Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions

Area of Science:

• Molecular Electronics
• Condensed Matter Physics
• Surface Science

Background:

• Electrical transport in molecular junctions is crucial for nanoelectronic devices.
• Self-assembled monolayers (SAMs) of alkanedithiols offer a platform for studying charge transport at the molecular level.
• The Simmons model is a theoretical framework for describing tunneling transport through potential barriers.

Purpose of the Study:

• To investigate electrical transport properties of alkanedithiol SAMs in large-area molecular junctions.
• To apply and validate the Simmons model for describing tunneling current and capacitance.
• To determine key parameters like barrier height and effective mass and their dependence on molecular length.

Main Methods:

• Fabrication of large-area molecular junctions using alkanedithiol SAMs.
• Electrical transport measurements (current-voltage characteristics) and impedance spectroscopy.
• Analysis of data using the Simmons model, incorporating image potential effects.
• Determination of dielectric constant via impedance measurements.

Main Results:

• Electrical transport up to 1 V was accurately described by the Simmons model for octanedithiol to tetradecanedithiol SAMs.
• A consistent effective mass of 0.28 was determined, aligning with theoretical predictions.
• Barrier heights ranged from 4-5 eV and showed systematic variation with molecular length.
• A dielectric constant of 2.1 was obtained from impedance measurements.

Conclusions:

• The Simmons model, including image potential, effectively describes electrical transport in alkanedithiol SAMs.
• Molecular length influences barrier height, while effective mass remains constant across different lengths.
• The study provides valuable insights into charge transport mechanisms in molecular junctions for potential electronic applications.