Growth dynamics and pattern formation of ice and CCl4 crystals under pressure

平衡晶体形状由Wulff结构唯一定义，该结构给出了固定体积的总的、取向相关的表面自由能的最小化。因此，低能量方向主导形状。另一方面，生长和熔体形状接近平衡的表面取向依赖动力学。最慢的增长方向最终占主导地位的渐近增长的形状，留下一个完全刻面的分子光滑的取向，而最快的熔体取向占主导地位的稳态熔体形状。我们用高压压砧装置制造了冰晶，并研究了晶体形状的生长-融化不对称性。在粗糙化温度以上，平衡形状是部分刻面的圆盘。我们发现生长和熔化的盘状晶体的形状之间的不对称性;（a）的邻面逐渐衰减，但在熔化过程中的发展;（B）粗糙的表面生长的曲率减小，但熔化的曲率增加，而生长或熔化与时间呈线性关系。这些结果可能是由于不同的动力学之间的分子附着和detaches.Below一个粗糙化的温度，我们观察到，而二维稳定的融化形状的冰是由六个平面的边界，与小面的生长形状的相似性是化妆品，平面是不是正确的小面，但旋转30度的棱镜小面。的动力学定量描述使用的熔体生长形状演变的几何模型。

Equilibrium crystal shapes are uniquely defined by the Wulff construction that gives a minimization of the total, orientation-dependent, surface free energy for a fixed volume. Thus, the low energy orientations dominate the shape. On the other hand, growth and melt shapes near equilibrium are determined by surface orientation dependent kinetics. The slowest growing orientations ultimately dominate the asymptotic growth shape, leaving a fully faceted molecularly smooth orientations, whereas the fastest melt orientations dominate the steady state melt shapes. Using a high pressure anvil cell we produced ice crystals and examined the growth-melt asymmetry in crystal shape.Above a roughening temperature an equilibrium shape is a partially-faceted disk. We found asymmetry between growth and melt shapes of the disk crystal ; (a) the vicinal surfaces gradually decay during growth but develop during melting ; (b) the rough surfaces grow with decreasing curvature but melt with increasing curvature while grow or melt linearly with time. These results may be due to the different kinetics between the molecular attachment and detachment processes.Below a roughening temperature we observe that while the two dimensional steady melt shapes of ice are bounded by six planes, the similarity with faceted growth shapes is cosmetic ; the planes are not proper facets but rotated 30 degrees from the prism facets. The dynamics is described quantitatively using a geometric model for the melt-growth shape evolution.