In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers

Area of Science:

• Molecular Electronics
• Materials Science
• Surface Chemistry

Background:

• Molecular junctions offer potential for novel electronic devices.
• Controlling functionality in molecular electronic devices is a key challenge.
• Self-assembled monolayers (SAMs) are promising building blocks for molecular electronics.

Purpose of the Study:

• To demonstrate in-place, reversible switching between resistor and diode functionality in molecular tunneling junctions.
• To investigate the role of molecular interface properties, specifically hydration, in controlling junction behavior.
• To explore external stimuli for modulating junction rectification.

Main Methods:

• Fabrication of tunneling junctions using SAMs with carboxylic acid groups.
• Modulation of junction properties via controlled hydration and dehydration using water and scavengers.
• Characterization using eutectic Ga-In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO) top-contacts.
• Spectroscopic and probe measurements (X-ray photoelectron spectroscopy, Kelvin probe) to confirm proposed mechanisms.
• Demonstration of light-driven modulation using spiropyran photoacid.

Main Results:

• Reversible switching between resistor and diode behavior was achieved in molecular tunneling junctions.
• Junction rectification is significantly influenced by the hydration state of carboxylic acid groups at the interface.
• The observed phenomena are intrinsic to the molecular layer and not dependent on the specific top-contact material.
• A mechanism involving the lowering of the Lowest Unoccupied Molecular Orbital (LUMO) and potential Stark shift explains the diode behavior.
• Light-driven modulation of rectification was successfully demonstrated.

Conclusions:

• Molecular tunneling junctions can be controllably switched between resistive and diode states through reversible changes in molecular properties (hydration).
• This molecular-level control offers a pathway towards reconfigurable circuits and novel functionalities in molecular electronics.
• The findings are platform-independent, highlighting the potential of SAM-based devices.