Development of a cryogen-free sub-3 K low-temperature scanning probe microscope by remote liquefaction scheme

• Published in: Review of scientific instruments 2023-09, Vol.94 (9)
• Main Authors: Ma, Ruisong, Li, Hao, Shi, Chenshuai, Wang, Fan, Lei, Le, Huang, Yuanzhi, Liu, Yani, Shan, Huan, Liu, Li, Huang, Shesong, Niu, Zhi-Chuan, Huan, Qing, Gao, Hong-Jun
• Format: Article
• Language: English
• Subjects: Chambers; Continuous flow; Cooling curves; Cryogenic cooling; Cryogenic temperature; Heat exchangers; Helium; Liquefaction; Low temperature; Microscopy; Reliquefaction; Scanning probe microscopes; Scanning tunneling microscopy; Scientific apparatus & instruments; Transfer lines; Vibration
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/5.0165089

We developed a new scheme for cryogen-free cooling down to sub-3 K temperature range and ultra-low vibration level. An ultra-high-vacuum cryogen-free scanning probe microscope (SPM) system was built based on the new scheme. Instead of mounting a below-decoupled cryocooler directly onto the system, the new design was realized by integrating a Gifford-McMahon cryocooler into a separate liquefying chamber, providing two-stage heat exchangers in a remote way. About 10 L of helium gas inside the gas handling system was cooled, liquefied in the liquefying chamber, and then transferred to a continuous-flow cryostat on the SPM chamber through an ∼2 m flexible helium transfer line. The exhausted helium gas from the continuous-flow cryostat was then returned to the liquefying chamber for reliquefaction. A base temperature of ∼2.84 K at the scanner sample stage and a temperature fluctuation of almost within ±0.1 mK at 4 K were achieved. The cooling curves, tunneling current noise, variable-temperature test, scanning tunneling microscopy and non-contact atomic force microscopy imaging, and first and second derivatives of I(V) spectra are characterized to verify that the performance of our cryogen-free SPM system is comparable to the bath cryostat-based low-temperature SPM system. This remote liquefaction close-cycle scheme shows conveniency to upgrade the existing bath cryostat-based SPM system, upgradeability of realizing even lower temperature down to sub-1 K range, and great compatibility of other physical environments, such as high magnetic field and optical accesses. We believe that the new scheme could also pave a way for other cryogenic applications requiring low temperature but sensitive to vibration.