Cross-plane transport in a single-molecule two-dimensional van der Waals heterojunction

Two-dimensional van der Waals heterostructures (2D-vdWHs) stacked from atomically thick 2D materials are predicted to be a diverse class of electronic materials with unique electronic properties. These properties can be further tuned by sandwiching monolayers of planar organic molecules between 2D materials to form molecular 2D-vdW heterojunctions (M-2D-vdWHs), in which electricity flows in a cross-plane way from one 2D layer to the other via a single molecular layer. Using a newly developed cross-plane break junction (XPBJ) technique, combined with density functional theory calculations, we show that M-2D-vdWHs can be created, and that cross-plane charge transport can be tuned by incorporating guest molecules. More importantly, the M-2D-vdWHs exhibit distinct cross-plane charge transport signatures, which differ from those of molecules undergoing in-plane charge transport

Heteroatom-Induced Molecular Asymmetry Tunes Quantum Interference in Charge Transport through Single-Molecule Junctions

We studied the interplay between quantum interference (QI) and molecular asymmetry in charge transport through a single molecule. Eight compounds with five-membered core rings were synthesized, and their single-molecule conductances were characterized using the mechanically controllable break junction technique. It is found that the symmetric molecules are more conductive than their asymmetric isomers and that there is no statistically significant dependence on the aromaticity of the core. In contrast, we find experimental evidence of destructive QI in five-membered rings, which can be tuned by implanting different heteroatoms into the core ring. Our findings are rationalized by the presence of antiresonance features in the transmission curves calculated using nonequilibrium Green’s functions. This novel mechanism for modulating QI effects in charge transport via tuning of molecular asymmetry will lead to promising applications in the design of single-molecule devices

Transition from tunneling leakage current to molecular tunneling in single-molecule junctions

数十年来，半导体工业一直遵循基于“摩尔定律”所设定的发展蓝图，逐步提升集成电路芯片上晶体管的集成度和运行速度，减小器件尺寸。为探索这一尺寸极限，课题组基于机械可控裂结技术自主开发了具有飞安级电学测量和亚纳米级位移控制灵敏度的科学仪器，在国际上首次获取了一系列具有不同重复单元的寡聚苯乙炔类分子电导随电极间距的演变关系，并发现随着电极间距的缩小，器件电输运由通过分子器件电流占主导逐步转变到由隧穿漏电流占主导。对于本研究中具有最小尺寸的寡聚苯乙炔分子器件，其由于隧穿漏电流所制约的尺寸极限可小至0.66 nm，预示了有机分子器件在未来电子器件小型化方面具有重要的应用潜力。 这一研究工作是在化学化工学院洪文晶教授、萨本栋微纳研究院杨扬助理教授以及英国Durham University的MartinR. Bryce教授共同指导下完成的。能源材料化学协同创新中心iChEM Fellow刘俊扬博士为论文第一作者，博士研究生郑珏婷、李瑞豪和硕士研究生黄晓艳、唐永翔、皮九婵、本科生王飞等参与了研究工作。田中群教授、毛秉伟教授和师佳副教授为论文工作提供了重要指导。【Abstract】The tunneling leakage current will be a major quantum obstacle during miniaturization in the semiconductor industry down to the scale of several nanometers. At this scale, to promote charge transport and overcome the tunneling leakage current between the source and drain terminals, molecular electronic junctions offer opportunities by inserting molecules between these two electrodes. Employing a series of oligo(aryleneethynylene) (OAE) molecules, here we investigate the transition from tunneling leakage current to molecular tunneling in the single-molecule devices using mechanically controllable break junction (MCBJ) technique, and the transition distances of the OAE molecular junctions were determined and even down to 0.66 nm for OAE2 molecular junction, which demonstrates that the intrinsic charge transport properties of a single-molecule device can be outstripped from the tunneling leakage current. Consequently, molecular electronic devices show the potential to push the ultimate limit of miniaturization to the scale of several angstroms.This work was supported by the National Key R&D Program of China (2017YFA0204902). This work was also generously supported by the Young Thousand Talent Project of China, the EC FP7 ITN “MOLESCO” project number 606728, the National Natural Science Foundation of China (nos. 21703188, 21673195, 21503179), and the China Postdoctoral Science Foundation (2017M622060). 该工作获得科技部国家重点研发计划课题（2017YFA0204902），国家自然科学基金委（21673195、21703188、21503179）以及中国博士后科学基金（2017M622060）等项目的资助，也得到了固体表面物理化学国家重点实验室、能源材料化学协同创新中心的支持

Transition from Tunneling Leakage Current to Molecular Tunneling in Single-Molecule Junctions

The tunneling leakage current will be a major quantum obstacle during miniaturization in the semiconductor industry down to the scale of several nanometers. At this scale, to promote charge transport and overcome the tunneling leakage current between the source and drain terminals, molecular electronic junctions offer opportunities by inserting molecules between these two electrodes. Employing a series of oligo(aryleneethynylene) (OAE) molecules, here we investigate the transition from tunneling leakage current to molecular tunneling in the single-molecule devices using a mechanically controllable break-junction technique, and the transition distances of the OAE molecular junctions were determined and even down to 0.66 nm for OAE2 molecular junction, which demonstrates that the intrinsic charge-transport properties of a single-molecule device can be outstripped from the tunneling leakage current. Consequently, molecular electronic devices show the potential to push the ultimate limit of miniaturization to the scale of several angstroms

Switching of Charge Transport Pathways via Delocalization Changes in Single-Molecule Metallacycles Junctions

To explore the charge transport through metalla-aromatics building blocks, three metallacycles complexes were synthesized, and their single-molecule conductances were characterized by using mechanically controllable break junction technique. It is found that the conductance of the metallacycles junction with phosphonium group is more than 1 order of magnitude higher than that without phosphonium group. X-ray diffraction and UV–vis absorption spectroscopy suggested that the attached phosphonium group makes metallacycles more delocalized, which shortened the preferred charge transport pathway and significantly enhanced the single-molecule conductance. This work revealed that the delocalization of metalla-aromatics could be used to switch the charge transport pathway of single-molecule junctions and thus tune the charge transport abilities significantly