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<p>We report a passive infrared near-field microscopy method that achieves ~ 10&#xa0;nm spatial resolution in the long-wavelength infrared region (<i>λ</i> = 14.1 ± 0.5&#xa0;μm). The technique employs a scattering-type scanning near-field optical microscope that requires no external illumination. Instead, the tungsten probe detects thermally excited evanescent waves generated by spontaneous charge carrier fluctuations at the sample surface. A two-step electrochemical etching process, combining AC etching for taper formation and DC etching for apex refinement, was developed to fabricate sharpened tungsten tips with apex radii below 10&#xa0;nm. Near-field measurements on lithographically patterned Au/SiO<sub>2</sub> samples revealed thermal contrast with ~ 10&#xa0;nm lateral resolution, surpassing the conventional 20&#xa0;nm limit. Comparative analysis with a coarser tip confirmed that smaller apex radii yield higher spatial resolution, highlighting the critical role of tip sharpness in passive s-SNOM. This passive approach enables non-invasive, ultra-high-resolution thermal imaging and opens new opportunities for nanoscale infrared metrology.</p>

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Achieving 10 nm Spatial Resolution in Thermal Near-Field Microscopy with Sharpened Tungsten Tip

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月18日

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  • Kuan-Ting Lin,
  • Jizhou Tang,
  • Yusuke Kajihara

摘要

We report a passive infrared near-field microscopy method that achieves ~ 10 nm spatial resolution in the long-wavelength infrared region (λ = 14.1 ± 0.5 μm). The technique employs a scattering-type scanning near-field optical microscope that requires no external illumination. Instead, the tungsten probe detects thermally excited evanescent waves generated by spontaneous charge carrier fluctuations at the sample surface. A two-step electrochemical etching process, combining AC etching for taper formation and DC etching for apex refinement, was developed to fabricate sharpened tungsten tips with apex radii below 10 nm. Near-field measurements on lithographically patterned Au/SiO2 samples revealed thermal contrast with ~ 10 nm lateral resolution, surpassing the conventional 20 nm limit. Comparative analysis with a coarser tip confirmed that smaller apex radii yield higher spatial resolution, highlighting the critical role of tip sharpness in passive s-SNOM. This passive approach enables non-invasive, ultra-high-resolution thermal imaging and opens new opportunities for nanoscale infrared metrology.