Properties of novel one-dimensional metals on solid surfaces

There.is越来越多的兴趣。在纳米尺度材料的相变中，包括电荷密度波（CDW）相变，其由具有低维电子系统的金属材料中的电子-声子相互作用驱动，并且与输运性质的变化相关联。由于固体表面和界面提供准二维电子系统，因此长期以来一直致力于寻找CDW相变，最近在有趣的表面相变的发现中结出了果实。利用角分辨光电子能谱、表面X射线衍射、扫描隧道显微镜、低能电子衍射和第一性原理全电子密度泛函计算等方法，对350-400 K温度下，在0.65 ML In覆盖的Cu（001）表面上观察到的相变进行了详细的研究。该表面在低温（LT）相中表现出c（4x 4）结构，并经历向高温（HT）p（2x2）相的可逆转变。最重要的发现是从与CDW形成相关的能隙的温度依赖性和CD.W相的衍射轮廓推导出来的。前一个结果清楚地证明了在Tc（ε）= 400 K时CDW带隙的BCS行为，支持了弱耦合的CDW理论，后一个结果则明确地表明发生了属于二维Ising普适类的有序无序相变.在Tc（晶格）= 345 K时。这些看似矛盾的结果表明，这两种性质不同的相变在同一温度范围内同时发生，这是由于涨落效应的增强和表面系统固有的独特维数。我们还研究了Al/Pd（001）表面二维合金岛的扩散和合并，Ti/Pd（001）表面合金p4 g晶格畸变的电子驱动机制及氢吸附对p4 g晶格畸变提升的影响。

There.is a growing interest. in phase transitions in nanometer-scale materials, which include charge-density-wave (CDW) phase transitions, which are driven by the electron-phonon interaction in metallic materials with low-dimensional electron systems and are associated with changes in transport properties.As solid surfaces and interfaces provide quasi-two-dimensional electron systems, efforts have long been paid to find CDW transitions, which fruited recently in the discovery of intriguing surface phase transitions. We have carried out a detailed study, by means of angle-resolved photoemission, surface X-ray diffraction, scanning tunneling microscopy, low-energy electron diffraction and first-principles all-electron DFT calculation, on the phase transition observed at 350-400 K on the Cu(001) surface covered with 0.65-ML In. The surface exhibits a c(4x4) structure in the low-temperature (LT) phase and undergoes a reversible transition to high-temperature (HT) p(2x2) phase. The most important finding was deduced from the temperature dependence of the energy gap associated with the CDW formation and the diffraction profile from the CD.W phass. While the former results shows a clear evidence for the BCS-like behavior of the CDW gap with Tc(elec) = 400 K, supporting the weak-coupling'CDW theory, the latter result indicates unambiguously that the orderdisorder phase transition classified into 2D Ising universality class takes place. at Tc(lattice) = 345 K. These seemingly contradicting results point to a scenario that the two qualitatively different phase transitions take place concertedly at the same temperature range, which we ascribe to the enhanced fluctuation effect and the unique dimensionality inherent to surface systems.We also studied on the diffusion and coalescence of the 2D surface alloy islands on Al/Pd(001), the electronic driving mechanism of the p4g lattice distortion and its lifting by hydrogen adsorption on the Ti/Pd(001) surface alloy.