Abstract
The scattering-type scanning near-field optical microscope (s-SNOM) has become a powerful imaging and nano-spectroscopy tool, which is widely used in the characterization of electronic and photonic devices, two-dimensional materials and biomolecules. However, in the published literature, nano-spectroscopy is mainly employed in the mid-infrared band, and the near-infrared (NIR) nano-spectroscopy with broadband spectral range has not been well discussed. In the present paper, we introduce a home-built near-field NIR spectroscopy and imaging set-up that is based on a laser-driven light source (LDLS). By mapping the Ge-Au periodic grating sample and the photonic topology device, a ~30 nm spatial resolution and the excellent capability of characterizing complex samples are demonstrated. Spectra obtained by experiment reveal the optical band-gap of Ge with a spectral resolution of 25 cm−1, and a spectral range from 900 to 2000 nm. This technology is expected to provide a novel and unique approach for near-field NIR spectroscopy and imaging.
Highlights
Conventional optical microscopy and micro-spectroscopy are based on the principle of optical imaging; according to the Abbe diffraction limit theorem, the best spatial resolution of conventional optical microscopy and micro-spectroscopy is about half of the light wavelength
This approach curve is obtained by setting the reference mirror to the zero path difference (ZPD) position and recording the 2Ω signal, as we retract the sample away from the atomic force microscope (AFM) tip
These results suggest that the spatial resolution (~30 nm) of our set-up is on the order of the diameter of the AFM tip-apex and not limited by the diffraction limit of the illumination wavelength
Summary
Conventional optical microscopy and micro-spectroscopy are based on the principle of optical imaging; according to the Abbe diffraction limit theorem, the best spatial resolution of conventional optical microscopy and micro-spectroscopy is about half of the light wavelength. We describe our home-built near-field imaging and spectroscopy set-up based on this light source.
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