Characterization of the nanoparticle suspension by operando absorption spectrophotometry during sputtering onto liquids

Although the synthesis of nanoparticles (NPs) by low-pressure plasma-based sputtering onto liquids offers many advantages as compared to classic wet-chemistry-based approaches, not much is known about the nanoparticle formation mechanism in these conditions. Here, we report about an operando absorption spectrophotometry setup which allows recording time- and space-resolved spectra of the liquid into which the sputtered metal atoms are incorporated. The measurements are carried out during the plasma treatment but also afterward while keeping the sample inside the vacuum chamber. The device capabilities therefore allow studying the evolution of unstable systems, i.e., combination of sputtered atoms and host liquids for which aggregation may appear even during the plasma treatment time. As a model system, silver atoms are deposited onto a silicone oil which may be stirred or not. Our operando analysis provides qualitative and quantitative data and highlights that the nanoparticle formation and aggregation dynamics vary according to the process conditions.