Development of Urtla-High Vacuum, Low Temperature, High Magnetic Field Scanning Tunneling Microscope.

我们构建了一台超高真空、低温扫描隧道显微镜，它可以在高达11T的磁场和光照下工作。在磁场高达11T的氦气温度下，观察到了HOPG的晶格图像。对于2H-NbSe_2，成功地获得了具有CDW带隙的隧道谱。然而，对于石墨，却没有得到重复性很好的隧道谱。这被认为是因为光谱严重依赖于STM针尖的条件，产生了隧道电流的随机涨落，这大于态密度的能量依赖所固有的电流。为了获得最佳的测量条件，有必要对STM针尖条件进行表征。数据分析的改进对于获得高质量的隧道电流数据也是重要的。对超导缝隙和涡旋的观测目前正在进行中。我们尝试观察了HOPG的局部氟化表面和在HOPG衬底上的纳米石墨烯薄片的点阵图像。氟化HOPG表面的晶格图像由碳原子和引入的氟原子之间形成共价sp3-键而产生的氟化位组成，这些位被具有√&lt；3&gt；×√&lt；3&gt；超晶格的区域所包围。将点阵图像与理论预测的结果进行了比较。以纳米金刚石颗粒为原料，采用电泳法和热处理相结合的方法在HOPG衬底上制备了纳米石墨烯薄膜。STM观察表明，制备的纳米石墨烯的面内尺寸约为10 nm，层间距为0.36-0.37 nm。层间距大于块体石墨的层间距(0.335 nm)，表明层间相互作用明显减弱。

We constructed an ultra-high vacuum, low-temperature scanning tunneling microscope, which could be operated under high magnetic field up to 11T and illumination of light. The lattice images of HOPG were observed at helium temperature under the magnetic field up to 11T.The tunneling spectra showing a CDW gap were successfully obtained for 2H-NbSe_2. However, well reproducible tunneling spectra could not be obtained for graphite. This is considered to be caused by that the spectra depend seriously on the condition of STM tips, producing random fluctuation of tunneling current, which is larger than the current intrinsic to the energy dependence of the density of states. It is necessary to characterize the STM tip condition for obtaining an optimum measurement condition. The improvement of data analysis is also important for obtaining high quality data of tunneling current. The observations of the superconducting gap and vortices are now under way. We tried to observe lattice images of locally fluorinated surface of HOPG and nano-sized graphene sheet on an HOPG substrate. The lattice image of fluorinated HOPG surface consists of fluorinated sites generated by the formation of covalent sp^3-bondings between carbon atoms and introduced fluorine atoms, which are surrounded by the region having a √<3>×√<3> superlattice. The lattice image is compared with that theoretically predicted. Nano-graphene sheet is prepared on an HOPG substrate by a combination of electrophoretic technique and heat treatment using nano-sized diamond particles. STM observations suggest that the prepared nano-graphene have an in-plane size of ca. 10nm and an inter-layer distance of 0.36-0.37nm. The inter-layer distance larger than that of bulk graphite (0.335nm) evidences a considerable reduction of the inter-layer interaction.