George R. Jones

NBS determination of the fine-structure constant, and of the quantized Hall resistance and Josephson frequency-to-voltage quotient in SI units

Results of US National Bureau of Standards (NBS) experiments to realize the ohm and the watt, to determine the proton gyromagnetic ratio by the low-field method, to determine the time dependence of the NBS representation of the ohm using the quantum Hall effect, and to maintain the NBS representation of the volt using the Josephson effect, are appropriately combined to obtain an accurate value of the fine-structure constant and of the quantized Hall resistance in SI units, and values in SI units of the Josephson frequency-to-voltage quotient, Planck constant and elementary charge. >

NIST Measurement Service for DC Standard Resistors

At the National Institute of Standards and Technology (NIST), the U.S. representation of the ohm is based on the quantum Hall effect, and it is maintained and disseminated at various resistance levels by working reference groups of standards. This document describes the measurement systems and procedures used to calibrate standard resistors and current shunts of nominal decade values in the resistance range from 10 Ω to 10 Ω. Resistance scaling techniques used to assign values to the working standards are discussed. Also included is an assessment of the calibration uncertainties at each resistance level.

A measurement of the NBS electrical watt in SI units

The National Bureau of Standards (NBS) electric watt in SI units to be: W/sub NBS//W=K/sub W/=1-(16.69+or-1.33) p.p.m. The uncertainty of 1.33 p.p.m. has the significance of a standard deviation and includes the best estimate of random and known or suspected systematic uncertainties. The mean time of the measurement is May 15, 1988. Combined with the measurement of the NBS ohm in SI units: Omega /sub NBS// Omega =K/sub Omega /=1-(1.593+or-0.022) p.p.m., this leads to a Josephson frequency/voltage quotient of E/sub J/=E/sub 0/(1+(7.94+or-0.67) p.p.m.) where E/sub 0/=483, 594 GHz/V. >

Display Reflectance Model Based on the BRDF

Abstract Many flat panel displays (FPDs) have anti-reflection surface treatments that differ in character from those of traditional cathode-ray-tube displays. Specular reflection models (mirror-like, producing a distinct image) combined with diffuse (Lambertian) reflection models can be entirely inadequate to characterize the reflection properties of such displays. A third reflection component, called haze, exists between specular and diffuse. Display metrology should account for the haze component of reflection. That is best done using the bidirectional reflectance distribution function (BRDF). The effects of using oversimplified reflectance models are discussed in contrast with a parameterized BRDF.

Epitaxial graphene homogeneity and quantum Hall effect in millimeter-scale devices

Quantized magnetotransport is observed in 5.6 × 5.6 mm2 epitaxial graphene devices, grown using highly constrained sublimation on the Si-face of SiC(0001) at high temperature (1900 °C). The precise quantized Hall resistance of [Formula: see text] is maintained up to record level of critical current Ixx = 0.72 mA at T = 3.1 K and 9 T in a device where Raman microscopy reveals low and homogeneous strain. Adsorption-induced molecular doping in a second device reduced the carrier concentration close to the Dirac point (n ≈ 1010 cm-2), where mobility of 18760 cm2/V is measured over an area of 10 mm2. Atomic force, confocal optical, and Raman microscopies are used to characterize the large-scale devices, and reveal improved SiC terrace topography and the structure of the graphene layer. Our results show that the structural uniformity of epitaxial graphene produced by face-to-graphite processing contributes to millimeter-scale transport homogeneity, and will prove useful for scientific and commercial applications.

The NBS Absolute Ampere Experiment

We have constructed a current balance with superconducting field coils for the realization of the SI ampere by comparing mechanical to electrical work. The estimated ultimate accuracy of the realization is 0.1 ppm. We describe and present preliminary results obtained with a room temperature version of the apparatus.

Report on the New NBS Determination of the Proton Gyromagnetic Ratio

We describe a new measurement of the proton gyromagnetic ratio in H2O, ¿¿p, now in progress at NBS, including the construction of a single layer precision solenoid, the measurement of its dimensions by an inductive technique, and our latest dimensional measurement results. We also discuss other improvements made since our last ¿¿p determination.

Characteristics of precision 1 Ω standard resistors influencing transport behaviour and the uncertainty of key comparisons

National measurement institutes (NMIs) participate in international key comparisons organized by the Bureau International des Poids et Mesures (BIPM), the Regional Metrology Organizations (RMOs) or the Consultative Committees of the Comit? International des Poids et Mesures (CIPM) in order to provide evidence of equivalent reference standards and measurement capabilities. The US National Institute of Standards and Technology (NIST) and the National Measurement Institute of Australia (NMIA) have recently examined power loading and several other influences on the value of precision transportable 1?? resistors that can increase the uncertainty of key comparisons. We have studied the effects of temperature, barometric pressure, humidity, power loading and heat dissipation in oil on transportable wire-wound 1?? resistance standards that are based on different alloys and construction principles. This work focuses on standards manufactured from 1970 through 2000 by the NMIA made of Evanohm alloy and on Thomas-type resistors designed in the 1930s and made of Manganin alloy. We show that the relative standard uncertainty related to transport can be less than 0.01??????1 when using certain resistors of these two types that are characterized and selected for stability. We describe the characterization process, and relate the environmental influences to the physical design, as well as to the mechanical properties and condition of the standards.

High resistance scaling from 10 kΩ and QHR standards using a cryogenic current comparator

We describe a cryogenic current comparator (CCC) bridge for resistance scaling that provides improved measurement uncertainty over a range of resistance values from 100 kOmega to 1 GOmega. This CCC is designed for high resistance scaling based directly on a quantized Hall resistance (QHR) standard as well as comparisons of resistance ratios of 1, 10 and 100. The QHR-to-decade-value winding ratio offset is chosen so as to approximately cancel the offset produced by resistive decade windings.

A survey of the components of display-measurement standards

Several display standards are reviewed and distinctive elements are compared. With flat panel displays becoming more common and the CRT displays being so well established, the associated standards activities can be somewhat bewildering, even overwhelming. This paper attempts to identify complementary and inconsistent elements of related display standards.