Thickness-Dependent Charge Transport in Three Dimensional Ru(II)- Tris(phenanthroline)-Based Molecular Assemblies

Area of Science:

• Molecular electronics
• Organic electronics
• Nanoscale charge transport

Background:

• Understanding charge transport in molecular junctions is crucial for developing novel electronic devices.
• The influence of molecular film thickness and temperature on charge transport mechanisms requires further investigation.

Purpose of the Study:

• To fabricate and characterize large-area molecular junctions using ruthenium(II)-tris(phenanthroline) [Ru(Phen)3].
• To investigate the temperature- and thickness-dependent charge transport phenomena in these nanometric junctions.
• To elucidate the charge transport mechanisms, including resonant tunneling and Poole-Frenkel conduction.

Main Methods:

• Fabrication of ITO/[Ru(Phen)3]/Al molecular junctions via electrochemical deposition.
• Characterization of current-voltage (j-V) curves to analyze charge transport.
• Analysis of thickness-dependent attenuation (β) and activation energy (Ea) for transport mechanisms.

Main Results:

• Successfully fabricated large-area molecular junctions with tunable Ru(Phen)3 film thicknesses (4-16 nm).
• Observed symmetric j-V curves indicating efficient long-range charge transport with weak attenuation (β = 0.70–0.79 nm⁻¹).
• Identified distinct charge transport mechanisms: resonant tunneling in thinner junctions (3.9 nm) and thermally activated Poole-Frenkel conduction (Ea ≈ 43 meV) in thicker junctions (10–16 nm).

Conclusions:

• Ruthenium(II)-tris(phenanthroline) molecular junctions exhibit efficient charge transport with thickness-dependent mechanisms.
• The observed "molecular signature" highlights the potential of Ru(Phen)3 for nanoscale electronic applications.
• Strong electronic coupling and accessible conduction channels contribute to the observed transport properties.