Double Tips for In-Plane Polarized Near-Field Microscopy and Spectroscopy

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

Highly (001)-textured p-type WSe2 Thin Films as Efficient Large-Area Photocathodes for Solar Hydrogen Evolution

Abstract Highly (001)-textured, photoactive WSe2 thin films have been prepared by an amorphous solid-liquid-crystalline solid process promoted by palladium. By increasing the thickness of the Pd promoter film (≥10 nm) the structure and texture of the WSe2 films can be improved significantly. However, these as-crystallized WSe2 films are only weakly photoactive in a 0.5 М H2SO4 electrolyte under AM 1.5 solar irradiation which we attribute to an inefficient photogenerated charge transfer across the WSe2/electrolyte interface via the prevailing van der Waals planes of the WSe2 crystallites. In this work photochemically deposited platinum on the p-type WSe2 photocathode is used for an efficient electron transfer thus inducing the hydrogen evolution reaction. Upon illuminating the WSe2 photocathodes in a Pt-ion containing electrolyte, the photogenerated electrons reduce Pt+ to Pt leading to the precipitation of Pt islands, preferentially at edge steps of the WSe2, i.e. at the grain boundaries of the WSe2 crystallites. The increasing amount of Pt islands at the grain boundaries linearly enhances the photocurrent density up to 2.5 mA cm−2 at 0 VRHE in sulfuric acid, the highest reported value up to now for WSe2 thin films