Post-growth purification of Co nanostructures prepared by focused electron beam induced deposition

TL;DR

This paper introduces an in-situ purification method for Co nanostructures created by FEBID, using heating, hydrogen exposure, and electron irradiation to produce pure, ferromagnetic cobalt layers suitable for advanced nanotechnology applications.

Contribution

The study demonstrates a novel purification process combining annealing, hydrogen atmosphere, and electron irradiation to achieve pure, ferromagnetic Co nanostructures from FEBID deposits.

Findings

Achieved carbon- and oxygen-free Co layers about 20 nm thick.

Post-processed structures exhibit metallic electrical behavior.

Samples show ferromagnetic properties at low temperatures.

Abstract

In the majority of cases nanostructures prepared by focused electron beam induced deposition (FEBID) employing an organometallic precursor contain predominantly carbon-based ligand dissociation products. This is unfortunate with regard to using this high-resolution direct-write approach for the preparation of nanostructures for various fields, such as mesoscopic physics, micromagnetism, electronic correlations, spin-dependent transport and numerous applications. Here we present an in-situ cleaning approach to obtain pure Co-FEBID nanostructures. The purification procedure lies in the exposure of heated samples to a H$_2$ atmosphere in conjunction with the irradiation by low-energy electrons. The key finding is that the combination of annealing at $300^\circ$C, H$_2$ exposure and electron irradiation leads to compact, carbon- and oxygen free Co layers down to a thickness of about 20\,nm starting from as-deposited Co-FEBID structures. In addition to this, in temperature-dependent electrical resistance measurements on post-processed samples we find a typical metallic behavior. In low-temperature magneto-resistance and Hall effect measurements we observe ferromagnetic behavior.