Determination of the Avogadro constant and the redefinition of the kilogram

Abstract

Avogadro constant (<italic>N</italic>_A) is a fundamental physical constant which constructs the relationship between the microscopic and macroscopic world. The accurate determination of <italic>N</italic>_A can be used for redefining the base units, e.g. kilogram and mole, so that can promote the development of the International System of Units. An effective route to determine <italic>N</italic>_A directly is the modern X-ray crystal density method, in which several parameters of the single crystal silicon, such as molar mass, density and lattice parameter should be measured accurately. The key technologies related to this method includes: the growth of highly pure silicon crystals, the manufacture of the silicon sphere, determination of the atomic mass of the silicon isotopes, X-ray interferometry, precision optical interferometry, and the determination of the thickness as well as the chemical composition of the ultra-thin film. The recent progress and potential direction in future of this research is reviewed in this paper. The significance of <italic>N</italic>_A in the fundamental metrology is also demonstrated by the case of the kilogram redefinition.