A Measurement System for the Determination of h/e2in Terms of the SI Ohm and the Maintained Ohm at the NPL

A measurement system comprising several stages has been developed to determine the value of the quantum Hall resistance, RH (= h/ie2), in silicon MOSFET and GaAs/Gai-xAlxAs heterostructure devices, at temperatures>0.3 K and in magnetic fields <14.5 T for the i = 2 and i = 4 plateaus. For this system, when operating under ideal conditions the expected overall one-standard deviation random uncertainties for a single measurement of RH in terms of ??SI and ??NPL, are 0.11 and 0.08 ppm, respectively. The results of several measurements on a silicon MOSFET and a GaAs/Ga1-xAlx As heterostructure device are presented leading to a mean value of h/e2 = 25812.8083(46)??SI.