Low terahertz-band scanning near-field microscope with 155-nm resolution

We report on the design and implementation of a scattering-type scanning near-field microscope working in the low terahertz-band under ambient conditions for nanoscopic investigations of physical properties and characteristics at sample surfaces and interfaces in the microwave and millimeter wave bands. Employing a nano-tip that oscillates vertically at a frequency Omega as the antenna, and a subharmonic mixer as the receiver, and corresponding demodulation algorithms, the back-scattered light carrying tip-sample interaction information is effectively extracted, while excluding almost all of the background noises. The amplitude and phase images constructed from signals demodulated at various harmonics (n Omega, n = 1 - 4) are obtained while scanning an Au-Si step structure with the newly developed microscope, and a resolution of 155 nm (similar to lambda/20,000) has been demonstrated at the fourth harmonic frequency (4 Omega) working at 110 GHz, with signal-to-noise ratio (SNR) equal to 44.4 dB on the Au surface and 36.2 dB on the Si surface, demonstrating the power of this new instrument for micro/nano-resolution studies in the millimeter wave band.

Automated summary

This study introduces a scattering-type scanning near-field microscope operating in the low terahertz band for nanoscopic investigations of sample surfaces and interfaces in the microwave and millimeter wave bands. By employing a nano-tip antenna and subharmonic mixer receiver with demodulation algorithms, high-resolution amplitude and phase images were achieved while scanning an Au-Si step structure, demonstrating the potential of this new instrument for micro/nano-resolution studies in the millimeter wave band.