Abstract: Here, Co/Ag binary nanoparticle superlattices were engineered. It is demonstrated that the Ag/Co nanoparticle size ratio is the dominating factor in the formation of binary nanoparticle superlattices. However, regardless of the relative ratio concentration of Co and Ag nanoparticles, the deposition temperature, Td markedly changes the crystalline structure of binary superlattices. A systematic study of these parameters is presented in order to shed light on the driving force in the formation of binary metallic nanoparticle superlattices...