Addressing the Quantitative Challenges of X-Ray Line Interferences

Microanalysts face challenges while using Energy-Dispersive X-ray Spectroscopy (EDS) or Wavelength-Dispersive X-ray Spectroscopy (WDS) to perform quantitative analysis of materials containing elements that have interfering X-ray lines.

Rigorous interference corrections are usually a part of the electron-probe microanalysis (EPMA) software for WDS. However, such corrections are often inaccessible to the SEM user. This article discusses the quantitative analysis of a Ti-V-Al-Fe sample comprising two phases with slight variations in iron and vanadium content to demonstrate some of these challenges.

EDS和WDS定量分析

After mounted and uncoated in thick section, the Ti-V-Al-Fe metal sample was analyzed in an FESEM. A Thermo Scientific™ UltraDry™ EDS detector (Figure 1) and the Thermo Scientific™ NORAN™ System 7 microanalysis system (NS7) (Figure 2) were used to acquire the EDS spectra and spectral images. The Thermo Scientific™ MagnaRay™ WDS spectrometer (Figure 3) was used for WDS spectral collection and measurements.

图1。超级EDS检测器

图2。诺兰系统7

图3。MagnaRay WDS

Noran System 7软件用于处理EDS和WDS数据。EDS和WDS定量分析以15kV的加速电压进行，并通过以10kV的加速电压进行EDS光谱成像来减轻相互作用体积。

It was not possible to perform elemental mapping due to the slight variations in phase composition. TheThermo Scientific™ COMPASS™ spectral phase mapping software，用于确定相位。

Experimental Results

Unique phases were identified based on the principle component analysis of the EDS spectrum at each pixel as depicted in Figures 4 and 5, showing the presence of tiny, normally ~5µm, V-rich (~13 wt% V) grains along the boundaries of bigger, normally ~10µm, V-poor (~3 wt% V) grains. In addition, roughly 1.6wt% Fe was present in the V-rich grains. Table 1 summarizes the EDS (standardless and standards-based) and WDS quantitative results.

Figure 4.Backscattered electron image

Figure 5.指南针相位图：V-poor相是紫色的；富含V的阶段是黄色的

Table 1.Quantitative analyses of a Ti-Al-V alloy

		EDS		WDS
		无标准	Standards-based	Standards-based
		筛选	筛选	vMeas.	vDiff.
v-rich谷物	al	3.46	3.63	3。29	3。29
	ti	81.2	83.4	78.3	78.3
	v	13。8	13。2	15.8	16.9
	铁	1。61	1。55	1。54	1。54
	Total	100.0	101.8	98.9	100.0
v-poor谷物	al	6。42	6。77	5.23	5.22
	ti	90.7	93.4	90.0	90.0
	v	2.87	2.75	6。49	4.49
	铁	0.07	0.06	0.26	0.26
	Total	100.0	103.0	102.0	100.0

The separation of the Ti Kβ line (4.931 keV) from V Kα line (4.948 keV) is by mere 17eV. EDS cannot differentiate these X-ray lines, whereas WDS can differentiate them but with a poor resolution (Figure 6). V is counted on the Kα line in the WDS quantitative analyses. The over-estimate of the V concentration is the impact of this interference in the WDS quantitative analyses of these phases.

Figure 6.WDS的能量扫描在V -Kα的VKα和-rich Grains的VKα上覆盖在同一光谱区域的EDS光谱上

由于VKαX射线的事实，这种影响的程度较高。没有严格的干扰校正，就无法从中获得准确的结果WDS analysesof both grain types.

可以使用三种方法解决此缺点。首先，VKβ线是一个吸引人的峰值，由于该样品中没有干扰能管线，因此可以进行计数。然而，需要很长时间的获取时间（> 10倍）来计算富含V晶粒中的VKβ线。V-poor晶粒中非常低的V浓度（〜3 wt％）使得不可能将VKβ线与背景区分开。

第二种方法是差异方法，其中其他元素的WT％从100％中减去，其余表示V浓度。这种方法需要只有一条线很复杂，但是对其余元素进行了准确的测量。

Performing EDS quantitative analysis with standards is the third method, wherein the assumption is the accuracy of WDS is better than that of EDS. Nevertheless, in this case, well-developed peak deconvolution methodologies with both standards based and standardless EDS quantitative analysis help EDS provide more accurate results than WDS.

结论

WDS is an essential tool to corroborate the presence or absence of interfering elements. Nevertheless, the ability to completely resolve interfering X-ray lines is essential for the WDS spectrometer, without which it is not possible to use the instrument for accurate quantitative analysis with no interference corrections.

Moreover, the concept of phase mapping with WDS element maps is confounded by these interfering energy lines. In cases where WDS is incapable, accurate results can be obtained from modern EDS quantitative analysis, thanks to the peak deconvolution methodologies.

此外，Compass软件在组合物中只有略有变化的相之间辨别，从而产生了全面的相位图，并对每个阶段进行准确的定量分析。

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.

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