First-principles Study Of The Physical Properties For Graphyne Nanotubes And Graphene Nanomeshes

Since the discovery of nanomaterials, scientists have found out that carbonnanomaterials possess unique physical properties. Carbon nanomaterials have attracted agreat deal of attention due to their excellent properties that is highly expected to beapplied in practical applications. The Graphene and Graphyne are new allotrope ofcarbon and they were discovered by researchers very recently. The Graphyne nanotubes(GNTs) and Graphene nanomeshes (GNMes) have stimulated considerable experimentaland theoretical researches because of their particular physical properties. In addition, thestudy of their properties not only has important basic scientific significance but also hasapplication value. In this thesis, we have calculated the electronic and mechanicalproperties of GNTs. We have focused on the magnetic and electronic properties ofGNMes with the purpose of regulating the band gap of Graphene and exploring thesource of its magnetism.In this paper, first principles calculations were carried out to evaluate the physicalproperties of GNTs and GNMes, and the main results and conclusions are summarized asfollows:1. The electronic structure and mechanical property of various diameters zigzag andarmchair GNTs have been investigated. The calculation indicated that: GNTs aresemiconductors with the direct band gap in the range of0.40eV~1.3eV. Due to curvatureeffects, the band gap decreases with the increase of GNTs’ diameters. The calculatedYoung’s modulus of GNTs is between0.44and0.50Tpa. For zigzag GNTs, the Young’smodulus decreases with the increases of tube diameter while increase as tube diameterincreases for armchair GNTs.2. The effect of defects on the band structure and magnetic property of GNMes havebeen calculated. Our results show that: we can classify the GNMes into nonmagneticones and magnetic ones depending on the unit cell that has or not has an equal number ofcarbon atoms on corresponding sublattices. Graphene consists of two atomic sublatticesof A and B, Na (Nb) is the number of carbon atoms of A and B. If Na is not equal to Nb,the GNMes have nonzero global magnetic moment and local mognetic moment. Theglobal magnetic moment and local moment are zero, when Na is equal to Nb. For the nonmagnetic GNMes, increasing the distance between neighbor defects with the fixedhole geometric structure causes the GNMes to vary from semimetal to semiconductorwith a periodicity of three. Both the quantum confinement and nanoscale patterning playan important role in determining the electronic properties of GNMes.