Lichte Hannes, Geiger Dorin, Linck Martin
Triebenberg Laboratory, Institute of Structure Physics, Technische Universität Dresden, Germany.
Philos Trans A Math Phys Eng Sci. 2009 Sep 28;367(1903):3773-93. doi: 10.1098/rsta.2009.0126.
Electron holography allows the reconstruction of the complete electron wave, and hence offers the possibility of correcting aberrations. In fact, this was shown by means of the uncorrected CM30 Special Tübingen transmission electron microscope (TEM), revealing, after numerical aberration correction, a resolution of approximately 0.1 nm, both in amplitude and phase. However, it turned out that the results suffer from a comparably poor signal-to-noise ratio. The reason is that the limited coherent electron current, given by gun brightness, has to illuminate a width of at least four times the point-spread function given by the aberrations. As, using the hardware corrector, the point-spread function shrinks considerably, the current density increases and the signal-to-noise ratio improves correspondingly. Furthermore, the phase shift at the atomic dimensions found in the image plane also increases because the collection efficiency of the optics increases with resolution. In total, the signals of atomically fine structures are better defined for quantitative evaluation. In fact, the results achieved by electron holography in a Tecnai F20 Cs-corr TEM confirm this.
电子全息术能够重建完整的电子波，因此提供了校正像差的可能性。事实上，使用未经校正的CM30特殊图宾根透射电子显微镜（TEM）就证明了这一点，在进行数值像差校正后，其在幅度和相位上的分辨率均达到了约0.1纳米。然而，结果表明其信噪比相对较差。原因在于，由枪亮度给出的有限相干电子流必须照亮至少四倍于像差所给出的点扩散函数宽度的区域。随着使用硬件校正器，点扩散函数大幅缩小，电流密度增加，信噪比相应提高。此外，由于光学系统的收集效率随分辨率提高，在图像平面中原子尺度上发现的相移也会增加。总体而言，原子级精细结构的信号在定量评估中得到了更好的定义。实际上，在Tecnai F20 Cs校正TEM中通过电子全息术获得的结果证实了这一点。
