Kasai Jun, Koyama Tomoki, Yokota Munenori, Iwaya Katsuya
UNISOKU Co., Ltd., Hirakata, Osaka 573-0131, Japan.
Rev Sci Instrum. 2022 Apr 1;93(4):043711. doi: 10.1063/5.0084888.
We report the design and performance of a cryogen-free, pulse-tube refrigerator (PTR)-based scanning probe microscopy (SPM) system capable of operating at a base temperature of near 5 K. We achieve this by combining a home-made interface design between the PTR cold head and the SPM head, with an automatic gas-handling system. The interface design isolates the PTR vibrations by a combination of polytetrafluoroethylene and stainless-steel bellows and by placing the SPM head on a passive vibration isolation table via two cold stages that are connected to thermal radiation shields using copper heat links. The gas-handling system regulates the helium heat-exchange gas pressures, facilitating both the cooldown to and maintenance of the base temperature. We discuss the effects of each component using measured vibration, current-noise, temperature, and pressure data. We demonstrate that our SPM system performance is comparable to known liquid-helium-based systems with the measurements of the superconducting gap spectrum of Pb, atomic-resolution scanning tunneling microscopy image and quasiparticle interference pattern of Au(111) surface, and non-contact atomic force microscopy image of NaCl(100) surface. Without the need for cryogen refills, the present SPM system enables uninterrupted low-temperature measurements.
我们报告了一种基于无液氦脉冲管制冷机（PTR）的扫描探针显微镜（SPM）系统的设计与性能，该系统能够在接近5 K的基温下运行。我们通过将PTR冷头与SPM头之间的自制接口设计与自动气体处理系统相结合来实现这一目标。该接口设计通过聚四氟乙烯和不锈钢波纹管的组合，以及通过两个冷级将SPM头放置在被动隔振台上，这两个冷级使用铜热连接与热辐射屏蔽相连，从而隔离PTR的振动。气体处理系统调节氦气热交换气体的压力，有助于冷却到基温和维持基温。我们使用测量的振动、电流噪声、温度和压力数据讨论了每个组件的影响。通过对Pb的超导能隙谱、Au(111)表面的原子分辨率扫描隧道显微镜图像和准粒子干涉图案以及NaCl(100)表面的非接触原子力显微镜图像的测量，我们证明了我们的SPM系统性能与已知的基于液氦的系统相当。由于无需补充低温制冷剂，当前的SPM系统能够进行不间断的低温测量。
