Limburg Bart, Thomas James O, Sowa Jakub K, Willick Kyle, Baugh Jonathan, Gauger Erik M, Briggs G Andrew D, Mol Jan A, Anderson Harry L
Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, UK.
Nanoscale. 2019 Aug 8;11(31):14820-14827. doi: 10.1039/c9nr03754c.
The electronic and magnetic properties of single-molecule transistors depend critically on the molecular charge state. Charge transport in single-molecule transistors is characterized by Coulomb-blocked regions in which the charge state of the molecule is fixed and current is suppressed, separated by high-conductance, sequential-tunneling regions. It is often difficult to assign the charge state of the molecular species in each Coulomb-blocked region due to variability in the work-function of the electrodes. In this work, we provide a simple and fast method to assign the charge state of the molecular species in the Coulomb-blocked regions based on signatures of electron-phonon coupling together with the Pauli-exclusion principle, simply by observing the asymmetry in the current in high-conductance regions of the stability diagram. We demonstrate that charge-state assignments determined in this way are consistent with those obtained from measurements of Zeeman splittings. Our method is applicable at 77 K, in contrast to magnetic-field-dependent measurements, which generally require low temperatures (below 4 K). Due to the ubiquity of electron-phonon coupling in molecular junctions, we expect this method to be widely applicable to single-electron transistors based on single molecules and graphene quantum dots. The correct assignment of charge states allows researchers to better understand the fundamental charge-transport properties of single-molecule transistors.
单分子晶体管的电学和磁学性质严重依赖于分子电荷态。单分子晶体管中的电荷输运以库仑阻塞区域为特征，在这些区域中分子的电荷态是固定的且电流被抑制，它们被高电导的顺序隧穿区域分隔开。由于电极功函数的变化，通常很难确定每个库仑阻塞区域中分子物种的电荷态。在这项工作中，我们提供了一种简单快速的方法，通过观察稳定性图高电导区域中电流的不对称性，基于电子 - 声子耦合的特征以及泡利不相容原理，来确定库仑阻塞区域中分子物种的电荷态。我们证明以这种方式确定的电荷态分配与从塞曼分裂测量中获得的结果一致。与通常需要低温（低于4K）的磁场相关测量不同，我们的方法在77K时适用。由于电子 - 声子耦合在分子结中普遍存在，我们预计这种方法将广泛适用于基于单分子和石墨烯量子点的单电子晶体管。电荷态的正确分配使研究人员能够更好地理解单分子晶体管的基本电荷输运性质。
