arXiv subjects

Sameh Okasha

Publications and source records attributed to Sameh Okasha.

3 recordsLinked to original sources

arXiv2026

TetMaG-Guided Design and Operando Electron Holography Validation of Current-Induced Domain-Wall Motion in 3D Curved and Cornered Fe Nanobridges

Three-dimensional (3D) magnetic nanostructures offer new opportunities for controlling domain-wall (DW) configurations beyond the limitations of planar systems, providing promising architectures. However, the realization of reliable 3D magnetic devices requires precise control of geometry-dependent DW behaviour and quantitative experimental validation of the resulting magnetic states. Here, we combine TetMaG micromagnetic simulations, focused electron beam induced deposition (FEBID), and off-axis electron holography to investigate the influence of curvature and corner geometries on DW behaviour in 3D magnetic nanobridges. TetMaG simulations predict fundamentally different magnetic properties for curved and cornered geometries. Cornered nanobridges act as preferential DW pinning sites, stabilizing localized magnetic configurations and enabling controlled switching between neighbouring pinning positions. While curved nanobridges promote gradual magnetization rotation, reduced pinning, and smoother DW motion. These optimized geometries were fabricated with high structural fidelity using FEBID and subsequently characterized by quantitative electron holography. Electron holography measurements revealed magnetic induction maps that matched the simulated magnetization configurations, providing direct experimental validation of the TetMaG predictions. Curved and cornered geometries exhibited distinct DW characteristics governed by their local structural features, demonstrating the critical role of geometry in tailoring magnetic behaviour in 3D systems. Operando current-biasing experiments further revealed current-induced DW motion, including the displacement of a tail-to-tail DW into a head-to-tail configuration within corner structures.

cond-mat.mes-hall↗

arXiv2025

The Role of Dwell Time on Advancing 3D Nano-printing of Complex Iron Nanostructure Geometries using Focused Electron Beam Induced Deposition

The shift from two- to three-dimensional structures is not only a prominent trend in nanomagnetism but also reflects a broader movement across nanotechnology as a whole. Fields such as nanoelectronics, nanophotonics, data storage are poised to benefit from a new generation of greener, more versatile and multifunctional technologies enabled by this transition to 3D structures. While significant challenges remain, recent progress in bottom-up lithography, advanced microscopy, and computational techniques has made the future realization of these advancements increasingly feasible. Focused electron beam-induced deposition, is a cutting-edge direct-write nanofabrication technique used to manipulate matter at the nanoscale, combined with the unique magnetic properties of nanomaterials. It has gained significant attention in recent decades due to its potential applications in magnetic memories, such as racetrack memory. Consequently, substantial efforts have been directed toward developing nanofabrication techniques and characterizing magnetic nanoelements of various metal depositions. In our work, Fe-based nanostructures have been fabricated precisely using iron pentacarbonyl as a precursor. These structures include nanowires, 5-um bridges, rings, tetrapods, spirals and flower-like nanostructures. The deposition parameters, including electron beam dwell time, beam current, and precursor flux, have been further refined, have been further refined, enabling the precise fabrication of complex geometries.

cond-mat.mes-hall↗

arXiv2021

Atomic Layer Deposition of Aluminum (111) Thin Film by Dimethylethylaminealane Precursor

We report the growth of aluminum (111) thin film by atomic layer deposition (ALD) technique with dimethylethylaminealane (DMEAA) as a precursor. It is found that the metallic underlayer is essential to grow uniform aluminum films by DMEAA precursor. As a titanium thin film is used as the underlayer, grown aluminum thin film shows (111) orientation irrespective of substrates. The lattice constant and superconducting transition temperature of the aluminum thin films are the same as the bulk one. These findings suggest that ALD technique provides high quality of the aluminum thin films and have potential for the applications of superconducting devices. We discuss ALD technique with DMEAA precursor is the promising method for fabricating vertical small Josephson tunnel junctions, which can be used as the superconducting quantum bits.

cond-mat.supr-con↗