金刚石(111)/Al界面形成及性能的第一性原理研究

First-principles study of formation and performance of diamond(111)/Al interface

针对金刚石/Al界面的形成和性能,采用第一性原理计算方法,研究了Al原子在H终止金刚石表面的吸附及其迁移行为,以及金刚石/Al界面的结构与黏附功.结果表明:Al原子吸附对金刚石原子表面结构不敏感,且表面迁移激活能非常小,其原因是Al与H原子间没有形成化学键,仅有少量电荷转移,为物理吸附;由吸附位置生长而形成的金刚石/Al界面为亚稳结构,不具有能量稳定性.本文结果为理解金属纳米掩膜的形成机理提供重要的理论参考.

The simple and convenient metallic mask method is a significant method of preparing diamond nanostructures.The metallic mask method has poor repeatability and can not give the ideal results,because it is supported by no theory about formation of surface mental nanoparticles and its technological parameters are optimized by no experimental techniques that are expensive either.Aiming at the formation and performance of the diamond/Al interface,this paper adopts the first-principles to study the adsorption and migration behavior of Al atoms on the H-terminated diamond surface and the structure of the diamond/Al interface.The results show that the highest adsorption energy is at the T4 position,which is only 0.181 eV,through comparing the adsorption energies of Al atoms at the highly symmetrical positions(Top,Br,H3 and T4)on the surface of the H-terminated diamond(111).The adsorption energies at these different positions are similar and the maximum difference is only 0.019 eV.There is formed no chemical bond,although Al has partial charge transfer on the H-terminated surface through the analysis of differential charge density and worse layout distribution.This phenomenon can be considered as electrostatic adsorption.That is to say,the adsorption of Al atoms are physical adsorption.The smooth potential energy surface also makes it easier for Al atoms to migrate on the diamond surface.The calculation results reveal that the migration activation energies of the two possible migration paths(from T4 position to Br position and from T4 to Top position)are 0.011 eV and 0.026 eV respectively.The above results imply that the metal Al and diamond are mainly connected by weak force,so the adhesion work of the three diamond/Al interface structures is compared based on the geometric stacking structure.The results show that the adhesion work of the three interfaces is around 0.These results indicate that the stability of the diamond/Al interface is not high and the stable structure of the interface is easily destroyed when the external environment changes.This speculation can be confirmed in molecular dynamics.When the simulated temperature is 300℃,the liquefied metal Al obviously accumulates into spheres.According to the above research results,we deduce that the metallic mask method does not require high requirements for the relationship between the metal and the substrate material,which depends mainly on the surface topography of the base material.This research provides an important theoretical reference for understanding the formation mechanism of metal nanomasks.