Objective
Background:
One of the main objectives of the Metrology is redefining the mass unit in terms of atomic or fundamental constants in order to replace the definition in terms of the artefact kept at the BIPM. If the uncertainty associated to the Avogadro constant (NA) could be reduced at values less than 1x10-8 it would be possible to fix a conventional value for it. Since the atomic mass of 12C has been fixed equal to 12,00, the kilogram would be defined: the mass of (1000 g/12g) NA atoms of 12C.This 'atomic' definition holds also for other substances, since the value of their molar mass is sufficiently accurate (at 1x10-8 level). One of the promising methods for NA determination, leading also to the standard realisation, is the x-ray crystal method: it considers that in an ideal (Silicon) crystal the macroscopic density (p) is equal to that of the cubic unit cell, e.g. to the ratio between the mass of eighth Si atoms (molar mass M(Si)/ NA) and the volume of the cubic cell (a0)3with side a0. At present, through the absolute determination of these quantities, NA is determined with an accuracy of 0,5ppm, but a discrepancy of 3ppm, not yet explained since 1994, exists between two NA determinations carried out on two crystals, equally pure, perfect, grown in Europe and in Japan.
Objectives:
This project, through:
1) the structural, chemico-physical characterisation of crystals grown with different techniques, but from the same materials;
2) differential determinations in different points of crystals of the quantities involved in NA measurements;
3) a comparative investigation of the sensitivity of methods detecting the density of vacancy and voids in crystals ,aims at finding a qualitative and quantitative justification of this discrepancy , which represents a limit, not only for a new mass unit definition, but also to the improvement of silicon quality for the Nanoelectronics devices of next generation.
Work programme:
a) confirming the hypothesis that the discrepancies come from different characteristics of the materials;
b) checking (to exclude) the influence of inaccurate determinations determining the most significant properties of crystalline silicon, of evaporated films and porous silicon. Collecting all data concerning the same Si material, in view of its application as reference material (lattice parameter, isotopic composition, density standard);
c) constructing a lattice comparator operating in Bragg geometry for lattice spacing comparisons;
d) determining the limits of homogeneity and repeatability of crystals grown with current techniques.
State of progress: The project started on the 1/11/1998.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences mathematics pure mathematics geometry
- natural sciences chemical sciences inorganic chemistry metalloids
- engineering and technology nanotechnology nanoelectronics
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Coordinator
10135 TORINO (TURIN)
Italy
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