Morphological manipulation of tin nanostructures via pulse width modulation of potential step cycling in hydrochloric acid containing polyvinylpyrrolidone

A series of tin nanostructures including of two-dimensional, three-dimensional dendrites and polyhedrons have been facilely fabricated via applying one double potential step (DPS) or cyclic potential step (CPS) on Ag₄₀Sn₆₀ alloy substrates in HCl solution containing polyvinylpyrrolidone (PVP). The formation of Sn nanostructures undergoes two stages: an electrochemical dissolution and redeposition process. It is found that the diffusion distance of Sn²⁺ ions during dissolution periods determines the ionic distribution and then growth rate determining steps in the following redeposition periods (i.e. diffusion control or crystallization control). The Sn²⁺ ionic diffusion distance is shortened by adding PVP to decrease the ionic diffusion coefficient, and shortening pulse width of CPS to decrease the ionic diffusion times. The transformation mechanism of the growth modes during redeposition periods is discussed from perspective of the correlation between the crystal growth and mass transfer. The formation of dendrites is governed by the diffusion limited aggregation (DLA) mode and oriented attachment growth mechanism. The polyhedral growth is attributed to the synergistic effect of the fast deposit kinetics and the surface capping of PVP molecule. PVP molecule act as the complex agent, surface capping agent and stabilizer to affect the diffusion of Sn²⁺ ions and crystal growth.