Effects Of Oxygen-containing Functional Groups On Transport Properties Of Graphene Nanoribbons

The effects of oxygen-containing functional groups on the electronic transportproperties in one-dimensional carbon nanotube and graphene nanoribbons areinvestigate by using the density functional theory in combination with thenonequilibrium Green’s function method. Our results indicate that the electronictransport of carbon nanotubes and graphene nanoribbons is significantly affected bythe oxygen-containing functional groups. It is an effective approach to modulate theelectronic properties by oxidization with rational design. Our works offer usefulinformation for designing tunable nanoscale devices on the basis of carbon nanomaterials. The primary coverage of this dissertation is as follows:(1) The electronic structures and transport properties of (10,0) single-walled carbonnanotube ((10,0)(SWNT)) with oxygen-containing defect complex are investigated.The complex delocalizes the local states of (10,0) SWNT induced by mono-anddi-vacancy but strengthens the localization of the states induced by the Stone-Walesdefect. As a result, the complex partially restores the transmission of (10,0) SWNTwith vacancies, but reduces the transmission of (10,0) SWNT with Stone-Walesdefects. However, the oxygen-containing defect complex only slightly influences thetransmission gap and threshold voltage of the system.(2) We have investigated the transport properties of zigzag-edged graphenenanoribbons (ZGNRs) with oxygen edge decoration (passivated by the ketone (C=O)or ether (C-O-C), denoting as ZGNR-CO and ZGNR-C2O, respectively). We find thatboth ZGNR-CO and ZGNR-C2O induce the semiconductor-metal transition andenhance the transmission conductance within ‘transparent’ electrodes. However, whensandwiched by Au (111) electrodes, Au|ZGNR-CO|Au enhances the transport whileAu|ZGNR-C2O|Au depresses the transport in comparison with Au|ZGNR-H|Au. It isfound that the transport properties of the edge oxidized ZGNRs within Au (111)electrodes depend on the electronic states around the Fermi level which determine thenumber of the effective transport channels. The states of Au|ZGNR-CO|Au aredelocalized on the edge oxygen atoms as well as the inner edge carbon atoms,introducing extra transport channels. Moreover, in comparison with Au|ZGNR-H|Au,the effective transport channels of Au|ZGNR-CO|Au increase at given applied bias.However, the states of Au|ZGNR-C2O|Au are localized on the ribbon, blocking theeffective transport channels.(3) The transport properties of the junction assembled by zigzag graphenenanoribbons (ZGNRs) and Au electrode (Au/ZGNR) are investigated. It is found thatthe Au/ZGNR junctions behave as a typical diode with Schottky barrier at the contact.Our results indicate that although the oxidization at the contact slightly influences theSchottky barrier, the I-V characteristic is effectively modulated. Such effect derivesfrom the impact of the oxidization on the coupling between the ZGNRs and Auelectrode.(4) The effects of edge oxidization on electronic transport properties of zigzag graphene nanoribbons (ZGNRs) with local strain are investigated. We apply localaxial compression and local transverse stretch, related to the deformation of zigzag-and armchair-direction, respectively. The quantum calculation indicates that theelectronic transport of7ZGNR-H is robust but that of both7ZGNR-CO and7ZGNR-C2O are suppressed with the increase of local strain. The edge oxidization ofC=O still enhances electronic transport within the local strain because local strainhardly disturbs the local states around the Fermi level, but the edge oxidization ofC-O-C effectively depresses the electronic transport of ZGNRs since the states aroundthe Fermi level become uniform on the ribbon and are sensitive to the local strain.(5) The transport properties of zigzag graphene nanoribbons (ZGNRs) decorated bycarboxyl group (OH) chains are systematically investigated. ZGNRs with nine zigzagcarbon chains (9ZGNR) decorated by mOH(m is the number of oxidized carbonchains) are taken as typical systems. We find that the OH chains can effectivelymodulate the electronic structures and transport properties of the9ZGNR. Thesystems behave as metal when m≤4, and a transmission plateau up to6G0is foundaround the Fermi level when m=3. However, the9ZGNR-mOH systems becomesemiconductors when m>4. Interestingly,9ZGNR-7OH and9ZGNR-8OH behave asn-type semiconductors. It is found that such modulation depends on the edge states aswell as the oxygen atoms at the interface. When the width of undecorated carbonregions is smaller than3, Peierls instability induces the metal-semiconductortransition.