Modification of Stranski-Krastanov growth on the surface of nanowires.

The heteroepitaxial growth of strained islands on a planar substrate offers an attractive route to the fabrication of quantum dots (QDs). To obtain more functions and superior properties, recent efforts have focused on using nanowires (NWs) as substrates to produce attractive structures that combine QDs with NWs. As the lateral size of an NW is large, it is possible that islands are formed on the side walls of the NW. However, no islands exist, and the lateral surface is rather smooth in thin, core-shell NWs. The existing theoretical models on the growth on planar and patterned substrates are not appropriate for the growth transition on the surface with nanoscale curvature. We thus urgently need to understand the basic physics involved in the strain-induced growth on the surface with nanoscale curvature. Here, we established a theoretical model to study the strain-induced growth on the surface, which showed that the Stranski-Krastanov (SK) mode can change to the Frank-van der Merwe (FM) mode due to the limit of the surface to the island's lateral growth. Using the model to investigate the heterostructured core/shell nanowires (NWs), we found, in addition to the SK mode on thick NWs and the FM mode on thin NWs, that there is a multiplex mode on medium NWs which includes the initial layer growth, the intermediate islands' growth and the final layer growth again. The established theoretical model not only explained some puzzling experimental results but also provided useful information to design and control the epitaxial growth on the surface with nanoscale curvature.