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

• Published in: Review of scientific instruments Vol. 94; no. 3; pp. 033902 - 33909
• Main Authors: Zhou, Junze, Gashi, Arian, Riminucci, Fabrizio, Chang, Boyce, Barnard, Edward, Cabrini, Stefano, Weber-Bargioni, Alexander, Schwartzberg, Adam, Munechika, Keiko
• Format: Journal Article
• Language: English
• Published: United States 01.03.2023
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/5.0104012

The ability to correlate optical hyperspectral mapping and high resolution topographic imaging is critically important to gain deep insight into the structure–function relationship of nanomaterial systems. Scanning near-field optical microscopy can achieve this goal, but at the cost of significant effort in probe fabrication and experimental expertise. To overcome these two limitations, we have developed a low-cost and high-throughput nanoimprinting technique to integrate a sharp pyramid structure on the end facet of a single-mode fiber that can be scanned with a simple tuning-fork technique. The nanoimprinted pyramid has two main features: (1) a large taper angle (∼70°), which determines the far-field confinement at the tip, resulting in a spatial resolution of 275 nm, an effective numerical aperture of 1.06, and (2) a sharp apex with a radius of curvature of ∼20 nm, which enables high resolution topographic imaging. Optical performance is demonstrated through evanescent field distribution mapping of a plasmonic nanogroove sample, followed by hyperspectral photoluminescence mapping of nanocrystals using a fiber-in-fiber-out light coupling mode. Through comparative photoluminescence mapping on 2D monolayers, we also show a threefold improvement in spatial resolution over chemically etched fibers. These results show that the bare nanoimprinted near-field probes provide simple access to spectromicroscopy correlated with high resolution topographic mapping and have the potential to advance reproducible fiber-tip-based scanning near-field microscopy.