Scannning Tunneling Microscopy Based on Chemically Modified Tips

用扫描隧道显微镜(STM)研究了单醚和双醚的单分子膜，为STM针尖的化学修饰识别官能团提供了新的范例。用4-巯基苯甲酸(4MBA)修饰的针尖在扫描隧道显微镜(STM)图像上观察到显示单分子膜上醚氧位置的明亮线条，它能与醚氧形成氢键。然而，对于未修饰的尖端或用没有可用于形成氢键的官能团的硫酚修饰的尖端，这种明亮的线条是不存在的。在二醚的STM图像中，用4MBA修饰的针尖观察到的乙醚氧的亮度取决于乙醚氧的取向。这些结果支持选择性对比度增强与样品和针尖之间氢键的形成有关。用4-硫代吡啶(4MP)化学修饰扫描隧道显微镜(STM)金针尖，测量了5，15-双(4-十八烷氧基苯基)卟啉(Por-H2)及其锌(II)、镍(II)配合物(Por-Ni)的扫描隧道显微镜(STM)金针尖的STM。这些化合物的单分子层在溶液-高定向热解石墨(HOPG)界面自发形成。用4MP修饰的TIP测量的卟啉中心的STM图像显示亮点，而用未修饰的TIP测量的STM图像显示卟啉中心为暗凹陷。卟啉中心的亮度似乎是由于Por-H2的氢键相互作用和Por-Zn和Por-Ni的配位相互作用而促进的电子隧穿。有趣的是，Por-Zn的中心比Por-H2和Por-Ni的中心更亮。此外，用4MP修饰的尖端的STM测量可以区分混合单层中的Por-Zn和Por-H2或Por-Ni。

Monolayers of-mono-and diethers were studied with scanning tunneling microscopy (STM) as a new example for the chemical modification of STM tips for functional groups recognition. Bright lines revealing the positions of the ether oxygens of the monolayers were observed in STM images with tips modified with 4-mercaptobenzoic acid (4MBA) which can form hydrogen bond with ether oxygens. Such bright lines, however, were absent with unmodified tips or tips modified with thiophenol, which has no functional groups available for hydrogen bond formation. In the STM images of diethers, the brightness of the ether oxygens observed with 4MBA-modified tips was modulated depending upon the orientation of the ether oxygens. These results support that selective contrast enhancements are associated with hydrogen bond formation between sample and tip. It is demonstrated that chemical modification of STM tips allows not only selective recognition but also orientation-sensitive observation of functional groups.Chemical modification of scanning tunneling microscopy (STM) gold tips with 4-mercaptopyridine (4MP) was used for STM measurements of 5,15-bis(4-octadecyloxyphenyl) porphyrin (Por-H2) and its zinc(II) (Por-Zn) and nickel(II) complexes (Por-Ni). Monolayers of these compounds spontaneously form at the solution-HOPG (highly oriented pyrolytic graphite) interface. STM images of porphyrin centers measured with 4MP-modified tips exhibited bright spots while those measured with unmodified tips exhibited the porphyrin centers as dark depressions. The brightness of porphyrin centers seems to result from facilitated electron tunneling due to hydrogen bond interactions for Por-H2 and due to coordination interaction for Por-Zn and Por-Ni. Interestingly, the centers of Por-Zn were brighter than those of Por-H2 and Por-Ni. In addition, STM measurements with 4MP-modified tips allowed to distinguish Por-Zn from Por-H2 or Por-Ni in mixed monolayers.