Fluctuation in Interface and Electronic Structure of Single-Molecule Junctions Investigated by Current versus Bias Voltage Characteristics

• Published in: Journal of the American Chemical Society Vol. 140; no. 10; pp. 3760 - 3767
• Main Authors: Isshiki, Yuji, Fujii, Shintaro, Nishino, Tomoaki, Kiguchi, Manabu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.03.2018
• Subjects: electric power; electronic equipment; energy; fullerene; pyrazines; statistical analysis
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.7b13694

Structural and electronic detail at the metal–molecule interface has a significant impact on the charge transport across the molecular junctions, but its precise understanding and control still remain elusive. On the single-molecule scale, the metal–molecule interface structures and relevant charge transport properties are subject to fluctuation, which contain the fundamental science of single-molecule transport and implication for manipulability of the transport properties in electronic devices. Here, we present a comprehensive approach to investigate the fluctuation in the metal–molecule interface in single-molecule junctions, based on current–voltage (I–V) measurements in combination with first-principles simulation. Contrary to conventional molecular conductance studies, this I–V approach provides a correlated statistical description of both the degree of electronic coupling across the metal–molecule interface and the molecular orbital energy level. This statistical approach was employed to study fluctuation in single-molecule junctions of 1,4-butanediamine (DAB), pyrazine (PY), 4,4′-bipyridine (BPY), and fullerene (C60). We demonstrate that molecular-dependent fluctuation of σ-, π-, and π-plane-type interfaces can be captured by analyzing the molecular orbital (MO) energy level under mechanical perturbation. While the MO level of DAB with the σ-type interface shows weak distance dependence and fluctuation, the MO level of PY, BPY, and C60 features unique distance dependence and molecular-dependent fluctuation against the mechanical perturbation. The MO level of PY and BPY with the σ+π-type interface increases with the increase in the stretch distance. In contrast, the MO level of C60 with the π-plane-type interface decreases with the increase in the stretching perturbation. This study provides an approach to resolve the structural and electronic fluctuation in the single-molecule junctions and insight into the molecular-dependent fluctuation in the junctions.