用于阿伏加德罗项目的硅球表面氧化层测量装置研究

Study of Instrument for Measuring Oxide Layer on Surface of Silicon Sphere Used for Avogadro Project

基于单晶硅原子计数原理实现阿伏加德罗常数精密测量以及质量千克单位的复现,需要测量单晶硅球体的质量和体积,球表面几个纳米厚的非均匀氧化层分布的精密测量,是确定上述参量修正值的关键。用劳厄晶向法和激光标记确定了硅球表面坐标系统,比较了不同的硅球驱动方式,建立了基于光谱椭偏仪的自动化扫描测量装置,考察了扫描系统的重复性、稳定性;给出了NIM#3号硅球扫描结果,表明表面氧化层椭偏扫描的短期重复性水平达到0.04 nm。

The precision measurement of Avogadro constant and realization of mass unit kg based on atom counting of single crystal silicon require the measurement of the mass and volume of a silicon sphere. The non-homogeneously distributed oxide layer, which is several nanometer thick on the surface of the sphere, is key to the correction value of the above parameters. The coordination system of the Si sphere is determined by Laue crystallography and laser marking. Different driving approaches of the Si sphere are compared. The automatic scanning instrument is set up based on spectroscopic ellipsometer. The repeatability and stability are investigated, with the scanning results of the NIM#3 Si sphere being presented. It is indicated that the short-term repeatability of the ellipsometric scanning of the surface oxide layer reaches 0.04 nm.