Chalmers University of Technology, Göteborg, Sweden.
Ultramicroscopy. 2011 May;111(6):604-8. doi: 10.1016/j.ultramic.2010.12.024. Epub 2010 Dec 28.
Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti(2)AlC grains in different materials as well as on large M(23)C(6) precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the (13)C isotope, and calculating the concentration of (12)C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti(2)AlC an additional difficulty arises from the overlap between C(2)(+), C(4)(2+) and Ti(2+) at the mass-to-charge 24 Da.
与金属材料的原子探针分析相比，碳化物相的分析会导致分子离子的形成和多重事件增强。此外，许多多重事件似乎由来自材料中相邻位置的两个或多个离子组成。由于离子探测器的限制，测量通常会低估碳浓度。已经在不同材料中的 SiC、WC、Ti(C,N) 和 Ti(2)AlC 晶粒以及钢中的大型 M(23)C(6)沉淀上进行了使用激光脉冲原子探针断层扫描的分析。使用标准评估方法，获得的碳浓度比已知化学计量比预期的低 6-24%。仅使用 (13)C 同位素并根据天然同位素丰度计算 (12)C 的浓度，结果显著改善。这证实了获得过低碳浓度的主要原因是探测器的死时间，主要影响碳，因为它更频繁地作为多重离子蒸发。在 Ti(C,N) 和 Ti(2)AlC 的情况下，由于在质荷比 24 Da 处 C(2)(+)、C(4)(2+) 和 Ti(2+)之间的重叠，会出现另一个困难。
