Tuning the conductance of H2O@C60 by position of the encapsulated H2O

Abstract

The change of conductance of single-molecule junction in response to various external stimuli is the fundamental mechanism for the single-molecule electronic devices with multiple functionalities. We propose the concept that the conductance of molecular systems can be tuned from inside. The conductance is varied in C60 with encapsulated H2O, H2O@C60. The transport properties of the H2O@C60-based nanostructure sandwiched between electrodes are studied using first-principles calculations combined with the non-equilibrium Green's function formalism. Our results show that the conductance of the H2O@C60 is sensitive to the position of the H2O and its dipole direction inside the cage with changes in conductance up to 20%. Our study paves a way for the H2O@C60 molecule to be a new platform for novel molecule-based electronics and sensors.

Figure 1. Schematic illustration of the H₂O@C₆₀–based junction used in the transport calculations.

White atoms: H, grey: C, golden: Au, red: O.

Figure 2. Local currents between the carbon atoms and the water molecule, where the radius of the cylinder is proportional to the current density.

Green currents represent the positive transport direction (along the z direction), and blue currents represent the negative direction (along the –z direction). The current is calculated at 0.5 V. It is obvious that the C₆₀ molecule cannot act as a Faraday cage because there are a number of current channels between the encapsulated water molecule and the C atoms.

Figure 3

(a,b) The conductance, its change ratio, and the total energy at zero bias for H₂O@C₆₀ junctions with the encapsulated water molecule at different positions; (c,d) the conductance, its change ratio, and the total energy for H₂O@C₆₀ junctions with the dipole of the water molecule pointing in different directions. All conductance changes and total energies shown are relative to those of the H₂O@C₆₀ junction with the water molecule at the relaxed position. Negative change ratio represents conductance decreasing while positive change ratio represents it increasing. It is clear that, with the same contact geometry, the conductance is dependent not only on the position of the encapsulated water molecule, but also on the dipole direction of the water molecule.