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First-principles Studies And Designs Of Nano Materials And Devices Based On Carbon

Posted on:2010-05-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y F P OuFull Text:PDF
GTID:1101360278457306Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
By performing first-principles electronic structure and transport quantum calculations,we have demonstrated the electronic structure and transport properties of several carbon-based nano-materials.Several carbon-based device design proposals are presented after our theoretical calculations.Firstly,we have investigated the electron transport properties across an all carbon molecular junction based on Fulleren molecules(C20/C70 or C20 chain),connecting with two single wall carbon nanotubes.It is shown that the Landauer conductance of this system can be tuned within several orders of magnitude not only by varying the electrode-molecule distance and changing the orientation of the molecule,but also by rotating one of the tubes around the symmetry axis of the system.This fact could make this pure-carbon molecular system a possible candidate for a nano-electronic switching device.Moreover,our results reveal that molecular configuration selection, structure relaxation and doping would play important roles in such device designs.Secondly,we have systematically explored the basic electronic and transport properties of graphene nanoribbons,and the effects of edge-vacancy defects, divacancies defects and gas adsorption at divacancies defects are focused on.It is discovered that the concentration,position and orientation of the defects impact energy band structure and transport properties.The physical origin may be that the defects change the geometric structure and destroy the symmetry of the ribbons, contributed to the effect of quantum scale too.Further study shows it is more stable for gases to attach to the ribbon at divacancies defects from the perspective of the energy,conforming to the experiment results.Thirdly,we have investigated the chemical functionalization of semiconducting graphene nanoribbons(GNRs) with Stone-Wales(SW) defects by carboxyl(COOH) groups,and it is the fact that functionalizated defective GNRs will be a possible candidate for chemical sensors in the future.It is found that the geometrical structures and electronic properties of the GNRs changed significantly by the interactions between SW defects and carboxyl groups.With the increase of the axial concentration of SW defects COOH pairs,electrical conductivity of the system could be considerably enhanced and the system would transform from semi-conducting behavior to p-type metallic behavior finally.Finally,two kinds of T structure and cross-bar structure junctions based on GNRs have been designed,and the intrinsic electronic transport properties and effective boron(or nitrogen) doping of these junctions have been demonstrated.It is found that the electronic transport characteristics of the junctions very sensitively depends on their own geometric features including their chirality,length and the width and height of the branches.These intrinsic features could make such quasi-2D junction a possible candidate for nanoelectronic devices in which conductivity can be controlled.
Keywords/Search Tags:carbon-based nano-materials, First-principles, Fulleren, carbon nanotubes, graphene nanoribbon, nanoelectronic switch, the effect of defects, chemical functionalization, material design, device design
PDF Full Text Request
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