Dynamical Study On Defects In Hexagonal Patterns Self-Assembled By Block Copolymers

It's increasingly hard for traditional lithography to meet the needs of the process.The "bottom-up" induced self-assembly technology,as an new effective way to obtain various micro-target structure templates(5-100nm),has been widely concerned in recent years,and has been considered to be the most promising and most likely updated solution to the nano-etching technology.As a typical soft material system,block copolymers can form various phase structures via self-assemble,but the phase structures are often full of defects under the influence of the thermal fluctuation of the system.Therefore,studying the generation,annihilation and evolution mechanism of defects would be of great significance to obtain the established structure.most of the research are mainly about the nucleation and phase splitting behavior of block copolymers self-assembled in AB/C mixed system and the design mechanism of defect patterns by now,while the study on the motion evolution of defects of soft material is not enough.Based on this consideration,this paper mainly studies the dynamic evolution behavior of defects,and focuses on analyzing the motion and interaction mechanism of the defects.The first chapter introduces the background and research methods of the study.The second chapter studies the nucleation and phase separation process of AB system are studied using Time-Dependent Ginzburg-Landau Theory(TDGL),and the influences of separation strength A?,noise Ar,and outfield strength Ax/y on the nu-cleation and phase separation of the system,and meanwhile,gets the appropriate simulate parameters:fA=0.4,A?=1.24,Ax=0.01,?y=0.002,Ar=0.004.Due to the influence of the heat fluctuation on the self-assembly process,there are often defects what are very different from each other in the phase structure.Therefore in the third chapter,it is investigated how the evolution process of the single defect is influenced by A?,Ar and ?x/y,the result shows when A? increases,defects will be fixed without moving.That's because the separation strength makes the interaction of blocks be intensified,and the small fractions are compressed resulting in that the defects are fixed,whereas the increasing of the radius of cylindrical structure increases the density in the small fractions.The influence of Ar ? ?x/y on the motion of a single defect is inconspicuous,but too much noise will destroy the order degree of the system,and too much external field will stretch or squeeze the cylin-drical structure at the boundary.Comparing with blade dislocation motion in hard material,there are two types of defect motion in block copolymer system:Climbing and sliding.For climbing,the moving direction of the defect is perpendicular to the sliding surface,and the total cylinder will be reduced by one for each moving by layer.Meanwhile,the moving speed of the defect is almost uniform.With the disappearance of the 5-degree defect center,the lattice structure only needs to make minor adjustment to get the ordered structure,that is,the energy barrier to be overcome is relatively small during the defect climbing.Whereas sliding,the moving direction is along the slip surface,total number of cylinder remains unchanged during the sliding of the defect,and the movement of defects is mainly made by jostling each other of cylinders on the sliding surface,but meanwhile the adjustment of lattice on both sides of the defects led to the sliding resistance force is bigger,and defects cannot slip unless overcoming the bigger base,so the sliding movement goes relatively slowly.The extra half plane of atoms cannot eliminate quickly when the defect moves to the upper and lower boundaries,so that the defects detain for a long-time in the boundary,this appearance is the opposite of hard material.In chapter 4,the interaction in defect evolution is discussed.The evolution can be divided into defect an-nihilation and defect generation according to the configuration before and after the reaction,and the interaction needs to meet the requirements:(1)the vector conservation condition:the Burgers vector is equal before and after the defect reaction,i.e ?bbefore=?bafter;(2)Energy reduction condition:the total dislocation energy after the reaction is less than before the reaction,i.e ?|b|before2??|b|2after.Then,we simply show that the or-dered structure such as BCC,FCC and HCP can be obtained by introducing the directed pattern in the condition of three-dimensional confined space,which provides an example for the subsequent study on the nucleation and phase separation behavior of spatial spherical phase structure(that is,how to nucleate in a confined space).Chapter 5 shows the conclusion.This thesis mainly studies the defect structure of block copolymer self-assembly in the condition of the two-dimensional film constraint,the study is conducted in many ways,including the nucleation and phase split-ting of AB system,the influences on the evolution of a single defect,the interaction between two defects,defect movement mechanism and the nucleation and phase separation behavior in the condition of three-dimensional confined space.The results put forward the mechanism of defect nucleation and of the evolution,and provide the experimental and theoretical evidence for the study of the soft matter system.