| SiGe alloy nanoparticles are a new class of semiconductor nanomaterials.The study of its microscopic properties is of great significance to the continuation of Moore's Law and the development of nano optoelectronic devices.Presently,there are few reports on SiGe nanomaterials,and the molecular dynamics simulation of rapid solidification of SiGe nanoparticles is still in its infancy.In this study,the Tersoff potential was used to simulate the rapid solidification process of liquid Si50Ge50 nanoparticles by the molecular dynamics method:?1?the rapid solidification process of liquid Si50Ge500 nanoparticles at 1×109 K/s cooling rate?2?the rapid solidification process of liquid Si50Ge50 nanoparticles at different cooling rates and?3?the rapid solidification process of SiGe alloy nanoparticles with different composition ratios of Si and Ge at 1×1010 K/s cooling rate.The simulation results were analyzed by various microstructure characterization methods such as radial distribution function,atomic average energy,coordination number,bond angle distribution function,dihedral angle distribution,the largest standard cluster analysis method and visualization.The main findings are as follows:At a cooling rate of 1×109 K/s,the liquid Si50Ge50 nanoparticles form a nanocrystal structure in which the zinc blende structure and the wurtzite structure are nested,and the shape is approximately spherical.The crystallization temperature of the system was about 1650 K,and a large number of[4-S000]and[3-S000]clusters were formed during the crystallization process.Affected by the change of particle size and surface effects,the[4-S000]clusters are mainly distributed inside the particles and the[3-S000]clusters are distributed on the surface of nanoparticles.When T>1450 K,the change of particle size has a great influence on the microstructure of Si50Ge50 nanoparticles.When T<1450 K,Si50Ge50 nanoparticles exhibit obvious surface effects,and its chemical activity is enhanced.During the crystallization process,Si50Ge50 nanoparticles went through two processes:nucleation and nucleation.At the initial stage of crystallization,a large number of small clusters are formed inside the system.When the temperature reaches a critical value,the small clusters grow rapidly to form crystal nuclei,and the crystal nuclei gradually condense and become larger as the temperature decreases.The microstructure evolution characteristics of liquid Si50Ge500 nanoparticles during rapid solidification process at different cooling rates(R1=1×1013 K/s?R2=1×1012 K/s?R3=1×1011K/s?R4=1×1010 K/s?R5=5×109 K/s?R6=2×109 K/s?R7=1×109 K/s)were studied.And the results show that:at the four cooling rates?R1,R2,R3 and R4?,no crystallization occurs in the liquid Si50Ge50 nanoparticles,and the system finally forms a random amorphous structure;the system crystallizes to form nanocrystalline particles containing a zinc blende structure and a wurtzite structure when the cooling rate is R5,R6,and R7.For a Si50Ge500 nanoparticle system with 1000 atoms,the key cooling rate of forming amorphous structure is between R4 and R5.The main influences of cooling rate on the microstructure of SiGe nanoparticles are as follows:the order degree of the system increases with the decrease of cooling rate;when the cooling rate is lower than the critical cooling rate of forming amorphous structure,the initial crystallization temperature of the system decreases with the cooling rate.At the cooling rate of 1×1010 K/s,the molecular dynamics method was used to simulate the rapid solidification process of Si100-xGex?x=0,20,40,50,60,80,100?nanoparticles in equilibrium liquid.It is found that the difference in the composition ratio of Si and Ge makes the difference in the microstructure of the nanoparticles.After the rapid cooling process,crystal structures were formed in Si20Ge800 and Ge nanoparticles,while amorphous structures were formed in Si,Si80Ge20,Si40Ge60,Si50Ge50 and Si60Ge40 nanoparticles,all of which only have short-range order.The influence of Si and Ge composition ratio on the microstructure of SiGe alloy nanoparticles during solidification is mainly as follows:The higher the Ge content,the higher the order degree of the system.At a cooling rate of 1×1010 K/s,the key component of forming crystal structures of the Si100-xGex nanoparticles is 60<x?80.When x?80,crystallization occurred and crystal structures were formed in SiGe nanoparticles;when x?60,only amorphous structures were formed. |
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