Growth of Well-Defined Cubic Hematite Single Crystals: Oriented Aggregation and Ostwald Ripening

Abstract

Single-crystalline R-Fe 2 O 3 submicron cubes with a well-defined shape have been successively synthesized via a simple hydrothermal process. X-ray diffraction patterns, transmission electron microscopy, field emission scanning electron microscopy, and selected area electron diffraction patterns were applied to characterize the as-synthesized samples. The results indicate that the growth of single-crystalline R-Fe 2 O 3 cubes can be attributed to cooperation of two principal mechanisms: oriented aggregation and Ostwald ripening. At the beginning, R-Fe 2 O 3 nanorods were first fabricated and formed cube-like aggregation following a "onedimensional (1D) f three-dimensional (3D)" mode, in which these nanorods orientedly aggregated on the surfaces of some cores by sharing common {012} faces. Then, the resulting polycrystalline aggregates would fuse into a single crystal, in which Ostwald ripening process was expected to carry out because oriented aggregation alone cannot result in well-defined R-Fe 2 O 3 cubes. The extended particle would further attract free-standing R-Fe 2 O 3 nanorods to orientedly attach on their surface, and the fusion process was repeated until nanorods were completely consumed. This kind of cooperation of two basic mechanisms may give us a new insight into the growth of R-Fe 2 O 3 crystals and opens a new way for controllable synthesis of other well-defined crystals in morphology and dimensionality.

Fabrication of diisopropylammonium bromide aligned microcrystals with in-plane uniaxial polarization

“…This analysis is statistical in nature and we did find isolated microcrystals wider than the average fitted width, but these were fewer in number. These observations suggest that the Ostwald ripening mechanism may be responsible for the microcrystal growth [41,42]. The arrows in figures 1(a)-(c) represent the direction in which the samples were suspended in the vertical slots, which also coincided with the direction of the gravitational force.…”

Synthesis of antibacterial silver-based nanodisks and dendritic structures mediated by royal jelly

“…It indicates that the growth of the dendritic structure could continue by Ostwald ripening mechanism. 36 To the best of our knowledge, this is the rst time that the preparation of dendritic Ag structures at room temperature, mediated by natural derived products is reported. It could be useful to shed further light on the crystallization phenomena and the development of novel sensor technologies based on the excellent SERS properties of Ag dendritic structures.…”

Oriented Attachment and Nonclassical Formation in Iron Oxides

“…The rates of crystal growth via OA and coarsening depend on factors such as crystallite size and solubility and particle-particle interactions, and the relative [40], (b) peanuts [43], (c) nanocubes [44], and (d) spindles [45]. The scale bars in (a) are 100 nm and 50 nm (inset).…”