Crystallization of highly supercooled glass-forming alloys induced by anomalous surface wetting.
Crystallization of highly supercooled glass-forming alloys induced by anomalous surface wetting.
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DOI：
10.1039/c9cp07021d
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发表时间：
2020-02
期刊：
影响因子：
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通讯作者：
Q. Bi;Chenchen Guo;Y. Lü
中科院分区：
文献类型：
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作者：
Q. Bi;Chenchen Guo;Y. Lü
采用分子动力学模拟方法研究了过冷Cu50Zr50薄膜在玻璃转变附近的晶化过程。自发成核观察到的模拟时间尺度相反，散装对应。我们发现，形核发生在自由表面由于部分润湿的核心熔体。异常润湿现象是密切相关的强密度分层所产生的表面：与表面分层的高密度增加过冷熔体的表面能，导致在结晶胚胎的一个方面是优先在膜表面上形成。基于表面的胚胎然后通过桥接薄膜的两个表面而发育成稳定的核。基于平均第一通过时间法的动力学和热力学分析表明，尽管有很高的过冷度，形核过程仍然遵循经典形核理论的描述。在成核中，缓慢的界面动力学成为主导，并诱导低成核速率，尽管成核势垒非常低。随后的晶体生长被发现进行准二维的方式与分歧的界面形态，这是类似于在玻璃形成液体中预测的结晶。
Crystallization in highly supercooled Cu50Zr50 films close to the glass transition is studied by using molecular dynamics simulations. Spontaneous nucleation is observed at the simulation timescale in contrast to the bulk counterpart. We find that nucleation occurs at free surfaces owing to the partial wetting of the nucleus by melt. The anomalous wetting phenomenon is closely related to strong density layering arising from the surface: the high density associated with surface layering increases surface energy of supercooled melts, resulting in that one facet of the crystalline embryo is preferentially formed on the film surface. The surface-based embryo is then developed into a stable nucleus by bridging two surfaces of thin films. The kinetics and thermodynamics analyses based on the mean first-passage time method show that the nucleation process still follows the description of the classical nucleation theory despite extremely high supercoolings. In nucleating, the slow interface dynamics becomes dominant and induces a low nucleation rate although the nucleation barrier is very low. The subsequent crystal growth is found to proceed in a quasi-two-dimensional manner with a ramified interface morphology, which is analogous to percolative crystals predicted in glass-forming liquids.