Yasushi Azuma

Counting the atoms in a 28Si crystal for a new kilogram definition

This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10−8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol−1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10−8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.

Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of

Surface layer determination for the Si spheres of the Avogadro project

N_A = 6.022 140 76(12) \times 10^{23}

Angle-resolved ultraviolet photoelectron spectroscopy of In-[perylene-3,4,9,10-tetracarboxylic dianhydride] system

mol

Thermal stress hardening of a-Si3N4/nc-TiN nanostructured multilayers

^{-1}

Angle-resolved UV photoelectron spectra (UPS) of thin films of perylene-3,4,9,10-tetracarboxylic dianhydride on MoS2

. The X-ray crystal density method has thus achieved the target relative standard uncertainty of

Density Determination of Silicon Spheres Using an Interferometer With Optical Frequency Tuning

2.0 \times 10^{-8}

Characterization of thin films of chloroaluminum phthalocyanine on MoS2 : HREELS, LEET and PIES study

necessary for the realization of the definition of the new kilogram.

Pendant group orientation of poly(2-vinylnaphthalene) thin film surface studied by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS)

For the accurate determination of the Avogadro constant, two 28Si spheres were produced, whose macroscopic density, in addition to other values, must be determined. To make a contribution to the new definition of the kilogram, a relative standard uncertainty of less than 2 ? 10?8 has to be achieved. Each silicon surface is covered by a surface layer (SL). Consequently, correction parameters for the SL are determined to be applied to the mass and volume determination of the enriched spheres. With the use of a large set of surface analysing techniques, the structure of the SL is investigated. An unexpected metallic contamination existing on the sphere surface enlarges the uncertainty contribution of the correction parameters above the originally targeted value of 1 ? 10?8. In the framework of this investigation this new obstacle is resolved in two ways. A new combination of analytical methods is applied to measure the SL mass mSL and the thickness dSL, including this new contamination, with an uncertainty of u(mSL) = 14.5??g and 14.4??g, respectively, and u(dSL) = 0.33?nm and 0.32?nm for the 28Si spheres AVO28-S5 and AVO28-S8, respectively.In the second part of the work, the chemical composition of these metallic contaminations is found to be Cu, Ni and Zn silicide compounds. For the removal of this contamination, a special procedure is developed, tested and applied to the spheres to produce the originally expected surface structure on the spheres. After the application of this new procedure the use of x-ray reflectometry directly at the spheres will be possible. It is expected to reduce the uncertainty contribution due to the SL down to 1 ? 10?8.

Low-Energy Electron Transmission Spectroscopy of Thin Films of Chloroaluminum Phthalocyanine on MoS2.

The In-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] system, obtained by the sequential evaporation of PTCDA and In on cleaved MoS2 surfaces, was measured by means of angle-resolved ultraviolet photoelectron spectroscopy. The results indicate that the four In atoms react with one PTCDA molecule. Using a model compound of the reaction product, In4PTCDA, the quantitative analysis of the take-off angle (θ) dependence of the photoelectron intensity from the new band shows that the band originates from the π state involving In 5pz atomic orbitals, and the In4PTCDA molecules lie tilted at the averaged tilt angle of the molecular plane β≅10°.