Electrical resistance measurements at 4.2 K have been made for various screw‐fastened thermal joints used at ultra‐low temperatures below 100 μK. The measured contact resistance for a gold‐plated joint varied in inverse proportion to a tightening torque of the screw. With a maximum tightening torque for a 4‐mm stainless‐steel screw, several types of the joints revealed to have contact resistances below 10 nΩ. A current‐decay method used to measure a small variation of contact resistance of less than 0.1 nΩ is also described.
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The disks were machined from a commercial grade copper (99.8% pure) and annealed at 950 °C for three days under oxygen gas flow A 1‐mm‐diam copper wire made from the same lot as the disks showed the RRR of 4000 after the same heat treatment.
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© 1990 American Institute of Physics.
1990
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