TERS operates by positioning a sharp metallic tip very close to the sample surface, typically within a few nanometers. When illuminated by a laser, the metallic tip creates a localized electromagnetic field known as a plasmon. This localized field enhances the Raman signal from the sample beneath the tip, enabling the detection of molecular vibrations with high spatial resolution. The enhancement effect is due to the surface plasmon resonance (SPR) of the metallic tip.
