When electron transfer meets electron transport in redox-active molecular nanojunctions

Area of Science:

• Electrochemistry
• Materials Science
• Nanotechnology

Background:

• Conducting polymers like polyaniline (PANI) are crucial for electronic devices.
• Fabricating and characterizing nanoscale junctions of these polymers presents significant challenges.
• Understanding charge transport mechanisms at the molecular level is key to advancing nanoelectronics.

Purpose of the Study:

• To develop a method for creating and characterizing polyaniline nanojunctions using scanning electrochemical microscopy (SECM).
• To investigate the charge transport properties of polyaniline within a micrometric gap.
• To differentiate and analyze electron transfer and electron transport processes within the nanojunction.

Main Methods:

• Utilized SECM to precisely position two microelectrodes with a micrometric separation.
• Electrochemically deposited polyaniline from the SECM tip to bridge the electrodes, forming nanojunctions.
• Characterized the PANI nanojunctions by measuring current-voltage characteristics and varying electrochemical potential (gate electrode).

Main Results:

• Polyaniline nanojunctions exhibited low conductances (<100 nS) in the oxidized state, suggesting transport through limited PANI wires.
• SECM enabled simultaneous observation of electron transfer and transport phenomena within the same experiment.
• Electron transfer current was found to be scan-rate dependent, while charge transport current varied with bias voltage.

Conclusions:

• SECM is a powerful tool for fabricating and characterizing polymer nanojunctions at the nanoscale.
• The study demonstrated control over charge transport in polyaniline nanojunctions, even across micrometric distances.
• Achieved single oligoaniline strand-controlled conductance, paving the way for molecular electronics.