Single-electron transport in H₂O@C₆₀ single-molecule transistors

Single-molecule transistors (SMTs) based on fullerenes and their derivatives have been recognized as a long-sought platform for studying the single-electron transport properties. H₂O@C₆₀ is a combination of fullerene and H₂O, a typical light molecule. Here we use the ‘molecular surgery’ technique to synthesize the H₂O@C₆₀ molecule and then construct the H₂O@C₆₀ SMTs, together with the C₆₀ SMTs. Evidences for single-electron transport have been obtained in our measurements, including explicit Coulomb blockade and Coulomb oscillations. We then calculate the detailed parameters of the H₂O@C₆₀ and C₆₀ SMTs using a capacitance model derived from the Coulomb diamond feature, which gives a capacitance ratio of 1:5.05:8.52 for the H₂O@C₆₀ SMT and 1:29.5:74.8 for the C₆₀ SMT. Moreover, the gate efficiency factor α turns out to be 0.0686 in the H₂O@C₆₀ SMT, about ten times larger than that in the C₆₀ SMT. We propose that the enhanced gate efficiency in H₂O@C₆₀ SMT may be induced by the closer attachment of molecular orbital electron clouds to the gate substrate due to polarization effects of H₂O.