A cryogenic scattering-type scanning near-field optical microscope

Scattering-type scanning near-field optical microscopy (s-SNOM) provides few nanometer optical spatial resolution and is compatible with nearly any form of linear and nonlinear optical spectroscopy. We have developed a versatile s-SNOM instrument operating under cryogenic and variable temperature (similar to 20-500 K) and compatible with high magnetic fields (up to 7 T). The instrument features independent tip and sample scanning and free-space light delivery with an integrated off-axis parabolic mirror for tip-illumination and signal collection with a numerical aperture of N.A. = 0.45. The optics operate from the UV to THz range allowing for continuous wave, broadband, and ultrafast s-SNOM spectroscopy, including different variants of tip-enhanced spectroscopy. We discuss the instrument design, implementation, and demonstrate its performance with mid-infrared Drude response s-SNOM probing of the domain formation associated with the metal-insulator transitions of VO2 (T-MIT similar or equal to 340 K) and V2O3 (TMIT similar or equal to 150 K). This instrument enables the study of mesoscopic order and domains of competing quantum phases in correlated electron materials over a wide range of controlled electric and magnetic fields, strain, current, and temperature. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789428]