Quantum Contact

本文利用安装在超高真空透射电子显微镜（TEM）试样位置的扫描隧道显微镜（STM），阐明了量子纳米接触处的量子力学现象，如量子化电导等。同时研制了一种新型原子力显微镜（AFM），用于研究原子力作用在AFM悬臂梁与衬底之间的纳米接触或纳米线上。结果表明：(1)利用STM-TEM测量了神奇数为7的螺旋多壳（HMS）金纳米线的电导率，发现由于电极与HMS接触区域的对称性破坏，导致电导率的整数量化被打破。(2)利用电子束稀释金膜，在150K温度下合成了金（和铂）单壁纳米管。(3)铜纳米线的量子电导率为半整数，但在100mT以上的磁场作用下基本没有变化。(4)金、铜、银、铂纳米触点均存在非线性电导。随着偏置电压的增加，电导正增加。(5)通过制作长银纳米线（绳）来研究电导量子化的断裂，该纳米线从AgI晶体表面生长，而尖端电极接近AgI表面上方。(5)研制了用于分析纳米接触元素的Cs（球差）校正透镜，以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.