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Carbon Nano-Materials Design and Related Physical Studies

Author: WangYin
Tutor: NingXiJing
School: Fudan University
Course: Atomic and Molecular Physics
Keywords: nano-materials design nano physics global optimization carbon clusters monatomic carbon chains time-going-backward quasi-dynamics method
CLC: TB383.1
Type: PhD thesis
Year: 2010
Downloads: 289
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Abstract


Traditionally, new materials are always proposed by a method like cooking, i.e., extensive experiments with different conditions are performed to occasionally encounter new materials with novel properties. During the past two decades, similar methods have also been used in the research of the nano-materials, whose sizes in at least one dimension are less then 100 nm. With the development of the computational abilities, new materials with fascinating properties are widely predicted nowadays via modern physical theories. However, some essential problems still remain unsolved:1. How to find the best condition for fabricating nano-materials with desired structures and properties? 2. How long can nano-materials with definite atomic configuration survive at room temperature? 3. How to find the most stable isomer and the most probable product isomers formed in a real growth process? If these problems can be solved theoretically, nano-materials with desired structure and properties can be easily produced.Considering that carbon is a dramatic chemical element with rich bond types and can form the most kinds of materials. We took the carbon nano-materials design as examples, with concentrating on the above three problems, performed the following theoretical work:An experimental method to prepare large carbon clusters with uniform sizes from small ones is proposed. Molecular dynamics simulation results show that clusters with uniform sizes can be prepared and their structures are mainly dependent on temperatures. Experimental methods were also proposed to prepare long monatomic carbon chain from graphene, to prepare doped carbon chains and to connect nanostructures on surfaces with carbon chains, these proposals are test by three kinds of molecular dynamic simulations based on Brenner potential, tight-binding method and Car-Parrinello method. Simulation results show that monatomic carbon chain with more than 100 atoms, which is significantly longer than the current existing monatomic carbon chains.A time-going-backward quasi-dynamics method is developed for global optimization of cluster structures. The most stable isomers of of Lennard-Jones cluster containing 38 atoms and the C60 cluster with Brenner potential can be easily obtained by this method. For small carbon clusters Cn (n=21-30), most of the potential energies optimized by this method are much lower than those obtained by a genetic algorithm [Chem. Phys. Lett.,364 213,2002]. Besides, the most probable isomers in the cluster growth process can also be obtained by this method.Developed a statistical model to predict the time it takes for a small cluster to transform from on isomer to another and the life time of monatomic carbon chain. Using this method, the transforming time between isomers at room temperature is calculated, deducing that the distribution of isomers at room temperature are similar to the distribution with equilibrium at high temperatures; the life time of carbon at room temperature is also calculated, indicating that carbon chain is very stale at room temperature.

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