Search

We report on nonreciprocity observations in several configurations of graphene-based quantum Hall devices. Two distinct measurement configurations were adopted to verify the universality of the observations (i.e., two-terminal arrays and four-terminal devices). Our findings determine the extent to which epitaxial graphene anisotropies contribute to the observed asymmetric Hall responses. The presence of backscattering induces a device-dependent asymmetry rendering the Onsager-Casimir relations limited in their capacity to describe the behavior of such devices, except in the low-field classical regime and the fully quantized Hall state. The improved understanding of this quantum electrical process broadly limits the applicability of the reciprocity principle in the presence of quantum phase transitions and for anisotropic two-dimensional materials.

As first recognized in 2010, epitaxial graphene on SiC(0001) provides a platform for quantized Hall resistance (QHR) metrology unmatched by other two-dimensional structures and materials. Here we report graphene parallel QHR arrays, with metrologically precise quantization near $1000\phantom{\rule{4pt}{0ex}}\mathrm{\ensuremath{\Omega}}$. These arrays have tunable carrier densities, due to uniform epitaxial growth and chemical functionalization, allowing quantization at the robust $\ensuremath{\nu}=2$ filling factor in array devices at relative precision better than ${10}^{\ensuremath{-}8}$. Broad tunability of the carrier density also enables investigation of the $\ensuremath{\nu}=6$ plateau. Optimized networks of QHR devices described in this work suppress Ohmic contact resistance error using branched contacts and avoid crossover leakage with interconnections that are superconducting for quantizing magnetic fields up to 13.5 T. Our work enables more direct scaling of resistance for quantized values in arrays of arbitrary network geometry.

Employing very simple electro-mechanical principles known from classical physics, the Kibble balance establishes a very precise and absolute link between quantum electrical standards and macroscopic mass or force measurements. The success of the Kibble balance, in both determining fundamental constants ($h$, $N_A$, $e$) and realizing a quasi-quantum mass in the 2019 newly revised International System of Units, relies on the perfection of Maxwell's equations and the symmetry they describe between Lorentz's force and Faraday's induction, a principle and a symmetry stunningly demonstrated in the weighing and velocity modes of Kibble balances to within $1\times10^{-8}$, with nothing but imperfect wires and magnets. However, recent advances in the understanding of the current effect in Kibble balances reveal a troubling paradox. A diamagnetic effect, a force that does not cancel between mass-on and mass-off measurement, is challenging balance maker's assumptions of symmetry at levels that are almost two orders of magnitude larger than the reported uncertainties. The diamagnetic effect, if it exists, shows up in weighing mode without a readily apparent reciprocal effect in the velocity mode, begging questions about systematic errors at the very foundation of the new measurement system. The hypothetical force is caused by the coil current changing the magnetic field, producing an unaccounted force that is systematically modulated with the weighing current. Here we show that this diamagnetic force exists, but the additional force does not change the equivalence between weighing and velocity measurements. We reveal the unexpected way that symmetry is preserved and show that for typical materials and geometries the total relative effect on the measurement is $\approx 1\times10^{-9}$., Accepted for publication in Scientific Reports

The magnet system for the Quantum Electro-Mechanical Metrology Suite (QEMMS) Kibble balance is being manufactured. The QEMMS Kibble balance will be used to measure masses nominally around 100 g and the magnet system will be able to generate forces up to 1 N. Some aspects of the magnet system and the measurement procedure used to determine the profile of the magnetic field are described here.

A new paradigm in laser power metrology has recently evolved. The measurement of photon pressure forces from the reflection of a laser from a high reflectivity mirror provides a means to quantify optical power in a fashion similar to methods used to realize the mass unit in the redefined SI. Because photon pressure forces are typically quite small, an electrostatic force balance (EFB) can be effectively used to interconvert between force and laser power within the International System of Units (SI). In this work, a portable version of the EFB is constructed and tested. The balance will be used to measure a photon pressure equivalent to 10 kilowatts of laser power (approximately 60 micronewtons) with an uncertainty on the order of 0.01%. A preliminary demonstration shows sufficient resolution for the required application.

On November 16 2018, about 60 countries met in Versailles, France and voted to redefine the System of Units(SI) based on seven defining reference constants. Since May 20 2019, the unit of mass is realized based on three fundamental reference constants: the Planck constant $h$ , the speed of light $c$ , and the unperturbed ground state hyperfine transition frequency of the cesium 133 atom $\Delta\nu_{Cs}$ . With this new definition of the unit of mass, scientists at the National Institute of Standards and Technology (NIST) realized masses in the range of 0.05 kg to 0.20 kg directly on the NIST primary realization, and compared the results to the traditional work-down. This abstract shows the advantage and the improvement in the measurement uncertainty of mass in the small range that was only possible after the redefinition.

Sufficient progress towards redefining the International System of Units (SI) in terms of exact values of fundamental constants has been achieved. Exact values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant N A from the CODATA 2017 Special Adjustment of the Fundamental Constants are presented here. These values are recommended to the 26th General Conference on Weights and Measures to form the foundation of the revised SI.

The special least-squares adjustment of the values of the fundamental constants, carried out by the Committee on Data for Science and Technology (CODATA) in the summer of 2017, is described in detail. It is based on all relevant data available by 1 July 2017. The purpose of this adjustment is to determine the numerical values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant N A for the revised SI expected to be established by the 26th General Conference on Weights and Measures when it convenes on 13–16 November 2018.

The design of the permanent magnet system for the new Quantum Electro-Mechanical Metrology Suite (QEMMS) is described. The QEMMS, developed at the National Institute of Standards and Technology (NIST), consists of a Kibble balance, a programmable Josephson voltage standard, and a quantum Hall resistance standard. It will be used to measure masses up to $100\,\mathrm{g}$ with relative uncertainties below $2\times 10^{-8}$. The magnet system is based on the design of the NIST-4 magnet system with significant changes to adopt to a smaller Kibble balance and to overcome known practical limitations. Analytical models are provided to describe the coil-current effect and model the forces required to split the magnet in two parts to install the coil. Both models are compared to simulation results obtained with finite element analysis and measurement results. Other aspects, such as the coil design and flatness of $Bl$ profile are considered., 9 pages, 12 figures, published in IEEE Trans. Instrum. Meas

Optomechanical accelerometers offer in situ traceability to the international system of units through laser interferometry, providing an alternative to a calibration chain using instrumented shakers. Here, we examine the ‘self-calibrating’ property of a prototype optomechanical accelerometer for use as a seismic reference. We report the optomechanically derived sensitivity of the accelerometer and compare this in situ calibrated output to input accelerations from an instrumented shaker, finding agreement to be within ±1%. The comparison spanned frequencies between 3 Hz and 30 Hz, and for sinusoidal accelerations with amplitudes ranging from 0.01 m s−2 to 0.6 m s−2. These results are evidence that optomechanically derived sensitivity calibration can be equivalent to established international methods for primary calibration.

Metallic transition metal dichalcogenides, such as tantalum diselenide $(\mathrm{TaS}{\mathrm{e}}_{2})$, display quantum correlated phenomena of superconductivity and charge density waves (CDWs) at low temperatures. Here, the photophysics of 2H-$\mathrm{TaS}{\mathrm{e}}_{2}$ during CDW transitions is revealed by combining temperature-dependent, low-frequency Raman spectroscopy and density functional theory (DFT). The spectra contain amplitude, phase, and zone-folded modes that are assigned to specific phonons and lattice restructuring predicted by DFT calculations with superb agreement. The noninvasive and efficient optical methodology detailed here demonstrates an essential link between atomic-scale and microscopic quantum phenomena.

This work presents precision measurements of quantized Hall array resistance devices using superconducting, crossover-free, multiple interconnections as well as graphene split contacts. These new techniques successfully eliminate the accumulation of internal resistances and leakage currents that typically occur at interconnections and crossing leads between interconnected devices. As a result, a scalable quantized Hall resistance array is obtained with a nominal value that is as precise and stable as that from single-element quantized Hall resistance standards.

We report the performance of a quantum standard based on epitaxial graphene maintained in a 5 T table-top cryocooler system. The $v=2$ resistance plateau, with a value of ${R}_{\mathbf{K}-{90}/2}$ , is used to scale to ${1}\ \text{k}{\Omega}$ using a binary cryogenic current comparator (BCCC) bridge. The preliminary uncertainties achieved with the BCCC are like those obtained in state-of-the-art measurements using GaAs-based devices. This quantum standard requires no liquid He and can operate continuously, allowing year-round accessibility to traceable resistance measurements.

We review correlated uncertainties among the accurate determinations of the Boltzmann constant that used the techniques of primary acoustic gas thermometry (AGT). We find correlated uncertainty contributions from four sources: (1) the uncertain chemical and isotopic compositions of the test gases that lead to an uncertain average molar mass, (2) measurements of the temperature, (3) measurements of the shape and dimensions of the cavity resonators, and (4) fitting acoustic resonance frequencies as a function of the pressure. Molar-mass-dependent uncertainties are correlated among those measurements that used argon with isotopic abundances determined using an isotopic standard prepared at the Korea Research Institute of Standards and Science in 2006. Correlated, cavity-dependent uncertainties result from using the same cavity for more than one measurement. Small, correlated uncertainties propagate into all the AGT determinations of when acoustic resonance frequencies are fit for using uncertain literature data for the Avogadro constant and for the thermal conductivity and the higher acoustic virial coefficients of helium or argon.

Using a watt balance and a frequency comb, a mass-energy equivalence is derived. The watt balance compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck constant is established by the practical realization of the electrical units derived from the Josephson and the quantum Hall effects. By using frequency combs to measure velocities and acceleration of gravity, the unit of mass can be realized from a set of three defining constants: the Planck constant h, the speed of light c, and the hyperfine splitting frequency of 133Cs.

Photocurrent oscillating with respect to backgate voltage is observed in graphene in the quantum Hall regime. The relationship between edge states chirality and carrier type is explored and interplay among exquisite processes is revealed.

We report the performance of a quantum Hall resistance standard based on epitaxial graphene maintained in a 5-T tabletop cryocooler system. This quantum resistance standard requires no liquid helium and can operate continuously, allowing year-round accessibility to quantized Hall resistance measurements. The $\nu = 2$ plateau, with a value of $R_{\mathrm {K}}$ /2, also seen as $R_{\mathrm {H}}$ , is used to scale to 1 $\text{k}\Omega $ using a binary cryogenic current comparator (BCCC) bridge and a direct current comparator (DCC) bridge. The uncertainties achieved with the BCCC are such as those obtained in the state-of-the-art measurements using GaAs-based devices. BCCC scaling methods can achieve large resistance ratios of 100 or more, and while room temperature DCC bridges have smaller ratios and lower current sensitivity, they can still provide alternate resistance scaling paths without the need for cryogens and superconducting electronics. Estimates of the relative uncertainties of the possible scaling methods are provided in this report, along with a discussion of the advantages of several scaling paths. The tabletop system limits are addressed as are potential solutions for using graphene standards at higher currents.

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value $h=6.626\,069\,79(30)\times 10^{-34}\,$J$\,$s. The relative standard uncertainty is $ 45\times 10^{-9}$. This result is $141\times 10^{-9}$ fractionally higher than $h_{90}$. Here $h_{90}$ is the conventional value of the Planck constant given by $h_{90}\equiv 4 /( K_{\mathrm{J-90}}^2R_{\mathrm{K-90}})$, where $K_{\mathrm{J-90}}$ and $R_{\mathrm{K-90}}$ denote the conventional values of the Josephson and von Klitzing constants, respectively., Comment: 22 pages, 8 figures, published in metrologia

We report on a 2012 comparison of gravity used to determine the Planck constant by the National Institute of Standards and Technology (NIST) and the National Research Council Canada (NRC) watt balances. The results provide verification of the gravity values used in recently published discrepant Planck constant determinations that play a vital role in the redefinition effort of the International System of Units (SI) and set an upper limit of 10 parts in 109 on the relative uncertainty contribution of gravity observations to future Planck constant determinations by the NIST and NRC watt balances. © 2013 BIPM & IOP Publishing Ltd., Erratum published in volume 50, issue 5, pages 557-8, October 2013. DOI: 10.1088/0026-1394/50/5/557

A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck constant is established by the practical realization of the electrical units derived from the Josephson and the quantum Hall effects. We describe in this paper the fourth-generation watt balance at the National Institute of Standards and Technology (NIST), and report our initial determination of the Planck constant obtained from data taken in late 2015 and the beginning of 2016. A comprehensive analysis of the data and the associated uncertainties led to the SI value of the Planck constant, h = 6.626 069 83(22) × 10(-34) J s. The relative standard uncertainty associated with this result is 34 × 10(-9).

In the past four years, we have constructed a new watt balance at the National Institute of Standards and Technology (NIST), with the goal to realize the unit of mass after the redefinition of the International System of Units, expected to occur in 2018. The new watt balance has been operational since the fall of 2015 and we describe our first measurements with it.

The National Institute of Standards and Technology (NIST) new watt balance (NIST-4) has been constructed for the realization of mass through an exact value of the Planck constant in the new International System of Units (SI). The total relative uncertainty goal for the instrument of a few parts in 108 requires the determination of the local acceleration of gravity, g, with parts in 109 accuracy at the location of the mass at the time mechanical and electrical forces are being compared. We describe the procedures used and give results for the measurements of the local acceleration of gravity in the new watt balance facility.

Graphene is a unique two-dimensional material with rich new physics and great promise for applications in electronic devices. Physical phenomena such as the half-integer quantum Hall effect and high carrier mobility are critically dependent on interactions with impurities/substrates and localization of Dirac fermions in realistic devices. We microscopically study these interactions using scanning tunneling spectroscopy (STS) of exfoliated graphene on a SiO2 substrate in an applied magnetic field. The magnetic field strongly affects the electronic behavior of the graphene; the states condense into welldefined Landau levels with a dramatic change in the character of localization. In zero magnetic field, we detect weakly localized states created by the substrate induced disorder potential. In strong magnetic field, the two-dimensional electron gas breaks into a network of interacting quantum dots formed at the potential hills and valleys of the disorder potential. Our results demonstrate how graphene properties are perturbed by the disorder potential; a finding that is essential for both the physics and applications of graphene., to be published in Nature Physics

This Resource Letter provides a guide to the literature on the physics of fundamental constants and their values as determined within the International System of Units (SI). Journal articles, books, and websites that provide relevant information are surveyed. Literature on redefining the SI in terms of exact values of fundamental constants is also included.

We experimentally investigate charge carrier transport in a graphene $p\ensuremath{-}n$ junction device by using independent $p$-type and $n$-type electrostatic gating which allow full characterization of the junction interface in the quantum Hall regime covering a wide range of filling factors $[\ensuremath{-}10\ensuremath{\le}({\ensuremath{\nu}}_{1},\phantom{\rule{0.16em}{0ex}}{\ensuremath{\nu}}_{2})\ensuremath{\le}10]$. Recent charge transport measurements across a graphene $p\ensuremath{-}n$ junction in this quantized regime presume that equilibration of all of the Landauer-B\"uttiker edge states occurs across the $p\ensuremath{-}n$ junction interface. Here we show that, in our devices, only the edge state associated with the lowest Landau level fully equilibrate across the $p\ensuremath{-}n$ junction, while none of the other edge states equilibrate to transmit current across the junction.

The electronic kilogram project of NIST has improved the watt balance method to obtain a new determination of the Planck constant h by measuring the ratio of the SI unit of power W to the electrical realization unit W90, based on the conventional values for the Josephson constant KJ−90 and von Klitzing constant RK−90. The value h = 6.626 069 01(34) × 10−34 J s verifies the NIST result from 1998 with a lower combined relative standard uncertainty of 52 nW/W. A value for the electron mass me = 9.109 382 14(47) × 10−31 kg can also be obtained from this result. With uncertainties approaching the limit of those commercially applicable to mass calibrations at the level of 1 kg, an electronically-derived standard for the mass unit kilogram is closer to fruition.

In early 2014, construction of a new watt balance, named NIST-4, has started at the National Institute of Standards and Technology (NIST). In a watt balance, the gravitational force of an unknown mass is compensated by an electromagnetic force produced by a coil in a magnet system. The electromagnetic force depends on the current in the coil and the magnetic flux integral. Most watt balances feature an additional calibration mode, referred to as velocity mode, which allows one to measure the magnetic flux integral to high precision. In this article we describe first measurements of the flux integral in the new watt balance. We introduce measurement and data analysis techniques to assess the quality of the measurements and the adverse effects of vibrations on the instrument., 7 pages, 8 figures, accepted for publication in IEEE Trans. Instrum. Meas. This Journal can be found online at http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=19

International audience; The Sixth International Comparison of Absolute Gravimeters was held from 5 June to 28 August 2001 at the Bureau International des Poids et Mesures (BIPM), Sèvres. Seventeen absolute gravimeters were used to make measurements at five sites of the BIPM gravity network. The vertical gravity gradients at the sites and the ties between them were also measured using seventeen relative gravimeters. For the first time the ties were also measured using absolute gravimeters. Various methods of processing the absolute and relative data were tested to calculate the results. The final results of ICAG-2001 are presented. The acceleration due to gravity at a height of 0.90 m is given as (980 925 701.2 ± 5.5) µGal and (980 928 018.8 ± 5.5) µGal for sites A and B, respectively, calculated using a combined adjustment of the absolute and relative data.

A new watt balance is being constructed at the National Institute of Standards and Technology (NIST) in preparation for the redefinition of the International System of Units and the realization of mass through an exact value of the Planck constant. The total relative uncertainty goal for this instrument of a few parts in $10^{8}$ requires that the local acceleration due to gravity be known at the location of a test mass with a relative uncertainty on the order of only a few parts in $10^{9}$. To make this determination, both the horizontal and vertical gradients of gravity must be known such that gravity may be tied from an absolute reference in the laboratory to the precise mass location. We describe the procedures used to model and measure gravity variations throughout the laboratory and give our results., 7 pages, 10 figures, accepted for publication in IEEE Trans. Instrum. Meas. It will appear at http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=19

A new watt balance is being constructed at National Institute of Standards and Technology (NIST) in preparation for the redefinition of the International System of Units and the realization of mass through an exact value of the Planck constant. We describe the procedures used and give results for the measurements of the local acceleration of gravity in the new watt balance facility., 29th Conference on Precision Electromagnetic Measurements, CPEM 2014, 24 August 2014 through 29 August 2014, Series: CPEM Digest

An improved determination of the ratio of power, measured in terms of the Josephson and quantum Hall effects, and also the meter, kilogram, and second, has been completed. The result is expressed as: W/sub 90//W=1+(8/spl plusmn/87)/spl times/10/sup -9/. This is an order of magnitude improvement from the last NIST (formerly NBS) determination. The Type A relative standard uncertainty (statistical) is 30 nW/W, and the Type B relative standard uncertainty is 82 nW/W. Type B uncertainty components are listed and discussed within the context of experimental procedure descriptions. Improvements for the next version of this experiment are also mentioned.

Using a moving coil watt balance, electric power measured in terms of the Josephson and quantum Hall effects is compared with mechanical power measured in terms of the meter, kilogram, and second. We find the Planck constant $h\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6.62606891(58)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}34}\mathrm{J}\mathrm{s}$. The quoted standard uncertainty (1 standard deviation estimate) corresponds to $(8.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8})h$. Comparing this measurement to an earlier measurement places an upper limit of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}/\mathrm{yr}$ on the drift rate of the SI unit of mass, the kilogram.

The effects of alignment uncertainties of the NIST watt balance with respect to local gravity and the magnetic flux density of the balance have been analyzed. Techniques for measuring all quantities relevant to misalignment have been developed. The components of the relative combined standard uncertainty of the measured value of the watt due to alignment uncertainties have been reduced to 20 nW/W, and potential improvements in the balance design have been identified which could ultimately lead to a reduction of that uncertainty to below 10 nW/W.

The National Institute of Standards and Technology (NIST) watt balance is an experiment to compare measurements of the watt using electrical references (volt, ohm) to those using mechanical references (length, time, mass). A coil within a radial magnetic field has a dual use of: (1) generating a voltage by moving at some velocity to calibrate the magnetic flux density, and, (2) generating a force with electrical current to balance the gravitational force of a mass. This experiment has had several improvements made to it in the last year. These include the incorporation of three-laser interferometry and a refractometer to improve the velocity measurements, temperature control and coil rotation damping to reduce drifts and stabilize laser and mechanical alignments, and a gravimeter to determine local gravity. Systematic errors and scatter in long-term measurements have been greatly reduced in the last year, but statistically significant deviations relative to within-run uncertainty still persist. The source of these deviations has not yet been identified. Recent within-run standard deviations are generally near 0.1 pW/W, which is the target precision of this present design.

A new refractometer with a variable length vacuum cell has been developed to eliminate errors caused by deformations in optical windows of the cell. The refractive index of air is determined by measuring the changes in the optical path difference between the air of interest and a vacuum as a function of the changes in the cell length. An optical phase modulation technique and a dark fringe detection method are used to obtain a high resolution in measuring the optical path difference by a double-pass Michelson interferometer. A combined standard uncertainty of 5/spl times/10/sup -9/ in the measurement of the refractive index of air has been achieved.

We report on a 2012 absolute gravity comparison performed at the National Institute of Standards and Technology (NIST), Gaithersburg, MD. Unique to this work is the direct comparison of gravitational measurement systems used in the determination of the Planck constant by NIST and the National Research Council Canada (NRC) watt balances. The results will provide verification of the gravity values used in recently published Planck constant determinations that play a vital role in the redefinition effort of the International system of Units (SI)., 2012 Conference on Precision Electromagnetic Measurements (CPEM 2012), 2012-07-1 - 2012-07-6, Washington, DC, USA

The scientific community is presently engaged in a historic attempt to fix the value of the Planck constant h so that it might ultimately serve as a base constant in a revised system of units. To assist this effort, NIST is examining its existing watt balance experiment, NIST-3, and will measure h once again, aiming at a final rigorous test of reproducibility. The main objectives are to modify and update the existing apparatus so that it can be used both to measure the Planck constant and to support other experiments related to the mise en pratique for mass, to attempt a determination of the Planck constant that is largely independent of previous NIST results, and to probe the discrepancy between the value of h measured in 2007 and other latest published results through a careful re-examination of the NIST-3 measurement procedures and uncertainty budget.

We report preparations underway at the National Institute of Standards and Technology (NIST) in the United States and at the National Research Council (NRC) in Canada to support the redefinition of the international system of units (SI) and the development of a Mise en pratique for the unit of mass. NIST and the NRC possess two of the world's most precise moving coil watt balances and are developing a collaborative plan to reconcile differences between the respective measurement platforms by testing their ability to mutually realize the kilogram from the Planck constant. The important role to be played by mass metrology and new facilities, such as the NIST magnetic levitation balance and the NRC vacuum comparator, to establish the necessary link between a mass as measured in vacuum and its value in air will be considered., 2012 Conference on Precision Electromagnetic Measurements (CPEM 2012), 2012-07-1 - 2012-07-6, Washington, DC, USA

Bilayer graphene has drawn significant attention due to the opening of a band gap in its low energy electronic spectrum, which offers a promising route to electronic applications. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Our scanning tunneling measurements reveal the microscopic nature of the bilayer gap to be very different from what is observed in previous macroscopic measurements or expected from current theoretical models. The potential difference between the layers, which is proportional to charge imbalance and determines the gap value, shows strong dependence on the disorder potential, varying spatially in both magnitude and sign on a microscopic level. Furthermore, the gap does not vanish at small charge densities. Additional interaction-induced effects are observed in a magnetic field with the opening of a subgap when the zero orbital Landau level is placed at the Fermi energy.

The effects of uncertainties in the alignment of the NIST watt balance with local gravity and the magnetic field of the balance have been analyzed, and techniques for measuring all misalignment parameters have been developed. The systematic uncertainty in the watt measurement due to alignment has been reduced to 0.04 /spl mu/W/W.

Reduction in the total uncertainty of the NIST watt balance is limited by the present configuration of the experiment. Most of the major uncertainty components arise from the fact that the experiment is performed in air. To reduce the contribution of these components, a vacuum system for the NIST watt balance has been constructed. The vacuum system and other future modifications to the NIST watt balance are discussed.

The present NIST watt balance has relative combined standard uncertainty of about 145 nW/W. The final results of this phase of the experiment are presented. Improvements in the Type B (nonstatistical) uncertainty contributions, along with several correction factors and noise sources, are also discussed.

This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants., Comment: 94 pages, 8 figures, 48 tables

We report observations of well developed half integer quantum Hall effect on mono layer graphene films of 7 mm x 7 mm in size. The graphene films are grown by chemical vapor deposition on copper, then transferred to SiO2/Si substrates, with typical carrier mobilities approximate to 4000 cm(2)/Vs. The large size graphene with excellent quality and electronic homogeneity demonstrated in this work is promising for graphene-based quantum Hall resistance standards and can also facilitate a wide range of experiments on quantum Hall physics of graphene and practical applications exploiting the exceptional properties of graphene. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3663972]

The National Institute of Standards and Technology (NIST) watt balance experiment completed a determination of Planck constant in 1998 with a relative standard uncertainty of 87 × 10(-9) (k = 1), concurrently with an upper limit on the drift rate of the SI kilogram mass standard. A number of other fundamental physical constants with uncertainties dominated by this result are also calculated. This paper focuses on the details of the balance apparatus, the measurement and control procedures, and the reference calibrations. The alignment procedures are also described, as is a novel mutual inductance measurement procedure. The analysis summary discusses the data noise sources and estimates for the Type B uncertainty contributions to the uncertainty budget. Much of this detail, some historical progression, and a few recent findings have not been included in previous papers reporting the results of this experiment.