High-purity 3D nano-objects grown by focused-electron-beam induced deposition

Abstract

To increase the efficiency of current electronics, a specific challenge for the next generation of memory, sensing and logic devices is to find suitable strategies to move from two- to three-dimensional (3D) architectures. However, the creation of real 3D nano-objects is not trivial. Emerging non-conventional nanofabrication tools are required for this purpose. One attractive method is focused-electron-beam induced deposition (FEBID), a direct-write process of 3D nano-objects. Here, we grow 3D iron and cobalt nanopillars by FEBID using diiron nonacarbonyl Fe2(CO)9, and dicobalt octacarbonyl Co2(CO)8, respectively, as starting materials. In addition, we systematically study the composition of these nanopillars at the sub-nanometer scale by atom probe tomography, explicitly mapping the homogeneity of the radial and longitudinal composition distributions. We show a way of fabricating high-purity 3D vertical nanostructures of ∼50 nm in diameter and a few micrometers in length. Our results suggest that the purity of such 3D nanoelements (above 90 at% Fe and above 95 at% Co) is directly linked to their growth regime, in which the selected deposition conditions are crucial for the final quality of the nanostructure. Moreover, we demonstrate that FEBID and the proposed characterization technique not only allow for growth and chemical analysis of single-element structures, but also offers a new way to directly study 3D core-shell architectures. This straightforward concept could establish a promising route to the design of 3D elements for future nano-electronic devices.

Focused electron beam induced deposition meets materials science

“…In early work by Hans Koops and collaborators, photonic crystals [138] and field emitters and electron optics structures were addressed [139,140,141]. Following this, suspended FEBID structures were demonstrated, see e. g. [142], and plasmonic structures came more into focus [143,144], as well as simple 3D structures, such as nano-pillars, with application in nanomagnetism [145,122,146]. Recently a nanospray liquid precursor FEBID process with strongly enhanced growth rates has been demonstrated by Andrei Fedorov's group [147].…”

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

“…2D Fe deposits can be grown with high purity and small crystal size in ultra-high vacuum environment, which is a too-demanding condition for many applications 22 . In the case of 3D magnetic deposits, the dispersion of composition values found in the literature is high, given the strong dependence of the growth mode to small changes in the numerous growth parameters 48,50 . To the best of our knowledge, the growth of pure and fully-crystalline 3D magnetic deposits by FEBID has not been reported so far and is likely not possible without post-processing.…”

“…Cobalt and iron deposits are amongst the FEBID materials with highest metallic content levels [47][48][49] . In this case, purity and crystallinity will have great impact in their electrical transport 31 and magnetic properties (saturation magnetization, magneto-crystalline anisotropy, coercive field, etc.)…”

Temperature-Dependent Growth Characteristics of Nb- and CoFe-Based Nanostructures by Direct-Write Using Focused Electron Beam-Induced Deposition

“…Over the last few years, this has led to the evolution of a simulation-guided 3D computer aided design (CAD) approach which was pioneered by Fowlkes and collaborators [11] and has been further developed towards a reliable instrument for 3D nano-fabrication even of complex nano-architectures, as was recently reviewed by Winkler et al [12]. For the fields of 3D nano-magnetism and nano-superconductivity, the precursors Co 2 (CO) 8 [1], Fe 2 (CO) 9 [13], HCo 3 Fe(CO) 12 [3] (FEBID), W(CO) 6 [14], and Nb(NMe 3 ) 2 (N-t-Bu) [7] (FIBID) have been used and proven to be particularly suited. With a view to the simulation-guided 3D CAD approach to nano-fabrication which uses the continuum model of FEBID/FIBID growth, a set of simulation parameters is required; see Reference [15] for a recent review.…”