Richter Silvia, Achuda Gaurav, Pinard Philippe T, Claus Tamme, Torrilhon Manuel
Central Facility for Electron Microscopy, RWTH Aachen University, Aachen 52074, Germany.
Oxford Instruments NanoAnalysis, High Wycombe HP12 3SE, UK.
Microsc Microanal. 2024 Aug 21;30(4):729-740. doi: 10.1093/mam/ozae066.
Electron probe microanalysis (EPMA) is a powerful tool for chemical characterization of materials on a microscopic scale. However, EPMA has the drawback that its information volume has a spatial extent of some 100 nm to a few µm. With the introduction of new electron sources, i.e., Schottky Thermal Field and Cold Field Emitter, where the electron beam is focused down to a few nm, measurements can be nowadays performed on the sub-micrometer scale. The goal of the work is to reveal the chemical composition of structures smaller than the excitation volume. New strategies are presented where the acquisition is performed at different positions on the sample and as a scan across a fine structure by using one or more single beam energies. Besides the well-known Monte-Carlo simulation, a deterministic model is also used. The deterministic model is based on moment equations of the Boltzmann equation. Inverse modeling is presented for several case studies. Due to the highly complex nonlinearity of the inverse model, an ill-posed and well-posed problem is shown as well. Finally, the method is extended to reconstruct 2D structures, i.e., rectangular shaped particles, with heterogeneous composition on lateral and depth scale.
电子探针微分析（EPMA）是一种在微观尺度上对材料进行化学表征的强大工具。然而，EPMA有一个缺点，即其信息量的空间范围约为100纳米至几微米。随着新型电子源的引入，即肖特基热场发射体和冷场发射体，电子束可以聚焦到几纳米，如今可以在亚微米尺度上进行测量。这项工作的目标是揭示小于激发体积的结构的化学成分。提出了新的策略，即在样品的不同位置进行采集，并通过使用一个或多个单束能量对精细结构进行扫描。除了众所周知的蒙特卡罗模拟外，还使用了确定性模型。确定性模型基于玻尔兹曼方程的矩方程。针对几个案例研究给出了反演建模。由于反演模型具有高度复杂的非线性，还展示了一个不适定和适定问题。最后，该方法被扩展到重建二维结构，即具有横向和深度尺度上成分不均匀的矩形颗粒。
