Post by Professor Lake Shore on Jan 31, 2017 17:33:37 GMT -5
In a CPX or CRX probe station, do you have any guidance on how to avoid contamination of a delicate sample during cool down to helium temperatures?
For helium temperature operation, residual gases in the probe station chamber will condense and freeze on the coldest surfaces, and, under normal operating conditions, the sample stage is often the fastest cooling stage of a cryogenic probe station. You can avoid contamination on your sample by maintaining the sample stage at room temperature during station cool down. An effective way to minimize the condensation on the sample, this procedure is often required when measuring a surface-sensitive sample, as well as any device where maintaining low contact resistance is critical. This is accomplished by allowing the radiation shield stage to cool first so that the majority of residual gas is attracted to it and not the sample mounted on the sample stage. Specifically, the temperature controller, which is used to precisely regulate sample stage and radiation shield temperatures, will keep the sample stage warm while the remainder of the refrigerator cools to base temperature, at which point, any residual gas in the chamber will condense on the 4 K shield stage. The step-by-step procedure for doing this can be found in Chapter 5 of the probe station manual. This feature is only available on CPX and CRX probe station models.