Homogeneity of matrix and nanocomposite layers as deposited by gas phase condensation (GPC) and PECVD processes

A vacuum deposition process for silver (Ag) nanocomposite thin films was designed by combining inert gas phase condensation (GPC) and plasma-enhanced chemical vapor deposition (PECVD) processes. Ag nanoparticles (NPs) were synthesized through the condensation of sputtered atomic vapor produced by gas flow sputtering (GFS). A low-pressure PECVD source was used for the direct encapsulation of the NPs inside plasma polymer layers obtained from organic precursors. Samples were transferred directly between NP and matrix sources, achieving safe-by-design in-vacuo fixation of NPs inside multilayer nano-composite coatings. Structural and optical characterizations were performed using Fourier-transform infrared (FTIR) spectroscopy, cross-section scanning electron microscopy (SEM), variable angle UV-NIR ellipsometry and UV-Vis spectrometry. The Ag NPs exhibited a mean size of 3 to 9 nm, with characteristic localized surface plasmon resonance (LSPR) peaks between 387 and 496 nm. A red shift was observed with increasing particle size, as well as a broadening of absorption peaks with increasing Ag content. Finite-difference time-domain (FDTD) simulations corroborated the experimentally observed optical response by confirming the spectral position of the plasmonic absorption peak evidenced in the optical characterization of Ag NPs – SiO x matrix multilayer nanocomposites. These results demonstrate the feasibility of producing t compositionally tunable Ag-based plasmonic nanocomposite thin films, suitable for optical and sensing applications, using a fully scalable in-vacuo process.