Quantum-trajectory Monte Carlo method for study of electron-crystal interaction in STEM.
Quantum-trajectory Monte Carlo method for study of electron-crystal interaction in STEM.
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DOI：
10.1039/c5cp02300a
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发表时间：
2015-07
期刊：
影响因子：
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通讯作者：
Zhu Ruan;R. Zeng;Y. Ming;Min Zhang;Bo Da;S. Mao;Z. Ding
中科院分区：
文献类型：
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作者：
Zhu Ruan;R. Zeng;Y. Ming;Min Zhang;Bo Da;S. Mao;Z. Ding
本文提出了一种新的量子轨迹蒙特卡罗模拟方法，用于研究电子束与结晶固体的相互作用，并将其应用于电子显微镜和光谱学。该方法将处理晶体中电子弹性散射和衍射的波希曼量子轨迹方法与沿量子轨迹路径的电子非弹性散射事件的蒙特卡罗采样相结合。我们研究了聚焦入射电子束在晶体中的电子散射和二次电子生成过程，从而理解了最近在扫描透射电子显微镜实验中获得的原子分辨率二次电子图像背后的成像机制。根据这种方法，波曼量子轨迹首先通过波函数计算得到，该波函数是由时间相关Schrödinger方程的多片法数值解得到的。撞击参数相关的内壳层激发横截面使得能够对沿原子柱行进的入射电子轨迹产生的电离事件进行蒙特卡罗采样，以激发高能撞击次级电子。在级联产生之后，用传统的蒙特卡罗模拟方法跟踪了极低能量真二次电子的输运和发射过程，以呈现图像信号。硅（110）晶体的模拟图像与实验图像的比较表明，二次电子图像的原子分辨机制主要是高能电子束产生的内壳电离事件。
In this paper, a novel quantum-trajectory Monte Carlo simulation method is developed to study electron beam interaction with a crystalline solid for application to electron microscopy and spectroscopy. The method combines the Bohmian quantum trajectory method, which treats electron elastic scattering and diffraction in a crystal, with a Monte Carlo sampling of electron inelastic scattering events along quantum trajectory paths. We study in this work the electron scattering and secondary electron generation process in crystals for a focused incident electron beam, leading to understanding of the imaging mechanism behind the atomic resolution secondary electron image that has been recently achieved in experiment with a scanning transmission electron microscope. According to this method, the Bohmian quantum trajectories have been calculated at first through a wave function obtained via a numerical solution of the time-dependent Schrödinger equation with a multislice method. The impact parameter-dependent inner-shell excitation cross section then enables the Monte Carlo sampling of ionization events produced by incident electron trajectories travelling along atom columns for excitation of high energy knock-on secondary electrons. Following cascade production, transportation and emission processes of true secondary electrons of very low energies are traced by a conventional Monte Carlo simulation method to present image signals. Comparison of the simulated image for a Si(110) crystal with the experimental image indicates that the dominant mechanism of atomic resolution of secondary electron image is the inner-shell ionization events generated by a high-energy electron beam.