二维Dirac电子材料纳米电极有机分子结界面构建与功能机理研究

In devices of structural controllable and being assembly cut organic molecule(s) with long spin life-time, the nature of the electrode materials used as well as the electrode-molecule interface is an important issue in the electron injection and transport property through the devices. Because of the difficult on the determination of the interfacial configuration between a conventional bulky metal and molecules in experiments, the result is not reproducible and comparable with that of the theoretically calculated one. However, the recent experimentally fabricated monolayers of graphene, silicene and phosphorene, as well as the corresponding nanoribbons have Dirac electronic properties with planar structure, high electron mobility, long coherence length, adjustable electronic structure, and determinable interfacial configuration with organic molecules. Based on our previous research experiences, this project is devoted to explore the scientific problems in construction of organic molecular devices with these Dirac material nanoelectrodes and their functionality and mechanism. By the first-principles calculations based on DFT+NEGF combined with the TB and covalent bond theory, we will study the topological edge states and band gaps of electronic structure and their manipulation via chemical modification and external fields for the electrodes, the interfacial configuration and strong/weak coupling between the molecule and electrode, with which may results in spin- and valley-dependent molecular energy level shifting and widening, the matching of molecular frontal orbital with electrode Fermi surface resulting in adjustment to the injected spin- and valley-polarization and transport, the molecular structural reconstruction as electron passing through, etc. In the view point of materials for molecular devices, the project proposals more selectable new electrode materials for the construction of molecular devices and understanding the associated principles. Further, it may provide a material fundamental with physical supporting for the Dirac material nanoelectrode molecular spin/valley devices with novel functionalities.

结构可控、可组装裁剪和较长自旋寿命的分子器件中，电极材料本身以及与分子界面性质对电子的注入与输运至关重要，常规金属体电极与分子接触界面实验上难以控制使结果重复性差难与理论计算比较, 而近年相继成功制备的石墨烯及硅烯、磷烯等二维结构与分子界面构型确定，且具有Dirac电子迁移率高、相干长度大、电子结构易调控等特点。基于我们前期研究基础，本项目探索这些材料纳米电极有机分子结的构建及功能与机理等科学问题。拟用基于密度泛函与非平衡格林函数的数值计算和紧束缚、价键理论与量子主方程解析分析相结合的方法，研究纳米电极拓扑边缘态、能隙等电子结构及其化学修饰与外场调控，电极-分子界面构型与成键性质、耦合对分子能级的展宽与移动、分子结构重整及前沿轨道与电极费米面附近能级的匹配，自旋/谷电子输运及随界面与分子长度的变化规律。该类研究有可能展现一些区别于金属电极分子结的新效应，为设计新颖分子电子器件提供物理基础。

分子器件有结构可控、可组装裁剪和较长自旋寿命的特点，而但电极材料本身以及与分子界面性质对电子注入与输运至关重要。金属体电极与分子接触界面实验上难以控制使结果重复性差难与理论计算比较, 近年相继成功制备的石墨烯及磷烯等二维材料与分子界面构型确定，且具有迁移率高、相干长度大、电子结构易调控等优点。本项目用基于密度泛函理论与非平衡格林函数数值计算和紧束缚解析分析相结合，主要研究了类石墨烯Dirac二维材料纳米结构，二维材料纳米电极与有机分子耦合界面的理论计算和二维材料纳米电极有机分子结输运性质及调控等几个问题。在黑磷烯纳米结构研究方面取得了较重要进展，采用手征(或螺旋)数/角/矢量，系统地表征了黑磷烯投影到平面上的晶向，预测了除常规锯齿和扶手椅边缘外的其它可能稳定存在的边缘形貌及其边缘态；对所有归纳出的锯齿类边缘条带，进一步发现宽度包含原子链数的奇偶性与镜面对称性的关系，以及决定两类不同边缘态特点和对外场不同的响应规律；发现两类中的“梭子”形边缘态是二重简并的，分属实空间不同边缘上下子层原子贡献，所以该简并可施加平面内电场解除，并提出了以两边缘子层设计场效应管的设想。还预计了锯齿边缘墨磷纳米条带（ZPNR）与有机分子界面单键和双键连接耦合的本质差异，发现双键结在低偏压0.08 V位置展现明显的负微分电阻效应，这是由于ZPNR在费米能级附近的边缘态与分子能级的特殊匹配产生，但是单键耦合不存在这种匹配。在此基础上，进一步获得了输运特性符合与电极材料性质无关但随分子长度指数衰减的规律，但指数衰减因子不但与电极材料类型有关（如金、石墨烯等），还与分子与电极的连接耦合方式（如键、晶向及相互取向等）密切相关。这一结果为分子电子器件的设计提供了精细的理论参考指导。