Controlled synthesis of core@shell nanoparticles (NPs) for certain applications is a difficult challenge in many nanotechnology projects. In this report, a conventional arrangement composed of a gas aggregation source is employed to generate the core nanoparticles, which are subsequently coated by the shell materials in a secondary planar magnetron sputtering. The important difference to the usual system is the application of the two opposing planar magnetrons in a closed field configuration. The prepared core Ag NPs by a gas aggregation source are coated/treated by the two magnetrons with Ti targets. Our findings clearly show that the shell thickness can be controlled by tuning the power delivered to the secondary magnetron plasma. Characterizations of the prepared films, by X-ray diffraction technique, disclose multi-crystalline cores covered by amorphous shells. Based on XPS and EDX measurements, different chemistry on the NPs surfaces and volume of the NPs can be achieved by tuning the operation conditions. Furthermore, the thermal annealing process leads to the growth of the crystallite size which results in emerging some microparticles caused by accelerating Ag surface mobility. The employed technique promises a reliable route to synthesize different heterogeneous NPs with stoichiometry tunable in a wide range for multi-functional devices.
In this study, iron carbide nanoparticles (NPs) were prepared by the plasma-based method using a gas aggregation source of NPs. In-flight plasma treatment of the NPs was performed to improve their temporal stability. The auxiliary radiofrequency plasma used for the in-flight treatment resulted in trapping of the NPs in the plasma for several 10s of seconds. Scanning electron microscopy and smallangle X-ray scattering analyses showed a decrease in the size of NPs due to the plasma treatment, whereas the X-ray diffraction analysis showed that the structure of the NPs changed from amorphous iron carbide to the crystalline Fe 3 C (cementite). In situ and ex situ X-ray photoelectron spectroscopy measurement confirmed better temporal stability of plasma-treated NPs against oxidation. 1 | INTRODUCTION Magnetic nanoparticles (NPs) are of great interest due to their use in data storage media, magnetic fluids, catalysis, drug delivery, imaging, magnetic separation, and many other applications. [1-6] In biomedicine, demands for magnetic properties of NPs are also complemented by demands for their biocompatibility. [7,8] This requirement can be fulfilled by the use of ironbased NPs due to the natural presence of iron in a human body. However, metal iron is highly reactive and immediately oxidizes in the atmosphere or aqueous media. Hence, due to oxidation, Fe NPs may lose their excellent magnetic properties during contact with biological tissues. The deposition of barrier shells over the Fe NPs may prevent oxidation. Metal, ceramic, or polymer shells are typically considered. Noble metals, Au or Pt, can effectively prevent oxidation and keep the toxicity of the NPs at a low level, though at a high cost. Ceramics are cheaper and also boast of good barrier properties; however, they may serve as a source of unwanted oxygen themselves. In the case of polymers, shells should be made thicker to hinder the diffusion of water and oxygen molecules through the free volume unoccupied by macromolecules. The fabrication of iron carbide NPs can be seen as a good alternative to bare iron, which immediately oxidizes in the atmosphere or in aqueous media. Iron carbide (Fe 3 C), also known as cementite, is stable in the air up to 200°C. Its bulk saturation magnetization is 140 emu/g, which is lower than that of iron (~220 emu/g), but higher than that of iron oxides (~90 emu/g). [9,10] Many studies have reported on the preparation of iron carbide NPs by wet chemistry methods.
Thin Al-Mg films were prepared by a DC magnetron sputtering on glass substrates covered with photoresist and subsequently free-standing samples were released from the substrate. The surface morphology, grain size and orientations were characterized by atomic force microscopy and transmission electron microscopy equipped with automated orientation and phase mapping software. The grain growth mechanism during sputtering is consistent with sputter deposition oblique incidence theory for growth. Strong preferred (110) orientation in direction perpendicular to the sample surface has been observed in all studied samples.
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