Sharath Tejas, Bradley R Mark
Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA.
Departments of Physics and Mathematics, Colorado State University, Fort Collins, Colorado 80523, USA.
Phys Rev E. 2022 Feb;105(2-1):024801. doi: 10.1103/PhysRevE.105.024801.
We develop a theory for the surface ripples produced by near-normal-incidence ion bombardment of a (001) GaAs surface with a small miscut along the [110] direction. We restrict our attention to the case in which the energy of the incident ions is below the sputter yield threshold and the sample temperature is just above the recrystallization temperature. Highly ordered, faceted ripples with their wave vector aligned with the [110] direction form when the ion beam is normally incident and there is no miscut. Two additional terms appear in the equation of motion when the beam is obliquely incident and/or there is a miscut: a linearly dispersive term and a nonlinearly dispersive term. The coefficients of these terms can become large as the threshold temperature for pattern formation is approached from above. In the absence of strong nonlinear dispersion, strong linear dispersion leads to ripples with a dramatically increased degree of order. These ripples are nearly sinusoidal even though they are on the surface of a single crystal. The exceptionally high degree of order is disrupted by nonlinear dispersion if the coefficient of that term is sufficiently large. However, by choosing the angle of ion incidence appropriately, the coefficient of the nonlinearly dispersive term can be made small. Ion bombardment will then produce highly ordered ripples. For a different range of parameter values, nucleation and growth of facets and spinodal decomposition can occur.
我们针对沿[110]方向有小错切的(001) GaAs表面在近垂直入射离子轰击下产生的表面波纹发展了一种理论。我们将注意力限制在入射离子能量低于溅射产额阈值且样品温度刚好高于再结晶温度的情况。当离子束垂直入射且不存在错切时，会形成波矢与[110]方向对齐的高度有序的刻面波纹。当束斜入射和/或存在错切时，运动方程中会出现另外两项：一个线性色散项和一个非线性色散项。当从上方接近图案形成的阈值温度时，这些项的系数会变大。在没有强非线性色散的情况下，强线性色散会导致波纹的有序度显著增加。即使这些波纹在单晶表面上，它们也几乎是正弦形的。如果该项的系数足够大，那么异常高的有序度会被非线性色散破坏。然而，通过适当地选择离子入射角，可以使非线性色散项的系数变小。然后离子轰击将产生高度有序的波纹。对于不同的参数值范围，会发生刻面的成核和生长以及旋节分解。
