面心立方晶体外延膜沉积生长中失配位错的结构与形成过程

Structure and formation of misfit dislocations in an epitaxial fcc film

用分子动力学方法对5%负失配条件下面心立方晶体铝薄膜的原子沉积外延生长进行了三维模拟.铝原子间的相互作用采用嵌入原子法(EAM)多体势计算.模拟结果再现了失配位错的形成现象.分析表明,失配位错在形成之初即呈现为Shockley扩展位错,即由两个伯格斯矢量为〈211〉/6的部分位错和其间的堆垛层错组成,两个部分位错的间距、即层错宽度为1·8nm,与理论计算结果一致;外延晶体薄膜沉积生长中,位错对会发生滑移,但其间距保持稳定.进一步观察发现,该扩展位错产生于一种类似于“局部熔融-重结晶”的表层局部无序紊乱-有序化过程;而这种表层局部紊乱或熔融则起自于失配应力作用下表层挤出四面体的形成,这种挤出四面体在大多数情况下可由原子间相互作用拉回,其消长呈统计涨落,而在个别情况下则发展成为局部紊乱区,成为其后位错形成的核心.

Three-dimensional molecular dynamics simulation of epitaxial growth of fcc aluminum film with a negative misfit of 0.05, under atomic deposition, has been carried out. An embedded atom method （EAM） potential is employed for computing atomic interaction in aluminum. Formation of misfit dislocation appears in the simulated growth process. Atomistic analysis of the film shows that, in the beginning the misfit dislocation consists of two Shockley partial dislocations with a stacking fault zone between them. The Burgers vectors of the two partial dislocations are of （211）/6 type, and the width of the stacking fault is - 1.8 nm, which agrees well with theoretical calculation. During further deposition growth, the dislocation pair can slide, but their distance remains stable. Further analysis shows that the dislocation pair forms in a local surface disordering-ordering process, like the local melting-crystallization. Atomic scale squeezed-out tetrahedrons are found to form near the surface and soon slide back in the manor of statistical fluctuation. Under some circumstances, however, a squeezed-out tetrahedron causes disorder of its neighboring atoms, and developes into the observed local disorder zone, which later becomes the nucleation site for the formation of the Shockley dislocation pair.