Three-dimensional core–shell ferromagnetic nanowires grown by focused electron beam induced deposition

Abstract

Functional nanostructured materials often rely on the combination of more than one material to confer the desired functionality or an enhanced performance of the device. Here we report the procedure to create nanoscale heterostructured materials in the form of core-shell nanowires by focused electron beam induced deposition (FEBID) technologies. In our case, three-dimensional (3D) nanowires (<100 nm in diameter) with metallic ferromagnetic cores of Co- and Fe-FEBID have been grown and coated with a protective Pt-FEBID shell (ranging 10-20 nm in thickness) aimed to minimize the degradation of magnetic properties caused by the surface oxidation of the core to a non-ferromagnetic material. The structure, chemistry and magnetism of nanowire cores of Co and Fe have been characterized in Pt-coated and uncoated nanostructures to demonstrate that the morphology of the shell is conserved during Pt coating, the surface oxidation is suppressed or confined to the Pt layer, and the average magnetization of the core is strengthened up to 30%. The proposed approach paves the way to the fabrication of 3D FEBID nanostructures based on the smart alternate deposition of two or more materials combining different physical properties or added functionalities.

Purified and Crystalline Three-Dimensional Electron-Beam-Induced Deposits: The Successful Case of Cobalt for High-Performance Magnetic Nanowires

“…Also, the presence of a 5 nm-thick layer of CoxOy covering the whole nanostructure can be detected in the HRTEM image, as a brighter, lower density thin layer at the surface. 52 The EELS chemical map also depicts an oxygen-rich layer of comparable size surrounding the nanowire (see Figure 2a). Interestingly, the oxygen content inside the nanowires is not perfectly homogeneous, but gradually increases from the core towards the surface.…”

“…The negative impact of the surface oxidation can be palliated by growing a protective shell to increase the overall net magnetization by 17%, still rather far from bulk cobalt. 53 However, the use of protective layers has been discarded in the current work in order to separate clearly the impact of annealing on the properties of the cobalt nanowires. The evolution of the nanowires' microstructure and chemical composition upon increasing annealing temperature is illustrated in Figure 1 In turn, this means that the grain size is becoming comparable to the diameter of the nanowire.…”

3D Nanoprinting via laser-assisted electron beam induced deposition: growth kinetics, enhanced purity, and electrical resistivity

“…Emerging applications include, but are not limited to, high strength nanolattices [2], optical metamaterials [3], accurate molecular detection [4], the study of biological systems important in determining cancer treatment options [5], and reliable, low cost, high performance magnetic hard disk drives [6]. A variety of fabrication techniques have been used to construct multi-dimensional nanostructures [7–10] with differing degrees of success.…”

Magnetic Nanowires and Nanotubes

“…The former method enabled the fabrication of structures such as core-shell nanowire spin valves (Chan et al 2010), CoO (10 nm)/Co (5 nm)/Cu (5 nm)/Co (5 nm), deposited through sputter deposition around the chemical vapour-deposited Ni NWs. Vertical and fully 3D core-shell nanostructures can be grown also by focused electron beam-induced deposition, such as Co NWs with a Pt shell (Pablo-Navarro et al 2016).…”