ABSTRACT
The adequate manipulation of nanometer-scale building blocks using dispersion systems is regarded as a fundamental technique to fabricate elaborate microstructures. Although a liquid flow with evaporation is generally regarded as an essential factor for the self-assembly of floating blocks, experimental evidence has not been sufficient to clarify the importance of the flow in the dispersion systems. In the present study, 2D nematic layers of sterically stabilized nanoscale calcite rods were achieved in a millimeter-scale region on a solid substrate via the very slow recession of an organic dispersion with evaporation. 2D random arrays of the nanorods were obtained via recession of the liquid in the same system without evaporation. When the nanorods were not sterically stabilized, 3D random arrays were formed even with evaporation. We demonstrated that the evaporation-driven flow of sterically stabilized nanorods to a confined space at the air-liquid-solid interface is essential for the formation of 2D nematic structures on a substrate.
ABSTRACT
The coercivity of magnetic nanoparticles is enhanced by the exchange coupling effect at the interface of ferrimagnetic and antiferromagnetic self-assembled monolayers. Antiferromagnetic Co3O4 nanocubes were regularly stacked on an ordered monolayer of ferrimagnetic Fe3O4 nanocubes by layer-by-layer manipulation using evaporation-driven self-assembly. The ordered arrangements of the ferrimagnetic and antiferromagnetic nanocubes are effective for the enhancement of the ferromagnetic character.
ABSTRACT
Sapphirinid copepods, which are marine zooplankton, exhibit tunable structural colors originating from a layered structure of guanine crystal plates. In the present study, the coloring portion of adult male of a sapphirinid copepod, Sapphirina nigromaculata, under the dorsal body surface was characterized to clarify the regulation and actuation mechanism of the layered guanine crystals for spectral control. The coloring portions are separated into small domains 70-100 µm wide consisting of an ordered array of stacked hexagonal plates ~1.5 µm wide and ~80 nm thick. We found the presence of chitin-based honeycomb frameworks that are composed of flat compartments regulating the guanine crystal plates. The structural color is deduced to be tuned from blue to achromatic via yellow and purple by changing the interplate distance according to vital observation and optical simulation using a photonic array model. The framework structures are essential for the organization and actuation of the particular photonic arrays for the exhibition of the tunable structural color.
Subject(s)
Chitin/ultrastructure , Color , Copepoda/ultrastructure , Guanine/chemistry , Zooplankton/ultrastructure , Adaptation, Biological , Animals , Chitin/chemistry , Copepoda/physiology , Crystallization , Male , Microscopy, Electron, Scanning , Predatory Behavior , Zooplankton/physiologyABSTRACT
Calcite nanorods â¼50 nm wide are thermally separated into nanoblocks. The fragmentation is ascribed to the ion diffusion on metastable crystal surfaces at temperatures (â¼400 °C) much lower than the melting point. The presence of water molecules enhances the surface diffusion and induces deformation of the nanorods even at â¼60 °C.
ABSTRACT
Uniformly sized building units are generally required to construct highly elaborate architectures over a wide range. Defined nanocubes of Co3O4 evolved from deformed precursor nanograins 2-5 nm in diameter through direct oriented attachment in a nonpolar medium. Uniformly sized primary nanocubes â¼8 nm on a side with {100} faces were formed by adjusting the coverage of the oxide nanograins with oleic acid. Larger nanocubes 20-40 nm on a side were produced with further direct oriented attachment of the primary nanocubes. Ordered arrays, such as superlattices, were found to be constructed by the indirect oriented attachment of the primary and larger nanocubes covered with organic molecules.
ABSTRACT
Oxide ion-conducting porous films were produced on a substrate by evaporation-induced self-assembly of rare earth-doped CeO2 (REDC) nanocubes 4-5 nm in size and subsequent mild calcination at 400 °C. Mesocrystalline structures comprising iso-oriented REDC nanocubes were formed by ordered assembly based on strict attachment of their {100} faces. Enhanced oxide-ion conductivities in a temperature range of 250-350 °C were observed on the mesocrystalline films consisting of Sm-doped CeO2 (SDC) nanocubes. The specific electrical properties of the mesocrystalline films are ascribed to improved surface-ion conduction due to a large specific surface area and a high crystallographic connectivity of SDC nanocubes.
ABSTRACT
Millimeter-scale mesocrystals and cross-lamellae mimicking the nanostructure of seashells were produced on a substrate through the three-dimensionally oriented assembly of c-axis-elongated calcite nanorods â¼50 nm wide and â¼500-1000 nm long by combining arrangement with evaporation-driven capillary force and alignment under an intense magnetic field.
Subject(s)
Biomimetic Materials/chemistry , Calcium Carbonate/chemistry , Magnetite Nanoparticles/chemistry , Nanotubes/chemistry , Crystallization , Electrons , Gold/chemistry , Magnetic Fields , Microscopy, Electron, Scanning , Microscopy, Electron, Transmission , Nanostructures/chemistry , X-Ray DiffractionABSTRACT
The combination of heterogeneous inorganic nanocrystals provides novel nanometer-scale architectures for exploration of novel functions. In the present study, heterogeneous bilayers, such as BaTiO3-Fe3O4 and Mn3O4-CeO2, are fabricated via layer-by-layer stacking of several rectangular nanoblocks 5-23 nm in size by evaporation-driven self-assembly. Specific heterojunctions between inorganic crystals are constructed by nanoscale simple brick work through spontaneous adjustment of the crystallographic orientations of the nanoblocks in the lower and upper layers.
ABSTRACT
Tetragonal 2D lattices are spontaneously formed by the self-assembly of homogeneous nanocubes. However, ordered arrays consisting of differently sized rectangular nanoblocks have not been achieved because the regulation of the assembly is weakened by the combination of binary units. In the present work, ordered arrays comprising binary nanocubes were investigated using the combination of 10 nm Pt nanocubes and 20 nm BaTiO3 nanocubes. Heterogeneous but ordered 2D tetragonal lattices were successfully produced using differently sized rectangular nanoblocks. The highly ordered self-assembly in the heterogeneous system requires the matching of the size ratio of binary nanocubes with the buffer effect of oleic acid covering the building units.
ABSTRACT
The formation of single-crystalline configurations by the oriented attachment of calcite was experimentally demonstrated as 3D bundles in a nonaqueous system. In the initial stage, 1D short chains elongated in the c direction were formed through the primary oriented attachment of calcite nanoblocks â¼30 nm in diameter. The 3D bundles were then produced through subsequent side-by-side oriented attachment of the 1D chains in the progressive stage. Finally, micrometer-sized single-crystalline architectures were constructed via large-scale oriented attachment of the nanoscale building blocks with a decrease in repulsion force due to the surface charge.
ABSTRACT
A nonclassical multistep pathway involving bottom-up and break-down stages for the evolution of calcite nanograins â¼50 nm in size was demonstrated in a basic aqueous system. Calcite nanofibrils â¼10 nm wide were produced as the initial crystalline phase via amorphous calcium carbonate through ion-by-ion assembly by the carbonation of Ca(OH)2 at a high pH of â¼13. Bundles â¼50 nm in diameter were then formed by the subsequent oriented attachment of the nanofibrils. Monodispersed calcite nanograins were finally obtained through spontaneous fragmentation of the fibrous forms via a decrease in pH by further carbonation.