利用电子束辐照与热能耦合探索金属晶体形核后生长的机理

理解金属形核后生长的机理对于制备结构可控的金属晶体至关重要。由于初形核的金属晶核尺寸小且结构极不稳定，使得对其生长的原子尺度表征非常困难。本研究基于原位球差校正透射电子显微镜技术，通过耦合电子束辐照和热能的方式激发、控制和观察始于自由原子的金属形核后生长的过程，揭示其中的机理。以金属有机化合物为前驱体，通过真空封管挥发法可控地制备附载于低成像衬度材料上的金属纳米晶。结合使用原位加热技术和电子束辐照，耦合热能与入射电子对金属的辐照作用，原位解离金属纳米晶为离散的自由原子。而后调控电子束束流和体系温度使自由金属原子自发弛豫、聚合以及形核生长，同时实现原子级分辨率原位观测，探索生长过程中包括晶面、缺陷和位错等形成的原理。并且选用直接电子相机及间断成像等方法降低电子束辐照对形核后生长的影响，揭示普适的金属形核后生长机理，最终建立生长模型，为金属可控生长提供理论指导和技术支持。

Understanding the post-nucleation growth mechanism of metal is essentially important for producing metal crystals with controllable structures. The just nucleated metal crystal nuclei have tiny sizes with extremely unstable structures, making the in-situ characterization of their growth processes very difficult. Based on in-situ spherical aberration corrected transmission electron microscopy technique, we intend to reveal the post-nucleation growth mechanism of metal by using coupled electron beam irradiation with thermal energy for stimulating, controlling and observing the post-nucleation growth of metal from free atoms. By volatilizing and dissociating metallo-organic compounds with tube sealing method, metal nanocrystals could be obtained on the selected substrates which have low imaging contrast. To dissociate the formed metal nanocrystals into free atoms, the in-situ heating technique will be combined with electron beam irradiation for coupling the thermal energy and irradiation effects on metal from incident electrons. Then by adjusting and reducing the dose rate of electron beam and temperature, the spontaneous relaxation, aggregation and nucleation and following post-nucleation growth of free metal atoms would be realized. All these processes will be direct observed and recorded with atomic resolution for exploring the mechanisms of crystalline facet, defect and dislocation formations. In addition, direct detection camera and non-continuous observation method will be applied to reduce the influence of electron beam irradiation on the post-nucleation growth processes. Thus, this study explores and reveals the general mechanism for the post-nucleation growth of different metals, builds the model for the growth of metals, providing new fundamental knowledge and technical support for the controllable growth of metals.