Research On High Quality Graphene Transfer Technology And Its Application In Ultrafast Optics

Graphene, the most ideal2D carbon material in the world, has been considered as a promising material for a wide range of potential applications due to its fascinating optical, electronic, mechanical, and thermal properties. Among all the fabrication techniques of graphene, chemical vapor deposition (CVD) is commonly regarded as a low cost and scalable technique to obtain large-area, and high-quality graphene films. Usually, large area graphene is best grown over metal substrates by CVD. However, for the practical application of graphene, an efficient and reliable method is required to transfer the graphene sheets from metallic substrates onto target substrates without degrading the quality of graphene. The transfer process plays an important role in determining the properties of the transferred graphene, which strongly affects the final performance of devices. Therefore, the application of graphene is closely related to its transfer technology. However, the graphene transfer technology still has many problems, wrinkles or cracks always emerge together with the process of transferring grapheme, which limits its further development and application. Based on the CVD-grown graphene on Cu, this thesis studied the high quality graphene transfer technology, and its application in ultrafast optics. The detailed contents are as follows:(1) The effect of the substrate on the transfer quality of graphene was investigated. We found that ultrasonic processing (UP) can significantly increase the hydrophilicity of the target substrate, rendering the transferred graphene with higher quality and less wrinkles and defects. More importantly, we also experimentally found that the UP treatment technique is also widely applicable for other substrates, such as sapphire, and optical fiber ferrule. We believe that this simple, low-cost and widely compatible graphene transfer method should have great potential application values in various photonics fields. Morever, the effect of annealing treatment was also investigated, and we experimentally found that annealing is a possible method to remove polymer residues on the transferred graphene.(2) High-performance graphene mode-locked erbium-doped fiber laser was built based on the high-quality graphene transfer technology. Upon ultrasonic processing the end-facet of the optical fiber, where graphene film is attached, yields a high performance graphene saturable absorber (SA) optical device with advantages of low optical loss and stability, which can be further incorporated into an erbium-doped fiber laser for better mode-locking performance, in terms of narrower pulse duration, higher conversion efficiency.