Growth Mechanism Of Several Two-Dimensional Atomic Crystals On Metal Substrates

Graphene is a typical two-dimensional(2D)atomic crystal with unique Dirac cone band structure and approximately massless fermions,which can be used in the ultra-fast electronic devices.However,graphene is a semimetal and has limitation in many applications.Recently,2D atomic crystals attract lot of attentions,such as silicene,phosphorene,boronene and their 2D allotrope monolayers.To realize industrial application,the synthesis of atomic crystals with high quality and large yield is required.By using computational materials science method,simulations on nucleation and growth of 2D atomic crystals can predict the experimental conditions and reduce the cost,which promotes the synthesis and application of novel 2D atomic crystals.Based on the density functional theory and classical crystal growth theory,we studied the growth process of graphene on ternary alloy substrate(Cu2NiZn).The dehydrogenation barrier of C2H4 on Cu2NiZn surface is lower than that on pure Cu surface,indicating that C2H4 is easy to be dehydrogenated into carbon atoms on Cu2NiZn surface.Then carbon atoms aggregate into clusters as the initial nuclei of graphene.For clusters with size smaller than 3,the formation energy of clusters on Cu2NiZn surface is smaller than that on Cu surface.Hence,the formation of small cluster is easier on Cu2NiZn surface.On the other hand,the permeation barrier of carbon atom from surface to subsurface is nearly zero on some regions of Cu2NiZn surface,which is beneficial to the dissolution of carbon atoms into the substrate.After substrate cooling,carbon atoms separate out and promote the growth of graphene.As a conclusion,Cu2NiZn is a potential substrate to synthesize graphene with high quality and large yield.Our study offers a guide for experimentalists to use alloy substrate to grow graphene with high quality.Considering that graphene is usually used as a heterojunction in the practical device application,we further studied the lateral epitaxial nucleation and growth behavior of graphene along the edge of h-BN and its effects on the quality of synthesized interface.Our study revealed that graphene preferred to nucleate and grow linearly along the edge of h-BN.Besides,the nucleation barrier of graphene at B-edge is smaller than that at N-edge.Under low carbon chemical potential,the nucleation barrier of graphene at B/N-edge is much lower than that on Cu terrace.Under high carbon chemical potential the nucleation barriers and rates of these two cases are comparable.Hence,by controlling the experimental conditions under low carbon chemical potential,the nucleation position of graphene can be limited at the B/N-edge.Further,the atomic continuous structure at the interface can be synthesized and orientations of graphene and h-BN are the same.As extension of the study on graphene,the interactions between a-,β-,y-phase graphynes and Ru,Rh,Pd substrates are calculated.Due to the C-C sp bonding,these transition metal substrates can stabilize α-,β-and γ-phase graphynes well.From chemical phase diagram,α-phase graphyne is thermodynamically most favorable in carbon poor environment,while the formation of graphene is dominant in carbon rich environment.β-andγ-phase graphynes are hard to synthesize.At last,nucleation and growth behavior of blue phosphorene in primary stage is studied.Increasing number of atoms(N)to 4 in the considered supercell,phosphorus atoms begin to aggregate into a zigzag chain.For N ≥ 11,phosphorus cluster adopts a five-six-ring based one dimensional motif.The unique growth behavior of phosphorus clusters is caused by the competition between interaction among phosphorus atoms and the attraction on phosphorus atoms by Au substrate.From the comparative calculations of blue phosphorene and black phosphorene on Au,Ag and Al surfaces,respectively,we propose that an active metal substrate is beneficial to the synthesis of blue phosphorene,while a relatively inert metal substrate is suggested to grow black phosphorene.