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Theoretical study M_x (M = Cu, Ag, Au) / graphene structure and stability

Author: JiaCaiZuo
Tutor: YuHaiTao
School: Heilongjiang University
Course: Physical and chemical
Keywords: graphene density functional theory electronic structure work function metal adsorption
CLC: O613.71
Type: Master's thesis
Year: 2011
Downloads: 110
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Abstract


The configurations and properties of M-adsorbed graphene （M = Cu, Ag, Au） systemswith coverages of 1/16, 1/8, 1/6, 1/4, and 1/2 and cluster-adsorbed graphene（Mx/graphene） systems with x = 2, 3, 4, and 5 are investigated by means of the densityfunctional theory plane-wave pseudopotentials method using a periodic slab model. Thesystem geometry structures, electronic structures, thermodynamics stability and fieldemission performance of all studied systems were explored systematically.Under different metal atom coverages, the most stable configuration of Cu/graphenewas found to be bridge-site adsorption structure. For Ag- and Au-adsorbed graphenesystems, the most stable structure is top-site configuration under low coverages while itis bridge-site configuration under high coverages.The differences of the binding energies of the same metal-adsorbed graphenes atdifferent adsorption sites decrease as the increasing coverage. Under low coverages, asthe atom radii of the adsorption metal atoms increases gradually, the system stabilityordering is Cu/graphene > Ag/graphene > Au/graphene. Under high coverages, thestability difference is relatively smaller than these in low ones.For the cluster-adsorbed graphene systems, the binding energies of Mx/graphene（M= Cu, Ag, Au; x = 2, 3, 4, 5） system increase as the increasing metal atom radii. Also,along with the increasing x value, the system binding energies increase, and becomenearly constant when x = 3, 4, and 5.The band structure analysis results indicated that metal/graphene systems keep theconductor properties of graphene. The calculated electronic structures demonstrated thatthe forming chemical bonds between metals and graphene occur among C2p and s and dorbitals of M （M = Cu, Ag, Au）. Furthermore, for these systems, the cohesion energydetermines the thermodynamics stability of a system. The bond population analysis results revealed that a chemical bond can be formed between metal and carbon atomsfor the Cu/graphene systems under different coverages. However, for the Ag/grapheneand Au/graphene systems, chemical interactions can be only observed under lowcoverages, and the van der Waals force between the interface layers is a generallybinding model under high coverages.The work function calculation results indicates that the metal atomic adsorption withlow coverages can effectively reduce the work function of adsorbed graphenes andimprove their field emission performance. As the increasing coverage, the interactionbetween metal and carbon layer is weakened, and the work function and field emissionperformance of a metal/graphene system are determined only by the work function ofmetal. Also, the metal atomic cluster adsorption can lower the work function ofgraphene and thus improve the field emission effect of graphene effectively.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Non-metallic elements and their compounds > Part Ⅳ family of non-metallic elements (carbon and silicon ) and its compounds > Carbon C
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