Sub-Monolayer Accuracy in Determining the Number of Atoms per Unit Area in Ultrathin Films Using X-ray Fluorescence
Sub-Monolayer Accuracy in Determining the Number of Atoms per Unit Area in Ultrathin Films Using X-ray Fluorescence
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DOI：
10.1021/acs.chemmater.8b02591
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发表时间：
2018-09-25
影响因子：
8.6
通讯作者：
Johnson, David C.
中科院分区：
文献类型：
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作者：
Hamann, Danielle M.;Bardgett, Dylan;Johnson, David C.
薄膜的组成和厚度决定了它们的物理性质，这使得测量薄膜中不同元素的原子数量的能力在技术和科学上都很重要。对于薄膜，在一定厚度以下，元素的x射线荧光强度与原子数成正比。由于实验几何和其他校正因素，将这种强度转换为每单位面积的原子数是具有挑战性的。因此，强度比更常用于根据标准或模型的元素比例来确定组成。在这里，利用x射线结构信息确定了20多个不同的晶体排列样品的单位面积原子数，这些样品具有完整的单位细胞厚度。强度和单位面积原子数之间的比例常数是由背景减去x射线荧光强度与计算出的每个元素的单位面积原子数的线性拟合确定的。结果表明，x射线荧光非常灵敏，能够测量各种样品基质中某些元素的不到1%的单层原子数的变化。使用校准值，生长并表征了8个单位电池厚度的MoSe2，证明了量化薄膜中单位面积原子数量的能力的有效性。
The composition and thickness of thin films determine their physical properties, making the ability to measure the number of atoms of different elements in films both technologically and scientifically important. For thin films, below a certain thickness, the X-ray fluorescence intensity of an element is proportional to the number of atoms. Converting this intensity to the number of atoms per unit area is challenging due to experimental geometries and other correction factors. Hence, the ratio of intensities is more commonly used to determine the composition in terms of element ratios using standards or a model. Here, the number of atoms per unit area was determined using X-ray structure information for over 20 different crystallographically aligned samples with integral unit cell thicknesses. The proportionality constant between intensity and the number of atoms per unit area was determined from linear fits of the background subtracted X-ray fluorescence intensity plotted versus the calculated number of atoms per unit area for each element. The results demonstrate that X-ray fluorescence is very sensitive, capable of measuring changes in the number of atoms of less than 1% of a monolayer for some elements in a variety of sample matrices. Using the calibrated values, an 8 unit cell thick MoSe2 was grown and characterized, demonstrating the usefulness of the ablity to quantify the number of atoms per unit area in a film.