Passive near-field imaging via grating-based spectroscopy

• Published in: Review of scientific instruments 2022-01, Vol.93 (1), p.013704-013704
• Main Authors: Sakuma, R., Lin, K.-T., Kim, S., Kimura, F., Kajihara, Y.
• Format: Article
• Language: English
• Subjects: Electron energy; Energy dissipation; Evanescent waves; Gratings (spectra); Liquid helium; Mechanical properties; Micropatterning; Near fields; Ohmic dissipation; Optical microscopy; Passive imaging; Resistance heating; Room temperature; Scientific apparatus & instruments; Spatial resolution; Spectra; Spectrum analysis; Surface analysis (chemical)
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/5.0059498

Passive scattering-type scanning near-field optical microscopy (s-SNOM) has recently been developed for studying long-wavelength infrared (LWIR) waves. It detects surface-localized waves without any external illumination or heating and enables the imaging of hot-electron energy dissipation and nanoscale Joule heating. However, the lack of a wavelength selection mechanism in the passive LWIR s-SNOM makes it difficult to perform a thorough analysis of the surface-localized waves. Here, we develop a novel passive scanning near-field optical spectroscopy with a diffraction grating. The spectroscopic optics are designed to exhibit a high signal efficiency and mechanical performance at the temperature of liquid helium (4.2 K). Using the developed passive LWIR near-field spectroscopy, the spectral information of thermally excited evanescent waves can be directly obtained without any influence from the external environment factors, including environmental heat. We have detected the thermally excited evanescent waves on a SiC/Au micropatterned sample at room temperature with a spatial resolution of 200 nm and a wavelength resolution of 500 nm at several wavelengths in the range of 14–15 µm. The obtained spectra are consistent with the electromagnetic local density of states calculated based on the fluctuation–dissipation theorem. The developed passive LWIR near-field spectroscopy enables the spectral analysis of ultrasmall surface-localized waves, making it a high-performance surface analysis tool.