Ex Situ and in Situ Surface Plasmon Monitoring of Temperature-Dependent Structural Evolution in Galvanic Replacement Reactions at a Single-Particle Level

Abstract

The galvanic replacement reaction has recently been established as a standard protocol to create complex hollow structures with various compositions and morphologies. In the present study, the structural evolution of Ag nanocubes with Au precursors is monitored at the single-particle level by means of ex situ and in situ characterization tools. We explore two important features distinct from previous observations. First, the peak maximum of localized surface plasmon resonance (LSPR) spectra abruptly shifts at the initial stage and reaches a steady wavelength of similar to 600 nm; however, the structure continuously evolves to yield a nanobox even during the late stages of the reaction. This steady wavelength results from a balance of the LSPR between the red-shift by the growth of the inner cavity and the blue-shift by the deposition of Au on the interior, as confirmed by theoretical simulations. Second, the change in morphology at different temperatures is first analyzed by both ex situ and in situ monitoring methods. The reaction at 25 degrees C forms granules on the surface, whereas the reaction at 60 degrees C provides flat and even surfaces of the hollow structures due to the large diffusion rate of Ag atoms in Au at a higher temperature. These plasmon-based monitoring techniques have great potentials to investigate various heterogeneous reaction mechanisms at the single-particle level.