The Organic Polymer Doped And Theoretical Study Of The Transport Of Organic Molecular Devices

This dissertation mainly includes the works in two fields. It is composed of two parts. The first part presents the theoretical research on physical property of the organic polymer. The results of this part are obtained by model hamiltonian. The second part discusses the charge transport of organic molecular devices. The results of this part are obtained by the first-principles calculation.The first part is composed of the first chapter and this chapter includes three subsections. The first subsection simply introduces the development history of organic polymer, then illustrates the quasi one dimensional characteristic of conducting polymer with polyacetylene. In the second subsection we first point out that there are two kinds of organic polymers, one is the polymer which has the degenerate ground state, the other is the polymer which has the nondegenerate ground state. Then we dicuss the doping effect of the polymer which has the degenerate ground state. We point out that in real polymers, doping not only causes charge transfer but also has effect on the electron hopping near the dopant. Our results show that once the hopping effect is considered, the charge carrier in trans-polyacetylene is soliton-antisolition pair, not the single polaron. This conclusion can explain the experimental result of polymer which has the degenerate ground state in the doping case. The third subsection discusses the doping effect of static polarizability of excited state in the polymer which has the degenerate ground state. We point out that the negative polarizability phenomenon can appear in the excited state of the polymer which has the degenerate ground state and the change of hopping can have effect on the negative polarizability strongly. It points out a way of making photonic and electronic switches.The second part includes the second chapter, the third one, the fourth one and the fifth one. The second chapter briefly introduces the molecular electronics which is a new subject, the main characterics of molecular devices, the Landauer picture of molecular transport and the microscopic mechanism of quantum transport. The most important thing is that we point out thetransmission function which can have effect on the current has close correlations with molecular self energy and charge effect. The third chapter introduces the strict theory of dealing with quantum transport: nonequilib-rium Green's function (NEGF). We derive the current formulae of coherent transport and noncoherent transport by the matrix NEGF and make the basis for the first-principles calculation. This chapter also simply introduces the molecular orbital theory (MOT). We point out the combination of MOT and NEGF can be used to do transport calculations from the first-principle level. We also point out in this chapter that this combination needs to use the traditional quantum chemistry software: Gaussian, but the partial source code of Gaussian must be rectified: the density matrix of closed system obtained by Roothaan equation must be replaced by the one of open system obtained by NEGF and the self-consistent iteration must be completed. The fourth chapter gives the concrete numerical calculation method of surface Green's function and density matrix. The fifth chapter gives the concrete applications of this self-consistent transport theory. This chapter includes three subsections. The first subsection introduces our study results about I-V curves of single benzene and its oligomers. We give the I-V curve of single benzene in theory and the result accords with the experimental one qualitatively. Our study to I-V curves of naphthalene-dithiol and anthracene-dithiol shows the nonclassical behavior of molecular transport. Our study to I-V curve of thiophene shows that its transport capacity is stronger than that of single benzene. The second subsection introduces our study to the oligomers of aromatic rings as current switch. The molecule in Reed's famous experiment is choosed to our study object. We point out the rotation of ring and the charge effect are the two main factors having effect on the current switch. In the last subsection, we study the gate bias effect of organic molecular current. Our numerical results show that organic molecular current can be adjusted and controlled by gate bias and gate bias effect of aromatic phenyl rings is stronger than that of fused ring thiophenes with the same aggregation degree and this effect can be strengthened with increase of the number of ring in small transport bias range. Our results supply a method to adjust and control the organic molecular current.