Lulu Zhang

Realization of the kilogram based on the Planck constant at NMIJ

The change of the definition of the kilogram has been proposed. The new definition will be based on the Planck constant. After the change, the National Metrology Institute of Japan (NMIJ) will realize the kilogram by using the x-ray crystal density method with a 28Si-enriched sphere. A pilot study to confirm the international equivalence of the ability to realize the kilogram from the new definition is ongoing, where the volume measurement of a 28Si-enriched sphere by optical interferometry and the sphere surface characterization by spectroscopic ellipsometry and x-ray photoelectron spectroscopy required for the realization are performed by NMIJ independently.

Surface Layer Analysis of Si Sphere by XRF and XPS

To reduce the uncertainty of the Avogadro constant for the new definition of the kilogram, the surface analysis of the Si sphere produced for the accurate determination of the Avogadro constant is indispensable. In this work, we conducted the surface quantitative analysis to find out the metallic contaminations of a Si sphere by x-ray fluorescence (XRF) spectroscopy. The x-ray photoelectron spectroscopy (XPS) investigations were also carried out to estimate the thickness of the oxide layer and clarify the chemical binding state of the carbonaceous contamination layer on the surface of a dummy Si sphere.

Final report on Key Comparison K67 and parallel Pilot Study P108: Measurement of composition of a thin Fe–Ni alloy film

The Key Comparison K67 and the parallel Pilot Study P108 on quantitative analysis of thin alloy films have been completed in the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of these inter-laboratory comparisons is to determine the degree of equivalence in the measurement capability of national metrology institutes (NMIs) and designated institutes (DIs) for the determination of the composition of thin alloy films. The measurand is expressed in atomic percent. A Fe–Ni alloy film with a certified composition was available for the participants of the inter-laboratory comparison. It has been used as a reference specimen to determine the relative sensitivity factors (RSF) of Fe and Ni for the different analytical methods used by the participants to determine the composition of the test sample. As was shown in the preceding Pilot Study P98, the degrees of equivalence in the measurement capabilities of the participants can be improved in that way. The composition of the reference specimen was certified by inductively coupled plasma mass spectrometry (ICP-MS) using the isotope dilution method. The in-depth and lateral homogeneity, determined in terms of elemental composition, of the certified reference sample and the unknown test sample were confirmed by secondary ion mass spectrometry (SIMS) using C60 primary ions by the leading laboratory. Five laboratories participated in the key comparison. Four of them used x-ray photoelectron spectroscopy (XPS) and one Auger electron spectroscopy (AES). One laboratory participated in the parallel P108 pilot study using electron probe micro analysis with an energy-dispersive spectrometer (ED EPMA) and XPS. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Mass measurement of 28 Si-enriched spheres at NMIJ for determination of the Avogadro constant

The Avogadro constant is determined accurately by applying the x-ray crystal density method to 28Si-enriched spheres, which is one of the practical methods for the kilogram redefinition. In this paper, we present the results of mass measurements of 28Si-enriched spheres, performed at NMIJ in 2014 for the determination of the Avogadro constant. The results of reproducibility of the cleaning effects on the mass of the spheres together with the influence of the BIPM Extraordinary Calibrations, are shown. With these achievements, NMIJ plans to participate in the Pilot Study aiming at the kilogram redefinition, where the mass measurements play an important role.

Thickness Measurement of Oxide and Carbonaceous Layers on a 28 Si Sphere by XPS

Surface layer characterization is crucial for the high-accuracy determination of the Avogadro constant using 28Si enriched spheres to redefine the kilogram. In this paper, we measured the thickness of the oxide layer (OL) and carbonaceous layer (CL) on a 28Si-enriched sphere by X-ray photoelectron spectroscopy (XPS). A mechanism for the rotation of the sphere was integrated into the XPS system to measure the thickness at different points on the surface of the sphere. A SI-traceable X-ray reflectometry system was used to determine an attenuation length for the Si 2p electrons in SiO2, which was an important parameter for the calculation of the oxide thickness on the Si sphere by XPS. The average thickness and uncertainty budget of the OL and CL were evaluated.

Interdiffusion studies for HfO2/Si by GIXR and XPS

Interdiffusion at the interface between an HfO2thin film and a Si substrate was studied using grazing incidence x-ray reflectivity (GIXR) and x-ray photoelectron spectroscopy (XPS). HfO2thin films were deposited on Si sub strates by the sputtering of a metal-Hf layer, and then they were oxidized/annealed in a N2/O2gas mixture with different O2concentrations. The GIXR and XPS results showed that the out-diffusion of Si atoms from the substrate increased with the oxygen concentration during high temperature annealing, and consequently, it resulted in the formation of a Si-rich Hf-silicate interlayer, i.e., lower-density Hf-silicate with greater thickness. The GIXR results of the interfacial structures were in agreement with the results of XPS and cross-sectional transmission electron microscopy.

Mass Measurement of 28 Si-Enriched Spheres at NMIJ for the Determination of the Avogadro Constant

The Avogadro constant,

Surface layer analysis of Si sphere by XRF and XPS

N_{mathbf {A}}

Study of interfacial structure of HfO2thin film on Si by grazing incidence x-ray reflectivity

, is the physical constant that connects microscopic and macroscopic quantities, and is indispensable especially in the field of chemistry. In addition, the Avogadro constant is closely related to the fundamental physical constants, namely, the electron relative atomic mass, fine-structure constant, Rydberg constant, and Planck constant. For several decades, the Avogadro constant has been determined using the x-ray crystal density (XRCD) method, which is currently one of the practical methods to redefine the kilogram based on fundamental physical constants. In this paper, we present the results of mass measurements of 28Si-enriched spheres, performed at the National Metrology Institute of Japan (NMIJ) in 2014, for the determination of the Avogadro constant using the XRCD method. The results of repeatability of the cleaning effect on the mass of the spheres and the determination of the physical adsorption of water vapor on the spheres are shown. These results establish the reliability of the mass measurement at NMIJ. In addition, we report the results of the mass measurements of 28Si-enriched sphere AVO28-S5c conducted in 2016 to participate in the Pilot Study organized by the Consultative Committee for Mass and Related Quantities aiming at the redefinition of the kilogram based on the fixed numerical value of the Planck constant.

Realization of the Kilogram Based on the Planck Constant at NMIJ

To reduce the uncertainty of the Avogadro constant for the new definition of the kilogram, the surface analysis of the Si sphere produced for the accurate determination of the Avogadro constant is indispensable. In this paper, we conducted the surface quantitative analyses to find out the metallic contaminations on a 1-kg natural Si sphere by X-ray fluorescence analysis. The X-ray photoelectron spectroscopy investigations were also carried out to estimate the thickness of the oxide layer and clarify the chemical binding state of the carbonaceous contamination layer on the surface of a dummy Si sphere.