Double Tips for In-Plane Polarized Near-Field Microscopy\nand Spectroscopy

Near-field optical microscopy and spectroscopy provide high-resolution\nimaging below the diffraction limit, crucial in physics, chemistry,\nand biology for studying molecules, nanoparticles, and viruses. These\ntechniques use a sharp metallic tip of an atomic force microscope\n(AFM) to enhance incoming and scattered light by excited near-fields\nat the tip apex, leading to high sensitivity and a spatial resolution\nof a few nanometers. However, this restricts the near-field orientation\nto out-of-plane polarization, limiting optical polarization choices.\nWe introduce double tips that offer in-plane polarization for enhanced\nimaging and spectroscopy. These double tips provide superior enhancement\nover single tips, although with a slightly lower spatial resolution\n(∼30 nm). They enable advanced studies of nanotubes, graphene\ndefects, and transition metal dichalcogenides, benefiting from polarization\ncontrol. The double tips allow varied polarization in tip-enhanced\nRaman scattering and selective excitation of transverse-electric and\n-magnetic polaritons, expanding the range of nanoscale samples that\ncan be studied.