Abstract Melting of 3D solids is often preceded by a premelting of their surface, a distinct process which begins at a temperature lower than TM (bulk melting temperature). Premelting is usually investigated by non-contact techniques like diffraction or elipsometry, revealing how the surface layer becomes progressively disordered with temperature. Although this disordered surface layer is called a “quasiliquid”, in most cases (except for ice) there is no way of telling whether it is a fluid or a disordered solid. One significant difference between these two states is in their resistance to shear, which should decrease if the surface becomes fluid. To address this question, we developed a mechanical method to measure the effective shear resistance of a metal surface. This property was not measured before. We applied this method to the surface of polycrystalline Gallium, and found that the surface shear resistance vanishes abruptly near the onset of premelting, about 9K below TM. This result confirms that the quasiliquid on the surface of Ga is a fluid.

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预熔过程中表面是否有流体？固体镓的表面抗剪切性研究

摘要 3D 固体的熔化通常先于其表面的预熔化，这是一个独特的过程，该过程始于低于 TM（整体熔化温度）的温度。预熔通常通过衍射或椭圆偏振等非接触式技术进行研究，揭示表面层如何随温度逐渐无序。尽管这种无序的表层被称为“准液体”，但在大多数情况下（冰除外），无法判断它是流体还是无序固体。这两种状态之间的一个显着区别在于它们的抗剪切性，如果表面变成流体，它应该会降低。为了解决这个问题，我们开发了一种机械方法来测量金属表面的有效抗剪强度。以前没有测量过该属性。我们将这种方法应用于多晶镓的表面，发现表面剪切阻力在接近预熔开始时突然消失，低于 TM 约 9K。这一结果证实了 Ga 表面的准液体是一种流体。