Highly anisotropic Dirac fermion and spin transport properties in Cu-graphane

Inspired by the successful synthesis of h Hv-graphane[Nano Lett.15903(2015)],a new two-dimensional(2D)Janus material Cu-graphane is proposed based on the first-principles calculations.Without the spin-orbit coupling(SOC)effect,Cu-graphane is a Dirac semimetal with a highly anisotropic Dirac cone,whose Fermi velocity ranges from 0.12×10^(5)m/s to2.9×10^(5)m/s.The Dirac cone near the Fermi level can be well described with an extended 2D Dirac model Hamiltonian.In the presence of the SOC effect,band splitting is observed around the Fermi level,and a large intrinsic spin Hall conductivity(ISHC)with a maximum value of 346(h/e)S/cm is predicted.Moreover,the spin Hall transport can be regulated by slightly adjusting the Fermi energy,e.g.,grid voltage or chemical doping.Our work not only proposes a new 2D Janus material with a highly anisotropic Dirac cone and a large ISHC,but also reveals that a large ISHC may exist in some Dirac systems.

Nearly Free Electron State in Graphane Nanoribbon Superlattice

Nearly free electron （NFE） state has been widely studied in low dimensional systems. Based on first-principles calculations, we identify two types of NFE states in graphane nanoribbon superlattice, similar to those of graphene nanoribbons and boron nitride nanoribbons. Effect of electron doping on the NFE states in graphane nanoribbon superlattice has been studied, and it is possible to open a vacuum transport channel via electron doping.

First principles study of field effect device through van der Waals and lateral heterostructures of graphene, phosphorene and graphane

Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding(DFTB) calculations of a field-effect device,based on lateral and vertical heterostructures of 2D materials. The device consists of a phosphorene channel protected by graphene sheets, which work as contacts and are divided into the source and drain by local hydrogenation of graphene, which gives insulating graphane. In this device composed of only 3 layers, single sheets of graphene-graphane can work as both leads and oxide gate, while also acting as protective layers for a phosphorene channel. We show how for perfect vd W heterostructures of graphane/phosphorene/graphane and graphene/phosphorene/graphene the Schottky barrier is deeply influenced by normal electric fields, and we characterize electronic transport of such a device. Finally, we characterize phosphorene channel doping and defects, which, at very high densities in the transport direction, enables transport inside the phosphorene bandgap.

Stability,defect and electronic properties of graphane-like carbon-halogen compounds

We perform first-principles total energy calculations to investigate the stabilities and the electronic structures of graphane-like structures of carbon-halogen compounds, where the hydrogen atoms in the graphane are substituted by halogen atoms. Three halogen elements, fluorine （F）, chlorine （C1） and bromine （Br）, are considered, and the graphane-like structures are named as CF, CC1 and CBr, respectively. It is found that for the single-atom adsorption, only the F adatom can be chemically adsorbed on the graphene. However, the stable graphane-like structures of CF, CC1 and CBr can form due to the interaction between the halogen atoms. The carbon atoms in the stable CF, CC1 and CBr compounds are in the sp3 hybridization, forming a hexagonal network similar to the graphane. The electronic band calculations show that CF and CC1 are semiconductors with band gaps of 3.28 eV and 1.66 eV, respectively, while CBr is a metal. Moreover, the molecular dynamics simulation is employed to clarify the stabilities of CF and CC1. Those two compounds are stable at room temperature. A high temperature （：〉 1200 K） is needed to damage CF, while CC1 is destroyed at 700 K. Furthermore, the effects of a vacancy on the structure and the electronic property of CF are discussed.

Thermodynamic Aspects of the Graphene/Graphane/Hydrogen Systems: Relevance to the Hydrogen On-Board Storage Problem

The present analytical review is devoted to the current problem of thermodynamic stability and related thermodynamic characteristics of the following graphene layers systems: 1) double-side hydrogenated graphene of composition CH (theoretical graphane) (Sofo et al. 2007) and experimental graphane (Elias et al. 2009);2) theoretical single-side hydrogenated graphene of composition CH;3) theoretical single-side hydrogenated graphene of composition C2H (graphone);4) experimental hydrogenated epitaxial graphene, bilayer graphene and a few layers of graphene on SiO2 or other substrates;5) experimental and theoretical single-external side hydrogenated single-walled carbon nanotubes, and experimental hydrofullerene C60H36;6) experimental single-internal side hydrogenated (up to C2H or CH composition) graphene nanoblisters with intercalated high pressure H2 gas inside them, formed on a surface of highly oriented pyrolytic graphite or epitaxial graphene under the atomic hydrogen treatment;and 7) experimental hydrogenated graphite nanofibers-multigraphene with intercalated solid H2 nano-regions of high density inside them, relevant to solving the problem of hydrogen on-board storage (Nechaev 2011-2012).

Pressure-induced Diels-Alder reactions in C_6H_6—C_6F_6 Co-crystal towards graphane structure

With support from the National Natural Science Foundation of China and the Top 1000-Talents Awards,the research team led by Dr.Zheng HaiYan(郑海燕)and Dr.Li Kuo(李阔)from the Center for High Pressure Science and Technology Advanced Research in Beijing recently synthesized H-F-substituted graphane(H,F-graphane)with a layered structure by compressing 1:1 C6H6-C6F6 co-crystal(abbreviated as CHCF).