Quantum Contact

本工作利用安装在超高真空透射电子显微镜样品位置的扫描隧道显微镜，阐明了量子纳米接触中的量子力学现象，如量子化电导。利用原子力显微镜(AFM)和超高真空透射电子显微镜(UHV-TEM)相结合的方法研究了原子力显微镜悬臂梁和衬底之间的纳米接触或纳米线上的原子力，得到了以下值得注意的结果：(1)利用扫描电子显微镜测量了幻数为7的螺旋多壳金纳米线的电导，发现电极与纳米线接触区域的对称性破坏了电导的整数量子化。(2)在电子束减薄金膜的过程中，在150K下合成了金(和铂)单壁纳米管。(3)铜纳米线具有半整数量子电导，但在100mT以下的磁场作用下不允许发生变化。(4)金、铜、银、铂纳米接触具有非线性电导特征。随着偏置电压的增加，电导呈正增长。(5)研究了针尖电极靠近AgI表面时，从AgI晶体表面生长出的长银纳米线(绳索)对电导量子化的破坏。(5)研制了用于纳米接触元素分析的Cs(球差)校正透镜，用于研究纳米接触中原子的电子散射。

The present work clarified the quantum mechanical phenomena at the quantum nano-contact, such as quantized conductance, by using STM (scanning tunneling microscope) installed in the specimen position of the UHV (ultra-high-vacuum) transmission electron microscope (TEM). A new AFM (atomic force microscope) combined UHV-TEM was also developed to study atomic forces acting on the nano-contact or on the nanowire that span between the AFM cantilever and the substrate.Some noticeable results are obtained as follows :(1)The conductance of the helical multi-shell (HMS) gold nanowire with magic number 7 was measured by using STM-TEM, to conclude that the integer quantization of the conductance is broken because of the symmetry breaking at the contact area of the electrode and the HMS. (2)Single wall nanotube of gold (and platinum) was synthesized at 150K during the thinning of the gold film by electron beam. (3)Copper nanowires display half integer quantum conductance, but they allow no change under application of magnetic filed up to 100mT. (4)Non-linear conductance was recognized for gold, copper, silver, and platinum nano-contacts. The conductance increased positively for increasing the bias voltage. (5)The breaking of the conductance quantization was investigated by making a long silver nanowire (rope), which grew from the AgI crystalline surface while the tip electrode approached above the AgI surface. (5)We developed Cs (spherical aberration) corrected lens for the analysis of elements at nano-contacts to study electron scattering at atoms in the nano-contact.