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Millimeter-Scale, Single-Crystal One-Third-Hydrogenated Graphene Successfully Constructed on Ru(0001) Scientists Construct Millimeter-Scale, Single-Crystal One-Third-Hydrogenated Graphene

Date:21-12-2018 Print

Two-dimensional (2D) atomic crystal materials provide a broad platform for the research of physics at the 2D limit. Functionalization can effectively enhance the diversity of 2D materials, creating more materials with unique properties. Graphene and other 2D atomic crystals have attracted wide interests in the field of condensed mater physics and materials science owning to their novel electronic, optical and mechanical properties.

Due to its unique properties, researchers have been exploring the functionalization of graphene using various methods. Chemical modification, such as hydrogenation, is an essential technique to functionalize graphene. With hydrogen atoms chemisorbed in a uniformly-periodic manner, crystalline hydrogenated graphene are effectively new kinds of 2D materials, such as “graphane”, “graphone” and 2D CxHy. These graphene derivatives have been theoretically predicted to exhibit unique electronic properties beyond pristine graphene. However, seeking methods to fabricate large-scale periodically-hydrogenated graphene with a specific carbon/hydrogen ratio is still an open challenge.

Recently, Prof. Hong-Jun Gao's group from Institute of Physics, Chinese Academy of Sciences successfully constructed millimeter-scale single-crystal one-third-hydrogenated graphene on Ru(0001). They found that the as-fabricated hydrogenated graphene is highly ordered (Figure 1). As the ratio of hydrogen and carbon is 1:3, the periodically-hydrogenated graphene is named "one-third-hydrogenated graphene" (OTHG). Combining experimental measurements with theoretical calculations, it is demonstrated that, in the OTHG, hydrogen atoms are arranged in a √3×√3/R30° superstructure with respect to the graphene lattice and chemisorbed on both sides of the graphene plane (Figure 2).

Scanning tunneling microscope (STM) image shows that the sample exhibits a moiré pattern with a periodicity of ~25.4 ? after cycles of hydrogen adsorption and subsequent annealing. Raman spectra indicate the formation of hydrogenated graphene with weak interaction with the substrate. Low energy electron diffraction (LEED) combined with STM images demonstrate that the single-crystalline OTGH sample has areas up to 16 mm2. In addition to the unique atomic structures, dI/dV spectra exhibit the typical V-shape dip instead of band gap around the Fermi energy. Density functional theory (DFT) calculations demonstrate that the freestanding OTHG has two tilted Dirac cones at the Fermi energy along one high-symmetry direction but a finite energy gap along other directions (Figure 3). The unique band structures of OTHG is originating from the selective hydrogen adsorption, suggesting strong anisotropic properties of this new 2D material.

This study entitled “Fabrication of Millimeter-Scale, Single-Crystal One-Third-Hydrogenated Graphene with Anisotropic Electronic Properties” was published on Advanced Materials.

The work was mainly supported by the National Science Foundation, the Ministry of Science and Technology of China and Chinese Academy of Science

Fig.1 Schematic, LEED patterns, Raman spectra and STM image of synthesis of periodically-hydrogenated graphene on Ru(0001). (Image by Institute of Physics)
Fig.2 Atomic configuration, high-resolution STM image and corresponding STM simulations of the OTHG on Ru(0001). (Image by Institute of Physics)
Fig.3 Scanning tunneling spectroscopy and calculated electronic structures of the OTHG. (Image by Institute of Physics)

Institute of Physics
GAO Hongjun

Key word:
Millimeter-scale, single crystal, hydrogenated graphene, anisotropy

Large-scale, periodically-hydrogenated graphene is fabricated on Ru(0001) has been achieved. Scanning tunneling microscope experiments and density functional theory calculations show a√3×√3/R30°atomic configuration and , demonstrating the periodically-hydrogenated graphene a candidate for future applications requiring anisotropic properties.