【作者】 张春小；

【导师】 钟建新；

【作者基本信息】 湘潭大学 ， 凝聚态物理， 2012， 博士

【摘要】 本文结合密度泛函理论与非平衡格林函数方法，系统研究了氧化对一维碳纳米管和石墨烯纳米条带电子输运性质的调制效应，同时研究了在金属电极条件下石墨烯纳米条带的电子输运性质。我们的研究为一维碳纳米材料在纳米器件中的应用提供了理论基础，本论文的主要结论包括：（1）研究了(10，0)单壁碳纳米管（SWCNT）的本征缺陷与氧分子（O2）耦合形成的缺陷复合体对纳米管电子结构和电子输运的调制效应。结果表明，缺陷复合体能够部分的修复空位引起的电子态局域，但是增强了Stone-Wales缺陷造成的电子态局域。因此，氧化提高了空位缺陷SWCNT的传输电导，但是压制了Stone-Wales缺陷SWCNT的传输电导。我们的研究还表明缺陷复合体几乎不影响纳米管的传输带隙和开启电压；（2）我们研究了边缘氧化对锯齿型石墨烯纳米条带（ZGNRs）电子输运的调制效应。研究中我们考虑了两种含氧官能团C=O（ZGNR-CO）和C-O-C（ZGNR-C2O）。我们发现：在透明电极条件下两种含氧官能团都能提高ZGNRs的传输电导。但是，在金电极的情况下，与Au|ZGNR-H|Au相比Au|ZGNR-CO|Au的电子传输得到增强而Au|ZGNR-C2O|Au的电子传输受到抑制。这是因为在Au|ZGNR-CO|Au系统中，边缘氧化不但保持了原有边缘C原子上的传输通道而且引入了新的有效传输通道，从而带来传输增益。而Au|ZGNR-C2O|Au在费米能级附近的电子态局域在纳米带上，阻断了电子传输通道，压制了器件的电输运；（3）研究了氧化对金电极与ZGNRs形成的器件结的电子输运的影响。我们发现因为在结处形成了肖特基势垒，所以Au/ZGNRs表现出典型的二极管整流特征。尽管结氧化对肖特基势垒的影响很小，但是结氧化影响了ZGNRs与Au电极间的耦合所以调控了器件结的I-V特性；（4）我们研究了局部应变对边缘ZGNRs电子传输的调制。结果表明:局部应对ZGNR-H的电子传输的影响非常微弱，但对边缘氧修饰的ZGNRs（ZGNR-CO和ZGNR-C2O）的电子输运的影响非常明显。由于局部应变很难扰动ZGNR-CO费米能级附近的电子态，所以相比于ZGNR-H，ZGNR-CO在局部应变条件下增强了电子传输；但是ZGNR-C2O随局部应变的增强电子传输逐渐被抑制，这是由于C-O-C使得费米能级附近的电子态离域在整个纳米带上，而局部应变造成了此电子态的局域从而阻断电子通道；（5）我们提出了通过羧基（OH）链表面修饰调制ZGNRs电子输运的方案。OH链修饰于ZGNRs上下表面形成的石墨烯纳米带氧化物（ZGNR-mOH，m表示被OH链修饰的碳链条数）。羧基链修饰能够有效的调制ZGNRs的电子结构及电子输运特性。在特征体系9ZGNRs中，当m≤4时9ZGNR-mOH表现出金属特性，这其中当m=3时，系统在费米能级附近出现6G0的传输平台。但是当m>4时，9ZGNR-mOH转变为半导体特性。特别是9ZGNR-7OH和9ZGNR-8OH表现为n型半导体。ZGNR-mOH的电子输运性质依赖于边缘态及界面态。当未被修饰的碳区域的宽度小于3条碳链时，派尔斯畸变引起了金属-半导体转变。更多还原

【Abstract】 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.更多还原