arXiv subjects

Stephen P. Giblin

Publications and source records attributed to Stephen P. Giblin.

4 recordsLinked to original sources

arXiv2019

Evidence for universality of tunable-barrier electron pumps

We review recent precision measurements on semiconductor tunable-barrier electron pumps operating in a ratchet mode. Seven studies on five different designs of pumps have reported measurements of the pump current with relative total uncertainties around $10^{-6}$ or less. Combined with theoretical models of electron capture by the pumps, these experimental data exhibits encouraging evidence that the pumps operate according to a universal mechanism, independent of the details of device design. Evidence for robustness of the pump current against changes in the control parameters is at a more preliminary stage, but also encouraging, with two studies reporting robustness of the pump current against three or more parameters in the range of $\sim\!5 \times 10^{-7}$ to $\sim\!2 \times 10^{-6}$. This review highlights the need for an agreed protocol for tuning the electron pump for optimal operation, as well as more rigorous evaluations of the robustness in a wide range of pump designs.

cond-mat.mes-hall↗

arXiv2019

Exploring a new ammeter traceability route for ionisation chamber measurements

We compared the performance of a commercial ammeter and a home-made integrating electrometer in reading ionisation chamber currents less than 100 pA. The integrating electrometer charges a capacitor with the unknown current and measures the resulting rate of change of voltage, whereas the ammeter uses a high-value resistor as the feedback element to an amplifier which converts current to voltage. The noise performance of both systems was very similar for averaging times less than 1000 seconds. Both systems were calibrated using a reference current source with 1 part per million (ppm) accuracy, revealing an error of 460 ppm in the electrometer indicated current, of unknown origin. This error is well within the uncertainty budget for radionuclide calibrations, but much larger than the individual uncertainties in the traceable calibrations of capacitance, voltage and time. The noise in the ionisation chamber current was much larger than the noise floor of both instruments, with tests providing strong indication that the excess noise originated in the high voltage source used for energising the chamber.

physics.ins-det↗

arXiv2018

Re-evaluation of uncertainty for calibration of $100$ M$Ω$ and $1$ G$Ω$ resistors at NPL

The uncertainty for calibrating $100$ M$Ω$ and $1$ G$Ω$ resistors using the NPL high-resistance CCC bridge has been re-evaluated, resulting in combined uncertainties of $\sim 0.1$ $μΩ/ Ω$, considerably smaller than the CMC entries of $0.4$ $μΩ/ Ω$ and $1.6$ $μΩ/ Ω$ respectively. This re-evaluation supports measurement of single electron pump currents with combined uncertainties of a few parts in $10^7$.

physics.ins-det↗

arXiv2015

Validation of the ultrastable low-noise current amplifier as travelling standard for small direct currents

An interlaboratory comparison of small-current generation and measurement capability is presented with the ultrastable low-noise current amplifier (ULCA) acting as travelling standard. Various measurements at direct currents between 0.16 nA and 13 nA were performed to verify the degree of agreement between the three national metrology institutes involved in the study. Consistency well within one part per million (ppm) was found. Due to harsh environmental conditions during shipment, the ULCA's transfer accuracy had been limited to about +/-0.4 ppm. Supplemental measurements performed at PTB indicate that further improvements in accuracy are possible. Relative uncertainties of 0.1 ppm are achieved by applying on-site calibration of the ULCA with a suitable cryogenic current comparator.

physics.ins-det↗