Today, there is an increasing demand for magnetic nanoparticles (NPs) because of their excellent physicochemical and magnetic properties involved in various applications such as biosensors, catalysts, and permanent magnets. Gas-phase condensation (GPC) methods are gaining more and more attention for synthesizing NPs with well-controlled size and crystallinity. However, the yield of NPs and target utilization rates are low for the conventional GPC method using planar targets. To address these issues, we develop a hollow cathode dc sputtering-based GPC system. Herein, the mechanism of synthesizing NPs is systematically investigated to tune the nucleation, growth, and crystallinity of NPs. The FeCo alloy tube target is used as a demonstration. Higher yield (∼4 times) and target utilization rate (∼18 times) compared to those for conventional planar target magnetron sputtering systems are obtained. Besides, an external magnetic field is applied to introduce the plasma heating effect, which could enhance the crystallinity and adjust the growth time of NPs. The NP yield could be further improved by integrating multiple hollow cathodes.
Bibliographical noteFunding Information:
This work was partially supported by ARPA-E (Advanced Research Projects Agency-Energy) project under Contract 0472-1595. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
- gas-phase condensation
- high yield
- hollow tube cathode
- magnetic nanoparticle
- plasma heating effect