Chen Ko-Feng, Lo Shen-Chuan, Chang Li, Egerton Ray, Kai Ji-Jung, Lin Juhn-Jong, Chen Fu-Rong
Department of Engineering and System Science, National Tsing Hua University, HsinChu 30013, Taiwan.
Micron. 2007;38(4):354-61. doi: 10.1016/j.micron.2006.06.004. Epub 2006 Jul 18.
This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an ESI series, to allow mapping of sp(2)/sp(3) ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/alpha-Fe(2)O(3)). Two problems, data undersampling and a convolution effect associated with extraction of the image-spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-spectrum obtained from the ESI series images has a quality as good as that of conventional electron energy-loss spectra. The L(3)/L(2) ratio of the reconstructed ESI spectrum is determined to be 3.30+/-0.30 and 5.0+/-0.30 for Fe and alpha-Fe(2)O(3), respectively. Our L(3)/L(2) ratio mapping shows an accurate correspondence across the Cu/Fe/alpha-Fe(2)O(3) region. The effect of delocalization and chromatic aberration on the ESI resolution is discussed and estimated to be about 2 nm for the case of L(3)/L(2) ratio mapping.
本文展示了电子能谱成像（ESI）在氧化铁体系价态映射方面的适用性。我们之前为ESI系列开发了一套信号处理方法，用于绘制sp(2)/sp(3)比率、介电函数和能带隙图。在本研究中，这些方法被用于生成氧化铁薄膜（Fe/α-Fe₂O₃）的价态图。通过使用三次多项式插值和最大熵反卷积，克服了两个问题，即数据欠采样以及与从芯损图像系列中提取图像光谱相关的卷积效应。结果，从ESI系列图像获得的重建图像光谱具有与传统电子能量损失谱相当的质量。对于Fe和α-Fe₂O₃，重建的ESI光谱的L₃/L₂比率分别确定为3.30±0.30和5.0±0.30。我们的L₃/L₂比率映射在Cu/Fe/α-Fe₂O₃区域显示出准确的对应关系。讨论了离域和色差对ESI分辨率的影响，对于L₃/L₂比率映射的情况，估计约为2 nm。
