Study On Surface Structure Controlled Growth And Pattern Formation Far From Equilibrium

Chaos theory,Relativity and Quantum Mechanics are the three greatest discoveries of the twentieth century.Among them,chaos and quantum mechanics break the Laplace-style deterministic causality of the macroscopic world,and reveal that the world is complex,with nonlinear and non-equilibrium characteristics.Therefore,in the past half century,nonlinear science has ushered in a vigorous development,of which pattern dynamics and fractal theory are its two main research branches.In nature and human society,self-organized structures or patterns can be seen everywhere,such as the markings on the surface of animals,the shell of mollusks,the Karman vortex street in the sky,the school of fish,and the chemical waves in chemical reactions.How these patterns are the universal underlying physical mechanism induced by the interaction of diffusion and various nonlinear terms(reaction and/or convection)has attracted widespread attention from scientists.At present,pattern dynamics,as a horizontal science,its research fields have spanned many disciplines such as mechanics,ecology,epidemiology,biology,physics,chemistry,mathematics,and materials science which is the main problem of nonlinear science.In the field of materials science,there are mainly two experimental systems that can generate patterns:the Liesegang ring precipitation system and the coffee ring effect system.Although predecessors have made some achievements and understandings in the study of material-like patterns,the development of pattern dynamics in the field of materials or even the entire field is very slow.This is because self-organized patterns only appear in systems far from thermodynamic equilibrium and often with nonlinear dynamics,the progress of pattern research is strongly dependent on experimental innovations and the discovery of new pattern systems.In this paper,we will introduce the discovery of a new pattern system,that is,the presence of very abundant nano-scale SiO2 patterns on the surface of liquid metals.Fractal growth phenomena exist widely in nature and experimental systems.In condensed matter physics,materials with fractal morphology have different physical properties than traditional materials,such as special optical,mechanical,and electronic properties.Especially for two-dimensional materials(such as graphene,boron nitride,etc.),the fractal morphology far from thermodynamic equilibrium may bring some completely new physical properties.However,the non-equilibrium morphologies of two-dimensional boron nitride(h-BN),such as the self-similar Koch snowflake morphology,are rarely studied.Therefore,this thesis has carried out a series of researches on the controlled growth and pattern formation of surface structures far away from equilibrium from the aspects of experiment and mechanism:Chapter 1 briefly introduces the research background,including fractal and pattern dynamics in theory,The research overview of the experiment;In chapters two and three,we introduce a new nanoscale reaction-diffusion pattern system that we discovered experimentally,namely the spatiotemporal self-organized pattern of abundant SiO2 on the surface of liquid metal Cu;The fourth chapter is about the controlled synthesis and mechanism research of the non-equilibrium structure of 2D h-BN far away from the equilibrium condition.The main contents and research results of this paper are as follows:1.Non-equilibrium morphology transition of SiO2 particle aggregation on Cu surface:from fractal to radial Spoke pattern.Fractal growth is the typical aggregate morphology of materials far from equilibrium.For example,in this chapter,SiO2 particles exhibit typical fractal growth behavior on solid Cu substrates.To realize the research on the surface growth of SiO2 farther away from the equilibrium state,we used the exotic properties of the surface of the liquid metal substrate to complete the breakthrough morphology transformation from the fractal growth of SiO2 particles(solid Cu substrate)to a more complex radial Spoke pattern(liquid Cu substrate).Furthermore,the liquid copper surface provides an ideal nanomanipulation platform for micro-nanoscale Spoke patterns,and we obtain non-trivial Archimedes tile-assembled arrays.Based on the reaction-diffusion model of bacterial pattern,we proposed that the active movement of SiO2 active particles near the wave crest played a key role in the formation of the Spoke pattern by liquid metal.Our findings provide an effective experimental tool for the development and application of novel non-equilibrium morphological materials in the future.2.Discovery of a new pattern system:abundant SiO2 nanoscale pattern on the surface of liquid metal Cu.Due to the high coupling between the huge surface tension and excellent fluidity of liquid metal and the aggregation reaction of SiO2 particles,the complexity of the system is greatly increased,resulting in the birth of a new pattern system that can generate abundant nanoscale SiO2 materials.In addition to the Spoke pattern in the previous chapter,the new system also has a large number of space-time pattern phenomena,such as labyrinth pattern,ring pattern,target wave,spiral wave and turbulent flow,etc.Moreover,the new system exhibits a large-span pattern evolution,which is a rare experimental system for the study of pattern dynamics.Through a lot of analysis and research,it is found that SiO2 particles are similar to surfactants on the surface of liquid metal,and form a very complex reaction-diffusion-convection process under the combined action of the violent Marangoni turbulence and particle aggregation reaction.It is the delicate combination of these three that finally leads to the emergence of rich patterns.Furthermore,through the study of pattern dynamics,it is found that the Turing and Hopf bifurcations of front dynamics play a crucial role in the pattern evolution.Finally,we perform a brief numerical simulation of the pattern evolution of the new experimental system.It is worth noting that through the comparative study with the bacterial pattern and the coffee ring system pattern,it is found that there is a profound similarity between the three systems,which is also a breakthrough discovery.This work also bridges the gap between particulate matter patterns and pattern dynamics,and provides a novel cross-research experimental system.3.Morphology regulation and mechanism of single-layer h-BN thin films far from equilibrium.The morphology management of 2D materials plays a crucial role in their physical properties.We use the chemical vapor deposition(CVD)method to study and explore the growth regulation and mechanism of monolayer h-BN thin films far from equilibrium.First,by gradually diluting the concentrations of the precursors TMB and NH3,we successfully controlled the non-equilibrium morphology of h-BN thin films,and fabricated a single-layer h-BN Koch snowflake structure for the first time,laying the foundation for the study of its novel physical properties.With the gradual dilution of the gas source,the system keeps moving away from equilibrium,and the morphology of h-BN changes from triangular domains to "strawberry" domains with jagged edges,Koch snowflakes,and finally to DLA fractals.They are the result of diffusion-limited kinetic control through growth mechanism studies.Secondly,we can also mediate the occurrence of h-BN fractal pattern through the experimental method of severe imbalance of precursor chemical potential,which also provides another effective experimental method for fractal research of other materials.