Controlled sputter deposition of oxide nanoparticles-based composite thin films

Abstract

This study explores the feasibility of deposition of composite films based on nanoparticles (NPs) using a magnetron-based gas aggregation source of NPs. First, we investigate the deposition conditions and properties of the individual components of the composite films, namely, NPs prepared using Cu and W targets. We thoroughly discuss that the generation of NPs might be more efficient in the Ar atmosphere in the case of W target due to an enhanced direct emission of NP seeds from the target and/or a longer lifetime of the seeds in the plasma. To operate reasonable fluxes of NPs for both targets, O2 was added into the gas mixture. Lower O2 flow rates promote enhanced seed formation of NPs, while higher flow rates exhibit a dominant target poisoning effect, reducing the flux of NPs. We demonstrate that a fine-tuning of O2 flow rate allows us to control the resulting crystal structure of the NPs. Fully oxidized NPs were produced at O2 flow rates of 1.30sccm and 1.50sccm for Cu and W targets, respectively. Subsequently, CuO/WO3 composite films were prepared using our in-house-built software as alternating NPs-based layers. To demonstrate the capabilities of the deposition technique, three different CuO/WO3 multilayers were prepared, each with a specific thickness of the individual layers (80nm, 40nm, and 10nm, which corresponds to a monolayer of NPs). Scanning electron microscopy imaging shows well-defined layers with the intended thickness. In addition, XRD analysis confirms that all three multilayers exhibit practically identical patterns, indicating the same volumetric ratio of CuO and WO3 NPs in the investigated films.