A First-principles Study On The Structure And Physical Properties Of Graphene Nanoribbons And Graphene-like Materials

With the development of society,the research of low-dimensional nanomaterials has become the key to the development of nanodevices.Low-dimensional nanomaterials have rich properties,and their electronic and magnetic properties will affect the information storage and transmission efficiency of future nanodevices.Graphene has broad application prospects due to its unique physical and chemical characteristics,large-scale integrated circuits,etc.,which made a huge impact in many fields such as physics,chemistry,biology,etc.The first-principles calculation plays a vital role in the theoretical prediction and experimental evidence of low-dimensional nanomaterials.The main content of this paper is through the first-principles calculation based on density functional theory to study the geometry structures,electronic properties and magnetic mechanism of several graphene-based low-dimensional nanomaterials.These include:the study of the intrinsic electronic characteristics and magnetic coupling mechanism of transition metal decorated one-dimensional chiral edge graphene nanoribbons,and the simulation of the effect of carrier doping on it;The electronic characteristics and energy band regulation of the Zn₃Si₂monolayer.The specific research results are as follows:First,we predict a family of chiral graphene nanoribbons decorated by transition metal atoms(TM-c GNR;TM=Fe,Co,Ni,Cu,Zn)using first-principle calculations.All considered one-dimensional(1D)TM-c GNRs,except non-magnetic(NM)Ni-and Zn-c GNR,are magnetic semiconductors with high structural stability.In particular,Fe-c GNR favors a ferromagnetic(FM)groundstate,which is tunable into a half-metallic state under charge doping.Its local magnetic moments interact with each other through a long-range pi-mediated FM p-d exchange interaction in the graphene conjugate frame.Charge doping was further shown to stabilize or change the magnetism that a FM to AFM transition of Fe-c GNR occurs at a doping level of 0.002 holes/atom.All these result shed considerable light on carbon-based spintronics.Secondly,Based on density functional theory,a 2D material Zn₃Si₂ in honeycomb transition-metal silicide with intrinsic Dirac cones has been predicted.Zn₃Si₂monolayer is dynamically and thermodynamically stable under ambient conditions.Importantly,Zn₃Si₂ monolayer is a room-temperature 2D Dirac material with a spin-orbital coupling energy gap of 1.2 me V,which has an intrinsic Dirac cone arising from the p-d band hybridizations.Hole doping leads to the spin polarization of the electron,which results in Dirac Half-metal feature with single-spin Dirac Fermion.This novel stable 2D transition-metal-silicon-framework material holds promises for electronic device applications in spintronics.