Electrical Field Effect In Graphene Nanoribbon And Identify The Concentration Of H Adatom On Graphene

From2004, the physicist Andre Geim and Konstantin Novoselov inUniversity of Manchester successfully separate graphene from graphite inexperiment, confirm it can maintain solely. Because of its special physics andchemical properties, it has extensive application prospects on composites,electronic components and transistor, sensor, adsorbing material, and so on.Graphene is composed of a single carbon atom and is the most thin and thehardest nano material in the world, it is almost completely transparent, and theresistance rate is extremely low, electron transfers quickly. In the paper, basedon the primary principle of density functional calculations, normconserving-pseudoptential and super cell model, study the electric field effect ongraphene nanoribbon and identify the concentration of H adatom on graphene bydispersion curve and density of state. The main works in our study are asfollows: Firstly, the electric field effect in ultrathin zigzag graphene nanoribbons,containing three or four zigzag carbon chains, is studied by first principlecalculations, and the change of conducting mechanism is observed withincreasing the in-plane electric field perpendicular to the ribbon. Wider zigzaggraphene nanoribbons have been predicted to be spin-splitted for both valenceband maximum (VBM) and conduction band minimum (CBM) with appliedelectric field and become half-metal due to vanishing the band-gap of one spinwith increasing applied field. The change of VBM for ultrathin zigzag graphenenanoribbons is similar to wider ones when applied electric field exists. However,in ultrathin zigzag graphene nanoribbons, there are two kinds of CBM, forwhich one is spin-degenerate and the other is spin-splitted, and both of them aretunable by electric field. Moreover, the two CBM’s are spatially separated inmomentum space. The conducting mechanism changes from spin-degenerateCBM to spin-splitted CBM with increasing the applied electric field. Our resultsare confirmed by density functional calculations with both LDA and GGAfunctionals, in which LDA always underestimate the band gap of crystals butGGA normally produces a bigger band gap than LDA.Second, depend on the Density functional perturbation theory to calculatethe vibrational spectra of the concentration of H adatom on graphene. Identifythe concentration of H adatom on graphene by the different of dispersion curveand density of states. Because of the chemical properties of hydrogen atoms, themost stable adsorption on graphene is the upper of carbon atoms, namely the top, it corresponding to the calculation result fit of hydrogen adsorptionconfigurations. With the decrease of hydrogen coverage, the vibration intensityof high frequency characteristics is decreasing, the value of frequency increasesgradually, the change is more and more gentle, finally tends to the configurationof the infinite graphene adsorption of a hydrogen atom. When the coveragedegree is50%, the interaction is intense to make the crystal structure ofgraphene transformation, disturb the symmetry, and change the intrinsicvibration mode. As a result, there has two high frequency characteristics ofvibration and it is the characteristic of high cover degree. With the decrease ofcover degree, there is no obvious change to graphene,s symmetry, the two highfrequencies return to degenerate. This theory predicts that can help guidemeasurement and characterization of hydrogen coverage of graphene onexperiment.Finally, based on the bombardment of various halogen atoms, thecarbon-carbon (C-C) bond of naphthalene can be cleaved selectively withrespect to the bombardment position. The ab-initio molecular dynamics (MD) isemployed to study the processes of converting naphthalene into chainhydrocarbon that can be made into alkane as liquid fuel. The critical conditionsof reaction are studied for ring opening of naphthalene. The cohesive energy,lifetime of products and heat of combustion are considered to define a practicalcost model for the reaction. The most suitable condition is found with respect tothe lowest cost. The effects of negative charge and ether solution are also explored. The negative charge makes the cost lower while the diethyl ethermakes the cost higher. From the analysis of charge population, charge transfersbetween naphthalene and halogen, which help us to understand the mechanismof ring opening. Analyzing the energy gap of molecular orbitals, the opticalstability of reactants is also discussed. Future studies can be expected to convertthe product into liquid alkane by hydrogenation.