4. THz Near-Field Microcopy
In our lab, we have been developing apertureless THz near-field microscopes (THz-NFMs) based on an atomic force microscope (AFM), both theories and measurement techniques (KR Patent 10-1466807 and US/Japan/Germany Patents pending). At present, our THz-NFM is the only one in the world that can do broadband (0.3-2 THz) THz pulse near-field imaging with nanometer spatial resolution
Self-Consistent Near-Field Scattering Theory
K. Moon et al., Optics Express 12, 11539 (2011)
We demonstrated quantitative analysis and measurements of near-fields interactions in a terahertz pulse near-field microscope. We developed a self-consistent line dipole image method for the quantitative analysis of the near-field interaction in THz scattering-type scanning optical microscopes. The measurements of approach curves and relative contrasts on gold and silicon substrates were in excellent agreement with calculations.
Quantitative Coherent Scattering Spectra of THz Near-Field Microscope
K. Moon et al., Appl. Phys. Lett. 101, 011109 (2012)
We present quantitative coherent measurements of scattering pulses and spectra in terahertz apertureless near-field microscopes. Broadband near-field image contrasts for both amplitude and phase spectra are measured directly from time-domain scattering signals with an unprecedentedly high single-scan signal-to-noise ratio (~48 dB), with approach curves for both short (<200 nm) and long (up to 82 lm) ranges. By using the line dipole image method, we obtain quantitative broadband THz imaging contrasts with nanoscale resolution.
THz Broadband Subsurface Nanoimaging
K. Moon et al., Nano Letters 15, 549 (2014)
Combined with terahertz (THz) time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, for the first time, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the subsurface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to λ/3300, at 1 THz, while the AFM only provides a flat surface topography.
