Raman scattering at plasmonic junctions shorted by conductive molecular bridges

Area of Science:

• Surface-enhanced Raman spectroscopy
• Plasmonics
• Molecular electronics

Background:

• Raman scattering provides molecular vibrational information.
• Plasmonic junctions are sensitive to molecular interactions.
• Conductive molecular bridges can alter electronic properties.

Purpose of the Study:

• To investigate the relationship between Raman scattering fluctuations and molecular conductive bridges.
• To demonstrate the tracking of chemical bond dynamics at a single-molecule level.
• To understand the role of molecular structure in plasmonic junction behavior.

Main Methods:

• Utilizing a gold atomic force microscope (AFM) tip in contact with a silver surface.
• Coating the silver surface with biphenyl-4,4'-dithiol (a dithiol) or biphenyl-4-thiol (a monothiol).
• Recording Raman trajectories at the plasmonic junction to observe intensity spikes and spectral switching.

Main Results:

• Observed intensity spikes and switching between line and band spectra in Raman scattering.
• Correlated these spectral changes with the formation and breaking of molecular conductive bridges.
• Found that fluctuations were absent when using the monothiol, indicating the necessity of dithiol bridging.
• Successfully tracked the dynamics of chemical bond formation and breaking.

Conclusions:

• Raman scattering intensity spikes and spectral switching are indicative of plasmonic junction shorting via molecular conductive bridges.
• The formation and breaking of chemical bonds in dithiols can be directly monitored through these plasmonic junction dynamics.
• Molecular structure, specifically the presence of dithiol linkages, is crucial for observing these conductive bridging phenomena.