Sorbier Loïc, Rosenberg Elisabeth, Merlet Claude
Direction Physique et Analyse, Institut Français du Pétrole, BP3, 69390 Vernaison, France.
Microsc Microanal. 2004 Dec;10(6):745-52. doi: 10.1017/s1431927604040681.
A signal loss is generally reported in electron probe microanalysis (EPMA) of porous, highly divided materials like heterogeneous catalysts. The hypothesis generally proposed to explain this signal loss refers to porosity, roughness, energy losses at interfaces, or charging effects. In this work we investigate by Monte Carlo simulation all these physical effects and compare the simulated results with measurements obtained on a mesoporous alumina. A program using the PENELOPE package and taking into account these four physical phenomena has been written. Simulation results show clearly that neither porosity nor roughness, nor specific energy losses at interfaces, nor charging effects are responsible for the observed signal loss. Measurements performed with analysis of carbon and oxygen lead to a correct total of concentration. The signal loss is thus explained by a composition effect due to a carbon contamination brought by the sample preparation and to a lesser extent by a stoichiometry of the porous alumina different from a massive alumina. For this kind of high specific surface porous sample, a little surface contamination layer becomes an important volume contamination that can produce large quantification errors if the contaminant is not analyzed.
在对诸如多相催化剂之类的多孔、高度分散材料进行电子探针微分析（EPMA）时，通常会报告信号损失。一般提出的用于解释这种信号损失的假说是指孔隙率、粗糙度、界面处的能量损失或充电效应。在这项工作中，我们通过蒙特卡罗模拟研究了所有这些物理效应，并将模拟结果与在介孔氧化铝上获得的测量结果进行了比较。我们编写了一个使用PENELOPE软件包并考虑这四种物理现象的程序。模拟结果清楚地表明，孔隙率、粗糙度、界面处的特定能量损失或充电效应均不是观察到的信号损失的原因。对碳和氧进行分析的测量结果得出了正确的总浓度。因此，信号损失是由样品制备过程中带来的碳污染以及程度较小的多孔氧化铝与块状氧化铝不同的化学计量比所导致的成分效应所解释的。对于这种高比表面积的多孔样品，如果不分析污染物，那么一点点表面污染层就会变成重要的体积污染，从而可能产生较大的定量误差。
