Synthesis of Self-Supporting Gold Microplates on Soft Substrates through Infiltration Growth Mechanism

Direct growth of high-quality gold microplates (Au MPs) on substrates using chemical methods presents many advantages, such as being free from plate aggregation, bending, and contamination by small particles, when compared to microplates deposited on substrates by solution-phase synthesis. In this study, we present a facile chemical synthesis strategy to obtain self-supporting Au MPs on soft polydimethylsiloxane (PDMS) substrates, where the center of the Au MPs is elevated above the substrate. We demonstrate that the coexistence of halide ions and a soft substrate is crucial for the formation of self-supporting Au MPs. The halide ions play a pivotal role in preventing the deposition of Au atoms on the top {111} facet through the halide passivation mechanism, while the weak interactions between Au MPs and the soft substrate allow Au atoms to infiltrate beneath and preferentially grow on the bottom {111} facet, which gradually raises the Au MPs and forms self-supporting structures. It is worth emphasizing that self-supporting Au MPs are rarely synthesized, and elucidating the infiltration growth mechanism provides new insights into microcrystal growth. Furthermore, our study shows that self-supporting Au MPs possess unique characteristics for creating sealed nanocavities with femtoliter volumes and also providing excellent acoustic phonon resonances with extended vibrational lifetimes. We anticipate that self-supporting Au MPs may open new opportunities in various applications, compared to substrate-supported Au MPs.