Pulling and Stretching a Molecular Wire to Tune its Conductance

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Conductance of molecular wires typically decreases exponentially with length.
• Understanding charge transport in single molecules is crucial for molecular electronics.
• Polythiophene wires on surfaces present a model system for studying charge transport.

Purpose of the Study:

• To investigate the current-conductance relationship in polythiophene wires during mechanical manipulation.
• To explain the observed anomalous current increases during the pulling of molecular wires.
• To explore the potential for mechanically controlled single-molecule electronic devices.

Main Methods:

• Utilized a scanning tunneling microscope (STM) to pull polythiophene wires from a gold (Au(111)) surface.
• Measured the electrical current traversing the STM junction during the wire-lifting process.
• Performed ab initio simulations to model the experimental observations and understand the underlying physics.

Main Results:

• Observed abrupt increases in current during the pulling of polythiophene wires, contradicting expected exponential decay.
• Correlated these current jumps with the detachment of molecular subunits from the wire.
• Simulations confirmed that mechanical stress release within the wire explains the anomalous current behavior.

Conclusions:

• Mechanical stress plays a significant role in the charge transport properties of single molecular wires.
• The observed phenomenon provides a mechanism for mechanically gating current in single-molecule devices.
• This work opens avenues for developing novel mechanically controlled single-molecule electronic components.