Stepwise growth of decahedral and icosahedral silver nanocrystals in DMF

Silver nanocrystals were synthesized by reducing AgNO₃ in N,N-dimethylformamide (DMF) solution. Besides decahedral and icosahedral nanoparticles, a series of their intermediate particles, which consist of a combination of two and more tetrahedra, are obtained. It was found that decahedral and icosahedral nanoparticles are not formed through assembling of tetrahedra formed separately but produced through the stepwise growth of tetrahedral units on specific facets in DMF. A simple combination model, of tetrahedral units suggested that the growth position of the fourth tetrahedral unit determines whether a decahedron or icosahedron is finally produced. In the formation of icosahedron, the crystal growth occurs inside of decahedral units. No further growth from decahedron to icosahedron was observed, indicating that there is a large energy barrier for the addition of a tetrahedron unit to a decahedron. Our study gives new information on the stepwise growth mechanism of decahedra and icosahedra in DMF solution.