tip-enhanced raman spectroscopy

**TERS** (Tip-Enhanced Raman Spectroscopy) is a **nanoscale Raman technique that uses a metallic AFM/STM tip to amplify the Raman signal through plasmonic enhancement** — achieving spatial resolution below 10 nm, far beyond the diffraction limit of conventional Raman. **How Does TERS Work?** - **Metallic Tip**: A gold or silver AFM/STM tip positioned ~1 nm above the sample. - **Plasmonic Enhancement**: The laser-illuminated tip creates a localized electromagnetic "hot spot" that amplifies the Raman signal by 10$^4$-10$^6$. - **Nanoscale Resolution**: Signal comes only from the few nm² area under the tip apex -> sub-10 nm spatial resolution. - **Scanning**: Move the tip across the surface to build a nanoscale Raman image. **Why It Matters** - **Nanoscale Chemistry**: Chemical identification and structural analysis at the single-molecule level. - **Grain Boundaries**: Can characterize composition and stress at individual grain boundaries. - **2D Materials**: Maps strain, doping, and defects in graphene and TMDs at the nanoscale. **TERS** is **Raman spectroscopy through a nano-antenna** — using a plasmonic tip to magnify the Raman signal from a few-nanometer spot.