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为改善X射线晶体密度法测得的阿伏伽德罗常数的标准不确定度,研制了一种基于光谱椭偏术和二维Si球扫描机构的Si球表面氧化层厚度自动扫描测量系统,用于测量直径约93.6 mm、质量约1 kg的单晶Si球表面氧化层平均厚度。用本文系统对标准Si球表面进行400点扫描测量实验,得到氧化层厚度分布,且测得其平均厚度为6.00(22)nm。测量结果可将由氧化层导致的阿伏伽德罗常数测量相对不确定度降低至2.5×10-8。
In order to improve the standard uncertainty of Avogadro’s constant measured by X-ray crystal density method, an automatic scanning measurement system of Si surface oxide layer thickness based on spectral ellipsometry and two-dimensional Si ball scanning mechanism was developed. Used to measure the average thickness of oxide layer on the surface of monocrystalline Si spheres with a diameter of about 93.6 mm and mass of about 1 kg. Using the system of this paper, the surface of standard Si ball was measured by scanning at 400 points. The thickness distribution of oxide layer was obtained and the average thickness was 6.00 (22) nm. The measurement results reduce the relative uncertainty of the Avogadro number measurement due to the oxide layer to 2.5 × 10 -8.