Aligned cuboid iron nanoparticles by epitaxial electrodeposition

Abstract

Aligned, individual iron square cuboid nanoparticles have been achieved by taking advantage of epitaxial, three-dimensional-island growth on GaAs(001) during electrodeposition at low deposition rates. The nanoparticles exhibit lateral dimensions between 10 and 80 nm and heights below 40 nm. Surface {100} facets predominate with a thin crystalline oxide shell that protects the nanoparticles during prolonged storage in air. The single crystallinity of the iron in combination with structural alignment leads to an in-plane magnetic anisotropy. These immobilized, oriented, and stable nanoparticles are promising for applications in nanoelectronic, sensor, and data storage technologies, as well as for the detailed analysis of the effect of shape and size on magnetism at the nanoscale.

Role of Hydrogen Evolution during Epitaxial Electrodeposition of Fe on GaAs

“…The reason is the magnetocrystalline anisotropy of bcc Fe, which causes the <110> direction to be the magnetically harder axis in bcc iron. Previous discussion 17 revealed that other possible contributions to the in-plane magnetic anisotropy, based on, e.g., shape anisotropy, dipolar interaction between the islands, and/or edge effects are expected to be negligible in comparison to the magnetocrystalline anisotropy. This makes FMR a valuable tool to detect epitaxial alignment, especially for cases like the present one where direct structural investigation by X-ray diffraction is hampered by low material volume and overlapping peaks with the substrate.…”

“…Epitaxial growth of bcc Fe results in a magnetic anisotropy in the substrate plane that is measurable by comparing the FMR spectra along the <100> and <110> directions. 17 Calculations 21 and experiments 17 show that the resonance spectrum shifts to higher B values when the external B-field is applied along a <110> direction, in comparison to the case where B is applied along a <100> direction. The reason is the magnetocrystalline anisotropy of bcc Fe, which causes the <110> direction to be the magnetically harder axis in bcc iron.…”

“…For epitaxial electrodeposition of Fe on GaAs, most often the substrate is immersed electrically "hot", but the underlying mechanism for an improvement has not been conclusively identified. 9,13,17 For the same electrolyte as used in the present study, we recently showed that the electrically "hot" immersion with a potential applied before and during immersion, gives better epitaxial properties according to the FMR results. 17 The role of the hydrogen evolution proposed in the present study can explain this favorable effect: in the case of "hot" immersion, a strong hydrogen evolution and Fe deposition are initiated immediately, and the As-H adsorption layer cannot form during immersion prior to Fe deposition.…”

“…9,13,17 For the same electrolyte as used in the present study, we recently showed that the electrically "hot" immersion with a potential applied before and during immersion, gives better epitaxial properties according to the FMR results. 17 The role of the hydrogen evolution proposed in the present study can explain this favorable effect: in the case of "hot" immersion, a strong hydrogen evolution and Fe deposition are initiated immediately, and the As-H adsorption layer cannot form during immersion prior to Fe deposition. We expect that also the use of a high |j| or E initiation pulse that removes the As-H adsorption layer on GaAs formed during immersion prior to Fe deposition is beneficial for the epitaxial interface formation.…”

“…Recently, we demonstrated that epitaxial Fe nanocuboids can be achieved when the deposition is stopped prior to coalesce of the nuclei in a lower-concentration electrolyte with reduced deposition rate. 17 The identification of the factors affecting the epitaxial alignment requires a study of the initial processes of film deposition. Additional processes occurring at the polarized solid electrode/liquid electrolyte interface must be considered, in contrast to preparation in vacuum.…”