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• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
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  • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
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  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
  • C09D1/02—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances alkali metal silicates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/70—Additives characterised by shape, e.g. fibres, flakes or microspheres
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
  • C01P2002/82—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by IR- or Raman-data
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/03—Particle morphology depicted by an image obtained by SEM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/30—Particle morphology extending in three dimensions
  • C01P2004/32—Spheres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K7/00—Use of ingredients characterised by shape
  • C08K7/22—Expanded, porous or hollow particles
  • C08K7/24—Expanded, porous or hollow particles inorganic
  • C08K7/26—Silicon- containing compounds

Definitions

• the present invention relates to methods for reducing defects during spherical oxide particle alignment, spherical oxide particles treated by such methods, and photonic crystals comprising the spherical oxide particles. More specifically, the present invention relates to a method of improving the volume stability of monodispersed silica particles, thereby reducing the production of cracks (defects) during particle alignment.
• Monodispersed spherical oxide particles play an important role as raw materials in the preparation of functional ceramic materials.
• commonly used monodispersed silica particles have been widely used as raw materials for photonic crystals and coating agents, (non)conductive thin films, and the like, by virtue of their characteristics exhibiting different optical, crystalline, and spectroscopic properties depending on the orientation of particles arranged in certain directions. Accordingly, the technology of controlling such monodispersed silica particles in one-dimensional, two-dimensional, and three-dimensional manners in a large area without generating any defects is very important in utilizing monodispersed silica photonic crystals for various purposes of devices.
• Monodispersed silica particles there are various methods for preparing monodispersed spherical silica particles, one of which is a general method known as Stoeber synthesis. With this method, it is possible to prepare monodispersed silica particles having various particle sizes in the range of from 10 nm to 2,000 nm.
• Monodispersed silica particles in general, are synthesized using a sol-gel method in which tetraethylorthosilicate (TEOS; Si(OC 2 H 5 ) 4 ) precursors are hydrolyzed in a solution of a mixture of alcohols, water, and ammonia in a specific ratio, and then ammonia catalyzes the formation of particles.
• TEOS tetraethylorthosilicate
• a self-assembled silica array having a hexagonally closed pack structure can be applied to photonic crystals and lithographic masks using a photonic band gap.
• self-assembled silica photonic crystals are the focus of attention as novel switching and wave-guiding mediums.
• silica alignment methods indirect methods using lithography and holography, and self- assembly methods such as sedimentation, vertical deposition, spin coating, slide coating, and the like, are known.
• self- assembly methods such as sedimentation, vertical deposition, spin coating, slide coating, and the like.
• silica particles synthesized by the Stoeber method contain large amounts of moisture and organic products inside and on the surface of the particles, if such silica particles undergo arrangement without any specific treatment, the moisture or organic products may evaporate during arrangement or during subsequent device fabrication. Such evaporation may result in changes in the size, refractive density, permittivity, surface roughness, etc., of the silica particles, which may adversely affect the regularity of the arranged particles. In particular, when crystals having a large area or large volume are needed, small changes caused by such evaporation are very likely to lead to defects.
• the present invention provides a method of treating spherical oxide particles involving subjecting oxide particles to heat treatment above room temperature.
• the heat treatment is performed above room temperature, specifically at least 100°C, more specifically at least 200°C, much more specifically at least 400°C, or most specifically at least 550°C, and conventionally 1000°C or below, specifically 900°C or below, more specifically 800°C or below, or most specifically 750°C or below.
• the above heat treatment is maintained until no substantial reduction in weight of the spherical oxide particles occurs.
• the spherical oxide particles have a monodispersed distribution and, specifically, are silica particles having a monodispersed distribution.
• the present invention also relates to spherical oxide particles treated by the method described above.
• moisture, solvents, by-products, etc., remaining in the oxide particles are removed by evaporation or decomposition.
• the spherical oxide particles thus obtained exhibit at least one of the following
• the weight is reduced by 12% by weight or less, specifically 10% by weight or less, or most specifically 9% by weight or less.
• the specific surface area is increased by 9% or less, specifically 8% or less, or most specifically 7% or less.
• the size is reduced (based on change in average diameter) by 1.5% or less, specifically 1.3% or less, or most specifically
• the transmittance at 960 cm " is increased by 9% or less, specifically 8% or less, most specifically 7% or less, compared with the transmittance at 1 100 cm "1 .
• the present invention also relates to the use of the spherical oxide particles described above, specifically to photo devices comprising regularly arranged spherical oxide particles, such as photonic crystals and coating agents,
• monodispersed silica particles that are synthesized by a sol-gel method are treated with heat to remove moisture and organic products remaining on the surface of or inside the particles by evaporation or decomposition and induce in advance structural modification inside and on the surface of the particles which may occur at high temperatures.
• heat to remove moisture and organic products remaining on the surface of or inside the particles by evaporation or decomposition and induce in advance structural modification inside and on the surface of the particles which may occur at high temperatures.
• FIG. 1 illustrates the results from a thermogravimetric analysis of the silica powder prepared in Example 1 (a) and untreated silica powder (b)
• FIG. 2 shows scanning electron microscope (SEM) photographs of the silica powder which was heat treated in Example 1 (a) and untreated powder (b).
• FIG. 3 shows the FT-IR spectra of silica powders: (a) represents the silica powder heat treated in Example 1, while (b) represents untreated powder.
• FIG. 4 shows photographs of the silica particles observed under a transmitting electron microscope (TEM): (a) and (b) represent the silica powders that were heat treated in Example 1, while (c) and (d) represent untreated powders.
• TEM transmitting electron microscope
• FIG. 5(a) shows a small angle X-ray scattering spectrum analysis of silica powder: the dotted line represents silica powder heat treated in Example 1, while the solid line represents untreated powder.
• FIG. 5(b) shows a small angle X-ray scattering spectrum analysis of powders which were heat treated at 60°C, 150°C, 250°C, 350°C, 450°C, 550°C, 700°C, 800°C, 900°C, and 1000°C, respectively.
• FIG. 6 is a TEM photograph of silica heat treated at 1000°C.
• FIG. 7 shows SEM photographs of heat treated silica particles aligned on the silicon wafer substrate ((a) and (b) are observed under a magnification of 1 ,000; while
• FIG. 8 shows SEM photographs of untreated silica particles aligned on a silicon wafer substrate ((a) and (b) are observed under a magnification of 1 ,000; while (c) and
• Monodispersed spherical silica particles (230 nm (prepared in accordance with the Stoeber synthesis), 450 nm (prepared in accordance with the Stoeber synthesis), and 980 nm (purchased from Polysciences, Inc.) in diameter, respectively) were dried at room temperature for 24 hours, and then heated in air up to 550°C at a rate of 2°C/min, maintained at 550°C for 4 hours, and cooled to 25°C over 30 minutes.
• the weight changes of the heat treated silica powders were determined using a thermogravimetric analyzer (TA Instruments, Inc., Q600 SDT). The result is illustrated in FIG. 1 together with the result obtained from untreated silica powder. While only about a 2.1% by weight reduction was shown in the heat treated silica powder (a) at temperatures ranging from 210 to 280°C, the untreated silica powder (b) decreased by 9.2% by weight in the same range. In addition, during the heat treatment above 280°C, untreated silica powder continued to decrease in weight, and a weight reduction reached to 1 1.6% by weight at 550°C.
• the specific surface areas of silica powders before and after the heat treatment were measured using a surface area analyzer (BEL Japan, Inc., BELSORP-max).
• the powders were heat treated in vacuo at 100°C for 1 hour and their surface areas were determined under a nitrogen atmosphere.
• the heat treated ones were found to have a specific surface area of 20.35 m 2 /g while the untreated ones were found to have a specific surface area of 18.62 m /g. This result indicates that much of the moisture and organic products remaining on the surface and pore wall of the silica particles were removed during heating, whereby the specific surface area increased by about 9%.
• FIG. 3 illustrates an FT-IR spectrum curve of KBr pellets of silica powder heat treated in Example 1 (a) observed using a Mattson FT-IR spectrometer (IR300) with that of untreated silica powder (b) for comparison. It was confirmed from FIG. 3 that after the heat treatment of silica powders, moisture shown at wavelengths ranging from 3100 to 3700 cm “1 was markedly reduced and silicone hydroxyl group (Si-OH) shown at a wavelength of 960 cm "1 decreased, but silicone oxide group (Si-O-Si) shown at wavelengths of 1 100 cm “1 and 820 cm “1 increased. This indicates that moisture was removed during the heat treatment as explained with respect to FIG. 1 above. It can also be interpreted that as hydroxyl groups on the surface of the silica powder are removed, condensation reactions between silicone hydroxyls are triggered, leading to an increase in silicone oxides.
• Si-OH silicone hydroxyl group
• Si-O-Si silicone oxide group
• FIG. 4 shows photographs of silica particles heat treated in Example 1 observed under a TEM (FEI, Tecnai G2) [(a) and (b)]. These photographs show that the surface of heat treated silica particles was very smooth compared with that of the untreated silica particles [(c) and (d)]. It can be understood that moisture and organic products remaining on the surface were evaporated and silicone hydroxyls were condensed to silicone oxides during the heat treatment as explained with respect to FIG. 3 above, whereby the surface was rendered even.
• FIG. 5(a) Changes in size and surface roughness of silica particles according to heat treatment were determined using small angle X-ray scattering (SAXS, Anton Paar, SAXSess mc , measured in a solid phase).
• SAXS small angle X-ray scattering
• FIG. 5(a) The comparison between heat-treated silica powder (dotted line) and untreated silica powder (solid line) is illustrated in FIG. 5(a).
• small Q value portions Q ⁇ 0.4 nm '1
• large Q value portions 0.7 ⁇ Q ⁇ 2 nm "1
• the segment between the two regions is a Fractal region in which a transition segment between the two regions is detected and this is associated with the size of particles.
• FIG. 5(b) shows a TEM photograph of the silica powder heat treated at 1000°C. The photograph shows that it is impossible to recognize the shape of the individual particles and that the particles agglomerate to exist in a big lump form.
• a portion of the silica particles heat treated in Example 1 was taken to prepare 20 ml of a 1 wt% aqueous solution, and the solution was treated in an ultrasonic bath for 1 hour so as to disperse the particles.
• a 1 cm x 5 cm silicon wafer substrate was dipped vertically in the white colloidal suspension of dispersed silica particles and then placed in an oven maintained at 60°C for 18 hours so as to allow the moisture to slowly evaporate while arranging the silica particles on the surface of the substrate.
• the silica particle-arranged substrate was isolated from the solution, dried at room temperature for 1 hour, and then placed in an oven at 60°C for 24 hours so as to allow the moisture to slowly evaporate.
• untreated silica particles were arranged on a silicon wafer and dried in the same fashion as described above.
• silica particles Since there are little changes in size and morphology of heat treated silica particles, defects originating from particle shrinkage or morphology change occurring during alignment or drying after the alignment can be minimized. Accordingly, it is possible to arrange silica particles in a regular manner in a large area and prepare a three-dimensionally large photonic crystal. In addition, since the stability of the silica particles are greatly enhanced with heat treatment, processing time can be prolonged and processing temperatures can be selected from room temperature to several hundreds Celsius degrees.
• Photonic crystals composed of crack-free, regularly aligned silica particles can be used for a wide range of applications, in particular as waveguide, distributed Bragg reflector (DBR), etc., in the optical communication field, and as materials for various fields such as opals, optical coatings, antistatic films, sensors, etc.
• DBR distributed Bragg reflector

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• 2010
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