Wang Zhong Lin
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA.
Micron. 2003;34(3-5):141-55. doi: 10.1016/s0968-4328(03)00024-6.
This paper reviews the recent progress in the following areas. (1) In quantitative high-resolution transmission electron microscopy, the theoretically calculated images usually give better contrast than the experimentally observed ones although all of the factors have been accounted for. This discrepancy is suggested due to thermal diffusely scattered (TDS) electrons, which were not included in the image calculation. The contribution from TDS electrons is especially important if the image resolution is approaching 0.1 nm and beyond with the introduction of Cs corrected microscopes. A more rigorous multislice theory has been developed to account for this effect. (2) We proved that the off-axis holography is an ideal energy filter that even filters away the contribution made by TDS electrons in the electron wave function, but conventional high-resolution microscopy do contain the contribution made by phonon scattered electrons. (3) In electron scattering, most of the existing dynamical theories have been developed under the first order diffuse scattering approximation, thus, they are restricted to cases where the lattice distortion is small. A formal dynamical theory is presented for calculating diffuse scattering with the inclusion of multiple diffuse scattering. By inclusion of a complex potential in dynamical calculation, a rigorous proof is given to show that the high order diffuse scattering are fully recovered in the calculations using the equation derived under the distorted wave Born approximation, and more importantly, the statistical time and structure averages over the distorted crystal lattices are evaluated analytically prior numerical calculation. This conclusion establishes the basis for expanding the applications of the existing theories. (4) The 'frozen lattice' model is a semi-classical approach for calculating electron diffuse scattering in crystals arisen from thermal vibration of crystal atoms. Based on a rigorous quantum mechanical phonon excitation theory, we have proved that the frozen lattice mode is an excellent approximation and no detectable error would be possible under normal experimental conditions.
本文综述了以下几个领域的最新进展。（1）在定量高分辨率透射电子显微镜中，尽管已考虑了所有因素，但理论计算图像通常比实验观察图像具有更好的对比度。这种差异被认为是由于热漫散射（TDS）电子造成的，而图像计算中并未包含这些电子。随着Cs校正显微镜的引入，当图像分辨率接近0.1纳米及更高时，TDS电子的贡献尤为重要。已经开发出一种更严格的多切片理论来解释这种效应。（2）我们证明了离轴全息术是一种理想的能量滤波器，它甚至可以滤除电子波函数中TDS电子的贡献，但传统的高分辨率显微镜确实包含声子散射电子的贡献。（3）在电子散射中，大多数现有的动力学理论是在一阶漫散射近似下发展起来的，因此，它们仅限于晶格畸变较小的情况。提出了一种形式动力学理论，用于计算包含多重漫散射的漫散射。通过在动力学计算中包含复势，给出了一个严格的证明，表明在使用扭曲波玻恩近似导出的方程进行计算时，高阶漫散射在计算中得到了完全恢复，更重要的是，在数值计算之前，对扭曲晶格上的统计时间和结构平均值进行了解析评估。这一结论为扩展现有理论的应用奠定了基础。（4）“冻结晶格”模型是一种半经典方法，用于计算晶体中由晶体原子热振动引起的电子漫散射。基于严格的量子力学声子激发理论，我们证明了冻结晶格模式是一种很好的近似，在正常实验条件下不会有可检测到的误差。
