Cai Zenghua, Chen Shiyou, Wang Lin-Wang
State Key Laboratory of Precision Spectroscopy , Key Laboratory of Polar Materials and Devices (MOE) , Department of Electronics , East China Normal University , Shanghai 200241 , China . Email:
Collaborative Innovation Center of Extreme Optics , Shanxi University , Taiyuan , Shanxi 030006 , China.
Chem Sci. 2019 Sep 24;10(46):10706-10715. doi: 10.1039/c9sc04100a. eCollection 2019 Dec 14.
Radiolysis ionization under electron beam illumination induces dissociation and damage of organic and biological molecules; thus, it is impossible to image the related materials by transmission electron microscopy (TEM). To understand the atomistic mechanism of radiolysis damage, we developed a systematical procedure based on real-time time-dependent density functional theory (rt-TDDFT) for simulating the radiolysis damage processes of molecules; this procedure can describe the ionization cross sections of the electronic states and the fast dissociation processes caused by hot carrier cooling and the Auger decay on deep levels. For the radiolysis damage of CHO, our simulation unexpectedly showed that there is strong competition among three different dissociation paths, including fast dissociation caused by nonadiabatic cooling of the hot carrier; fast dissociation caused by Auger decay, which induces double ionization and Coulomb explosion; and slow dissociation caused by increased kinetic energy. As the energy of the incident electron beam changes, the time scales of these dissociation paths and their relative contributions to the molecule damage change significantly. These simulation results explain the measured mass spectra of the CHO dissociation fragments and also provide clear competition mechanisms for blocking these dissociation paths in the TEM imaging of organic and biological materials.
电子束照射下的辐射分解电离会导致有机和生物分子的解离与损伤；因此，无法通过透射电子显微镜（TEM）对相关材料进行成像。为了理解辐射分解损伤的原子机制，我们基于实时含时密度泛函理论（rt-TDDFT）开发了一种系统程序，用于模拟分子的辐射分解损伤过程；该程序能够描述电子态的电离截面以及由热载流子冷却和深能级俄歇衰变引起的快速解离过程。对于CHO的辐射分解损伤，我们的模拟意外地表明，在三种不同的解离路径之间存在强烈竞争，包括热载流子非绝热冷却导致的快速解离；俄歇衰变引起的快速解离，其会诱导双电离和库仑爆炸；以及动能增加导致的缓慢解离。随着入射电子束能量的变化，这些解离路径的时间尺度及其对分子损伤的相对贡献会发生显著变化。这些模拟结果解释了CHO解离碎片的测量质谱，也为在有机和生物材料的TEM成像中阻断这些解离路径提供了清晰的竞争机制。
