Thermopower of amine-gold-linked aromatic molecular junctions from first principles

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Single-molecule junctions offer a platform for studying fundamental charge transport phenomena.
• Thermopower (Seebeck coefficient) and electrical conductance are key experimental probes of molecular electronics.

Purpose of the Study:

• To explain experimental measurements of the thermopower (S) and electrical conductance (G) for oligophenyldiamine-gold single-molecule junctions.
• To demonstrate the consistency between separate measurements of S and G.
• To highlight the importance of accurate electronic structure calculations for molecular junctions.

Main Methods:

• Utilizing a self-energy corrected scattering-state approach based on density functional theory (DFT).
• Comparing theoretical predictions of S and G with experimental data.
• Investigating the dependence of S on the number of phenyl rings (N) and contact atomic structure.

Main Results:

• Calculations with self-energy corrections accurately predict low-bias S and G values, showing good agreement with experiments.
• The Seebeck coefficient (S) was found to vary linearly with N, with a gradient β(S) of 2.1 μV/K, matching experimental findings.
• DFT calculations without self-energy corrections significantly overestimate S and β(S).
• The thermopower (S) is sensitive to contact atomic structure, more so than electrical conductance (G).

Conclusions:

• The study confirms the consistency of thermopower and electrical conductance measurements in single-molecule junctions.
• Accurate treatment of junction electronic level alignment, including self-energy corrections, is essential for describing off-resonant tunneling.
• This work validates theoretical approaches for understanding charge transport in molecular electronics.