Studies Of Dirac Material On Preparation, Characterisation And Applications

Dirac material is one type of crystal materials with special band structure. Graphene and topological insulator emerged in recent years possessing characteristic Dirac cone is typical Dirac material. Graphene as 2D Dirac material is a monolayer of sp2 carbon atoms arranged in hexagonal lattices. Graphene possesses excellent conductivity(carrier mobility more than 2 × 105 cm2/V·s). Besides, graphene has outstanding transparency, the one-layer graphene can transmit ~97.7% light. What’s more, graphene also possesses large specific surface area(2630 m2/g), superior biocompatibility and affinity. Therefore, sensors based on graphene can effective prevent the deformation of molecule and act as the enrichment for molecule, can be applied in the area of SERS. Topological insulator is different from conductor,semiconductor and insulator. The bulk of the topological insulator presents an insulator state, while in the surface we can achieve a conducting state. Due to the controllable stoichiometric ratio and large band gap of the topological insulator, topological insulator will be a promising material for the application in the field of spintronics, optoelectronic device, quantum computation and electrochemistry. Benefiting from the unique band structure, Dirac material has been attracting extensively scientific interests from both experimental and theoretical communities in the recent years as a result of their distinctive band structures and physical properties, which exhibit extensive application prospect.In this study, we demonstrated the direct deposition of graphene on dielectric substrate using chemical vapor deposition system with a two-temperature reactor and discussed the effect of the growth parameters for the quality of graphene. We offered direct deposition of graphene film on the standard single mode, which promoted the achievement of the fiber mode locking and sensors based on graphene. We combined GO, Ag nanoparticles and PSi forming the GO/Ag/3D-Si SERS substrate and realized the detection of R6 G. Core-shell graphene@Cu nanoparticles(G@CuNPs) have been directly deposited onto the G@Cu substrate to form the all-sided-isolated G@CuNP/G@Cu SERS substrate using the CVD system with a designed process. We offered a catalyst-free CVD method for the fabrication of the graphene-Bi2Se3 hybrid with controlled graphene layers and discussed the influencing mechanism of the growth parameters for the morphology of the product in detail. The main works were as follows:(1) We proposed the direct growth and deposition of uniform and high-quality graphene layers on dielectric surfaces. The temperature gradient in the tube is crucial for the facile synthesis of graphene on SiO2. Two different growth mechanisms govern the reaction in different zones. In zones closed to the high-temperature zones, Cu atoms act as the nuclei to capture C atoms. In the low-temperature zone, C atoms directly deposit on the surface and act as the nuclei. Sufficient and well-proportioned Cu atoms are needed to prepare high-quality graphene. This method paves a way toward practical applications for graphene, especially in electronic and optoelectronic devices.(2) We demonstrated the direct deposition and growth of uniform graphene layers on the SMF surfaces. A Cu-vapor-assisted CVD process was introduced to understand the mechanism of graphene growth on the SMF. Via controlling the flow of the gas before the growth process, we can regulate the morphology of the prepared sample. With a large flow of the gas before the growth process, uniform graphene layers can be obtained, while the CNTs can be fabricated with a lower one. What’s more, the growth time also plays a crucial role in the layers of the prepared graphene film. This method provides a promising transfer-free way for the fabrication of saturable absorber for passive mode-locked laser with the graphene or CNTs.(3) We fabricated a SERS substrate based on GO/Ag/PSi using a convenient and low-cost method. On the top of the obtained GO/Ag/PSi, the bio-compatibility, homogeneity and chemical stability were demonstrated by the detection of R6 G. The contrast experiments using PSi, GO/PSi, Ag/PSi and GO/AgA/PSi further indicated that the GO was fairly favorable for the synthesis of well distributed Ag nanoparticles on the PSi substrate and thus achieved the SERS signal with high sensitivity, perfect bio-compatibility, good homogeneity and chemical stability. With the assist of FDTD, the perfect SERS behaviors obtained in experiment were confirmed by theoretical calculations. Our results suggest the novel GO/Ag/PSi could be a promising and sensitive SERS substrate for molecule detection in areas of medicine, food safety and biotechnology.(4) We proposed a novel, facilely synthesized and low-cost graphene-Cu sandwich coupling system as the SERS substrate. The graphene covered Cu nanoparticles are easily formed on the graphene@Cu foils by using the designed growth process. The two enhancement mechanisms of the EM(Cu nanoparticles) and CM(graphene) are combined to give the overall SERS enhancement of the fabricated G@CuNP/G@Cu substrate. More importantly, the stability of the G@CuNP/G@Cu substrate is improved, benefiting from that graphene layer can acts as the passivation layer to inhibit the surface oxidation of the Cu nanoparticles and Cu substrate. The SERS results show that the all-sided isolated structure is a promising substrate for applications in chemical and biological detection because of its long-term stability and superior SERS performance.(5) We demonstrated the direct growth and deposition of uniform and high-quality Bi2Se3 on the G/SiO2/Si substrate. The graphene medium layer, temperature of the substrtate, growth time and gas flow is crucial for the facile synthesis of Bi2Se3 crystal material. The influencing mechanism of these growth parameters are discussed in detail. We can successfully obtain Bi2Se3 thin film and paltes in our case. This method presents us a promising and economical technique for fabrication of the Bi2Se3 thin film and plates and will promote the practical applications of this magical material.