First Principles Investigations Of The Electronic Transport And Optoelectronic Properties In Annulene-based Molecular Devices

With the development of electronics and minimization of electronic device,it has been a trend to use single molecules or molecular cluster,such as organic molecules and biomolecules,to construct functional electronic devices.Furthermore,the research of electrical and optical properties for these devices has become an independent subject,that is,molecular electronics.Progress in microfabrication and self-assembly techniques has made it possible to design a single-molecule device.As the electronic transport plays a key role in the operation of molecular devices,it is of fundamental importance to obtain a comprehensive understanding of the electronic transport properties of molecular junctions.Organic molecules are the most powerful candidates for constructing molecular devices with the weaker spin-orbit and hyperfine interactions.1,6-methano[10]annulene is a kind of fascinating organic molecule since it holds distinctive geometric structures and fantastic electronic properties.The moleculehas attracted much attention because of its stable ?-conjugated structure and significant aromatic feature,thus it is an ideal subject to experiment.Up to now,the transport properties of the molecule are still open question.In present study,we choose Fe,Co or Ni chains as electrodes.Using density functional theory combined with nonequilibrium Green's function,we designed several annulene-based molecular spintronic devices and investigated the quantum transport and optoelectronic properties.The research background and the development of the molecular devices has been introduced in the first chapter.The second chapter is mainly about the corresponding theoretic methods adopted in the current thesis including DFT and NEGF,which ineludes Born-Oppenheimer approximation,Hartree-Fock self-consistent field and density functional theory.When we use density functional theory to do calculation,the selection of basis sets is needed,which is elucidated in the third chapter.In chapter three and chapter four,we calculate the currents and photocurrents of the two different structures of molecular devices with the magnetization directions of the two magnetic electrodes transformed.Our results show that these devices have outstanding spin-filter capabilities and exhibit giant magnetoresistance effect,and that with Ni chains as electrodes,the device has the best transport properties,the change of devices structure has impacted on their transport.Furthermore,we investigated the spin-polarized optoelectronic properties of the device with Ni electrodes and found that the spin-polarized photocurrents can be directly generated by irradiating the devicewith infrared,visible or ultraviolet light.But the corresponding microscopic mechanisms are different.More importantly,if the magnetization directions of the two electrodes are antiparallel,the photocurrents with different spins are spatially separated,appearing at different electrodes.This phenomenon provides a new way to simultaneously generate two spin currents.