Design and testing of low temperature part of an UHV SPM microscope

TL;DR

This paper describes the development and testing of a low-temperature, ultra-high vacuum scanning probe microscope capable of operating from 20 K to 700 K, utilizing cryogenic helium and liquid nitrogen cooling systems.

Contribution

It introduces a novel flow cooling system with a flexible transfer line and demonstrates the feasibility of using liquid nitrogen as a cost-effective coolant for lower temperature operation.

Findings

Successful operation at 20 K with helium cooling.

Achieved stable temperature control with optimized flow system.

Liquid nitrogen cooling enabled operation above 100 K.

Abstract

We have developed low temperature part of an ultra high vacuum scanning probe microscope (UHV-SPM) working at variable temperature within the range from 20 K to 700 K. To achieve the required temperature range, a flow cooling system using cryogenic helium (~5 K) as a coolant was designed. The system consists of a flow cryostat and a flexible low-loss transfer line connecting a Dewar vessel with the flow cryostat. We have also tested liquid nitrogen (~ 77 K) as an alternative low-cost coolant. Using nitrogen, the microscope can operate at temperatures of about 100 K and higher. As the flow of the coolant through the cryostat can cause thermally induced two-phase flow fluctuations resulting in instability in temperatures, preliminary tests were done in order to find ways of avoiding the temperature oscillations and optimising the cooling process.