Size and Concentration Determination of Colloidal Nanocrystals by Small-Angle X-ray Scattering
Size and Concentration Determination of Colloidal Nanocrystals by Small-Angle X-ray Scattering
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DOI：
10.1021/acs.chemmater.8b00903
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发表时间：
2018-06-26
影响因子：
8.6
通讯作者：
Hens, Zeger
中科院分区：
文献类型：
--
作者：
Maes, Jorick;Castro, Nicolo;Hens, Zeger
准确测定纳米物体的尺寸对纳米科学和技术的发展至关重要。在这里，我们提供的程序大小准球形胶体纳米晶体（NC）的小角X射线散射（SAXS）。使用2.5至10 nm PbS NC作为模型系统，该协议概述了通过背景校正提取净NC SAXS图案，并将散射X射线强度校准到绝对尺度。NC尺寸分布通过拟合校正的SAXS图案或者参数化的分析分布或者通过Monte Carlo方法构造的分布来检索。我们比较了这两种方法，并表明，它们产生几乎相同的估计NC直径的情况下，NC合奏与单分散和单峰的尺寸分布。扩展分析PbSe，CdSe和CdS NC，我们提供SAXS校准的尺寸曲线范围从2.5到7 nm，其中涉及NC直径和NC带隙能量，使用吸收光谱法测定。与通过透射电子显微镜（TEM）校准的尺寸曲线相比，我们系统地发现，SAXS校准分配一个更大的直径比TEM校准与给定的带隙的NC。我们将这种差异归因于在TEM图像中精确测量小物体尺寸的困难。最后，我们证明，NC浓度可以直接从SAXS模式中提取，标准化到绝对尺度，基于SAXS的浓度与使用吸光度光谱法获得的浓度相差小于10%。
The accurate determination of the dimensions of a nano-object is paramount to the development of nanoscience and technology. Here we provide procedures for sizing quasi-spherical colloidal nanocrystals (NCs) by means of small-angle X-ray scattering (SAXS). Using 2.5 to 10 nm PbS NCs as a model system, the protocols outline the extraction of the net NC SAXS pattern by background correction and address the calibration of scattered X-ray intensity to an absolute scale. The NC size distribution is retrieved by fitting the corrected SAXS pattern either to parametrized analytical distributions or to a distribution constructed through a Monte Carlo approach. We compare the two methods and show that they yield nearly identical estimates of the NC diameter in the case of an NC ensemble with a monodisperse and monomodal size distribution. Extending the analysis to PbSe, CdSe, and CdS NCs, we provide SAXS-calibrated sizing curves ranging from 2.5 to 7 nm, which relate the NC diameter and the NC band-gap energy as determined using absorbance spectroscopy. In comparison with sizing curves calibrated by means of transmission electron microscopy (TEM), we systematically find that SAXS calibration assigns a larger diameter than TEM calibration to NCs with a given band gap. We attribute this difference to the difficulty of accurately sizing small objects in TEM images. To close, we demonstrate that NC concentrations can be directly extracted from SAXS patterns normalized to an absolute scale and that SAXS-based concentrations differ less than 10% from concentrations obtained using absorbance spectroscopy.