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Using a three dimensional-quasi-one dimensional-three dimensional model to depict the point contact between a scanning tunneling microscope tip and a metal crystal, by indenting the tip into a metal surface and then withdrawing we have studied the electron transport properties of the microstructure. By means of the single electron approximation and the transfer matrix method, we solve the Schr?dinger equation for this three dimensional system, and calculate the variation regularity of its conductance by quantum mechanics method. The variation of the conductance with constricting and stretching of the constriction is studied, and the quantization of the conductance in units of 2e2/h and 2×2e2/h are obtained.

According to the first principles, we investigate the structure, electronic, and magnetic properties of fluorinated graphene doped with external X (Al, P, Ga, As, Si) atoms at double vacancies, and find that like double vacancy doping of graphene, this kind of the fluorinated graphene divacancy substitution is also an ideal choice for substitutional doping. The results show that the electronic property and magnetic property of the fluorinated graphene both have large changes: the fluorinated graphene doped with Al (Ga) atoms can cause the semiconductor-to-metal transitions and induce magnetic moments. The fluorinated graphene doped with P (As) atoms becomes spin-polarized semiconductor. The Si doped fluorinated graphene keeps the semiconductor properties unchanged and has no magnetic moments. Through the further discussion about the mechanism of magnetism the relation between the doping concentration and magnetic property is obtained, and the magnetic properties in different doping situations are found to be caused by the different orbital electrons of different atoms. The divacancy substitutional doping behaviors enrich not only the doping ways of fluorinated graphene materials, but also its distinctive electronic and magnetic characteristics, which make this doping structure have potential applications in future electronic devices.

Transport through the quantum wire with many side-coupled quantum chains is investigated by using a recursive Green's function technique. We obtained the modulation rules of the parameters N and NU, which are the number of side-coupled quantum chain and the quantum-dot number of side-coupled quantum chain, respectively. The results show that the recursive Green's function method not only can conveniently tune the model and the number of the quantum chain, but also can be applied to study the varied nanofabrication of quantum devices.

We have introduced a method for the calculation of electron transport in a multi-terminal quantum system based on the recursive Green's function technique. The corresponding transport equation is presented by scattering matrix, which is exp ressed by Green's function. Using this method, the multi-terminal device can be simplified as a standard two-terminal device, which is convenient in treating th e mesoscopic device. It is found that the transmission and reflection probabilit ies of the two multi-terminal quantum systems show complex spectra. The results show that the special node can destroy the symmetrical conductance spectra, and there is a new conductance peak in the low-energy region. This method can also b e applied to the study of electron transport of complex mesoscopic structures.