Cryogenic Scattering-type Scanning Near-field Optical Microscopy

Scattering-type scanning near field optical microscopy (s-SNOM) has become an important branch of modern optical techniques in the past decade, which allows nanoscale imaging over a broad spectral range. This informative technique is feasible to study the electrodynamics of correlated quantum materials with a spatial resolution down to 10 nm. As a powerful scanning probe microscopy, although the importance of cryo-SNOM has been universally recognized, the realization remains to be a challenging task. Based on the experience of cryo-AFM, we built a set of s-SNOM operating with variable sample temperature down to 10 K. The scanning probe is located in ultra high vacuum chamber with He-bath cryostat maintaining low temperature and combined with a molecule beam epitaxy (MBE) system. The nine home-made positioners of the scanning system function well at low temperature. The system is equipped with CO₂ laser which can provide long-time stable light source. Our cryo-SNOM has been tested at liquid nitrogen temperature, which shows good performance and is promising to work well below 10K.