跃变比判别热解Si-C-N陶瓷EELS定量分析的有效性

Using jump-ratio method to validate quantitative EELS analysis in precursor-derived Si-C-N ceramics

电子能量损失谱(EELS)分析方法的运用为材料研究领域提供了有力的定性和定量手段。通过对内壳层电子激发谱跃变比的计算,能够获得样品相对厚度的参考信息。这一方法弥补了实验条件在同步采集等离子激发谱和内壳层电子激发谱方面的局限性,并为辨别EELS定量的可靠性提供依据。本文以Si3N4为例,对跃变比随样品相对厚度的变化规律进行了研究,并在低于最佳样品厚度的范围内得到了可靠的定量结果。类似的跃变比变化规律能够运用于成份均一的Si-C-N热解样品,然而对于非均一的Si-C-N退火样品则不适用。

EELS analysis offers a powerful qualitative and quantitative method in materials research. The jump-ratio of core-loss edge has been widely employed in EELS mapping, however, early study exhibited there is also an. intimate correlation between jump-ratio and sample thickness in TEM. Due to the experimental limitation to measure the sample thickness during the quantitative analysis, we set up this work using jump-ratio of Si-L~,3 edge to monitor the suitable range of thickness in the precursor-derived Si-C-N ceramics. The correlation of Si-L2.3 jump-ratio and relative thickness is first demonstrated in the reference Si3 N4 material, which reveals a reliable quantitative results below the optimum specimen thickness of about one mean-free-path. Similar effect is also found in the as-pyrolyzed Si-C-N ceramics that exhibits a uniform composition in the amorphous matrix, hence its EELS quantification results are equally reliable. However, such method cannot be applied in the cases with non-uniform composition, such as in the annealed Si-C-N ceramics where the amorphous matrix was further phase-separated.