Local heating and Raman thermometry in a single molecule

Area of Science:

• Nanoscale science
• Physical chemistry
• Spectroscopy

Background:

• Characterizing local thermal effects at the nanoscale is challenging due to the nonequilibrium nature of heat transfer.
• Understanding single-molecule thermal properties is crucial for controlling chemical reactions and material properties at the molecular level.

Purpose of the Study:

• To develop and demonstrate a method for characterizing the local thermal properties of a single molecule under current-induced heating.
• To investigate the temperature-dependent behavior and decomposition pathways of a single fullerene (C60) molecule.

Main Methods:

• Utilized tip-enhanced anti-Stokes Raman spectroscopy to probe vibron populations in a single C60 molecule.
• Applied statistical analysis using a Bose-Einstein distribution to define an effective temperature (Teff).
• Correlated spectroscopic data with controlled current heating to observe molecular responses.

Main Results:

• Successfully defined an effective temperature (Teff) for the single C60 molecule, indicating local thermal equilibrium despite overall nonequilibrium conditions.
• Observed an increase in Teff up to approximately 1150 K with increasing current, preceding molecular decomposition.
• Identified decomposition temperature consistent with ensemble measurements, validating the methodology.
• Utilized Raman spectroscopy's chemical sensitivity to identify potential reaction pathways and products.

Conclusions:

• Developed a practical, noninvasive method for detecting local heating effects within single molecules under nonequilibrium conditions.
• Demonstrated the ability to statistically define and measure effective temperature at the single-molecule level.
• Provided insights into the thermal stability and decomposition mechanisms of C60 molecules, relevant for nanoscale thermal management and molecular electronics.