Properties of novel one-dimensional metals on solid surfaces

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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.