Lin Hong, Yau S-T, Vekilov Peter G
Center for Microgravity and Materials Research, University of Alabama in Huntsville, Huntsville, Alabama 35899, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Mar;67(3 Pt 1):031606. doi: 10.1103/PhysRevE.67.031606. Epub 2003 Mar 25.
In studies of crystal formation by the generation and spreading of layers, equidistant step trains are considered unstable-bunches and other spatiotemporal patterns of the growth steps are viewed as ubiquitous. We provide an example to the opposite. We monitor the spatiotemporal dynamics of steps and the resulting step patterns during crystallization of the proteins ferritin and apoferritin using the atomic force microscope. The variations in step velocity and density are not correlated, indicating the lack of a long-range attraction between the steps. We show that (i) because of its coupling to bulk transport, nucleation of new layers is chaotic and occurs at the facet edges, where the interfacial supersaturation is higher; (ii) step bunches self-organize via the competition for supply from the solution; and, (iii) bunches of weakly interacting steps decay as they move along the face. Tests by numerical modeling support the conclusions about the mechanisms underlying our observations. The results from these systems suggest that during crystallization controlled by transport, with weakly or noninteracting growth steps, the stable kinetic state of the surface is an equidistant step train, and step bunches only arise during nucleation of new layers. Since nucleation only occurs at a few sites on the surface, the surface morphology may be controllably patterned or smoothened by locally controlling nucleation.
在关于通过层的生成和扩展来研究晶体形成的过程中，等距的台阶列被认为是不稳定的束状物，而生长台阶的其他时空模式则被视为普遍存在。我们给出了一个相反的例子。我们使用原子力显微镜监测了铁蛋白和脱铁铁蛋白结晶过程中台阶的时空动力学以及由此产生的台阶模式。台阶速度和密度的变化并不相关，这表明台阶之间缺乏长程吸引力。我们表明：（i）由于与体相传输的耦合，新层的成核是混沌的，并且发生在界面过饱和度较高的晶面边缘；（ii）台阶束通过对溶液供应的竞争进行自组织；以及（iii）弱相互作用台阶的束在沿晶面移动时会衰减。数值模拟测试支持了关于我们观察结果背后机制的结论。这些系统的结果表明，在由传输控制的结晶过程中，生长台阶相互作用较弱或不相互作用时，表面的稳定动力学状态是等距的台阶列，并且台阶束仅在新层成核期间出现。由于成核仅发生在表面的少数位置，因此可以通过局部控制成核来可控地对表面形态进行图案化或使其平滑。
