Nanev Christo N
Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
Ann N Y Acad Sci. 2006 Sep;1077:194-207. doi: 10.1196/annals.1362.014.
The long-standing problem of face morphology is discussed. Special emphasis is put on macroscopically flat faces, whose growth, under low supersaturations, is driven by dislocations possessing some screw component. The most general case, where the crystal face is pierced by more than one screw dislocation, is considered. If performed under sufficiently low supersaturation, the growth leads to the formation of the face morphology corresponding to the minimum of the surface-free energy. The thermodynamic driving force for face flattening is the difference in the surface-free energy of the vicinal faces of the hillocks (emanating from screw dislocations) and that of a singular face, which can truncate the valley between the growth hillocks. The hillock slope gives the quantitative relation between energetics and kinetics. The result of the considerations is that the lower the supersaturation, the more important is the role of the surface-free energy in face flattening. Another factor, particularly under sufficiently low supersaturations, is the effective increase in the local supersaturation at the valley separating two growth hillocks. The reason is that the dislocation strain energy vanishes there. (This is most evident when two dislocations of opposite sign are considered.) Besides, the valley floors are concave regions on the crystal surface, where the building blocks are bound more strongly. Thus, the kinetic reason for face flattening is the relative preference for incorporation of atoms, arriving from the ambient phase, at the valley floor. Note that accelerated step annihilation in the valley floor should be a universal factor, which favors face flattening under any supersaturation. The amount of flattening in the growth situation is determined by the interplay between supersaturation and thermodynamics.
讨论了长期存在的晶面形态问题。特别强调了宏观上平坦的晶面，其在低过饱和度下的生长是由具有一定螺旋分量的位错驱动的。考虑了最一般的情况，即晶面被多个螺旋位错穿透。如果在足够低的过饱和度下进行生长，会导致形成对应于表面自由能最小值的晶面形态。晶面平坦化的热力学驱动力是小丘（由螺旋位错产生）的相邻晶面与奇异晶面之间表面自由能的差异，奇异晶面可以截断生长小丘之间的谷地。小丘的斜率给出了能量学和动力学之间的定量关系。考虑的结果是，过饱和度越低，表面自由能在晶面平坦化中的作用就越重要。另一个因素，特别是在足够低的过饱和度下，是在分隔两个生长小丘的谷地处局部过饱和度的有效增加。原因是位错应变能在那里消失。（当考虑两个相反符号的位错时，这一点最为明显。）此外，谷地底部是晶体表面的凹形区域，在那里结构单元结合得更紧密。因此，晶面平坦化的动力学原因是来自环境相的原子相对更倾向于在谷地底部掺入。请注意，谷地底部加速的台阶湮灭应该是一个普遍因素，它有利于在任何过饱和度下晶面的平坦化。生长情况下的平坦化程度由过饱和度和热力学之间的相互作用决定。
