Australian Center for Microscopy and Microanalysis, The University of Sydney, New South Wales 2006, Australia.
Microsc Res Tech. 2011 Sep;74(9):799-803. doi: 10.1002/jemt.20958. Epub 2010 Nov 3.
A limiting characteristic of the atom-probe technique is the nondetection of ions and this embodies a significant "missing information" problem in investigations of atomic clustering phenomena causing difficulty in the interpretation of any atom-probe experiment. It is shown that the measurable cluster-size distribution can be modeled by a mixed binomial distribution. A deconvolution method based upon expectation-maximization (EM) algorithm is presented to obtain the original physical distribution from an efficiency-degraded distribution, thereby providing means to calculate accurate cluster number densities from atom probe results. The accuracy of this restoration was predominantly dependent upon the detector efficiency and was proved to be highly accurate in the case of conventional atom-probe detector efficiencies (ε = 57%). Such considerations and measures are absolutely necessary when the number density of clusters and small precipitates is in any way regarded as important. We conclude that limitations in detector efficiency are more limiting for cluster-finding analyses via atom-probe techniques than spatial resolution issues, and therefore the current endeavors for improving detector technologies are well found.
原子探针技术的一个限制特征是无法检测离子，这在研究原子聚集现象时存在着显著的“信息缺失”问题，给任何原子探针实验的解释都带来了困难。研究表明，可测量的团簇尺寸分布可以通过混合二项式分布来建模。提出了一种基于期望最大化（EM）算法的去卷积方法，从效率降低的分布中获得原始物理分布，从而为从原子探针结果计算准确的团簇数密度提供了手段。这种恢复的准确性主要取决于探测器的效率，并且在传统的原子探针探测器效率（ε=57%）的情况下被证明是非常准确的。当簇和小沉淀物的数密度在任何方面被认为是重要的时，都需要考虑这些因素和措施。我们得出结论，对于通过原子探针技术进行的簇探测分析，探测器效率的限制比空间分辨率问题更为重要，因此，目前努力改进探测器技术是有意义的。
