Investigation of bulk and surface melting from microscopic view point

虽然融化转变在我们的乳品生活中是普遍可见的，但从微观角度来看，对融化的理解仍然是一个悬而未决的问题。由于非简谐振动起着至关重要的作用，EXAFS(扩展x射线吸收精细结构)谱可以从局域结构和非简谐振动的角度研究熔化现象。在这项工作中，我们首先用EXAFS研究了块体材料在低温下的热性质，用量子统计方法估计了原子间相互作用势。这里采用路径积分等效势(PIPP)方法。为了将PIEP方法应用于金属，提出并组合了嵌入原子方法。在实验中，我们开发了一种新的超高真空盒，用于从低温到高温的表面EXAPS测量。我们用EXAFS测量方法研究了KCl上的KBr超薄外延膜和石墨上的镍、铜等超薄外延薄膜的各向异性非简谐表面振动。

Although melting transition is commonly observable in our dairy lives, the understanding of melting is still an open question in the microscopic point of view. Since anharmonic vibration plays an essential role, the EXAFS (extended x-ray-absorption fine structure) spectroscopy is useful to investigate the melting phenomenon from the view point of local structure and anharmonic vibration. In this work, we have first of all examined thermal properties of bulk materials at low temperature using EXAFS by estimating interatomic potentials with the quantum statistical approach. Here the path-integral effective-potential (PIEP) method was employed. In order to apply the PIEP method to metals, the embedded atom method was formulated and combined. In experiments, we have developed new ultrahigh vacuum chmaber for surface EXAPS measurements from low to high temperatures. We have investigated anisotropic anharmonic surface vibrations of ultrathin epitaxial flims such as KBr on KCl and Ni and Cu on graphite by means of temperature-dependent EXAFS measurements.