Ion Beam Formation and Modification of Cobalt Nanoparticles

Abstract

This article reviews the size-dependent structural properties of ion beam synthesized Co nanoparticles (NPs) and the influence of ion irradiation on the size, shape, phase and structure. The evolution of the aforementioned properties were determined using complementary laboratory-and advanced synchrotron-based techniques, including cross-sectional transmission electron microscopy, small-angle X-ray scattering and X-ray absorption spectroscopy. Combining such techniques reveals a rich array of transformations particular to Co NPs. This methodology highlights the effectiveness of ion implantation and ion irradiation procedures as a means of fine tuning NP properties to best suit specific technological applications. Furthermore, our results facilitate a better understanding and aid in identifying the underlying physics particular to this potentially technologically important class of nanomaterials.

Reaction mechanism and additional lithium storage of mesoporous MnO2 anode in Li batteries

“…In the EXAFS, the intensity of the Mn-Mn peak, associated with the Mn metal with a shorter bond length than that of the bulk Mn metal, is increased. Bond length shrinkage is one of the observed structural changes as the nanoparticle size decreases compared to the bulk standard [63][64][65][66][67]. Because all surfaces are energetically unfavorable compared to the bulk side, the surface energy is reduced by altering the atomic geometry of the local surface by relaxation/reconstruction, which shortens the bond length [64,68].…”

“…Because all surfaces are energetically unfavorable compared to the bulk side, the surface energy is reduced by altering the atomic geometry of the local surface by relaxation/reconstruction, which shortens the bond length [64,68]. The increasing Mn metal peak intensity in the slope region is associated with the reduction of the remaining highly disordered manganese oxide [60] and the clustering by packing between the highly disordered Mn metal nanoparticles with large surface-to-volume ratios [65,67]. Based on previous reports, the capacity in this slope region is attributed to the formation of an electrolyte-derived surface layer, known as the SEI [46][47][48][49] and polymer gel-like film [69,70].…”

X-ray tracking of structural changes during a subnanosecond solid-solid phase transition in cobalt nanoparticles

“…Further, as also discussed in Ref. [26], on heating the phase transformation from hcp to fcc is generally complete, whereas the fcc-to-hcp transformation on cooling is generally only partial, in line with very recent theoretical studies of the effect of cooling rates on the microstructural evolution of nanocrystalline Co [31]. In the context of these studies the pressure, heating/cooling rate, grain size, and impurities have been identified as sources of the differing results regarding phase transformations [26,28,31].…”

“…The crystal structure of Co nanoparticles at room temperature has been demonstrated to depend on the synthesis route and processing history of the sample due to almost isoenergetic crystal phases [26]. Apart from the metastable phase produced by the above-mentioned solution-phase synthesis route, for small nanoparticles (<20 nm) the fcc structure appears to be favored at room temperature in nanoparticles created by sputtering, with mixed-phases observed for mediumsized particles (30-40 nm) and hcp structure for large-size particles (>40 nm) [27].…”

“…A study of larger Co nanoparticles (∼100 nm) using in situ heating in a transmission electron microscope setup showed a mixed fcc/hcp phase at room temperature, an observation which was concluded to arise from incomplete transformation to the hcp structure during rapid cooling of the nanoparticles formed via a pulsed wire evaporation synthesis method [28]. In the limit of slow cooling, purely fcc nanoparticles can be formed via ion implantation and annealing in solid matrices, 2469-9950/2019/100(24)/245425 (8) 245425-1 ©2019 American Physical Society following which irradiation by energetic heavy ions can induce a transformation to either an amorphous phase [29] or to a crystalline hcp phase, a transformation surmised to take place without the involvement of a liquid-phase intermediate but rather arising from a large transient shear stress due to local heating [26,30]. Further, as also discussed in Ref.…”