Electronics and Chemistry: Varying Single-Molecule Junction Conductance Using Chemical Substituents

Using amine-gold link chemistry 11, we have previously demonstrated that we can measure the conductance of single molecules reliably and reproducibly and relate the measured conductance to molecular conformations 12

Latha Venkataraman

2007

Scholarcy highlights

  • We measure the conductance of single molecule junctions by breaking Au point contacts in a 1,2,4-trichlorobenzene solution of molecules 6 Conductance traces measured as a function of tip-sample displacement reveal quantized conductance steps observed at multiples of G0, the fundamental quantum of conductance
  • Repeated measurements give a statistical assessment of the junction properties presented as conductance histograms with the peak in the histogram representing the most probable measured conductance value for the molecular junction
  • For all the substituents listed in Table 1, the histograms measured with the disubstituted benzenes do not differ from the control histograms in solvent alone
  • We plot in Figure 2A, the measured molecular conductance for the series tested against the vertical ionization potential calculated for the isolated molecules based on density functional theory 13-15. There is very limited experimental data available across the series of molecules under study for a comparison
  • We see in Figure 2A that the molecular junction conductance decreases with increasing ionization potential, for molecules with a more deeply bound highest occupied molecular orbital the conductance is reduced
  • Our measurements show that electron donating substituents, which shift the HOMO level up, increase the junction conductance they must decrease ΦB
  • We have measured the conductance of diamino benzene with different substituents that shift the molecular levels relative to the Au Fermi level in the single molecule junctions measured

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