Synthesis of Gold NPs-Containing Thin Films from Metal Salt Injection in Ar or Ar–NH3 DBDs

This study focuses on metal/polymer nanocomposite thin films made by atmospheric pressure Plasma-Enhanced Chemical Vapor Deposition. The aerosol of isopropanol-dissolved tetrachloroauric acid (HAuCl4:3H2O gold salt) is injected in a dielectric barrier discharge to synthesize plasmonic nanocomposite thin films. Argon is used as carrier gas with or without 133 ppm addition of ammonia (NH3) to respectively get or not a Penning mixture. Results show that NH3 largely influences the salt reduction and thin film properties. According to the aerosol characterization, the size distribution at the plasma entrance supports that isopropanol mainly evaporates before injection in the plasma. The salt initially dissolved in each droplet precipitates during evaporation before injection as solid nanoparticles of about 30 nm diameter with eventual traces of solvent. Then, the nanocomposite thins film are studied. Optical properties, as plasmonic resonance, are characterized by UV–visible absorption spectroscopy. The chemical composition is analyzed using X-ray photoelectron spectroscopy and Raman spectroscopy, complemented by X-ray diffraction analysis as well as chemical mapping obtained by Energy dispersive spectroscopy coupled to scanning electron microscopy (SEM) operating in Scanning Transmission Electron Microscopy mode. Additionally, the morphology of the deposits is investigated by atomic force microscopy and SEM, highlighting the influence of NH3 gas on the film nature and therefore its role in the overall deposition process. Finally, optical emission spectroscopy of the plasma gives clue to better understand the effect of NH3. The overall results show that the salt nanoparticles are reduced in the plasma phase leading to non-aggregated metal Au NPs embedded in a carbon-based matrix formed by isopropanol polymerization. The presence of NH3 in the plasma unambiguously decreases the salt reduction and affects the thin film properties, consequently changing their plasmonic response related to the size, concentration, and composition of the embedded NPs.