Panoramic view of particle morphology for growth mechanism exploration: A case study of micron-sized five-fold twinned Ag particles from vapor condensation

Nobel metal particles of designed morphology have found many ingenious applications in fields such as catalysis, plasmonics, metamaterials, etc. A thorough investigation of influential factors that determine the particle morphology is desirable. Micron-sized Ag particles prepared by physical vapor deposition usually result from two-step growth: condensation from dense vapor followed by continual growth of the sessile particles landing on substrate. The primary particle-substrate contact may be the decisive factor in determining the particle morphology which in turn needs be precisely characterized. Here we report investigation on the growth process of five-fold twinned Ag particles towards targeted morphology by using scanning electron microscopic imaging at variable incidence angles, in conjunction with 3D modelling, so as to reveal the particle-substrate contact profile and to infer the growth mechanism. Five-fold twinned Ag particles were obtained at large yield on SiO2/Si(1 0 0), MgO(1 0 0) and LaAlO3(1 0 0) substrates. Results show that fivefold twinned Ag particles on SiO2/Si(1 0 0) substrate are usually fully developed, demonstrating higher symmetries (I(h)or D-5h) and acute contact angles, while on MgO(1 0 0) and LaAlO3(1 0 0) substrates the particles are usually heavily truncated with a contact characterized by also some obtuse angles. Difference in morphology occurs in the secondary growth stage where Ag atom migration along the particle-substrate interface may or may not be allowed. A set of parameters including contacting facet/contact angles and the height-edge length ratio are proposed for the morphology description of the five-fold twinned particles on support. Our work has resolved the influential factors in determining the morphology of large metal particles from physical vapor deposition where continual growth of sessile particles landing on substrate plays a pivotal role. By manipulating the particle-substrate contact and the secondary growth stage, five-fold twinned metal particles with designed morphology can be prepared for specific applications.