单晶硅球法是阿伏伽德罗常数量值精密测量以及质量重新定义的一种重要方案。单晶硅球表面的氧化层厚度关系到硅球质量和直径测量结果的修正，并在阿伏伽德罗常数的相对测量不确定度中占到很大比例。讨论了表面层测量中影响椭偏测量的几个基本问题，即单晶硅球不同晶向的光学常数以及表面曲率对椭偏光束的散射效应，评估了对氧化层厚度测量不确定度的影响；对于所采用的间接法的不确定度分量进行了分析。该研究为硅球表面层测量提供了实验和理论依据。

Single crystal silicon (Si) sphere method is an important scheme for precise measurement of Avogadro constant and redefinition of kilogram. The surface oxide layer thickness is related to the correction of the measured mass and diameter of the single crystal sphere, and contributes a large proportion of the relative uncertainty of the Avogadro constant. We discuss several basic problems in measuring the sphere surface by ellipsometer, i.e., the influence of the crystal- orientation- dependent optical constants and surface curvature induced ellipsometric light beam scattering. And the uncertainty components for the adopted indirect method are analyzed. The study provides both experimental and theoretical bases for the measurement research in surface layer on Si sphere.