Phase Field Crystal Model Simulation Of Interfacial Dislocation Networks In Ultrathin Film-substrate Surface System

When the ultrathin films are stacked on the surface of substrate,because of the appearence of mismatch and interaction between the film and the substrate surface,the dislocation networks can be spontaneously formed at the interface of film and substrate driven by the competition between the elastic energy in the film and the interaction energy of film-substrate.Interfacial dislocation networks not only affect the electri-cal and mechanical properties of the system,but also can be used as high-precision self-assembly templates for the synthesis of nanoclusters.Because the formation and evolution of interfacial dislocation networks in ultrathin film-substrate surface systems usually has the characteristics of diffusion time scale in time and multi-scale in space,here the mechanism of formation and evolution of the interface dislocation network is studied in detail by using the amplitude equation of phase field crystal model which can describe the phenomenon with diffusion time scale and micro/nano spatial scale under atomic resolution.Firstly,we reveal the formation mechanism of spiral triangle interfacial dislocation networks in the ultrathin film-substrate surface system based on dislocation theory,and explain the transition process from herringbone dislocation network to spiral triangle dislocation network in the system from the perspective of dislocation reaction.The system includes both lattice mismatch and twist mismatch resulting in mixed dislocation formation with screw dislocation component and edge dislocation component.Due to the generation of mixed dislocations,the dislocation network is bent to form the spiral triangle dislocation net,^work.The transformation of the herringbone dislocation network to the spiral triangle dislocation network is essentially the process of two threading dislocations annihilating and forming three screw partial dislocations.Then,the reason for the formation of the triangular interfacial dislocation loop array in the ultrathin film-substrate surface system and the influencing factors of its dissolution kinetics are exposed from the perspective of the competition between elastic energy and interlayer interaction energy.It is precisely because of the existence of the fault energy of substrate surface,three intrinsic and extrinsic stacking areas arranged around the nodes in the spiral triangle dislocation network are expanded and shrinked,respectively,induced by enhancing the interlay er interaction potential.And that leads to the formation of a lower energy triangular dislocation loop array.Continuing to enhance the interlayer interaction potential,the dislocation loops in the system will accelerate to dissolve gradually until disappear,and its dissolution rate is affected by the stacking fault energy of substrate surface and the mismatch between film and substrate surface.In addition,the formation and disappearance of the triangular dislocation loop array both undergo phase transitions.Finally,the interlayer interaction potential of the original amplitude equation of crystal phase field model is improved to describe the specifical ultrathin film-substrate surface system.Based on the calculation of density functional theory(DFT),we pro-pose a method for constructing the interlayer interaction potential of crystal phase field model which can accurately describe the energy difference of each stacking state in the graphene-metal surface system.And the formation of dislocation network in differ-ent graphene-FCC metal(111)surface systems was simulated through the amplitude equation of crystal phase field model embedded the new interlayer interaction potential and the calculated results agree well with scanning tunneling microscope(STM)exper-iments.It was found that the geometric topological structure of the dislocation network in graphene-FCC metal(111)surface system depends on the shape of the sliding poten-tial energy surface when the graphene slides on the metal surface.