Advances in Electron Optics
Advances in Electron Optics
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电子光学的进展
DOI：
10.1007/978-3-662-07766-5_5
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
H. Rose
中科院分区：
文献类型：
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作者：
H. Rose
阐明固体的原子结构是高分辨率透射电子显微镜的主要目标。所有成像显微镜可达到的分辨率取决于所采用的辐射（例如光、声音、带电粒子）的波长和成像透镜的缺陷。不使用透镜的显微镜（例如扫描隧道显微镜或原子力显微镜）的分辨率不受衍射的限制。不幸的是，这些显微镜只能对样品的表面进行成像，而有关原子块结构的详细信息对于阐明真实固体物体的特性是必要的。只有考虑电子的波动性质才能充分准确地描述透射电子显微镜 (TEM) 中的图像形成。从源传播到仪器最终图像平面的电子波穿过物体前后区域中的宏观电磁场以及物体内的微观场。宏观场在几个电子波长的距离内不会发生明显变化。这种行为与样本内原子产生的微观场的行为不同。因此，可以在几何光学框架内非常准确地描述电子通过仪器静态场的传播，几何光学将电子视为经典粒子。为了解释衍射，只需通过半经典 WKB 近似来考虑有限电子波长的影响 [1]。然而，这种方法对于样本的原子场是失败的。为了准确地描述电子波通过物体的传播，需要严格的波机械处理。由于这个问题极其复杂，我们只能通过在薄非晶物体的情况下采用玻恩近似来近似解决它，或者在晶体样本上采用多层和布洛赫波方法，如第 1 章所述。 2.目前用于确定电子显微镜宏观场内电子波传播的所有程序均假定等晕条件。这意味着系统的传输特性不依赖于物体内散射体的横向位置。这些
The elucidation of the atomic structure of solids is a major goal of highresolution transmission electron microscopy. The attainable resolution of all imaging microscopes is determined by the wavelength of the radiation employed (eg light, sound, charged particles) and the defects of the imageforming lenses. The resolution of microscopes that do not use lenses, such as the scanning tunneling microscope or the atomic force microscope, is not limited by diffraction. Unfortunately, these microscopes can only image the surface of the sample whereas detailed information about the atomic bulk structure is necessary for elucidating the properties of real solid objects. Image formation in the transmission electron microscope (TEM) can only be described sufficiently accurately by taking into account the wave nature of the electron. The electron wave propagating from the source to the final image plane of the instrument traverses macroscopic electromagnetic fields in the regions in front of and behind the object and microscopic fields within the object.The macroscopic fields do not vary appreciably over distances of several electron wavelengths. This behaviour differs from that of the microscopic fields produced by the atoms within the specimen. As a consequence, the propagation of the electrons through the static fields of the instrument can be described very accurately within the frame of geometrical optics, which considers the electrons as classical particles. In order to account for diffraction it suffices to consider the effect of the finite electron wavelength by means of the semi-classical WKB approximation [1]. However, this approach fails for the atomic fields of the specimen. In order to describe accurately the propagation of the electron wave through the object a rigorous wave-mechanical treatment is required. Owing to the extreme complexity of this problem one can tackle it only approximately by employing the Born approximation in the case of thin amorphous objects, or the multi-slice and Bloch-wave approaches for crystalline specimens, as detailed in Chap. 2. All present procedures for determining the propagation of the electron wave within the macroscopic fields of the electron microscope assume isoplanatic conditions. This implies that the transfer properties of the system do not depend on the lateral position of the scatterers within the object. These