First-Principles Studies of Metal-Carbon Nanotube Systems

This dissertation, "First-principles Studies of Metal-carbon Nanotube Systems" by Houlong, Zhuang, 庄厚龍, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstracts of thesis entitled FIRST-PRINCIPLES STUDIES OF METAL-CARBON NANOTUBE SYSTEMS Submitted by Zhuang Houlong for the degree of Master of Philosophy at The University of Hong Kong August, 2007 Carbon nanotubes (CNTs) have attracted considerable attention as promising materials for applications in Nano-Electro-Mechanical systems, CNT-based composites and next generation electronic devices. To explore the full potential of CNTs, it is important to understand their intrinsic mechanical and electronic properties when they are functionalized by external materials such as metal coverage of CNTs. In reality, CNTs will have intrinsic defects such as Stone-Wales defects, single vacancy and its derivative point defects. Defects in CNTs have been reported to affect not only mechanical properties but also electronic, magnetic and hybridization characteristics. In this thesis the role of single vacancy defect in CNTs is investigated in details, using spin density functional theory. We first investigate the adsorption of 3d transition-metal atoms on the defective (5, 5) CNT. The binding energies between CNT and transition metals are found to be significantly enhanced when vacancy defects are introduced into the CNT. The results also indicate that the 3d transition-metal atoms acting as substitution defects can substantially modify the electronic structure of CNTs. Stable CNT-metal systems could therefore become promising engineering materials in many fields such as CNT devices for various spintronics applications and CNT metal-matrix composites. We then study the coupling effects of magnetic and mechanical properties of defective (5, 5) CNT. The failure stress, strain, and Young's modulus are quantitatively calculated. Magnetic moment and tensile strain show an interesting relationship. Analysis of electronic structure indicates that the reconstructed "perpendicular" bond attributes to the strong dependence of magnetic properties on mechanical deformation. These results show that the CNT-metal systems could be used as NEMS devices. Finally, to explore the potential applications of CNT-metal system as junctions in nanoelectronics, we study the contact properties between semiconducting double wall carbon nanotube (DWCNT) and palladium. The DWCNT-Pd system has been considered as a nano-sized field-effect transistor (FET). We obtain the stable atomic geometry and analyze the corresponding electronic structures. It is found that shell interactions between the inner wall and outer wall could narrow the overall band gap of either (8, 0) or (17, 0) nanotube, but the inner wall is screened by an outer wall when contacted with Pd, and has a negligible effect on field-effect characteristics. This is consistent with experimental measurement. We also study the Schottky barrier at the metal/DWCNT junction. (377 words) Zhuang Houlong DOI: 10.5353/th_b3939578 Subjects: Carbon Nanotubes Density functionals