A common observation in metal-based ͑specifically, those with AlO x tunnel junctions͒ single-electron tunneling ͑SET͒ devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that ͑1͒ brief measurements over short periods of time can mask the underlying drift, ͑2͒ we have not found any reproducible technique to eliminate the drift, and ͑3͒ two-level fluctuators ͑TLFs͒ in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in good agreement with our charge offset drift observations. We conclude that, while the Si devices are not perfect and defect-free, the defects are stable and noninteracting; in contrast, the interacting, unstable glasslike defects in the metal-based devices are what lead to the charge offset drift. We end by suggesting some particular directions for the improvement in fabrication, and in particular, fabrication with crystalline metal-oxide barriers, that may lead to charge offset drift-free behavior.

We describe a non-traditional optical power meter which measures radiation pressure to accurately determine a laser's optical power output. This approach traces its calibration of the optical watt to the kilogram. Our power meter is designed for high-accuracy and portability with the capability of multi-kilowatt measurements whose upper power limit is constrained only by the mirror quality. We provide detailed uncertainty evaluation and validate experimentally an average expanded relative uncertainty of 0.016 from 1 kW to 10 kW. Radiation pressure as a power measurement tool is unique to the extent that it does not rely on absorption of the light to produce a high-accuracy result. This permits fast measurements, simplifies power scalability, and allows high-accuracy measurements to be made during use of the laser for other applications.

We have developed a new method for measuring the value of breakdown voltage in air for electrode separations from 400 nm to 45 m. The electrodes used were thin film Au lines evaporated on sapphire. The resulting capacitors had an area of 80ϫ 80 m 2 . We demonstrate the ability to deduce the value of the separation of the plates by the value of the capacitance. The data acquired with this method do not agree with Paschen's law for electrode separations below 10 m, as expected from previous experiments. Amongst the improvements of our method are the measurement of plate separation and the very small surface roughness ͑average of 6 nm͒.

The problem of charge offset drift in single-electron tunneling (SET) devices can preclude their useful application in metrology and integrated devices. We demonstrate that in tunable-barrier Si-based SET transistors there is excellent stability, with a drift that is in general less than 0.01e; these devices exhibit some unwanted sensitivity to external perturbations including temperature excursions. Finally, we show that these devices can be “trained” to minimize their sensitivity to abrupt voltage changes.

In this work, we perform high accuracy measurements of thermophysical properties for the National Institute of Standards and Technology standard reference material for 316L stainless steel. As these properties can be sensitive to small changes in elemental composition even within the allowed tolerances for an alloy class, by selecting a publicly available standard reference material for study our results are particularly useful for the validation of multiphysics models of industrial metal processes. An ohmic pulse-heating system was used to directly measure the electrical resistivity, enthalpy, density, and thermal expansion as functions of temperature. This apparatus applies high current pulses to heat wire-shaped samples from room temperature to metal vaporization. The great advantage of this particular pulse-heating apparatus is the very short experimental duration of 50 ls, which is faster than the collapse of the liquid wire due to gravitational forces, as well as that it prevents any chemical reactions of the hot liquid metal with its surroundings. Additionally, a differential scanning calorimeter was used to measure specific heat capacity from room temperature to around 1400 K. All data are accompanied by uncertainties according to the guide to the expression of uncertainty in measurement. Jeffrey W. Sowards: Formerly with NIST.