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

Abstract

Focused electron beam induced deposition (FEBID) is considered the ultimate direct-write lithography technique for three-dimensional (3D) structures.However, it has not been possible yet to obtain 3D deposits by FEBID with the same purity and crystallinity of the corresponding bulk materials. In the present work, purified and crystalline 3D cobalt nanowires of diameter below 90 nm have been fabricated by ex-situ high-vacuum annealing at 600 ºC after FEBID growth. While increasing the metallic content of the nanowires up to 95% at., the thermal annealing process induces the recrystallization of the pseudo-amorphous as-grown structure into bulk-like, hcp and fcc crystallites with lateral sizes comparable to the nanowire's width. The net magnetization increases 80% with respect to as-grown values, up to 1.61  0.06 T, near bulk cobalt. This achievement opens new pathways for applications of this synthetic method in the fabrication of either individual or arrays of 3D high-purity and crystalline cobalt nanowires for high-density memory and logic devices, nanosensors and actuators, and could be a viable method to obtain other pure and crystalline 3D materials by FEBID.

High Volume-Per-Dose and Low Resistivity of Cobalt Nanowires Grown by Ga+ Focused Ion Beam Induced Deposition

“…In addition, the capability of FEBID for the growth of complex three-dimensional (3D) magnetic structures is being explored in the rising field of 3D nanomagnetism [26].FEBID has long suffered from two disadvantages when compared to other nanofabrication techniques: the material purity and the growth speed. In the last years, various growth strategies and post-growth purification treatments have been successfully developed to enhance the material purity of magnetic deposits that are grown by FEBID [27][28][29][30][31][32]. However, the growth speed of magnetic nanostructures by FEBID continues to be a bottleneck regarding its broader use.…”

NanoSQUID Magnetometry on Individual As-grown and Annealed Co Nanowires at Variable Temperature

“…These observations agree very well with the structural and chemical characterization performed on NWs grown and annealed under the same experimental conditions. 27 Ex-situ annealing magnetic FEBID nanostructures seems, therefore, to be a very promising strategy to routinely produce high-quality, pure and crystalline nanomagnets with large spatial and lateral resolution. In addition, our measurements demonstrate the enormous convenience of using YBCO nanoSQUID sensors for the magnetic characterization of nanoscopic magnets.…”

Comparison between Focused Electron/Ion Beam-Induced Deposition at Room Temperature and under Cryogenic Conditions

“…However, single-step resist-free nanolithography processes have the advantage of being simple if the right material can be produced. In fact, great effort has been made in recent years to obtain functional materials by FEBID and FIBID, which can include a purification step [73,74]. In most FEBID and FIBID processes, the required charge dose is high, giving rise to long processing times with the exception of Pt deposits by FIBID, which require an irradiation dose of around 10 3 µC/cm 2 [20].…”