点缺陷对碳管-石墨烯纳米带异质结自旋电子学特性的影响机制研究

The quasi one dimensional (1D) carbon-based nanomaterials, such as carbon nanotube (CNT) and graphene nanoribbon (GNR), are widely regarded as the most promising candidates to make next generation electronic devices because of their novel electronic structure and outstanding transport properties. As is well known, the presence of various types of disorder during preparation is generally inevitable. The physical mechanism for spin-dependent characteristics influenced by the disorder is emerging as the key issue and of significance for the practical applications of nanodevices in the field of spintronics. We propose the heterojunction model constructed by the organic combination of CNT and GNR as the components for spintronics on the basis of recent experimental progresses and theoretical demonstrations. In order to effectively modulate the spin-dependent characteristics of the heterojunction, we will take full advantage of vacancy defects, heteroatoms as well as microstructural defects. As a consequence, the influence of point defects on the spin-dependent characteristics is becoming one of the most crucial theoretical problems that need to be addressed. This project is devoted to the comprehensive prediction of spin-dependent electronic transport properties of CNT-GNR heterojunction with different chiralities by further developing the technique that making use of density functional theory combined with non-equilibrium Green's function. Taken the influences of bend on the interactions between heterojunction and the electrodes into account, our theoretical investigations are dedicated to the fundamental understanding of the physical mechanism, and eventually establishing the parameter system to effectively control the spin-dependent characteristics of the nanodevices by point defects, which is of vital importance to the building of the novel nanodevices for spintronics and able to provide the theoretical basis as well as accurate performance prediction method.

准一维碳基纳米材料，特别是碳纳米管和石墨烯纳米带，因其独特的电子结构和优异的电子输运特性而被广泛地认为是制造新型自旋电子器件的理想材料，但实验制备中难以避免各种无序的产生，无序对电子自旋特性影响的物理机制成为自旋电子学器件实用化的关键课题。本项目根据当前的理论和实验研究结果，提出将两种准一维碳纳米材料有机地结合形成碳纳米管-石墨烯纳米带异质结构作为自旋电子学基础性器件，充分利用异质原子和空位缺陷两类点缺陷微结构更加有效地调控异质结的自旋电子学特性。因此，探索点缺陷对异质结自旋电子输运特性的影响机制成为一个亟待解决的重要理论课题。本项目采用密度泛函理论结合非平衡格林函数方法进一步发展对不同手性异质结构的自旋电子输运性能的预测,考虑弯折对异质结构和电极之间相互作用的影响，最后确立点缺陷对异质结构自旋电子输运性能影响的物理机制和参数调控体系，为新型自旋纳米电子器件设计提供理论依据和性能预测方法。

以碳纳米管和石墨烯纳米带为代表碳基低维纳米材料，因其独特的电子结构和优异的电子输运特性而被广泛地认为是制造新型自旋电子器件的理想材料，本项目提出充分利用异质原子和空位缺陷两类点缺陷微结构更加有效地调制异质结的自旋电子学特性，研究了异质结的形成机制和异质结对电子输运性质的影响机制。我们探索了两种类型的缺陷分布结构，发现在原子弛豫后在中间区域分别形成了对称和非对称性的异质结，异质结的形成提供了催化活性位，有利于碳纳米管的展开形成石墨烯纳米带。研究发现对称性的扶手椅型和对称性的锯齿型碳纳米管表现出不同的电子输运特性，这是由偏压打开更多的电子输运通道和轨道错位引起的电子输运抑制两个因素的竞争决定的。磁性原子掺杂结合双原子空位缺陷复合结构对体系的结构修饰可以调制电子能带结构成为半金属。研究发现空位缺陷结构和异质掺杂能够促进碳纳米管和石墨烯进行较为紧密的共价键连接，缺陷微结构的引入为功能化修饰提供了可能，具有较大潜力实现自组装连接。研究了点空位缺陷和点掺杂缺陷对石墨烯碳纳米管异质结稳定性的影响，发现对石墨烯碳纳米材料进行直接异质掺杂和吸附来实现对自旋电子输运性能的有效调控非常困难，但在空位缺陷和STW拓扑缺陷等结构畸变存在的情况下，不仅硼氮氧更易于掺入其中形成稳定结构。我们还对势函数进行了优化，为多尺度模拟计算提供了方便，针对不同的研究体系采用不同精度的势函数描述可以提高数值计算工作效率。此外，我们设计了锗基二维自旋电子学器件材料，在较小偏压下该器件的理论磁阻可达107，它的基本物理机制为铁磁状态下的输运开启和反铁磁下的自旋电子学输运抑制。研究了锗基五元环材料结构的稳定性和电子结构基本特性和砷基二维纳米材料的拓扑电子学特性。研究结果揭示了采用化学基团或小分子功能化的方法来调控低维材料的自旋电子态基本特性实现其在自旋电子学领域的应用是比较可行的方法。