Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT, 06511, USA.
Nat Commun. 2018 Mar 19;9(1):1129. doi: 10.1038/s41467-018-03604-2.
Supercooled liquids exhibit spatial heterogeneity in the dynamics of their fluctuating atomic arrangements. The length and time scales of the heterogeneous dynamics are central to the glass transition and influence nucleation and growth of crystals from the liquid. Here, we report direct experimental visualization of the spatially heterogeneous dynamics as a function of temperature in the supercooled liquid state of a Pt-based metallic glass, using electron correlation microscopy with sub-nanometer resolution. An experimental four-point space-time correlation function demonstrates a growing dynamic correlation length, ξ, upon cooling of the liquid toward the glass transition temperature. ξ as a function of the relaxation time τ are in good agreement with Adam-Gibbs theory, inhomogeneous mode-coupling theory and random first-order transition theory of the glass transition. The same experiments demonstrate the existence of a nanometer thickness near-surface layer with order of magnitude shorter relaxation time than inside the bulk.
超冷液体在其波动原子排列的动力学中表现出空间异质性。异质动力学的长度和时间尺度是玻璃转变的核心，并且会影响液体中晶体的成核和生长。在这里，我们使用具有亚纳米分辨率的电子相关显微镜，直接观察到 Pt 基金属玻璃过冷液体状态下随温度变化的空间异质动力学。实验的四点时空相关函数表明，随着液体冷却到玻璃化转变温度，动态相关长度 ξ 逐渐增加。 ξ 与弛豫时间 τ 的关系与 Adam-Gibbs 理论、非均匀模式耦合理论以及玻璃化转变的随机一级相变理论吻合良好。相同的实验还表明，在比体相中短得多的弛豫时间存在一个纳米厚度的近表面层。
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