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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >From the Cover: The liquid-liquid phase transition in silicon revealed by snapshots of valence electrons
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From the Cover: The liquid-liquid phase transition in silicon revealed by snapshots of valence electrons

机译：从封面开始：价电子快照显示的硅中的液相-液相转变

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The basis for the anomalies of water is still mysterious. Quite generally tetrahedrally coordinated systems, also silicon, show similar thermodynamic behavior but lack—like water—a thorough explanation. Proposed models—controversially discussed—explain the anomalies as a remainder of a first-order phase transition between high and low density liquid phases, buried deeply in the “no man’s land”—a part of the supercooled liquid region where rapid crystallization prohibits any experimental access. Other explanations doubt the existence of the phase transition and its first-order nature. Here, we provide experimental evidence for the first-order-phase transition in silicon. With ultrashort optical pulses of femtosecond duration we instantaneously heat the electronic system of silicon while the atomic structure as defined by the much heavier nuclear system remains initially unchanged. Only on a picosecond time scale the energy is transferred into the atomic lattice providing the energy to drive the phase transitions. With femtosecond X-ray pulses from FLASH, the free-electron laser at Hamburg, we follow the evolution of the valence electronic structure during this process. As the relevant phases are easily distinguishable in their electronic structure, we track how silicon melts into the low-density-liquid phase while a second phase transition into the high-density-liquid phase only occurs after the latent heat for the first-order phase transition has been transferred to the atomic structure. Proving the existence of the liquid-liquid phase transition in silicon, the hypothesized liquid-liquid scenario for water is strongly supported.
机译：水异常的依据仍然是神秘的。相当普遍的四面体配位系统（也包括硅）显示出相似的热力学行为，但缺乏水（如水）的详尽解释。拟议的模型（有争议的讨论）解释了异常现象，是高密度和低密度液相之间一阶相变的剩余部分，深埋在“无人区”中-过冷液相区域的一部分，快速结晶阻止了任何实验访问。其他解释怀疑相变的存在及其一阶性质。在这里，我们提供了硅中一阶相变的实验证据。利用飞秒持续时间的超短光脉冲，我们立即加热了硅的电子系统，而由重得多的核系统定义的原子结构最初保持不变。仅在一皮秒的时间尺度上，能量被转移到原子晶格中，从而提供能量来驱动相变。利用汉堡的自由电子激光器FLASH的飞秒X射线脉冲，我们跟踪了此过程中价电子结构的演变。由于相关相在电子结构上很容易区分，因此我们跟踪硅如何熔化成低密度液相，而第二相转变成高密度液相仅是在一阶潜热之后发生的。过渡已转移至原子结构。证明了硅中存在液相-液相转变，强烈支持了假设的水液-液方案。

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