Plasma‐based synthesis of iron carbide nanoparticles

Abstract

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.

Core@shell nanoparticles by inflight controlled coating

“…For the typical 3-inch planar magnetron, the residence time is shorter than 0.01 s. Therefore, the primary NPs must be slowed down. The approach using deceleration of the NPs by their collisions with the buffer gas was already successfully used in several publications [3,7,17,18]. The maximum thickness of the shell produced by in-flight coating was 2.5 nm for Au and Ti as reported in [3] and [18], respectively.…”

“…Thus, controlled synthesis of this type of nanomaterials is vital. As an example, protection of the core of the NPs by the bio compatible shell which prevents the oxidation and degradation of the magnetic NPs is essential for biomedical applications of magnetic NPs [2,3,7].…”

Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime for synthesis of core–shell nanoparticles

“…Hybrid NPs are also obtained by in-flight post-growth manipulation of the NPs obtained using the MSGA method [1]. For this purpose, the single-element NPs ejected from the MSGA source are passed through an auxiliary plasma region, localized immediately after the exit aperture [5][6][7]. This plasma region is independent of the magnetron plasma inside the MSGA cluster source, increasing the complexity of the experimental setup.…”