Inelastic Electron Transport and Ortho–Para Fluctuation of Water Molecule in H₂O@C₆₀ Single Molecule Transistors

Abstract

Light molecules such as H 2 O are the systems in which we can have access to quantum mechanical information on their constituent atoms. Here, we have investigated electron transport through H 2 O@C 60 single molecule transistors (SMTs). The H 2 O@C 60 SMTs exhibit Coulomb stability diagrams that show multiple tunneling-induced excited states below 30 meV. Furthermore, we have performed terahertz (THz) photocurrent spectroscopy on H 2 O@C 60 SMTs and confirmed the same excitations. From comparison between experiment and theory, the excitations observed below 10 meV are identified to be the quantum rotational excitations of the water molecule. Surprisingly, the quantum rotational excitations of both para-and ortho-water molecule are observed simultaneously even for a single water molecule, indicating that the fluctuation between the ortho-and para-water states takes place in a time scale shorter than our measurement time (∼1 min), probably by the interaction between the encapsulated water molecule and conducting electrons.

Effective Conduction Path of a C60 Chain in a Nanogap Electrode

“…In this study, a fullerene derivative of CPTA was used as the conductive channel material. Simple fullerenes such as C 60 and C 70 and variable endohedral fullerenes have been employed as single-molecule − or film − ,− devices. In comparison with these fullerenes, CPTA has advantages such as oversolvability in solution and uniform adhesion on the substrate surface .…”

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

“…[28][29][30][31][32][33][34] Furthermore, the ortho-para fluctuations have also been demonstrated in H 2 O@C 60 SMTs. [35] The fluctuation between ortho-and parawater states has been demonstrated on timescales shorter than 1 min. [35] However, in another single-molecule junction study of H 2 O@C 60 , it was found that H 2 O is electrostatically isolated.…”

“…[35] The fluctuation between ortho-and parawater states has been demonstrated on timescales shorter than 1 min. [35] However, in another single-molecule junction study of H 2 O@C 60 , it was found that H 2 O is electrostatically isolated. [36] In this work, we fabricated SMTs based on H 2 O@C 60 molecules.…”

How External Electric Field Modulates the Rotation Energy Profiles of Dipolar Dopants Inside C70: A Theoretical Interpretation with Electrostatic Shielding Effect Incorporated

“…[8e] Different responses of ortho and para spin isomers of water inside C 60 to external EFs were observed by Meier et al, who suggested a partial shielding explanation based on the analysis of the experimentally measured dipole moment. [12] Delaney and Greer calculated the overall EF inside C 60 and found that only 25% of the external EF imposed can penetrate into the cage, and create a spherical region (of radius 2 Å) with a constant field around the centroid of C 60 . [8a] They also employed different basis sets and found that the magnitude of EF penetration was barely changed.…”

“…The shielding effect of C 60 was illuminated in a combined experimental and theoretical study by Jarivs et al ., who found that the STM, non‐contact atomic force microscopy (ncAFM) and valence band X‐ray photoemission spectroscopy (VB‐XPS) cannot distinguish between empty C 60 and the ones filled with H 2 O, from the perspectives of orbitals, stiffness and the dielectric properties [8e] . Different responses of ortho and para spin isomers of water inside C 60 to external EFs were observed by Meier et al ., who suggested a partial shielding explanation based on the analysis of the experimentally measured dipole moment [12] . Delaney and Greer calculated the overall EF inside C 60 and found that only 25% of the external EF imposed can penetrate into the cage, and create a spherical region (of radius 2 Å) with a constant field around the centroid of C 60 [8a] .…”