Linköping University, Department of Physics, Chemistry, and Biology (IFM), Linköping SE-581 83, Sweden.
Ultramicroscopy. 2013 Sep;132:60-4. doi: 10.1016/j.ultramic.2013.03.015. Epub 2013 Mar 29.
A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the field evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within ±0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances.
在原子探针断层分析的成分测量中，主要的不确定来源源于将质谱中的峰或峰的一部分分配给其正确的身份时的不确定性。特别是，峰重叠是一个限制因素，而理想的质谱应该具有零展宽的正确位置的峰。在这里，我们报告了一种将实验质谱反卷积为这种理想光谱和描述由每个离子的场蒸发和检测引入的峰展宽的系统函数的方法。通过假设线性和时不变行为，推导出了一个描述峰形状和峰强度的方程组。通过最小化平方残差并通过最大熵方法正则化，将模型拟合到观察到的光谱。对于完全符合假设的合成数据，该方法将峰强度恢复到±0.33%以内。通过 Fe-Cr 数据示例说明了该模型在实验 APT 数据中的应用。了解峰形状不仅为更好地进行整体成分测定，而且为由于峰重叠或由同位素丰度约束的峰分离引起的测距误差的估计等提供了几种新的可能性。
