The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Enrico Massa - One of the best experts on this subject based on the ideXlab platform.
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Advances in the measurement of the 28 Si Lattice Parameter
CPEM 2010, 2010Co-Authors: Enrico Massa, Giovanni Mana, Ernest G. KesslerAbstract:This paper reports about the results of Lattice Parameter measurements aimed at determining the Avogadro constant by counting the atoms in enriched 28Si spheres.
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measurement of the Lattice Parameter of a silicon crystal
New Journal of Physics, 2009Co-Authors: Enrico Massa, Giovanni Mana, U Kuetgens, Luca FerroglioAbstract:The silicon crystal WASO04 is a reference in the adjustment of fundamental physical constants, but its Lattice Parameter has never been measured in absolute terms. In the framework of an international project meant to base the kilogram definition on the molar volume and the Lattice Parameter of 28Si, the WASO04 crystal has been used to manufacture an interferometer prototype for the performance testing and the fine-tuning of a new experimental apparatus for Lattice Parameter measurements by combined x-ray and optical interferometry. The present paper discusses the test results and gives an accurate Lattice Parameter determination. With respect to previous determinations, the value obtained, d220(WASO04)=192.015 570 2(10) pm, displays a four-fold improvement in accurracy.
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si Lattice Parameter measurement by centimeter x ray interferometry
Optics Express, 2008Co-Authors: Luca Ferroglio, Giovanni Mana, Enrico MassaAbstract:A combined X-ray and optical interferometer capable of centimeter displacements has been made to measure the Lattice Parameter of Si crystals to within a 3×10-9 relative uncertainty. This paper relates the results of test measurements carried out to assess the capabilities of the apparatus.
Thomas Michely - One of the best experts on this subject based on the ideXlab platform.
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Interplay of wrinkles, strain, and Lattice Parameter in graphene on iridium.
Nano letters, 2012Co-Authors: Hichem Hattab, Alpha T. N'diaye, Dirk Wall, Claudius Klein, Giriraj Jnawali, Johann Coraux, Carsten Busse, Raoul Van Gastel, Bene Poelsema, Thomas MichelyAbstract:Following graphene growth by thermal decomposition of ethylene on Ir(111) at high temperatures we analyzed the strain state and the wrinkle formation kinetics as function of temperature. Using the moire spot separation in a low energy electron diffraction pattern as a magnifying mechanism for the difference in the Lattice Parameters between Ir and graphene, we achieved an unrivaled relative precision of ±0.1 pm for the graphene Lattice Parameter. Our data reveals a characteristic hysteresis of the graphene Lattice Parameter that is explained by the interplay of reversible wrinkle formation and film strain. We show that graphene on Ir(111) always exhibits residual compressive strain at room temperature. Our results provide important guidelines for strategies to avoid wrinkling.
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Interplay of Wrinkles, Strain, and Lattice Parameter in Graphene on Iridium
Nano Letters, 2011Co-Authors: Hichem Hattab, Alpha T. N'diaye, Dirk Wall, Claudius Klein, Giriraj Jnawali, Johann Coraux, Carsten Busse, Raoul Van Gastel, Bene Poelsema, Thomas MichelyAbstract:Following graphene growth by thermal decomposition of ethylene on Ir(111) at high temperatures we analyzed the strain state and the wrinkle formation kinetics as function of temperature. Using the moiré spot separation in a low energy electron diffraction pattern as a magnifying mechanism for the difference in the Lattice Parameters between Ir and graphene, we achieved an unrivaled relative precision of ±0.1 pm for the graphene Lattice Parameter. Our data reveals a characteristic hysteresis of the graphene Lattice Parameter that is explained by the interplay of reversible wrinkle formation and film strain. We show that graphene on Ir(111) always exhibits residual compressive strain at room temperature. Our results provide important guidelines for strategies to avoid wrinkling.
Luca Ferroglio - One of the best experts on this subject based on the ideXlab platform.
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measurement of the Lattice Parameter of a silicon crystal
New Journal of Physics, 2009Co-Authors: Enrico Massa, Giovanni Mana, U Kuetgens, Luca FerroglioAbstract:The silicon crystal WASO04 is a reference in the adjustment of fundamental physical constants, but its Lattice Parameter has never been measured in absolute terms. In the framework of an international project meant to base the kilogram definition on the molar volume and the Lattice Parameter of 28Si, the WASO04 crystal has been used to manufacture an interferometer prototype for the performance testing and the fine-tuning of a new experimental apparatus for Lattice Parameter measurements by combined x-ray and optical interferometry. The present paper discusses the test results and gives an accurate Lattice Parameter determination. With respect to previous determinations, the value obtained, d220(WASO04)=192.015 570 2(10) pm, displays a four-fold improvement in accurracy.
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si Lattice Parameter measurement by centimeter x ray interferometry
Optics Express, 2008Co-Authors: Luca Ferroglio, Giovanni Mana, Enrico MassaAbstract:A combined X-ray and optical interferometer capable of centimeter displacements has been made to measure the Lattice Parameter of Si crystals to within a 3×10-9 relative uncertainty. This paper relates the results of test measurements carried out to assess the capabilities of the apparatus.
Eric J. Mittemeijer - One of the best experts on this subject based on the ideXlab platform.
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The Lattice Parameter of nanocrystalline Ni as function of crystallite size
Physica E-low-dimensional Systems & Nanostructures, 2011Co-Authors: J. Sheng, Udo Welzel, G K Rane, Eric J. MittemeijerAbstract:An anomalous dependence on crystallite size of the Lattice Parameter of nanocrystalline Ni as occurring in ultrathin Ni films and in ball-milled Ni powder was observed: Lattice contraction followed by Lattice expansion with decrease in crystallite size. These data were determined by application of detailed in-situ X-ray diffraction measurements during annealing treatments. To this end, the Lattice Parameter of Ni was accurately determined by correcting for influences of residual stress and stacking faults in the thin films and the ball-milled Ni powders, respectively. The non-monotonic variation of the Lattice constant was discussed in terms of competing mechanisms: interface stress induced contraction versus magnetic multidomain to single-domain transition occurring at about the crystallite size value where a minimum value for the Lattice Parameter is observed.
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nonmonotonic crystallite size dependence of the Lattice Parameter of nanocrystalline nickel
Applied Physics Letters, 2010Co-Authors: J. Sheng, Udo Welzel, Eric J. MittemeijerAbstract:A nonmonotonic crystallite-size dependence of the Lattice Parameter of ultrathin, nanocrystalline Ni films, i.e., Lattice contraction followed by Lattice expansion with decreasing crystallite size, was observed using in situ x-ray diffraction stress measurements combined with a dedicated thermal treatment called “loop annealing.” The expected Lattice contraction with decreasing crystallite size was found for nanocrystalline Cu and nanocrystalline Pd.
Friedhelm Bechstedt - One of the best experts on this subject based on the ideXlab platform.
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Lattice Parameter and energy band gap of cubic AlxGayIn1−x−yN quaternary alloys
Applied Physics Letters, 2003Co-Authors: Marcelo Marques, Lara K. Teles, Luisa Maria Ribeiro Scolfaro, Jürgen Furthmüller, J. R. Leite, Friedhelm BechstedtAbstract:First-principles total energy calculations, combined with a generalized quasichemical approach to disorder and compositional effects, are used to obtain the Lattice Parameter and the energy band gap of cubic AlxGayIn1−x−yN quaternary alloys. It is found that the Lattice Parameter a(x,y) fulfills a Vegard’s-like law; that is, it shows a linear dependence on the alloy contents x and y. The range of compositions for which the alloy is Lattice-matched to GaN is obtained. The energy band gap Eg(x,y) of the quaternary alloy deviates from a planar behavior displaying a two-dimensional gap bowing in the x–y plane. Analytical expressions that fit the calculated a(x,y) and Eg(x,y) surfaces are derived in order to provide ready access to the Lattice Parameter and energy band gap of the alloy for the entire range of compositions. The results are compared with data for the wurtzite phase alloys.
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Lattice Parameter and energy band gap of cubic alxgayin1 x yn quaternary alloys
Applied Physics Letters, 2003Co-Authors: Marcelo Marques, Lara K. Teles, Luisa Maria Ribeiro Scolfaro, Jürgen Furthmüller, J. R. Leite, Friedhelm BechstedtAbstract:First-principles total energy calculations, combined with a generalized quasichemical approach to disorder and compositional effects, are used to obtain the Lattice Parameter and the energy band gap of cubic AlxGayIn1−x−yN quaternary alloys. It is found that the Lattice Parameter a(x,y) fulfills a Vegard’s-like law; that is, it shows a linear dependence on the alloy contents x and y. The range of compositions for which the alloy is Lattice-matched to GaN is obtained. The energy band gap Eg(x,y) of the quaternary alloy deviates from a planar behavior displaying a two-dimensional gap bowing in the x–y plane. Analytical expressions that fit the calculated a(x,y) and Eg(x,y) surfaces are derived in order to provide ready access to the Lattice Parameter and energy band gap of the alloy for the entire range of compositions. The results are compared with data for the wurtzite phase alloys.
