Study of electronic states of surface material by using variable temperature scanning tunneling microscopy

扫描隧道显微镜(STM)隧道光谱是研究原子分辨率表面局域电子态的一种独特方法。这个项目的目的是将这种方法应用于材料表面电子态的研究，并澄清观察到的现象与电子态之间的关系。为此，我们改进了我们的扫描隧道显微镜，使其具有观察和在不同温度下工作的功能。在仪器中，我们制作了表面清洁和评估仪，以及对表面异物的清洁和评估仪。通过将这些样品转移到STM，我们可以测量表面的结构和局域隧穿光谱。利用工作在很低温度下的STM，我们研究了：1.在Ag/Ge(001)表面上寻找超导电性和磁通；2.在2H-NbSe_2表面上发现新的电荷密度波(CDW)；3.在2H-NbSe_2表面上磁性小粒子对超导电性的局域破坏。我们在2 K到10 K之间用隧道显微镜测量了费米能级附近的电子态密度，并阐明了它与表面结构和温度的关系。1.激光诱导分子从氯或氢吸附的硅表面脱附；2.硅表面的氢和氯交换反应；3.银吸附的Ge表面的原子结构；4.可见光和红外光诱导硅表面的局域隧道电流。我们观察了不同样品偏压下表面的STM图像，从原子分辨率上阐明了脱附位和反应位、小型AG/Ge表面合金的结构以及光生电流的来源。

Tunneling spectoscopy by a scanning tunneling microscope (STM) is used as a unique method for studying local electronic states at surfaces with atomic resolution. The aims of this project are to apply this method to the study of electronic states of materials at surfaces and to clarify the relation between the observed phenomena and the electronic states. For these purposes, we have imporoved our STM's to have the functions for spectoscopy and to operate at various temperature.In the instrumentations, we made surface cleaning and evaluation apparatuses together with those for foreign species on the surfaces. By transferring these sampoles to the STM,we can measure the structure of the surfaces and local tunneling spectra.Using an STM operating very low temperature, we studied ;1.search for superconductivity and magnetic flux at Ag/Ge (001) surfaces,2.new charge density wave (CDW) at 2H-NbSe_2 surfaces, and proximity of superconductivity to the CDW state,3.local breaking of superconductivity by magnetic small particles on the 2H-NbSe_2 surfaces.We measured electronic density of states around the Fermi level by tunneling spectoscopy between 2 K and 10 K,and clarified the dependence on the surface structure and temperature.At room temperature, we studied ;1.laser-induced molecular desorption from chlorine or hydrogen adsorbed Si surfaces,2.hydrogen and chlorine exchange reaction at Si surfaces,3.atomic structure of Ag adsorved Ge surfaces,4.visible and infra red light induced local tunneling current at Si surfaces.We observed STM images at various sample bias voltages on the surfaces, and clarified desorption sites and reaction sites, structures of small AG/Ge surface alloy, and the origin of light induced current with atomic resolution.