| The invention of scanning tunneling microscopy (STM) in 1982 enabled people to observe and study hylic world in atomic scale of real space for the first time. STM have achieved large number of accomplishment in many field of physics and chemistry. It can not only resolve the atomic structure of low dimensional material and measure many local properties and processes in physics and chemistry related to surface electronic behavior, but also manipulate atom or molecule and construct nanostructures. In chapter 1, we first introduced the invention and development of STM, and its basic principle, especially the Barteen perturbation theory. In order to understand the data acquired by STM, the work modes of our LT-STM would be described detailedly, including principle and application way of topographs, STS spectra and dI/dV mapping skill which is more useful for investigating the spatial distribution of local electronic states. For the applications of STM, we mainly introduced the atomic resolution for studying the structure, conformation or distribution of electronic states of research objects. We also introduced how to manipulate the nanostructure by STM and its application on single molecular chemical reactions.Semiconductor surfaces, especially silicon surfaces, are the main direction of researches of surface science. Si(111)7×7 reconstruction surface have been attracted many attention in experiments and theories because of complexity of surface structure. Various events such as adsorption, diffusion, growth, as well as manipulation of atoms in Si(111)7×7 surface are strongly influenced by adatom vacancies which are still less investigated in experiments. In chapter 2, we fully studied the electronic structures of four types of adatom vacancies in Si(111)7×7 surface by STM and theoretical calculations. A typical electronic state at -0.55V associate with single adatom vacancies was found in STS spectra and dI/dV maps, which is essentially attributed to the dangling bonds of two upward backbonded atoms around the adatom vacancy. Combined with our theoretical analysis, we demonstrated that the adatom vacancy can induce the images of one rest atom near the vacancy to be invisible in the dI/dV maps. In addition, we also discuss the electronic states of adatom vacancy in other energy.As a classical example of metal-induced silicon reconstruction, Si(111) 31/2×31/2 -Ag surface have been investigated intensively using a variety of techniques such as the angel resolved photoemission spectroscopy (ARPES) and STM. Three surface-state bands have been reported in previous researches: S1, S2 and S3. In chapter 3, we have used STM to spatial image the energy-resolved local density of electronic states on Si(111) 31/2×31/2 -Ag surface. Distinguishing the different features of dI/dV maps corresponding to different states, two new electronic states have been found, which were proved to be surface resonant states by theoretical calculations. The simulated topograghs and dI/dV maps accorded well with experiments. We also investigated the electronic states of one defect of Si(111) 31/2×31/2-Ag surface. Compared STM topogragh and theoretical calculations, the defect was identified to be a vacancy formed by a missing of an Ag small triangle. Below -1.0 V, the defect could be resolved in the topograghs and dI/dV maps. Especially in dI/dV maps, we found the defect can influenced the nearby electronic states as far as second neighbor of Si triangles. Above -1.0V the defective surface looks like the perfect surface in the topograghs and dI/dV maps, because the extended free-electron-like S1 surface state near the Fermi level is insensitive to the vacancy defects with small concentration. Moreover, theoretical LDOS images agree well with experimental dI/dV maps.STM tips with special structure or electronic states can detect detailed or covered information of sample in STM experiments, which can not be achieved by normal tips. Now some groups have focused on this field. In chapter 4, we have investigates the adsorption of cobalt phthalocyanine (CoPc) molecule on Au(111)- 22×31/2 surface with different monolayers. More importantly, we have studied the dI/dV spectroscopy measured on Co atom in CoPc molecule using two kinds of STM tips: W tip and Fe coated W tip. A strong peak at -0.4V in dI/dV spectroscopy measured by Fe coated W tip was not found by W tip. The electronic states of two tips and CoPc molecule were obtained by theoretical calculations and used to simulate the dI/dV spectroscopy. The results accorded with experiments very well. Theoretical analysis points out that the peak at -0.4V measured by Fe/W tip is resulting from highly matching of tip's and carbon atoms' orbitals. It shows that using different STM tips consisting of different transition metals do give reasonable and selectable experimental results, and it gives something interesting and important which will improve our understanding of STM data both experimentally and theoretically.Obtaining detailed understanding of various important factors that control the electron transport in single molecular electronic devices has become the primary objective in the field. All of the previous researches were thought to control the transport behavior through changing some properties of single molecules, and few utilized electrodes. In chapter 5, we presented a new method to control the transport behaviors of single molecule via matching of spatial symmetry between the d orbitals of the electrode and single molecule. And this method has been realized through the tunneling between the CoPc molecule adsorbed on Au(111) surface and the Ni STM tip. The STM current exhibited obvious negative differential resistance (NDR) behavior at -0.87 V. The simulated results accorded with experiments very well. Additionally, even for a Ni plate, the same NDR phenomenon should still be observed. It is conceptually important since this mechanism provides practical guideline for design of molecular functional electronic devices.
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