Development of a cryogenic passive-scattering-type near-field optical microscopy system.

Area of Science:

• Physics
• Materials Science
• Nanotechnology

Background:

• Passive scattering-type scanning near-field optical microscopy (s-SNOM) studies localized, long-wavelength infrared (LWIR) surface waves.
• External illumination is typically required for s-SNOM, limiting its application in certain low-temperature environments.

Purpose of the Study:

• To develop a cryogenic passive s-SNOM instrument for near-field detection without external illumination.
• To investigate thermally excited surface electromagnetic fields at cryogenic temperatures.

Main Methods:

• Implementation of a cryogenic passive s-SNOM instrument within a vacuum chamber with 4 K liquid-helium cooling.
• Utilizing a highly sensitive LWIR confocal optical system and a tuning fork-based atomic force microscope for near-field detection at 10.2 ± 0.9 µm.
• Investigating self-heated NiCr wire on SiO2 at 5 K.

Main Results:

• Achieved passive near-field detection with significantly reduced background thermal noise due to the cryogenic environment.
• Identified thermally excited fluctuating charges of conduction electrons as the origin of surface electromagnetic fields.
• Demonstrated the capability to study surface electromagnetic fields at extremely low temperatures.

Conclusions:

• The developed cryogenic passive s-SNOM is a powerful tool for investigating LWIR surface waves and electromagnetic fields in low-temperature environments.
• This technique offers a novel approach for studying phenomena like hot-carrier dissipation in ballistic conductors.
• The low background noise achieved at 4 K enhances the sensitivity and applicability of s-SNOM.