A Simple Method of Superlattice Formation: Step-by-Step Evaluation of Crystal Growth of Gold Nanoparticles through Seed-Growth Method

Self-assembled arrangement of monodisperse nanoparticles (NPs) forms one-dimensional (1D) to three-dimensional (3D) superlattice (SL) with many useful applications. A simple seed growth (S-G) method is presented to achieve monodisperse gold (Au) NPs and simultaneously arrange them into SL formation. It can simply be done by controlling the hydrophobicity of a capping surfactant and can very well be extended to semiconductor NPs such as PbS as well. It is demonstrated by step-by-step evaluation of a three-step S-G method in the presence of a series of strongly hydrophobic Gemini surfactants. NPs of each step are analyzed by transmission electron microscopy (TEM) and UV-visible measurements to evaluate the mode of aggregation in dried and colloidal bulk phases, respectively. Both studies show complementary results. Crystal growth of NPs is followed through different steps by measuring the X-ray diffraction (XRD) patterns. It allows one to identify different reaction conditions such as the number of nucleating centers (seeds) and concentration or the surfactant to achieve monodisperse morphologies of NPs. All studies pertaining to different steps of the S-G method under different reaction conditions collectively lead to a single conclusion that better capping ability of strongly hydrophobic surfactants allows NPs to achieve both monodisperse morphologies as well as SE formation simultaneously.