Electronic And Optical Properties And Its Strain Manipulation For Graphene Nanoribbons

Since successfully prepared at the end of 2004, graphene (single of several layers of carbon atoms) has been becoming one of the hot systems in condensed matter physics, material science, chemistry, information and biology technologies because its special structure and functions. Graphene owns the similar functions to those of carbon nanotubes and molecular electronic devices, with outstanding and unique physical, chemical and mechanical properties, and may be applied in the design of micro-nano-electronics, optoelectronics and spintronics devices other than the newly composite materials. The quasi-one-dimensional graphene is the unit cell for nano-devices based on graphene and can present the features of quantum confined systems, therefore, much attention has been paid to its physical properties. The main content of the thesis is the electronic and optical properties of graphene nanoribbons (carbon nanotubes included) and its strain manipulation.The thesis is divided into five chapters. In the first chapter, we give a brief introduction about the discovery and fabrication techniques of carbon nanotubes and graphene, the unique physical phenomena in graphene and the potential ap-plications of graphene and its nanoribbons in micro-nano-electronics.Chapter two, three and four are mainly our works. In the second chapter, us-ing the method of nonequilibrium Green's function, we investigate the electronic transport and optical properties of metallic zigzag carbon nanotubes irradiated with longitudinal polarized high-frequency electromagnetic field. It is demon-strated that, the electron density of states is sensitively dependent on the electron energy, the intensity and frequency of the external irradiated field; when the ir-radiated frequency is larger than the coupling between the carbon nanotubes and electrodes, the conductance decrease with the irradiated intensity while increase with the irradiated frequency; and we quantitatively discuss the optical dielectric function and electron energy loss spectra too. In the similar way, the stationary transmission coefficients of an electromagnetic field irradiated∧-shaped carbon nanotubes junction are demonstrated to be sensitively dependent on the electron energy, while the photon-assisted transmission coefficient and conductance depends on the irradiated intensity and frequency.Based on the intersubband transitional theory of semiconductors and the dipole transition approximation, using the linear response theory, chapter three investigates the optical properties of graphene nanoribbons irradiated with lon-gitudinal polarized electromagnetic field. It is demonstrated that, the transport and optical properties of armchair edge graphene nanoribbons, such as the real conductance, dielectric function and electron energy loss spectra are sensitively dependent on the irradiated frequency, and predict some new photon-assisted inter-subband transitions. Moreover, owing to the edge state and its optical transitions, zigzag edge graphene nanoribbons show richer optical structure than armchair edge graphene nanoribbons. It is pointed out that the predicted a series of phenomena may be observed by scanning tunneling microscopy and optical spectroscopy ex-periments, and be useful in the design of graphene-based nanoscale optoelectronic devices.In chapter four, we investigate the dispersion relation of the uniaxial strained armchair edge graphene nanoribbons by tight-binding approximation and the first-principle (Atomistic Toolkit software packet) calculations. The strain is found to be effective in the manipulation of the band gaps for armchair edge graphene nanoribbons. And we present the electron density of states, transmission spectra,Ⅰ-Ⅴcharacteristic curve and the intersubband absorption of armchair edge graphene nanoribbons, it is noted that the optical absorption frequency range and intensity may be effectively tuned by the external strains. Then, the electronic structure of zigzag edge graphene nanoribbons is demonstrated to be unsensitive to the external uniaxial strain, while theⅠ-Ⅴcharacteristic curve and intersubband absorption spectra of zigzag edge graphene nanoribbons are sensitive to the external strain, and the negative differential conductance of the strained 8-zigzag edge graphene nanoribbon may be useful in the design of nanoscale commutator devices.In chapter five, a summary of the work and a outlook of this topic are given.