Redistribution Layer (RDL), composed of layered dielectrics and electroplated copper materials, is a basic structure to rearrange numerous I/O pads on the chip surface in wafer-level advanced packaging. As the key chemicals in electrolyte baths, electroplating additives have undergone continuous development to meet the industrial needs for high-speed and fine-line/fine-pitch applications. Meanwhile, the intricate relationships between additive chemical structures and electroplated copper properties are yet to be well understood. In this work, a pair of triphenylmethane-based dye molecules, i.e., gentian violet (GV) and methyl green (MG), was comparatively investigated as levelers for high-speed RDL copper electroplating. Compared to GV, significantly stronger electrochemical polarization and tunable deposit morphology can be achieved by MG with just one extra quaternized amine terminal. Combining quantum chemical computations, in situ spectroelectrochemical analyses, and microstructural characterization, it is found that MG possesses enhanced electrostatic adsorption, surface coverage and multi-additive synergies, enabling tailored copper trace morphology. This study elaborates the adsorption mechanism and screening criteria of triphenylmethane-derived levelers, and presents a candidate additive structure for high-speed copper electroplating.

Ultrasmall gold (Au) clusters have been regarded as one of the prototypes materials for solar energy conversion due to their unique strong molecular-like light absorption properties. However, the light-induced aggregation of Au clusters into nanoparticles is one of the most important factors that restricts its application in photocatalysis. Although Au clusters aggregation has been widely demonstrated, the underlying mechanism for cluster fusion is still unclear due to the lack of experimental evidence. Herein, we report the direct observation of Au clusters on TiO₂ nanosheets aggregating when used as visible light photocatalysts for the reduction of nitroaromatics. Through in situ high-resolution transmission electron microscopy (TEM), the coexistence of two fusion mechanisms of Au clusters on TiO₂ under ultraviolet-visible (UV-Vis) light irradiation in air is identified, i.e., the migration and coalescence (MC) and Ostwald ripening (OR). Additionally, the correlation between the photostability of Au clusters and reaction atmospheres has been investigated, among which Au clusters have higher stability in an inert N₂ atmosphere or vacuum than the oxidizing atmospheres (i.e., air and O₂). These results indicate the inherent stability of Au cluster during photocatalysis, and instability comes from the consuming of ligand layer. This work not only discloses the underlying mechanism of Au cluster sintering but also provides guidelines for enhancing metal clusters-based photocatalysts stability.