Density comparison measurements of silicon crystals by pressure of flotation method

Since silicon single crystals are believed to be the most perfect crystals to be obtained at the present time, they are used for the density standard and the determination of the Avogadro constant. However, there exists molar volume discrepancies among them. It is thought that the problems exist in the degree of perfection of the silicon crystal. It is important, therefore, to study defect and impurity effects on the density of silicon in order to clarify the cause of the discrepancies. We have developed a density comparison measurement system based on the pressure of flotation method (PFM). Density differences for silicon spheres produced from a new FZ-silicon ingot of NRLM4 was measured. The second generation of this PFM apparatus is being installed in the National Metrology Institute of Japan (NMIJ).