Nanoscale Chemical Reaction Imaging at the Solid-Liquid Interface via TERS
Ashish Bhattarai1, Patrick Z El-Khoury1
1Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States.
The Journal of Physical Chemistry Letters
|May 11, 2019
Summary
Not all plasmonic hotspots are reactive. Tip-enhanced Raman scattering (TERS) revealed that chemical reactions on gold platelets occur at specific sites, not where optical fields are strongest, suggesting molecular crowding influences reactivity.
Area of Science:
- Plasmonics
- Surface Chemistry
- Nanophotonics
Background:
- Plasmonic nanostructures enable enhanced optical fields for chemical reactions.
- The precise location of chemical activity within these enhanced fields is not fully understood.
- Gold nanostructures offer a tunable platform for studying plasmon-enhanced chemistry.
Purpose of the Study:
- To investigate the correlation between optical field localization and chemical reactivity on plasmonic gold.
- To identify specific sites of plasmon-driven chemical transformation on gold nanostructures.
- To elucidate factors governing reaction site selectivity in plasmon-enhanced chemistry.
Main Methods:
- Utilized chemically functionalized monocrystalline gold platelets in aqueous solution.
- Employed a gold-coated tip-enhanced Raman scattering (TERS) probe for high-resolution imaging.
- Studied the plasmon-driven dimerization of p-nitrothiophenol (NTP) as a model reaction.
Main Results:
- TERS maps of NTP showed maximal optical field enhancement at the edges of gold platelets.
- Product maps of dimercaptoazobenzene revealed chemical transformation occurred only at specific sites.
- Reaction sites did not always coincide with regions of maximum optical field enhancement.
Conclusions:
- Optical field enhancement alone does not guarantee chemical reactivity.
- Molecular crowding and steric effects are critical factors in directing plasmon-driven NTP dimerization.
- Reaction site selectivity is influenced by factors beyond localized optical fields at the gold-water interface.
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