Phase evolution of magnetite nanocrystals on oxide supports via template-free bismuth ferrite precursor approach

Abstract

This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxidesupported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO 3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology. V

Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and Beyond

“…(d) A 3D atomic force microscrope (AFM) image of Fe 3 O 4 nanocrystals. Reproduced with permission from ref . Copyright 2012 American Institute of Physics.…”

“…The generated Bi 2 O 3 was vaporized during the spinel Fe 3 O 4 composite creation (Figure 7). 208 The morphology prepared by PLD is controlled by the power of the pulse, the flow rate of the gas, and the temperature of the substrate. 209 3.2.…”

Spontaneous Growth of Strain-Free Magnetite Nanocrystals via Temperature-Driven Dewetting

“…Since we exploit temperature-driven dewetting of a Fe 3 O 4 self-template layer to form the Fe 3 O 4 nanocrystal arrays, this approach is fundamentally unlike previous efforts that spontaneously grow the oxide nanocrystals by vapor phase deposition directly on the substrate. ,,, The method used in this work does not require other materials to be introduced to the substrate surface to promote spontaneous nanocrystal formation or growth. This is a significant distinction from previous reports on VLS − or “pillar and matrix” phase-separated nanocomposite phase decomposition growth, − ,− because we can guarantee that there are no impurities inadvertently doped into the Fe 3 O 4 nanopyramids. Finally, the template dewetting approach to Fe 3 O 4 nanocrystal array fabrication has a number of advantages over common solution-precipitation nanoparticle synthesis methods − that cannot be used to orient all nanoparticles in the same crystallographic direction or to attach each nanocrystal to a conducting substrate electrode, which is necessary for measuring the ferroelectric and dielectric properties.…”

“…If polycrystalline materials were used, it would be difficult to distinguish between intrinsic nanoscale size-dependent effects and the extrinsic influence of lower crystallinity caused by the presence of defects, dislocations, and grain boundaries. A common solution to this problem is to fabricate single-crystal nanostructures by self-assembly on a substrate surface, for example, in a catalyst-mediated vapor–liquid–solid (VLS) process − or by various direct vapor deposition techniques. − Previous studies have demonstrated spontaneous growth of nanorods, − nanopyramids, − nanoplates, , nanopillars, − and other nanocrystal shapes …”

Self‐Assembled Epitaxial Core–Shell Nanocrystals with Tunable Magnetic Anisotropy

“…In the case of CoO–CFO core–shell nanocrystals, we choose SrTiO 3 (STO) as the substrate because the lattice mismatch between STO and CoO/CFO (9.2%/7.4%) is much larger than that between CoO and CFO (1.5%) . Bismuth oxide (Bi 2 O 3 , with melting point of 824 °C is selected as a liquid additive to improve the diffusivity; Bi 2 O 3 is immiscible to CoO and CFO, and it could be removed by evaporation under the vacuum environment . The fabrication process of CoO (core)–CFO (shell) nanocrystals is shown in Figure b.…”