ABSTRACT
Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions ofmeta-linked benzene, namely electron-donating methoxy (-OMe) and electron-withdrawing nitryl (-NO2), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficientsT(E) indicates that -OMe and -NO2could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. -OMe could raise the antiresonance energy at position 4 while -NO2groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of -NO2substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.
ABSTRACT
In this paper, single molecular junctions of Para-phthalic acid and Meta-phthalic acid with Au electrodes were studied by STM break junction approach. Conductance values of 10-3.55 G0 and 10-3.70 G0 were found for Para-phthalic acid and Meta-phthalic acid, respectively. The conductance order between Para-phthalic acid and Meta-phthalic acid with Au is different from that with Cu, which can be contributed to the different coupling between molecules and electrodes; different through-space interaction is proposed for such phenomenon between Cu and Au electrodes. Furthermore, the breaking off distances can reflect the length of molecules. The current work presents the important role of electrode in single molecular junctions with different position anchoring groups.
ABSTRACT
In this paper, the contact configuration of single molecular junction is controlled through side group, which is explored by electrochemical jump-to-contact STM break junction. The conductance values of 2-methoxy-1,3-benzenedicarboxylic acid (2-M-1,3-BDC) is around 10-3.65 G0, which is different from that of 5-methoxy-1,3-benzenedicarboxylic acid (5-M-1,3-BDC) with 10-3.20 G0. Interestingly, the conductance value of 2-M-1,3-BDC is the same as that of 1,3-benzenedicarboxaldehyde (1,3-BDCA), while single molecular junctions of 5-M-1,3-BDC and 1,3-benzenedicarboxylic acid (1,3-BDC) give out similar conductance value. Since 1,3-BDCA binds to the Cu electrode through one oxygen atom, the dominated contact configuration for 1,3-BDC is through two oxygen atoms. The different conductance values between 2-M-1,3-BDC and 5-M-1,3-BDC can be attributed to the different contact configurations caused by the position of the side group. The current work provides a feasible way to control the contact configuration between the anchoring group and the electrode, which may be useful in designing future molecular electronics.