Theoretical Investigations On The Nonlinear Optical Properties Of Boronnitride Hybrid Graphene Nanoribbons And Carbon Nanotubes

The field of nonlinear optics（NLO） has attracted lot of interest in the last few decades because of the possible numerous applications in optical communication, optical computer and optical process of information etc. With the coming of information age, design and synthesis of nonlinear optical materials of high performance is important for the preparation and development of photoelectric device. Because graphene and carbon nanotube（CNT） can usually possess unique electronic structure and the excellent stability, they could be utilized for potential applications in many fields. The NLO properties of BN hybrid graphene nanoribbons（GNR） and CNTs have been theoretically investigated by using quantum chemical calculations. The relationship between molecular structures and NLO properties has also been explored. We hope the investigation would provide new insights and valuable theoretical clues for the rational design of more applicable and high-performance NLO materials. The main points of our work are presented in detail as follows:1. We investigated the NLO properties of four kinds of BN hybrid GNRs. The results indicate that, compared to BN hybrid CNTs, BN hybrid GNRs in our studied systems have better second-order NLO response. Besides, The BN hybrid modes in GNRs play a very important role in enhancing the first hyperpolarizability（β0）. For example, the B atom of the external or internal BN-hybrid GNRs locating on the edge or close to the edge of GNRs is more effective to enhance the first hyperpolarizabilities. Wherever in the external or internal BN hybrid GNRs, the size effect is very obvious for increasing β0. Moreover, the nonlinearity and transparency tradeoff could be modulated by controlling the position, size, and shape of BN nanoribbon in GRNs.2. We studied the structures and NLO properties of a set of BN hybrid CNTs with different C/BN ratios. The BN hybrid CNTs can be considered to be rolled from GNRs and BNNRs, named as（CBN）_T-NTs. The results show that with the increase of the ratio of C/BN in（CBN）_R-NTs, the static first hyperpolarizability rapidly increases. Besides, compared to another kind of（CBN）_T-NTs, whose structures can be seen to be connected from CNTs and BNNTs, our studied（CBN）_R-NTs show better stabilities, NLO responses, and transparencies in the visible light region. Moreover, both the tube diameter and the length effects are also studied with a hybrid ratio（1:1） of C/BN and it is found that the length effect is a more effective strategy for enhancing the first hyperpolarizability for（CBN）_R-NTs.