From Copper Nanoparticles to Alumina Encapsulated Porous Layers With Enhanced Mechanical Stability

Nanoparticle-based structures are of significance for emerging technologies from antimicrobial coatings to catalysts. Sputtering based fabrication routes are particularly promising whenever high purity and monodisperse particles are required. This work establishes quantitative synthesis-structure relations for Cu-nanoparticles (diameter < 10 nm), synthesized through magnetron sputtering inert gas condensation and high-power impulse hollow cathode sputtering. The two deposition methods are compared in terms of nanoparticle deposition rate, morphology and size distribution. While magnetron sputtering inert gas condensation with quadrupole mass spectrometry offers excellent control of the size distribution of single-crystal particles, high-power impulse hollow cathode sputtering enables deposition of polycrystalline nanoparticles at higher deposition rates with more efficient target utilization. Consequently, porous, randomly assembled nanoparticle-based films of up to 1.5 µm thickness have been fabricated. Stabilization of these structures via atomic layer deposition (ALD-Al2O3, thickness up to 20 nm) is demonstrated through electron microscopy and nanoscratching, linking nanoscale structure to macroscale mechanical performance. While ALD encapsulation at 120°C does not change the Cu microstructure, the scratch resistance of the films improves with increasing encapsulation layer thickness. These findings provide a direct pathway from fundamental surface engineering to thick and robust functional nanoparticle-based films for future bio-medical and energy applications.