Plasma-assisted synthesis and high-resolution characterization of anisotropic elemental and bimetallic core–shell magnetic nanoparticles

Abstract

SummaryMagnetically anisotropic as well as magnetic core–shell nanoparticles (CS-NPs) with controllable properties are highly desirable in a broad range of applications. With this background, a setup for the synthesis of heterostructured magnetic core–shell nanoparticles, which relies on (optionally pulsed) DC plasma gas condensation has been developed. We demonstrate the synthesis of elemental nickel nanoparticles with highly tunable sizes and shapes and Ni@Cu CS-NPs with an average shell thickness of 10 nm as determined with scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements. An analytical model that relies on classical kinetic gas theory is used to describe the deposition of Cu shell atoms on top of existing Ni cores. Its predictive power and possible implications for the growth of heterostructured NP in gas condensation processes are discussed.

Continuous gas-phase synthesis of core–shell nanoparticles via surface segregation

“…Recently, gas-phase synthesis techniques based on low-pressure multi-magnetron gas aggregation sourceswhere one target acts as the source of the core material and the others as one or more sources coating materialshave enabled the fabrication of core-shell particles with tunable sizes and shapes. 23,24 Apart from the demanding high vacuum requirements, 25 these methods oen suffer from nucleation of pure-element byproducts, [24][25][26] and achieving uniformity in bimetallic morphology is challenging as the nanoparticles generated by non-equilibrium, fast kinetics processes that do not include an additional annealing process oen include random and unpredictable metastable phases. 27,28 Having control over size, composition, and morphology is desirable, as it enables investigations of the nanoparticle properties' effects on various applications.…”

Gas-phase synthesis of nanoparticles: present status and perspectives

“…In order to overcome such limitation, few multi-magnetron approaches have been proposed in order to combine the different elements sputtered by more than one magnetron. Two of the proposed designs reside in the combination of a magnetron-based NPs source coupled with one or more magnetrons that in a second stage allow the formation of a shell on the NPs generated by the NPs source [6,7]. Another design incorporates 3 sputtering targets in the same magnetron head that is inserted in an aggregation zone [8,9].…”

Preparation of tunable-sized iron nanoparticles based on magnetic manipulation in inert gas condensation (IGC)

“…The increase of the aggregation length and the depth of the race-track are both supposed to trigger the formation of larger clusters. 25,38 Nevertheless, during the experiments, some uncommon size evolutions are observed. Figure 4 shows the combined influence of the increasing aggregation length and the depth of the race-track on NP size for two groups of experiment with significantly different backing plate thicknesses (0.…”

“…121, 024305-1 control through regulating the aggregation length, 25 gas flow 28 as well as the discharge current, 29 and the target utilization under the weakened magnetic field can be further improved. The modified magnetic field configuration not only broadens the attainable range of particle sizes for a selected target material but also promotes the particle shape and structure to experience great changes with varied size associated by the use of different backing plates.…”

“…The aim is to further decrease the minimum NP size that can be obtained by this technique based on the fact that the magnetic field configuration influences the cluster formation process enormously. [24][25][26] Compared with the originally strong magnetic field, in the absence of a backing plate, the target will feel a lower magnetic field resulting in a weakened plasma confinement and a broader target erosion zone. Furthermore, it should be noted that the total thickness (of the Fe target and the backing plate) should be limited to a level that still enables a sufficient magnetic field (typically $200-250 G) to be projected over the sputter target surface to ensure magnetron sputtering.…”