Surface- and tip-enhanced resonant Raman scattering from CdSe nanocrystals

Area of Science:

• Nanophotonics
• Quantum Dot Spectroscopy
• Surface-Enhanced Raman Scattering

Background:

• Quantum dots (QDs) offer tunable optical properties.
• Raman scattering is sensitive to material structure and quality.
• Enhancement techniques are needed for nanoscale analysis.

Purpose of the Study:

• To demonstrate surface- and tip-enhanced resonant Raman scattering (SERS and TERS) of optical phonons in CdSe QDs.
• To investigate the influence of substrate plasmonic properties on SERS enhancement.
• To achieve high-sensitivity phonon detection from CdSe QDs.

Main Methods:

• Fabrication of plasmonically active gold nanocluster arrays using electron-beam lithography.
• Deposition of CdSe QD monolayers using the Langmuir-Blodgett technique.
• Spectroscopic micro-ellipsometry for LSPR characterization and numerical simulations.
• Resonant SERS and TERS measurements tuned to QD band gap and LSPR energies.

Main Results:

• Achieved SERS enhancement factor of 2 × 10^3 for CdSe QDs.
• Detected higher-order longitudinal optical (LO) phonon modes, indicating high QD crystalline quality.
• Demonstrated resonant TERS with an enhancement factor of 10^4.
• Confirmed dominant electromagnetic mechanism for SERS enhancement based on nanocluster size dependence.

Conclusions:

• Resonant SERS and TERS are effective for studying optical phonons in CdSe QDs.
• The findings advance the capability for nanoscale phonon spectroscopy.
• This work is a significant step towards single QD phonon detection.