Properties of novel one-dimensional metals on solid surfaces

人们的兴趣与日俱增。在纳米材料的相变中，包括电荷密度波(CDW)相变，它是由具有低维电子系统的金属材料中的电子-声子相互作用驱动的，并与输运性质的变化有关。由于固体表面和界面提供了准二维电子系统，人们长期以来一直在努力寻找CDW相变，最近发现了有趣的表面相变。我们用角度分辨光电子能谱、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理论计算方法，对在350-400K温度范围内观察到的0.65-ML In覆盖的Cu(001)表面的相变进行了详细的研究。表面在低温(LT)相表现为c(4x4)结构，并经历了向高温(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关系和来自CD.W相的衍射谱推断出来的。前者的结果清楚地证明了Tc(Elec)=400K时CDW带隙的类BCS行为，支持了弱耦合的CDW理论，而后者的结果明确地表明，有序无序相变发生了，归类为2D Ising普适类。在T_c(晶格)=345K时，这些看似矛盾的结果表明，两个本质上不同的相变是在同一温度范围内发生的，这归因于表面系统固有的增强涨落效应和独特的维度。我们还研究了2D表面合金岛在Al/Pd(001)表面上的扩散和合并，p4g晶格变形的电子驱动机制和氢在Ti/Pd(001)表面合金上的吸附提升。

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.