Rose Harald H
Technical University Darmstadt, Institute of Applied Physics, Hochschulstrasse 6, 64289 Darmstadt, Germany.
Philos Trans A Math Phys Eng Sci. 2009 Sep 28;367(1903):3809-23. doi: 10.1098/rsta.2009.0062.
The attainable specimen resolution is determined by the instrumental resolution limit d(i) and by radiation damage. Solid objects such as metals are primarily damaged by atom displacement resulting from knock-on collisions of the incident electrons with the atomic nuclei. The instrumental resolution improves appreciably by means of aberration correction. To achieve atomic resolution at voltages below approximately 100 kV and a large number of equally resolved image points, we propose an achromatic electron-optical aplanat, which is free of chromatic aberration, spherical aberration and total off-axial coma. Its anisotropic component is eliminated either by a dual objective lens consisting of two separate windings with opposite directions of their currents or by skew octopoles employed in the TEAM corrector. We obtain optimum imaging conditions by operating the aberration-corrected electron microscope at voltages below the knock-on threshold for atom displacement and by shifting the phase of the non-scattered wave by pi/2 or that of the scattered wave by -pi/2. In this negative contrast mode, the phase contrast and the scattering contrast add up with the same sign. The realization of a low-voltage aberration-corrected phase transmission electron microscope for the visualization of radiation-sensitive objects is the aim of the proposed SALVE (Sub-A Low-Voltage Electron microscope) project. This microscope will employ a coma-free objective lens, an obstruction-free phase plate and a novel corrector compensating for the spherical and chromatic aberrations.
可达到的样品分辨率由仪器分辨率极限d(i)和辐射损伤决定。诸如金属之类的固体物体主要因入射电子与原子核的碰撞导致原子位移而受损。通过像差校正，仪器分辨率有显著提高。为了在低于约100 kV的电压下实现原子分辨率并获得大量等分辨率的图像点，我们提出了一种消色差电子光学齐明透镜，它没有色差、球差和全离轴彗差。其各向异性分量可通过由两个电流方向相反的独立绕组组成的双物镜或通过TEAM校正器中使用的倾斜八极杆来消除。通过在低于原子位移的碰撞阈值的电压下操作像差校正电子显微镜，并将非散射波的相位移动π/2或将散射波的相位移动-π/2，我们获得了最佳成像条件。在这种负对比度模式下，相位对比度和散射对比度以相同的符号相加。实现用于观察辐射敏感物体的低电压像差校正相位透射电子显微镜是所提议的SALVE（亚低电压电子显微镜）项目的目标。该显微镜将采用无彗差物镜、无障碍物相位板和一种新型校正器来补偿球差和色差。
