In situ real-time annealing of ultrathin vertical Fe nanowires grown by focused electron beam induced deposition

Focused Electron Beam Induced Deposition is a consolidated technique for the growth of three-dimensional (3D) nanostructures. However, this single-step nanofabrication method requires furtherefforts to optimize simultaneously dimensional and compositional properties, in particular for depositswith a high aspect ratio. More specifically, ferromagnetic 3D nanowires (NWs) with diameters in the sub-50 nm regime and high metallic contents up to 95 at. % attract great interest to improve thefinal per-formance of magnetic nanodevices such as magnetic tips for scanning probe microscopy. In this work, wereport on real-time monitoring during chemical purification and structural crystallization processes ofultra-narrow 3D Fe NWs (<50 nm in diameter achieved) by post-growthin situannealing in a trans-mission electron microscope. NW heating up to 700C in very high vacuum reveals the local increase ofthe metallic content along the entire NW length concomitant with the growth of large Fe single crystalsfrom initially amorphous compounds. A metallic purity of 95 at. % is observed in several regions,dramatically boosting the initial Fe content of 40 at. %. The real-timein situtracking of 3D nanostructuresduring thermal annealing is a key element to design and optimize novel purification processes for thefabrication of customized components to be integrated in spintronic, logic and sensing devices