Evolution of amorphous boron transformed into crystal nanospheres under electron beam irradiation

In this work, amorphous coralloid boron was successfully prepared in Cu-B-Mg alloy by adding magnesium and increasing cooling rate. Coralloid amorphous boron crystallized under electron beam irradiation and crystalline boron nanospheres were formed on amorphous substrate. The boron nanospheres possess a particle size between 5 and 20 nm. Boron nanospheres mainly exist as alpha-B structure. During the formation of boron sphere, a spherical black region was first formed in the amorphous boron substrate, and then the black region gradually crystallized and finally formed a complete boron sphere. Moreover, boron nanospheres were unstable in the initial stage and twin structure can be observed in this stage. As the electron beam irradiation time increased, the substrate gradually shrinked and the boron spheres gradually detached from the substrate.