Morphology and yield of W nanoparticles in gas aggregation: Pathways towards functional nanocomposite films

While gas aggregation cluster sources can tailor the chemistry, size, and shape of nanoparticles (NPs), low NP yield and instability over time still limit the fabrication of nanoparticle-based coatings or nanocomposite films. In this work, we propose controlled addition of ambient air as a nucleation source to enhance the efficiency and stability of the process. Additionally, the type of power source is varied, juxtaposing direct current and high-power impulse magnetron sputtering. Quadruple mass spectrometry and high-resolution transmission electron microscopy are used to monitor the deposition rate and morphology of tungsten NPs (size, shape, microstructure) as a function of process parameters. We observe significant variations in the deposition rate, the average diameter (3–5 nm), and the microstructure (amorphous vs. single-crystalline) of produced W NPs. The enhanced NP flux was exploited to demonstrate fast deposition of 500 nm thick W nanoparticle films as well as 200 nm thick nanocomposite films, consisting of a Cu matrix with incorporated W nanoparticles. For the latter we attribute refinement of the Cu matrix microstructure to two competing mechanisms: Formation of growth twins facilitated by W NPs and grain refinement due to residual air.