Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed du...Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.展开更多
Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfull...Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfully formed on the Au substrate. The Uniformity and stability of SAMs were confirmed through cyclic voltammetry（CV） and electrochemical reductive desorption. The investigation of transport properties of SAMs was achieved by conducting-probe atomic force microscopy（CP-AFM） with both Au and Pt tips. The results indicated that the conductance of OPE3-TTF was 17 and 46 times that of OPE3 for Au and Pt tips, respectively. Theoretical calculations are qualitatively consistent with the experimental results, suggesting that the diamine as anchoring group has a great potential in molecular electronics.展开更多
基金supported by the National Natural Science Foundation of China(21722305,21673195,21973079,and 21703188)the National Key R&D Program of China(2017YFA0204902)the Guangdong Basic and Applied Basic Research Foundation(2020A151511106).
文摘Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.
基金financially supported by the National Natural Science Foundation of China (Nos. 61571415, 61622406, 51502283)the National Key Research and Development Program of China (Nos. 2017YFA0207500, 2016YFB0700700)the "Hundred Talents Program" of Chinese Academy of Sciences (CAS)
文摘Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfully formed on the Au substrate. The Uniformity and stability of SAMs were confirmed through cyclic voltammetry（CV） and electrochemical reductive desorption. The investigation of transport properties of SAMs was achieved by conducting-probe atomic force microscopy（CP-AFM） with both Au and Pt tips. The results indicated that the conductance of OPE3-TTF was 17 and 46 times that of OPE3 for Au and Pt tips, respectively. Theoretical calculations are qualitatively consistent with the experimental results, suggesting that the diamine as anchoring group has a great potential in molecular electronics.
