Advanced sensing techniques require graphene with high quality and well-controlled surface chemistry. The intrinsic high mobility, low electrical noises and uniform graphitic crystallinity are the... Show moreAdvanced sensing techniques require graphene with high quality and well-controlled surface chemistry. The intrinsic high mobility, low electrical noises and uniform graphitic crystallinity are the prerequisites for high-performance graphene electronics. More importantly, chemical functionalization contributes to unlock the sensing potential of the graphene basal plane. This thesis focuses on manipulating the surface chemistry of a graphene monolayer and explores the impacts on the electrical and electrochemical properties for sensing applications. Heteroatoms like hydrogen, nitrogen and oxygen were systematically introduced into the graphene lattice as defect sites to modify the surface chemistry, and consequently the electronic properties and sensing performance. In summary, a correlation between the in-plane electron transport and the electrochemical activity of hydrogenated graphene was studied by modulating the density of H-sp3 defects. Moreover, cleaning effect on the graphene surface caused by hydrogenation process and the corresponding mechanism were discussed. The electrocatalysis of oxygen reduction reaction on nitrogen doped monolayer graphene was conducted to pinpoint the catalytic active sites. The mechanics of a centimeter-scale graphene floating on water was characterized by biaxial compression. Finally, the chemically modified graphene was tested for field-effect sensing of gas molecules. Show less
With the help of modern techniques of imaging processing and computing, image data obtained by electron cryo-microscopy of biomolecules can be reconstructed to three-dimensional biological models... Show moreWith the help of modern techniques of imaging processing and computing, image data obtained by electron cryo-microscopy of biomolecules can be reconstructed to three-dimensional biological models at sub-nanometer resolution. These models allow answering urgent problems in life science, for instance, the pathways directing the self-recovery system of cell, which certainly has great significance for all our lives. To determine these models, there are two main electron microscopic methods available, corresponding to its two main modes of operation: 3DEM single particle reconstruction and electron diffraction. This thesis focuses on the research and methods of 3DEM and electron diffraction, and its practical application in solving the structure of a 50S ribosomal complex, which clarifies the mechanism of cell recovery in heat shock stress. Preliminary research on a novel structure determination method by using nano-crystals resulted in a novel software suite __ EDiff __ which is a program for unit cell parameter determination, indexing and so on. Show less
