The Charge Transport Mechanism Of Functional Organic Molecule Devices

In the past decades, the rapid progresses in micro-fabrication and self-assemblytechniques have made it possible to control the molecules in nanoscale and toassemble them as the molecular device. These molecular devices are considered thesuitable candidate of electronic devices which trend toward the ongoingminiaturization. For this reason,the experimental and theoretical studies on themolecular device have attracted more and more attentions. In this thesis, we haveperformed first-principles calculations on the transport properties of sandwich systemsconstructed by”electrode-molecule-electrode”. We mainly studied some importantphysical problems of electronic transport properties for some functional organicmolecular devices, the effects of intermolecular interaction, side groups, coordinateatom, twisting of the structure of molecules, substituted atoms and gate voltage arestudied systematically. Some of the results have a good agreement with experimentaldata and theoretical predictions, and also contribute to understand the mechanics ofthe electronic transport process and guide to the design of molecular devices.In the beginning of the present thesis, the basic conception and the developmentof molecular devices have been exhibited, and then we introduced the first-principlesand non-equilibrium Green’s function method, and also put forward the plan of thefirst-principle calculation for the electron transport of the molecular devices.Using nonequilibrium Green’s function and first-principle calculations, weinvestigate the transport behaviors of a dimolecule device with Pyrene sandwichedbetween two gold electrodes. The results show that the molecule-electrode couplingeffect plays an important role in the conducting behavior of the system. By changingthe magnitude of coupling between the molecule and electrode, namely changing thedistance of the intermolecular interaction, a differenttransport behavior can beobserved in the system.Another of our work is to study the functional group to replace the electronictransport properties of organic molecules. By calculating results show that, when theamino substituted the Ethoxycarbonyl molecules hydrogen atom molecular orbitalHOMO is localized. Replace the Ethoxycarbonyl molecular hydrogen atom, but whenthe nitro, the LUMO of the molecule is localized. We can also replace theEthoxycarbonyl molecular hydrogen atoms in the pairs of hydroxyl groups and pairs of amino, molecular devices, electronic transmission capability has been greatlyweakened. Pairs of nitro substituted molecules hydrogen atoms, the electronictransmission capacity of the device is greatly enhanced. Most of Ethoxycarbonylmolecules are replaced by functional groups, the device will be a negative differentialresistance effect..