An explanation for bends of 1-dimensional nanorods

Growth of artificial pinning centers (APCs) in YBa₂Cu₃O_7-δ(YBCO) films are discussed. The APCs used in this research are BaZrO₃ and BaSnO₃ nanorods which are reported by Mele et al. TEM images show these nanorods gradually bend accordingly with approaching to a surface of films. This feature showed a growth pattern like a firework. We explain the feature of the nanorods as follows; At an early growth stage, films grow in a layer by layer growth mode. The surface of the films is flat and very smooth. After the early growth stage, the film surface gradually becomes rough, indicating the film grows in a Stranski-Krastanov growth mode. This roughness was caused by a spiral growth of films with many steps. At the step of YBCO films, nanorod materials such as BaZrO₃ are supplied from one direction. Then, the center of nanorods sifts to the same direction of the step flow. Then, the nanorods bend to the edge of the grains in the films. As a grain in spiral growth had a convex surface, nanorods bent to the direction perpendicular to the grain surface. Finally, nanorods in rough grains form firework structures.