物质的量的计量标准器

摩尔是一系统的物质的量。它不是质量单位，而是一种具有特定量纲的单位。体现这个单位的方法只能在实验室条件下实现。根据摩尔的定义，测定阿伏加德罗常数，就可以看成是实现了摩尔单位。     

阿伏加德罗常数测量与千克重新定义

当千克用固定普朗克常数h的方法定义时,X射线晶体密度法(XRCD)即被用来定义和复现千克,它采用对浓缩²⁸Si原子计数的方法来测量阿伏加德罗常数N_A,已将N_A和h的测量不确定度达到2×10^-8,并反过来确定硅球的质量实现对千克的量值复现。阐述了晶格常数、同位素、浓缩硅、硅球直径及表面氧化层等阿伏加德罗常数测量的关键技术的研究进展。介绍了原子计数法千克定义及其量值复现方法,该方法将为国际单位制改制之后我国质量量值复现提供参考。     

单晶硅球密度的绝对测量

单晶硅球密度的绝对测量是阿伏加德罗常数测量的关键技术。综述了单晶硅球密度测量的最新进展,包括硅球密度测量的技术原理、测量领域、影响因素、测量装置及最佳测量能力等等,分析了硅球密度测量的主要难点和关键技术,预测了相关研究的技术前景及发展趋势。     

阿伏加德罗常数测量研究最新进展

综述了阿伏加德罗常数（N_A）测量研究的最新进展。介绍了目前测N_A准确度较高的方法—X射线晶体密度法,该方法通过测量单晶硅的摩尔质量、宏观密度和晶格常数得到N_A。采用X射线晶体密度法有望实现NA相对测量不确定度达到2×10^-8。分析了当前限制NA测量准确度提高的关键研究内容:单晶硅摩尔质量、硅球直径和表面氧化层厚度的测量。并展望了NA测量未来的工作方向。     

质量基准研究的最新进展

质量基准是迄今唯一保留人工制品的SI单位.近年来,计量学家通过国际合作,试图基于自然的不变性质、阿佛加德罗常数和普朗克常数的概念重新定义质量基准.     

普朗克常数精密测量的历史和现状

普朗克常数是量子世界和可观测量子效应的基本标志。作为物理学中基本物理常数之一,它的精确测定对于质量计量的物理基准建立、量子效应精密测量及早期宇宙大爆炸物理特性研究等都有重要意义。经过一百多年来各种间接和直接方法测量,普朗克常数的精确值2019年才被定义。系统地回顾了这一历史进程,并展望普朗克常数精密测量领域的未来发展。     

当代计量科学发展的新趋势

回顾了计量科学在日常生活和科学研究方面的重要性,指出以实物计量基准建立的计量单位制存在的问题.分析了以基本物理常数(真空光速值c0,元电荷e,普朗克常数h,波尔兹曼常数kB和阿伏加德罗常数NA)和原子的物理特性(约瑟夫森效应和量子霍尔效应)进行计量基本单位量子化研究的重要性和紧迫性.介绍了长度、质量、电学量、温度和时间等计量基本单位量子化研究的新趋势.简单介绍了欧盟计量科学研究计划新动向.     

相调制光谱椭偏仪校准研究

对相调制光谱椭偏仪进行了用户级别的校准,结合椭偏理论简要讨论了校准的原理,测试结果表明椭偏角准确度达到0.01°.探讨了人为造成的准直调节不一致性以及样品膜层的不均匀性对样品测量结果的影响.对热氧化硅样片测量结果进行了统计分析,该工作是进一步研究椭偏仪误差和校准方法以及阿伏加德罗常数项目硅球表面层研究的基础.     

用Kossel衍射技术精确测定晶格常数

本文介绍利用JXA-3A电子探针、采用透射Kossel衍射技术,精确测定单晶体晶格常数的实验技术和分析方法。并用此技术精确测定纯镍和纯铁退火大晶粒薄膜试样的晶格常数,获得了满意的结果。对于纯铁试样,测定的晶格常数为: a±σ=0.286608±0.000022nm,Δa/a=1.54×10~(-4)     

基于光子能量测定的普朗克常数直接测量法

普朗克常数是物理学中的最小作用量子,是区分经典物理和量子物理的重要标志.因此,这一基本物理常数的精确测量,不管是对物质世界本源的理解、各种量子效应的实验观测,还是质量单位的重新定义都非常重要.普朗克常数的精密测量经历了 120多年的发展历史,建立了多种间接或直接的测量方法,直到2019年才给出其精确值.但相对于时间(或...     

The Avogadro constant: determining the number of atoms in a single-crystal ²⁸Si sphere

The Avogadro constant, the number of entities in an amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant--the product of the Planck constant and the Avogadro constant--is very well known via the measurement of the Rydberg constant, the Avogadro constant is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a new definition of the kilogram in terms of a fundamental constant. Here, we describe a new and unique approach to determine the Avogadro constant from the number of atoms in 1 kg single-crystal spheres that are highly enriched with the (28)Si isotope. This approach has enabled us to apply isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, N(A)=6.022 140 82(18)×10(23) mol(-1), is now the most accurate input datum for a new definition of the kilogram.     

Determination of the atomic weight of 28Si-enriched silicon for a revised estimate of the Avogadro constant

The much anticipated overhaul of the International System of Units (SI) will result in new definitions of base units in terms of fundamental constants. However, redefinition of the kilogram in terms of the Planck constant (h) cannot proceed without consistency between the Avogadro and Planck constants, which are both related through the Rydberg constant. In this work, an independent assessment of the atomic weight of silicon in a highly enriched (28)Si crystal supplied by the International Avogadro Coordination (IAC) was performed. This recent analytical approach, based on dissolution with NaOH and its isotopic characterization by multicollector inductively coupled plasma mass spectrometry, is critically evaluated. The resultant atomic weight A(r)(Si) = 27.976 968 39(24)(k=1) differs significantly from the most recent value of A(r)(Si) = 27.976 970 27(23)(k=1). Using the results generated herein for A(r)(Si) along with other IAC measurement results for mass, volume, and the lattice spacing, the estimate of the Avogadro constant becomes N(A) = 6.022 140 40(19) × 10(23) mol(-1).     

The determination of the Avogadro constant-not simply ametrological problem

A new round in the determination of the Avogadro constant is under way at Physikalisch-Technische Bundesanstalt (PTB) and at other national metrology institutes perhaps as a step toward an alternative definition of the SI unit of mass. The required measurements of the relevant crystal data are currently hampered by an (unexpected and not yet totally identified) imperfection of the crystal lattice. The vacancy content in ultra-pure silicon crystals was investigated using positron annihilation, density comparators, and X-ray diffraction methods. The results obtained were compared with theoretically predicted lattice deformations around vacancies and defect densities generated during the crystal growth process. The investigations made allow the conclusion to be drawn that the relative amount of unoccupied regular lattice sites does not exceed 10^-8. The relative difference of 3×10 ^-6 in silicon molar volumes recently observed cannot, therefore, be explained by differences in vacancy concentrations. The surface structure of the silicon bodies was investigated by ellipsometry. As a result, the native oxide layer seems to be detrimental to the accurate measurement of the volume of the silicon spheres. New considerations concerning special surface preparations and treatments are discussed     

Surface layer impurities on silicon spheres used in determinationof the Avogadro constant

The Avogadro constant is required to be determined with an uncertainty of less than 1×10^-8 in order to allow an atomic definition of the kilogram. A single-crystal silicon sphere 93.6 mm diameter is used for this determination. A thin surface layer (typically 2 nm to 5 nm thick on flats and 10 nm or more on spheres) of contaminants such as oxide, water and hydrocarbons on the sphere can significantly affect the measurements due to corrections for density changes and to phase change on reflection in the diameter measurement by optical interferometry. The stability of this surface layer as a function of time is also of importance because of ongoing measurements. The nature of this contamination has been investigated using optical ellipsometry and ion beam analysis. It is concluded that the composition and structure of the surface layer are affected by a number of parameters and that the most appropriate method of achieving the desired accuracy is to remove the surface layer by etching and to form a hard stable coating of controlled thickness and composition. This coating may be either silicon dioxide or silicon nitride     

实现质量量子基准的两种途径

基于基本物理常数定义新的国际单位制成为21世纪国际计量界研究的热点,然而目前一些常数的测定 尚未达到所需的不确定度范围。质量量子标准研究更是目前计量领域研究的重点和难点。经过30多年的发展, 硅球法和功率天平法取得了重大进展,但目前发表的测量结果之间尚存在10^-7量级的偏差。通过详细比较各国实 现质量量子基准的两种途径,指出无论是依靠普朗克常数&还是阿佛伽德罗常数,在现阶段,取代国际千克原器尚有很长的一段路需要摸索。     

关于修改“物质的量”,“摩尔”及阿伏伽德罗常数的定义和符号的建议

建议在ＳＩ中,将“物质的量”改为“物质微粒量”,它的符号仍用ｎ,量纲仍为Ｎ。将“摩尔”改为“阿伏伽德罗”,它的符号用Ａｖ。阿伏伽德罗常数的定义修改为“０．０１２ｋｇ碳—１２的原子数目,或１Ａｖ物质微粒的数目”,它的符号采用ＮＡ,而不用Ｌ。