Thin films are structures with thicknesses ranging from the atomic scale to the mesoscale that are used to alter the properties of a surface and/or serve as functional layers in devices. Thin metal films deposited from the vapor phase on weakly-interacting substrates, including oxides (TiO₂, ZnO, SiO₂ etc.) and two-dimensional (2D) materials (graphene, MoS₂, etc), are relevant for a wide array of technological applications, such as optical devices, nanoelectronic components, sensors, and catalytic devices. The weak interaction between deposit and surface in these film/substrate combinations leads to three-dimensional (3D) metal-layer morphological evolution in an uncontrolled manner; which often constitutes an important challenge toward integrating metal layers in key enabling devices. Thus there is a need for efficient growth manipulation strategies, such that metal films with controlled 3D and 2D microstructures and morphologies can be synthesized.

Surfactants, i.e., minority metal, non-metal, and gaseous species which are deployed to the growing surface together with film-forming species, have been shown to enable growth manipulation in a multitude of homo- and heteroepitaxial metal/metal and semiconductor/semiconductor systems. This work explores the viability of N₂ and O₂ surfactants to manipulate growth in model weakly-interacting Ag/SiO₂ and Au/SiO₂ systems.

Au and Ag are deposited by direct current (DC) magnetron sputtering on Si substrates covered with a 500 nm thick thermally grown SiO₂ layer. Gaseous N₂ and O₂ surfactants are introduced to the sputtering atmosphere either continuously during deposition or at well-defined points during growth, such that specific film-formation stages as targeted. Using a combination of in situ/real-time diagnostic tools and ex situ characterization techniques, it is shown that O₂ and N₂ cause Ag and Au, respectively, to grow flatter, i.e., 2D growth morphology is promoted. Moreover, by deploying surfactants selectively during early or late film growth stages and studying their effect on film morphological evolution, it is concluded that N₂ and O₂ effectively suppress the rate of island coalescence promoting formation of flatter films.

The overall results of this study are the first step toward establishing an atomic-scale understanding of the effect of surfactants on morphological evolution of metal films on weakly-interacting substrates. The knowledge generated herein is relevant for designing growth manipulation strategies in a wide range of technologically important film/substrate systems.