Multisegmented FeCo/Cu Nanowires: Electrosynthesis, Characterization, and Magnetic Control of Biomolecule Desorption

Abstract

In this paper, we report on the synthesis of FeCo/Cu multisegmented nanowires by means of pulse electrodeposition in nanoporous anodic aluminum oxide arrays supported on silicon chips.By adjusting the electrodeposition conditions, such as the pulse scheme and the electrolyte, alternating segments of Cu and ferromagnetic FeCo alloy can be fabricated. The segments can be built with a wide range of lengths (15 -150 nm) and exhibit a close-to-pure composition (Cu or FeCo alloy) as suggested by EDX mapping results. The morphology and the crystallographic structure of different nanowire configurations have been assessed thoroughly concluding that Fe, Co and Cu form solid solution. Magnetic characterization using vibrating sample magnetometry and magnetic force microscopy reveals that by introducing non-magnetic Cu segments within the nanowire architecture, the magnetic easy axis can be modified and the reduced remanence can be tuned to the desired values. The experimental results are in agreement with the provided simulations. Furthermore, the influence of nanowire magnetic architecture on the magnetically triggered protein desorption is evaluated for three types of nanowires: Cu, FeCo and multisegmented FeCo15 nm/Cu15 nm. The application of an external magnetic field can be used to enhance the release of proteins on-demand. For fully magnetic FeCo nanowires the applied oscillating field increased protein release by 83%, whereas this was found to be 45% for multisegmented FeCo15 nm/Cu15 nm nanowires. Our work suggests that a combination of arrays of nanowires with different magnetic configurations could be used to generate complex substance concentration gradients or control delivery of multiple drugs and macromolecules.

Tailoring Magnetic Anisotropy at Will in 3D Interconnected Nanowire Networks

“…High‐aspect‐ratio magnetic NW arrays are normally produced by template‐assisted deposition . When dissolving the template to work directly with the NWs, the whole structure collapses into a bunch of individual NWs without support, which makes it possible to be studied or used individually but makes their handling and integration into devices quite complex. Therefore, a further step in the research of magnetic NWs is to produce structures of interconnected wires at the nanoscale, as proposed, for example, in the first patent of the race‐track memory by IBM but never fabricated.…”

Ni-Co Alloy and Multisegmented Ni/Co Nanowire Arrays Modulated in Composition: Structural Characterization and Magnetic Properties

“…The first method allows for minimizing the co-deposition phenomenon that is present when different metallic ions can be electrodeposited at similar values of the deposition potential within each segment at the same time. Therefore, a purer chemical composition in each segment of the NW can be achieved in this way [31,35,36]. This synthesis procedure of subsequent segmented magnetic NWs can also lead to poor adhesion between layers with different chemical compositions, or uneven morphological growth, due to changes in the crystalline structure of the respective segments [37] but, at the same time, the assembling building blocks of consecutive segments of the NW having different material composition with a well-defined interface layer at the junctions, which can act as a pinning center for the magnetic domain wall's displacement along the wire length.…”

“…This synthesis procedure of subsequent segmented magnetic NWs can also lead to poor adhesion between layers with different chemical compositions, or uneven morphological growth, due to changes in the crystalline structure of the respective segments [37] but, at the same time, the assembling building blocks of consecutive segments of the NW having different material composition with a well-defined interface layer at the junctions, which can act as a pinning center for the magnetic domain wall's displacement along the wire length. This fact allows for the magnetization confinement in each NW segment and gives rise to NW arrays with a magnetic multi-domain structure [29,31,35].…”

Magnetometry of Individual Polycrystalline Ferromagnetic Nanowires

“…We determine the saturation magnetization, remanence, coercive fields, and saturating fields of electrodeposited polycrystalline nanowires composed of Ni and Ni 80 Co 20 . As a method for nanowire production, electrodeposition offers the widest material generality, geometric tenability, scalability, and multi‐material hybrid compatibility . A change of template size offers direct geometry tunability from several tens of nanometers to millimeters, spanning a variety of biological length scales.…”