Quantum interference has been intensively pursued in molecular electronics to investigate and utilize coherent electron transport at the ultra-small level. An essential type of quantum interference with drastic destructive-constructive switching, known as Fano interference, has been widely reported in various kinds of nanoelectronics electronic systems, but not yet been electrostatically gating in a single-molecule device. Here, we fabricate the three-terminal single-molecule transistors based on the molecule with a long backbone and a side group to demonstrate the gate-controllable Fano interference. By applying bias and gate voltages, the two-dimensional differential conductance map shows the noncentrosymmetrical Fano patterns. Combined with the electron transport model and the first principles calculations, the resonant parameters of the Fano interference can unveil the coupling geometry of the junction and the spatial distribution of the resonant states. Our findings provide an instrumental method to induce and utilize the quantum interference behaviours at the molecular level.
Haohan Li, Mykola Telychko, Linwei Zhou, Zhi Chen, Xinnan Peng, Wei Ji, Jiong Lu & Kian Ping Loh
Abstract
Formation of a two-dimensional (2D) supramolecular self-assembly and a 2D organometallic framework derived from a brominated N-heterocyclic aromatic molecule (4Br-TAP) on Au(111) and Ag(111) substrates were studied using chemical bond-resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (ncAFM) techniques combined with density functional theory (DFT) calculations. The 4Br-TAP-based 2D molecular framework on Au(111) is constructed by diverse Br···Br and Br···N noncovalent interactions, which are resolved with sub-angstrom resolution using combined STM and ncAFM imaging with a CO-functionalized tip and further quantified using DFT calculations. The distortion of molecular backbones, triggered by a highly nonuniform bonding environment, leads to lifting of the degeneracy of the intrinsic resonance structures of tetraazapyrene (TAP) moieties and emergence of two chiral Kekulé-like structures. In contrast, debromination of 4Br-TAP on Ag(111) leads to the formation of an ordered 2D organometallic framework linked by C–Ag–C bonds. Our results underpin the tremendous potential of the tip-functionalized ncAFM technique for microscopic identification of a complex interplay of intermolecular interactions and their associated impact on the molecular resonance structures.
Yutian Yang, Yingying Wang, Jingsi Qiao, Weiwei Zhao, Yuanfang Yu, Shaopeng Feng, Xuhong An, Jialin Zhang, Wei Ji, Xinran Wang, Junpeng Lu & Zhenhua Ni
Abstract
The functionality of 2D molecular crystal-based devices crucially depends on their intrinsic properties, such as molecular energy levels, light absorption efficiency, and dielectric permittivity, which are highly sensitive to molecular aggregation. Here, it is demonstrated that the dielectric permittivity of the 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) molecular crystals on monolayer WS2 substrates can be tuned from 4.62 in the wetting layer to 2.25 in the second layer. Its origin lies in the different molecular orientations in the wetting layer (lying-down) and in the subsequently stacked layers (standing-up), which lead to a positive Coulomb coupling (JCoup) value (H-aggregation) and a negative JCoup value (J-aggregation), respectively. Polarized optical contrast spectroscopy reveals that the permittivity of C8-BTBT is anisotropic, and its direction is related to the underlying substrate. The study offers guidelines for future manipulation of the permittivity of 2D molecular crystals, which may promote their applications toward various electronic and optoelectronic devices.
Jun Zhang, Linwei Zhou, Pengcheng Chen, Bingkai Yuan, Zhihai Cheng, Wei Ji & Xiaohui Qiu
Abstract
Catalytic bond cleavage and formation of transient intermediates on metal substrates play an essential role in surface synthesis and heterogeneous catalysis. Previous studies usually focus on the bond-breaking process, whereas the knowledge regarding the construction of dissociative moieties that lead to the final products is limited. Here, we investigate the facet-selective dissociation of dibenzotetrathiafulvalene (DBTTF) molecules on Cu(110) and Cu(100) surfaces using low-temperature scanning tunneling microscopy and first-principles calculations. Atomic resolution images enable the identification of various intermediates and reaction pathways on different facets. The dissociation of DBTTF molecules generated 1,2-BDT–Cu complex chains on Cu(110), while phenyl diradical superstructure islands were observed on Cu(100). The various chemical species found on different Cu facets were explained in the context of their formation energies related to the spatial inhomogeneity of surface electronic states. Our results address the effects of electronic and geometrical diversities on the surface mobility of intermediate products and subsequent on-surface reaction pathways.
Yanping Guo, Linlu Wu, Jinghao Deng, Linwei Zhou, Wei Jiang, Shuangzan Lu, Da Huo, Jiamin Ji, Yusong Bai, Xiaoyu Lin, Shunping Zhang, Hongxing Xu, Wei Ji & Chendong Zhang
Abstract
Semiconducting heterojunctions (HJs), comprised of atomically thin transition metal dichalcogenides (TMDs), have shown great potentials in electronic and optoelectronic applications. Organic/TMD hybrid bilayers hold enhanced pumping efficiency of interfacial excitons, tunable electronic structures and optical properties, and other superior advantages to these inorganic HJs. Here, we report a direct probe of the interfacial electronic structures of a crystalline monolayer (ML) perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA)/ML-WSe2 HJ using scanning tunneling microscopy, photoluminescence, and first-principle calculations. Strong PTCDA/WSe2 interfacial interactions lead to appreciable hybridization of the WSe2 conduction band with PTCDA unoccupied states, accompanying with a significant amount of PTCDA-to-WSe2 charge transfer (by 0.06 e/PTCDA). A type-II band alignment was directly determined with a valence band offset of ∼ 1.69 eV, and an apparent conduction band offset of ∼ 1.57 eV. Moreover, we found that the local stacking geometry at the HJ interface differentiates the hybridized interfacial states.
