Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
HighRI Optics, Inc., 5401 Broadway Ter 304, Oakland, California 94618, USA.
Rev Sci Instrum. 2023 Mar 1;94(3):033902. 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.
将光学高光谱映射和高分辨率地形成像相关联的能力对于深入了解纳米材料系统的结构-功能关系至关重要。扫描近场光学显微镜可以实现这一目标，但代价是探针制造和实验专业知识方面的大量工作。为了克服这两个限制，我们开发了一种低成本、高通量的纳米压印技术，将一个尖锐的金字塔结构集成到单模光纤的端面上，该光纤可以用简单的音叉技术进行扫描。纳米压印金字塔有两个主要特点：（1）大的锥角（约 70°），决定了尖端的远场限制，从而实现了 275nm 的空间分辨率、1.06 的有效数值孔径和（2）半径约为 20nm 的尖锐顶点，从而实现了高分辨率地形成像。通过等离子体纳米槽样品的消逝场分布映射展示了光学性能，然后使用光纤内光纤出光耦合模式对纳米晶体进行高光谱荧光映射。通过在二维单层上进行比较荧光映射，我们还显示出空间分辨率提高了三倍，超过了化学蚀刻光纤。这些结果表明，裸纳米压印近场探针可以简单地实现与高分辨率地形映射相关联的光谱显微镜，并有可能推进基于可重复光纤尖端的扫描近场显微镜。
