Annealing-Based Electrical Tuning of Cobalt–Carbon Deposits Grown by Focused-Electron-Beam-Induced Deposition

Abstract

An effective postgrowth electrical tuning, via an oxygen releasing method, to enhance the content of non-noble metals in deposits directly written with gas-assisted focused-electron-beam-induced deposition (FEBID) is presented. It represents a novel and reproducible method for improving the electrical transport properties of Co-C deposits. The metal content and electrical properties of Co-C-O nanodeposits obtained by electron-induced dissociation of volatile Co(CO) precursor adsorbate molecules were reproducibly tuned by applying postgrowth annealing processes at 100 °C, 200 °C, and 300 °C under high-vacuum for 10 min. Advanced thin film EDX analysis showed that during the annealing process predominantly oxygen is released from the Co-C-O deposits, yielding an atomic ratio of Co:C:O = 100:16:1 (85:14:1) with respect to the atomic composition of as-written Co:C:O = 100:21:28 (67:14:19). In-depth Raman analysis suggests that the amorphous carbon contained in the as-written deposit turns into graphite nanocrystals with size of about 22.4 nm with annealing temperature. Remarkably, these microstructural changes allow for tuning of the electrical resistivity of the deposits over 3 orders of magnitude from 26 mΩ cm down to 26 μΩ cm, achieving a residual resistivity of ρ/ρ = 0.56, close to the value of 0.53 for pure Co films with similar dimensions, making it especially interesting and advantageous over the numerous works already published for applications such as advanced scanning-probe systems, magnetic memory, storage, and ferroelectric tunnel junction memristors, as the graphitic matrix protects the cobalt from being oxidized under an ambient atmosphere.

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

“…Co-FEBID deposits were found by Begun et al to reach resistivity values below 25 µΩ·cm after performing post-growth purification treatments [29]. Similarly, after thermal annealing, Puydinger dos Santos et al attained a resistivity of ~26 µΩ·cm [30]. We also note that the Co polycrystalline bulk resistivity has been reported to be 11 µΩ·cm [40] and the resistivity of Co electrodeposited films can be as low as 8.2 µΩ·cm [41].…”

“…The situation is different for the NWs that were grown under high current and ion dose. In this case, the NWs exhibit a higher coercive field and the hysteresis loop is unusual and it seems to be a combination of two contributions: (1) a first loop (narrow and similar to that of the 1.5 pA-NW) coming from the rounded, homogeneous part of the NW where the magnetization reversal is through coherent rotation; (2) a second loop (square-shaped, coming from [29,30,33,34,39]. Figure 6 displays the MOKE loops of the Co-FIBID NWs, which were obtained after substraction of spurious high-field slopes and off-center compensation.…”

“…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.…”

“…Comparison of the electrical resistivity values of Co-FIBID and Co-FEBID deposits grown under different conditions reported in the literature[29,30,33,34,39].…”

Electrical Manipulation of a Single Nanowire by Dielectrophoresis

“…Their one-dimensional geometry, as well as unique possibilities for engineering of magnetic, electric and optic properties, make them to be promising nanostructures for a variety of applications, including chemical and biological sensors [6,7], field-effect transistors [8], advanced scanning probes and magnetic sensors [9], light-emitting diodes [10], lasers [11] and photodetectors [12,13]. Furthermore, NWs can be synthesized through a number of techniques, such as metal-organic epitaxy [14], focused-ion-beam (FIB) [8], focused-electronbeam-induced deposition (FEBID) [15], electron beam lithography [5] and electrodeposition [16,17], yielding to unique attributes, such as particular crystallographic properties, geometry and axial/coaxial heterostructures [18].…”