Glaeser Robert M, Downing Kenneth H
Department of Molecular and Cell Biology, Stanley/Donner ASU, University of California, Berkeley, CA 94720-3206, USA.
Microsc Microanal. 2004 Dec;10(6):790-6. doi: 10.1017/s1431927604040668.
Although the most familiar consequences of specimen charging in transmission electron microscopy can be eliminated by evaporating a thin conducting film (such as a carbon film) onto an insulating specimen or by preparing samples directly on such a conducting film to begin with, a more subtle charging effect still remains. We argue here that specimen charging is in this case likely to produce a dipole sheet rather than a layer of positive charge at the surface of the specimen. A simple model of the factors that control the kinetics of specimen charging, and its neutralization, is discussed as a guide for experiments that attempt to minimize the amount of specimen charging. Believable estimates of the electrostatic forces and the electron optical disturbances that are likely to occur suggest that specimen bending and warping may have the biggest impact on degrading the image quality at high resolution. Electron optical effects are likely to be negligible except in the case of a specimen that is tilted to high angle. A model is proposed to explain how both the mechanical and electron-optical effects of forming a dipole layer would have much greater impact on the image resolution in a direction perpendicular to the tilt axis, a well-known effect in electron microscopy of two-dimensional crystals.
尽管在透射电子显微镜中，通过在绝缘样品上蒸发一层薄导电膜（如碳膜）或直接在这种导电膜上制备样品，可消除样品充电最常见的后果，但仍存在一种更微妙的充电效应。我们在此认为，在这种情况下，样品充电可能会产生一个偶极片，而不是在样品表面形成一层正电荷。文中讨论了一个控制样品充电及其中和动力学因素的简单模型，作为试图将样品充电量降至最低的实验指南。对可能出现的静电力和电子光学干扰的合理估计表明，在高分辨率下，样品弯曲和翘曲可能对图像质量下降影响最大。除了样品倾斜到高角度的情况外，电子光学效应可能可以忽略不计。本文提出了一个模型，以解释形成偶极层的机械和电子光学效应如何在垂直于倾斜轴的方向上对图像分辨率产生更大影响，这是二维晶体电子显微镜中一个众所周知的效应。
