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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

The transport characteristics of graphene devices with low n- or p-type carrier density (∼10(10) -10(11) cm(-2) ), fabricated using a new process that results in minimal organic surface residues, are reported. The p-type molecular doping responsible for the low carrier densities is initiated by aqua regia. The resulting devices exhibit highly developed ν = 2 quantized Hall resistance plateaus at magnetic field strengths of less than 4 T.

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 discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interests. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapour deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this chapter, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapour deposition. We also discuss potential applications of such large scale synthetic graphene., Comment: 23 pages, 4 figures

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

This paper describes concepts and measurement techniques necessary for characterization of graphene in the development of graphene-based quantized Hall effect (QHE) devices and resistance standards. We briefly contrast the properties of graphene produced by three common processing methods and discuss the conditions necessary for well-developed resistance plateaus to be observed. Methods used to determine the graphene layer thickness are presented. The metrologically relevant characteristics of graphene are correlated with electrical transport measurements in strong magnetic fields.

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.

A new set of values of the basic fundamental constants has been recommended by the Committee on Data for Science and Technology (CODATA) (http://phvsics.nist.gov/cuu/Constants/). It is based on a least-squares adjustment that incorporates new data that became available before the closing date of 31 December 2006 (known as the 2006 LSA). A number of key advances in experiment and theory have led to significant improvements in our knowledge of the values of the constants. The consequences of the new results and how the values were determined will be discussed.

We present a brief overview of the presentations at the workshop on the determination of the fundamental constants (Eltville, 2015) and the contributions to the proceedings.

If nanomechanical testing is to evolve into a tool for process and quality control in semiconductor fabrication, great advances in throughput, repeatability, and accuracy of the associated instruments and measurements will be required. A recent grant awarded by the NIST Advanced Technology Program seeks to address the throughput issue by developing a high-speed AFM-based platform for quantitative nanomechanical measurements. The following paper speaks to the issue of quantitative accuracy by presenting an overview of various standards and techniques under development at NIST and other national metrology institutes (NMIs) that can provide a metrological basis for nanomechanical testing. The infrastructure we describe places firm emphasis on traceability to the International System of Units, paving the way for truly quantitative, rather than qualitative, physical property testing.

The electronic realization of the kilogram project using the new NIST watt balance has been fully operational on a daily basis for several months. Short-term noise is at an all time low with overnight runs exhibiting standard deviations of parts in 108. With the exception of the mass standard, each standard reference has been calibrated with an uncertainty below a part in 108. Recent improvements that have led to the enhanced performance and current results are discussed

The National Institute of Standards and Technology (NIST) has launched a five-year Microforce Realization and Measurement Project focusing on the development of an instrument and laboratory capable of realizing and measuring the SI unit of force below 5/spl times/10/sup -6/ N using the electrical units as the link to the International System of Units (SI). As a proof of principle, a prototype electromechanical balance has been developed to allow comparisons between mechanically and electrically derived forces up to 300 /spl mu/N with a resolution of 15 nN. Results from force comparisons using 1-, 10-, and 20-mg deadweights are presented.

The National Institute of Standards and Technology (NIST) has rebuilt the apparatus and facilities for the watt balance experiment. The goal is to electronically monitor the SI kilogram at an uncertainty of 10 nW/W. We discuss the design changes and available test results to illustrate the improvements of the system.

The characterization of material properties and mechanical performance of micro-electromechanical devices often hinges on the accurate measurement of small forces. Calibrated load cells of appropriate size and range are used, but are often not calibrated in a fashion traceable to the International System of Units (SI). Recently, we calibrated a piezoresistive cantilever in terms of SI force sensitivity. Here, we employ this device as a secondary force standard to calibrate another, optical lever based sensor in a force probe instrument, demonstrating an unbroken tracability chain to appropriate national standards.

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.

A transportable laser frequency standard at 3.39 /spl mu/m and 10.2 /spl mu/m was created. The complex consisted of He-Ne/CH/sub 4/ and CO/sub 2/ lasers. The first one was stabilized on 76 transitions of the F2(2)P(7)3 methane line. The third harmonic of CO/sub 2/ laser radiation was phase locked to the He-Ne/CH/sub 4/ laser frequency. Long-term stability of 10/sup -15/ was achieved. Absolute frequency of laser standard was measured with accuracy of 10/sup -13/.

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.

The NIST electronic kilogram experiment is being completely rebuilt into a vacuum chamber within a specially designed laboratory room. Major renovations include reference mass positioning equipment, structural alignment flexures, and a redesigned inductive coil. The goal is less than 10 nW/W uncertainty. Preliminary data on measurement capabilities are expected.

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]

To have confidence in force measurements made with atomic force microscopes (AFMs), the spring constant of the AFM cantilevers should be known with good precision and accuracy, a topic not yet thoroughly treated in the literature. In this study, we compared the stiffnesses of uncoated tipless uniform rectangular silicon cantilevers among thermal, loading, and geometric calibration methods; loading was done against an artifact from the National Institute of Standards and Technology (NIST). The artifact was calibrated at NIST using forces that were traceable to the International System of units. The precision and accuracy of the thermal method were found to be 5% and 10%, respectively. Force measurements taken with different cantilevers can now be meaningfully compared.

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.

The NIST watt balance experiment is being completely rebuilt after its 1998 determination of the Planck constant. That measurement yielded a result with an approximately 1×10(-7) relative standard uncertainty. Because the goal of the new incarnation of the experiment is a ten-fold decrease in uncertainty, it has been necessary to reexamine many sources of systematic error. Hysteresis effects account for a substantial portion of the projected uncertainty budget. They arise from mechanical, magnetic, and thermal sources. The new experiment incorporates several improvements in the apparatus to address these issues, including stiffer components for transferring the mass standard on and off the balance, better servo control of the balance, better pivot materials, and the incorporation of erasing techniques into the mass transfer servo system. We have carried out a series of tests of hysteresis sources on a separate system, and apply their results to the watt apparatus. The studies presented here suggest that our improvements can be expected to reduce hysteresis signals by at least a factor of 10-perhaps as much as a factor of 50-over the 1998 experiment.

Two-dimensional (2D) materials such as graphene have become the focus of extensive research efforts in condensed matter physics. They provide opportunities for both fundamental research and applications across a wide range of industries. Ideally, characterization of graphene requires non-invasive techniques with single-atomic-layer thickness resolution and nanometer lateral resolution. Moreover, commercial application of graphene requires fast and large-area scanning capability. We demonstrate the optimized balance of image resolution and acquisition time of non-invasive confocal laser scanning microscopy (CLSM), rendering it an indispensable tool for rapid analysis of mass-produced graphene. It is powerful for analysis of 1–5 layers of exfoliated graphene on Si/SiO2, and allows us to distinguish the interfacial layer and 1–3 layers of epitaxial graphene on SiC substrates. Furthermore, CLSM shows excellent correlation with conventional optical microscopy, atomic force microscopy, Kelvin probe force microscopy, conductive atomic force microscopy, scanning electron microscopy and Raman mapping.