Research on electronic states in a metallic quantum dot

点击翻译按钮获取中文摘要

We approached the research from three directions ; (1) investigation of 1-nm-scale metal cluster using a low-temperature STM, (2) investigation of 10-nm-scale metal particle made by electron-beam lithography, and (3) the development of nano-fabrication technique, and obtained the following results.1. We have obtained metal clusters coupled to a metal substrate via homogeneous tunnel barrier in three systems : Au cluster/the monomolecular film/Au(111) system, Au cluster/the dithiol thiol mixed molecular film/Au(111) system, and metal cluster/Al_2O_3 thin film /NiAl(110) system. Using them, we performed tunneling spectroscopy for many clusters systematically. The analysis of the I-V curves showed that the distribution of the offset charge, which is concentrated around zero, spreads with increase of the cluster size, and the non-neutral clusters appear when the size exceeds a certain value.2. We observed the discrete single-electron energy levels in a 10nm-Al particle using the fixed-electrode samples fabricated by electron-beam lithography. Distribution of level spacing was consistent, with the Wigner distribution.3. Other than direct EB lithography, angled-deposition method, mechanical break junction method, electro-chemical method and inorganic resist method were examined to make nano-gap electrodes. Fabrication process of SET made of 10nm gold colloidal particle was established and the transistor operation was verified. Using the break junction method, the number of conduction channels and their transmission coefficients were determined for superconducting Al atomic point contacts., and the current-phase relationship was determined.4. We also obtained several new findings in mesoscopic metal particles. They include the discovery of new vortex states in mesoscopic superconductors, the mechanism of TMR enhancement in ferromagnetic SETs, and the pressure effect of SET.