Research on electronic states in a metallic quantum dot

我们从三个方面进行了研究：(1)利用低温扫描隧道显微镜(STM)研究了1 nm尺度的金属团簇；(2)利用电子束曝光技术制备了10 nm尺度的金属颗粒；(3)纳米加工技术的发展，并取得了以下结果。在Au团簇/单分子膜/Au(111)体系、Au团簇/二硫醇混合分子膜/Au(111)体系和金属团簇/Al_2O_3薄膜/NiAl(110)体系中，我们获得了通过均匀隧道势垒耦合到金属衬底上的金属团簇。利用它们，我们系统地对多个团簇进行了隧道光谱研究。对I-V曲线的分析表明，偏置电荷的分布集中在零附近，随着团簇尺寸的增加而扩散，当团簇尺寸超过一定值时，出现非中性团簇。我们利用电子束光刻制作的固定电极样品，观察到了10 nm-Al颗粒中的离散单电子能级。水平间距分布符合维格纳分布。除了直接电子束光刻外，制备纳米间隙电极的方法还包括角度沉积法、机械断裂结法、电化学法和无机抗蚀剂法。确定了10 nm金胶粒子SET的制作工艺，并验证了晶体管的工作状态。利用断裂结法确定了超导Al原子点接触的传导通道数及其传输系数，并确定了电流-相关系。我们还在介观金属粒子方面得到了几个新的发现。其中包括介观超导体中新涡旋态的发现，铁磁组中TMR增强的机制，以及SET的压力效应。

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.