidence that new, large-scale 2D crystals with designed electronic properties can be realized by attaching other atoms and molecules onto graphene.