Oeiras R Y, da Silva E Z
Institute of Physics "Gleb Wataghin", University of Campinas-Unicamp, 13083-859 Campinas, SP, Brazil.
J Chem Phys. 2014 Apr 7;140(13):134703. doi: 10.1063/1.4869858.
Carbon linear atomic chains attached to graphene have experimentally been produced. Motivated by these results, we study the nature of the carbon bonds in these nanowires and how it affects their electrical properties. In the present study we investigate chains with different numbers of atoms and we observe that nanowires with odd number of atoms present a distinct behavior than the ones with even numbers. Using graphene nanoribbons as leads, we identify differences in the quantum transport of the chains with the consequence that even and odd numbered chains have low and high electrical conduction, respectively. We also noted a dependence of current with the wire size. We study this unexpected behavior using a combination of first principles calculations and simple models based on chemical bond theory. From our studies, the electrons of carbon nanowires present a quasi-free electron behavior and this explains qualitatively the high electrical conduction and the bond lengths with unexpected values for the case of odd nanowires. Our study also allows the understanding of the electric conduction dependence with the number of atoms and their parity in the chain. In the case of odd number chains a proposed π-bond (MpB) model describes unsaturated carbons that introduce a mobile π-bond that changes dramatically the structure and transport properties of these wires. Our results indicate that the nature of bonds plays the main role in the oscillation of quantum electrical conduction for chains with even and odd number of atoms and also that nanowires bonded to graphene nanoribbons behave as a quasi-free electron system, suggesting that this behavior is general and it could also remain if the chains are bonded to other materials.
实验上已经制备出了附着在石墨烯上的碳线性原子链。受这些结果的启发，我们研究了这些纳米线中碳键的性质及其对电学性质的影响。在本研究中，我们研究了具有不同原子数的链，并且观察到具有奇数个原子的纳米线呈现出与具有偶数个原子的纳米线不同的行为。以石墨烯纳米带作为引线，我们确定了这些链在量子输运方面的差异，结果是偶数和奇数编号的链分别具有低和高的电导率。我们还注意到电流与线尺寸的依赖性。我们结合第一性原理计算和基于化学键理论的简单模型来研究这种意外行为。从我们的研究来看，碳纳米线的电子呈现出准自由电子行为，这定性地解释了高电导率以及奇数纳米线情况下具有意外值的键长。我们的研究还使得能够理解电导率与链中原子数及其奇偶性的依赖性。在奇数链的情况下，一个提出的π键（MpB）模型描述了不饱和碳，这些不饱和碳引入了一个可移动的π键，极大地改变了这些线的结构和输运性质。我们的结果表明，键的性质在具有偶数和奇数个原子的链的量子电导振荡中起主要作用，并且与石墨烯纳米带键合的纳米线表现为准自由电子系统，这表明这种行为是普遍的，并且如果这些链与其他材料键合，这种行为也可能保留。
