Sharp, high numerical aperture (NA), nanoimprinted bare pyramid probe for optical mapping.

Area of Science:

• Nanotechnology
• Optical Microscopy
• Materials Science

Background:

• Correlating optical hyperspectral mapping with high-resolution topographic imaging is crucial for understanding nanomaterial structure-function relationships.
• Scanning near-field optical microscopy (SNOM) offers this capability but requires complex probe fabrication and expertise.
• Existing methods present challenges in cost and throughput for widespread adoption.

Purpose of the Study:

• To develop a low-cost, high-throughput nanoimprinting technique for creating fiber-tip SNOM probes.
• To enable correlated optical hyperspectral and topographic imaging with improved spatial resolution.
• To overcome the limitations of traditional probe fabrication and experimental complexity in SNOM.

Main Methods:

• A nanoimprinting technique was used to integrate a sharp pyramid structure onto the end facet of a single-mode fiber.
• The nanoimprinted probes feature a large taper angle (~70°) for far-field confinement and a sharp apex (~20 nm radius of curvature) for high-resolution topography.
• A simple tuning-fork feedback mechanism was employed for scanning, and optical performance was validated using plasmonic nanogrooves and nanocrystals.

Main Results:

• The nanoimprinted probes achieved a spatial resolution of 275 nm and an effective numerical aperture of 1.06.
• Demonstrated capabilities include evanescent field distribution mapping and hyperspectral photoluminescence mapping of nanocrystals.
• A threefold improvement in spatial resolution was observed compared to chemically etched fibers in photoluminescence mapping of 2D monolayers.

Conclusions:

• The developed nanoimprinting technique provides a simple and accessible method for creating fiber-tip SNOM probes.
• These probes facilitate correlated hyperspectral and high-resolution topographic imaging, advancing spectromicroscopy.
• The technique has the potential to significantly improve the reproducibility and accessibility of fiber-tip-based SNOM.