Gas aggregation cluster source (GAS) based on planar magnetron is very popular system for synthesis of various nanoparticles (NPs). Such source was used for production of NPs from different materials ranging from metals or metal oxides to organic compounds. In recent years, the focus shifts to the preparation of heterogeneous NPs. In this study, we report on the two strategies for the production of heterogeneous multicomponent NPs based on the GAS systems. The first is based on the utilization of the composite magnetron target of the GAS magnetron. The second is based on in-flight deposition of the shell on the already formed NPs after they left the GAS.
The composite target was made of copper sheet 3 mm thick and 3 inch in diameter with the tungsten pellets placed in the erosion zone. The sputtering took place in the water cooled aggregation chamber in argon atmosphere at pressures from 30 to 210 Pa and magnetron current up to 500 mA. Aggregation chamber was ended with conical orifice 2 mm in diameter facing on substrate placed in the distance 20 cm in the deposition chamber with the background pressure below 1 Pa. The amount of tungsten in the NPs was predetermined by the amount of pellets and tuned by plasma parameters. Surface chemistry was determined by XPS and NPs morphology by SEM and HRTEM. Very good segregation of the W core and Cu shell was observed by STEM that proved core@shell structure of produced NPs.
In the second case Ni NPs prepared by GAS with Ni magnetron target 1.5 mm thick were coated by copper by means of tubular magnetron (TMG). The magnetron was connected directly to the GAS and was ended by a nozzle similarly to the GAS. The diameter and length of the nozzle was adjusted in such a way that the pressure inside the TMG was about one half of the pressure inside the GAS. Due to that Ni NPs leaving the GAS were decelerated to the drift velocity of the gas and their residence time was increased. It was found that below 150 mA DC current the NPs can easily flight through the TMG but the Cu coverage of Ni NP is negligible. Self-pulsing of the deposition rate and voltage was observed between 150 and 250 mA. Above 250 mA no NPs passed through the TMG. However, if the magnetron current was pulsed it was possible to deposit NP also above this limit. It was shown that change of the pulse duty cycle leads to the change of Cu/Ni ratio and the size of fabricated NPs. Due to high miscibility of Ni and Cu core-shell structure was not observed in this case and produced NPs were alloy type with higher Cu content on the surface.
This work was supported by grant GACR 17-22016S from the Grant Agency of the Czech Republic.