Atomic structures of carbon nanomaterials studied by coherent electron diffraction

Electron diffraction;Carbon nanomaterials;Atomic structure;Carbon nanotube;Graphene;Nanodiamond

Zhang, Jiong

关键词: Electron diffraction;    Carbon nanomaterials;    Atomic structure;    Carbon nanotube;    Graphene;    Nanodiamond;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/24515/Zhang_Jiong.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Carbon has an amazing number of different structural forms because of the versatility of its chemical bonds, which put it among the most extraordinary and complex of elements in materials science. Carbon readily forms nanostructures or nanoforms. The allotropes of carbon nanoforms, including graphene, carbon nanotube (CNT), fullerene and nanodiamond, have opened up many opportunities in nanotechnology, and their importance has been highlighted with two Nobel Prizes awarded to fullerene in 1996 and graphene in 2010. However, structural characterization of carbon nanoforms still remains as a difficult challenge in carbon nanoscience. Electron diffraction probes the local structure with electrons interacting with matters much more strongly compared to other structural probes. This thesis reports an investigation of atomic structures of various carbon nanoforms including graphene, CNT and nanodiamond using electron diffraction techniques. The major findings are summarized below.In a multi-walled carbon nanotube (MWCNT), quantitative electron diffraction analysis reveals significant differences between the measured and the ideal tube diameter calculated based on the 1.421 Å carbon-carbon bond lengths. The results indicate that on average there are three different bond lengths in chiral walls and two different bond lengths in achiral due to the bending effect of the curvature of the CNTs. Furthermore, in-situ heating experiment of the same MWCNT shows large thermal contractions for all the walls of the MWCNT, and the coefficient of radial thermal contraction has strong diameter dependence.Electron diffraction evidences also suggest that the CNTs deviate from the ideal smooth tubular structure. Using a larger diameter CNT inside a MWCNT, I showed that the tube is corrugated and investigated the nature of the corrugations with temperature dependent electron diffraction. By measuring the atomic corrugations along the tube radial direction at different temperatures, I detected a thermal dynamical contribution to the atomic corrugations, which changes from ~0.2 Å at 297 K to 0.4 Å at 1073 K and there is also a large static corrugation at ~0.2 Å. The thermal displacements follow the Debye model with a Debye temperature of 284 K, which is an important parameter for understanding the thermal properties of CNTs.Graphene can be folded to create the folded structure with mechanical and electronic properties very different from the two-dimensional graphene sheet. The physics of graphene folding was investigated by the combined experimental, theoretical and simulation studies. The importance was demonstrated in understanding the stability of graphene folded edges. Through a statistical measurement of the structure of folded edges of graphene by electron diffraction, we found that free suspended graphene sheets tend to fold along armchair and zigzag directions. The preference was explained by considering the energetics of graphene folding and atomic simulation. The zigzag edge has AB stacking, while in the armchair edge, AB stacking is achieved in some areas by a small twist.The atomic structure of nanodiamonds synthesized by denotation method was studied by electron diffraction, imaging and spectroscopy. The results show that the detonation nanodiamonds have a majority of cubic diamond core smaller than the particle size. In addition, sub-ångström resolution of an individual nanodiamond was achieved bydiffractive imaging. The same particle was also tilted for stereo pair imaging with resolution improved by diffractive imaging, which provides a potential pathway to solve the three-dimensional structure of a single nanocrystal with atomic resolution.