Low-bias conductance mechanism of diarylethene isomers: A first-principle study

Tuning the polarity of charge carriers in N-heterocyclic carbene-based single-molecule junctions via atomic manipulation

Tuning the polarity of charge carriers at a single-molecular level is essential for designing complementary logic circuits in the field of molecular electronics. Herein, the transport properties of N-heterocyclic carbene (NHC)-linked single-molecule junctions are investigated using the ab initio quantum transport approach. The results reveal that the hydrogen atoms in NHCs function as a switch for regulating the polarity of charge carriers. Dehydrogenation changes the chemical nature of NHC anchors, thereby rendering holes as the major charge carriers rather than electrons. Essentially, dehydrogenation changes the anchoring group from electron-rich to electron-deficient. The electrons transferred to molecules from the electrodes raise the molecular level closer to the Fermi level, thus resulting in charge carrier polarity conversion. This conversion is influenced by the position and number of hydrogen atoms in the NHC anchors. To efficiently and decisively alter charge carrier polarity via atomic manipulation, a methyl substitution approach is developed and verified. These results confirm that atomic manipulation is a significant method for modulating the polarity of charge carriers in NHC-based single-molecule devices.

Silver electrodes provide higher conductance than gold for thiol-terminated oligosilane molecular junctions: the interfacial effect

The understanding of the interfacial effect on charge transport is essential in single-molecule electronics. In this study, we elucidated the transport properties of molecular junctions comprising thiol-terminated oligosilane with three to eight Si atoms and two types of Ag/Au electrode materials employing different interfacial configurations. First-principles quantum transport calculations demonstrated that the interfacial configuration determines the relative magnitude of the current between the Ag and Au electrodes, wherein the Ag monoatomic contact configuration presented a larger current than did the Au double-atom configuration. Further, the mechanism of electron tunneling from the interfacial states through the central σ channel was revealed. In contrast to Au double-atom electrodes, Ag monoatomic electrodes exhibit a higher current due to the presence of Ag-S interfacial states closer to the Fermi level. Our findings show that the interfacial configuration is a plausible way to generate the relative magnitude of current of thiol-terminated oligosilane molecular junctions with Au/Ag electrodes and provide further insight into the interfacial effect on the transport properties.

Design of multifunctional spin logic gates based on manganese porphyrin molecules connected to graphene electrodes

The spin-resolved transport properties of molecular logic devices composed of two Mn porphyrin molecules connected to each other via a six-carbon atomic chain were studied using the non-equilibrium Green's function combined with density functional theory. The molecules were symmetrically connected to armchair graphene nanoribbon electrodes through four-carbon atomic chains on the left- and right-hand sides. Our calculations revealed that the spin-resolved current-voltage curves depend on the initial spin setting of the transition metal Mn atoms and carbon atoms on the zigzag edges where the electrodes come in contact with the molecule. By simultaneously regulating the spin orientations of the intermediate functional molecules and the zigzag edges of the armchair graphene nanoribbon electrodes, seven spin polarization configurations were obtained. These configurations were examined in this study considering the spin-related symmetry of molecular junctions. By meticulously selecting different combinations according to the specific input and output signals, YES, NOT, OR, NOR, and XOR multifarious spin logic devices were created. The findings of this study are expected to contribute toward the extension of molecular junction functions in future spintronic integrated circuit design and further miniaturization.