Role of small additive particles in hexagonal structure formation by colloidal heteroepitaxy

In an experiment, two types of hexagonal structures, the primitive translation vector of which was parallel to that of substrate or rotated by 30°, were generated during colloidal heteroepitaxy. When colloidal particles smaller than the epitaxial particles were included as additives, the formation ratio of the two hexagonal structures changed depending on the size of the additive particles. To examine the dependence of the formation ratio of the two hexagonal structures on the size of the small colloidal particles, Brownian dynamics simulations were performed. Under a high particle density and strong interaction conditions, the hexagonal structure with a lower formation ratio without additives became the major product when additives much smaller than the epitaxial particles were included. Conversely, the hexagonal structure with a higher formation ratio without additives became difficult to form in the presence of additive particles. The effect of additive particles on the formation rates of hexagonal structures depended on whether the additive particles could intrude into the space between the substrate and epitaxial layer. Both hexagonal structures became more difficult to form as the additive particle size increased. At a specific ratio of the additive particle size to the substrate particle size, the formation ratio of the structure present in a lower content without additive increased because of the generation of a precursor structure.