Charge transport and rectification in molecular junctions formed with carbon-based electrodes

Area of Science:

• Nanotechnology
• Materials Science
• Condensed Matter Physics

Background:

• Scanning tunneling microscope-based break-junction (STM-BJ) technique is crucial for nanoscale charge transport studies.
• Typically, STM-BJ junctions use identical noble metal electrodes (e.g., gold, platinum, silver).
• Noble metal electrodes have a nearly constant density of electronic states near the Fermi level.

Purpose of the Study:

• To investigate charge transport in molecular junctions with dissimilar electrodes (gold tip, graphite substrate).
• To explore the potential for emergent functionality in hybrid molecular-scale devices.
• To understand the role of electrode material on conductance and rectification.

Main Methods:

• Utilized the STM-BJ technique with a gold tip and microfabricated graphite substrate.
• Fabricated and measured conductance of graphite/amine-terminated oligophenyl/gold molecular junctions.
• Performed state-of-the-art ab initio conductance calculations.

Main Results:

• Observed exponential decay of conductance with increasing molecular backbone length, similar to gold-gold junctions.
• Demonstrated electrical rectification in molecular junctions despite symmetric molecular structure.
• Calculations confirmed experimental results and explained rectification mechanism.

Conclusions:

• The energy-dependent density of states in graphite significantly influences charge transport and enables rectification.
• Hybrid molecular junctions with dissimilar electrodes can exhibit unique functionalities.
• This work paves the way for designing molecular junctions using layered 2D materials and diverse electrode combinations.