tipenhanced

Tip-enhanced refers to a family of near-field optical techniques that combine scanning probe microscopy with optical spectroscopy to obtain chemical and structural information at the nanoscale. In these techniques, a metallic AFM or STM tip coated with gold or silver is brought into close proximity to a sample and illuminated by a laser. The tip acts as an optical antenna, concentrating the electromagnetic field at its apex via localized surface plasmon resonance. The enhanced near-field interacts with the sample, boosting signals such as Raman scattering or fluorescence from molecules within a few nanometers of the tip. The scattered light is collected by a far-field detector while the tip is scanned to produce high-resolution images. The most established variant is tip-enhanced Raman spectroscopy (TERS), which can achieve spatial resolutions below 20 nanometers under favorable conditions, and can approach single-molecule sensitivity in ideal cases. In addition to Raman, tip-enhanced fluorescence and related methods use the same principle to enhance visible or near-infrared emission.

Applications include nanoscale chemical mapping of materials, polymers, biomolecules, and catalysts, providing information about composition, molecular orientation, and conformational states that are not accessible with conventional far-field spectroscopy. Challenges include reproducible tip fabrication, controlling tip-induced damage, background signals from the tip, and the need for sophisticated instrumentation and alignment. The field has grown since the early 2000s and continues to expand into bioimaging and materials science.