Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA.
Phys Rev E. 2017 Sep;96(3-1):032804. doi: 10.1103/PhysRevE.96.032804. Epub 2017 Sep 25.
We study the nanoscale terraced topographies that arise when a solid surface is bombarded with a broad ion beam that has a relatively high angle of incidence θ. We find that the surface is not completely flat between the regions in which the surface slope changes rapidly with position: Instead, small-amplitude ripples propagate along the surface. Our analytical work on these ripples yields their propagation velocity as well as the scaling behavior of their amplitude. Our simulations establish that the surfaces exhibit interrupted coarsening, i.e., the characteristic width and height of the surface disturbance grow for a time but ultimately asymptote to finite values as the fully terraced state develops. In addition, as θ is reduced, the surface can undergo a transition from a terraced morphology that changes little with time as it propagates over the surface to an unterraced state that appears to exhibit spatiotemporal chaos. For different ranges of the parameters, our equation of motion produces unterraced topographies that are remarkably similar to those seen in various experiments, including pyramidal structures that are elongated along the projected beam direction and isolated lenticular depressions.
我们研究了当固体表面受到具有较大入射角θ的宽离子束轰击时出现的纳米级梯田形貌。我们发现，在表面斜率随位置快速变化的区域之间，表面并不是完全平坦的：相反，小振幅的波纹沿着表面传播。我们对这些波纹的分析工作得出了它们的传播速度以及它们的幅度的标度行为。我们的模拟表明，表面表现出间断的粗化，即表面干扰的特征宽度和高度会随时间增长一段时间，但最终随着完全梯田状态的发展而趋于有限值。此外，随着θ的减小，表面可以从在表面上传播时随时间变化很小的梯田形貌转变为似乎表现出时空混沌的无梯田状态。对于不同参数范围，我们的运动方程产生的无梯田形貌与各种实验中观察到的形貌非常相似，包括沿投影光束方向拉长的金字塔形结构和孤立的透镜状凹陷。
