KR20110121020A - A method for reducing defects in spherical oxide particle alignment - Google Patents

Abstract

PURPOSE: A method for reducing the generation of defects in a spherical oxide particle arranging process is provided to obtain three dimensionally large size of crystals and to regularly arrange silica particles on a wide area. CONSTITUTION: The weight reduction of spherical oxide particles is less than or equal to 12 weight% after a heating process is implemented at 550 degrees Celsius or more. The specific surface area increasing rate of the spherical oxide particles is less than or equal to 9 weight% after the heating process is implemented at 550 degrees Celsius or more. The size shrinkage of the spherical oxide particles is less than or equal to 2% after the heating process is implemented at 550 degrees Celsius or more. The transmittance of the spherical oxide particles at 960 cm^-1 is 9% lower than that of the spherical oxide particles at 1100cm^-1 in an infrared ray spectrum measuring process.

Description

A method for reducing defects in spherical oxide particles arrangement {A METHOD FOR REDUCING DEFECTS IN SPHERICAL OXIDE PARTICLE ALIGNMENT}

The present invention relates to a method of reducing the occurrence of defects in the arrangement of spherical oxide particles, to the spherical oxide particles treated by the method, to a photonic crystal comprising the spherical oxide particles, and more particularly to improving the volume stability of monodisperse silica particles The present invention relates to a method of minimizing the occurrence of cracks in particle arrangement.

Monodisperse spherical oxide particles play an important role as raw materials for functional ceramic materials. In particular, the monodisperse silica particles, which are widely used, are widely used as raw materials for photonic crystals, coatings, and (non-) conductive thin films due to the characteristics of different minerality, crystallinity, and spectroscopic characteristics depending on the orientation of the particles arranged in a certain direction. It is used. Accordingly, the technique of controlling monodisperse silica particles in a wide area in one dimension, two dimensions, and three dimensions without generating defects in a large area is an important part in utilizing monodisperse silica photocrystals as devices for various applications.

There are many methods for producing monodisperse spherical silica particles, but one of the general methods is known as the Stoeber synthesis method. When using the Stover method, monodisperse silica particles can be produced in a variety of particle sizes over a range of 10-2,000 nm. Monodisperse silica particles are generally formed by hydrolysis of tetraethylorthosilicate (TEOS; Si (OC ₂ H ₅ ) ₄ ) precursor in a solution containing alcohol, water, and ammonia, followed by the action of an ammonia catalyst. It is synthesized by the sol-gel method. The sol-gel method has already been published in several publications (e.g. Stoeber et al., J. Colloid and Interface Sci., Vol 26, 1968, 62-69 and Zukoski et al., J. Non-Cryst.Solids, vol. 104, 1988, 95.).

Monodisperse spherical silica particles have various uses, such as light emitting materials, electronic materials, and biological materials. In particular, there are many applications in which silica particles use their self-assembly properties. For example, silica arrays self-assembled in hexagonally closed pack structures have photonic crystals and lithography using photonic band gaps. It can be used as a mask (lithographic mask). In the field of telecommunications, self-assembled silica photonic crystals are attracting attention as new switching and wave-guiding media.

In order to produce such a highly functional silica photonic crystal medium, the most important part is controlling the arrangement of the silica particles. Known silica array methods include indirect control methods using lithography and holography; There are self-assembly methods such as sedimentation, vertical deposition, spin coating, and slide coating. However, most of these methods are difficult to obtain a uniform particle arrangement without defects in a wide area of more than a micron size, and due to this problem, full-scale application is limited. In particular, in the case of requiring a three-dimensional array over a wide range, it is more difficult to suppress the generation of defects during the arrangement, making it difficult to commercialize.

The present inventors have come to solve the above-mentioned problem by thinking that the reason why it is difficult to arrange the monodisperse silica particles uniformly without the occurrence of bonding is not only in the difficulty in the arrangement process but also in the problems inherent in the silica particles. That is, in the case of silica particles synthesized by the Stover synthesis method, since a considerable amount of moisture and organic matter are contained inside and on the surface, when the silica particles are arranged as they are without any treatment, moisture or organic matter may be used during the arrangement process or subsequent device fabrication process. This can evaporate. As a result of this evaporation, the size, refractive index, dielectric constant, density, surface roughness, etc. of the silica particles may change, which may impair the regularity of the arranged particles. In particular, when large area crystals or large volume crystals are required, small changes resulting from evaporation are very likely to lead to defects.

An object of the present invention is that mono-disperse oxide particles, preferably mono-molecular silica particles, change particle characteristics (particle size, density, shape, refractive index, dielectric constant, surface roughness, etc.) according to external environment changes (temperature, humidity, etc.). The present invention provides a method for producing an oxide particle having a minimum occurrence of defects in particle arrangement, and a monodisperse oxide particle having excellent volumetric stability and minimizing defect occurrence such as cracking during particle arrangement through this method.

In order to achieve the above object, the present invention provides a method for treating spherical oxide particles comprising heating the spherical oxide particles at a temperature higher than room temperature.

In one embodiment of the invention the temperature in the heat treatment step is above room temperature, preferably at least 100 ° C, more preferably at least 200 ° C, even more preferably at least 400 ° C, most preferably at least 550 ° C, The temperature is 1000 ° C. or lower, preferably 900 ° C. or lower, preferably 800 ° C. or lower, and most preferably 750 ° C. or lower.

In another embodiment of the invention, the heat treatment step continues the heat treatment until substantially no weight loss of the spherical oxide particles occurs.

In a preferred embodiment of the present invention, the spherical oxide particles have a monodisperse distribution, and are preferably silica particles having a monodisperse distribution.

The present invention also relates to spherical oxide particles treated by the above treatment method, through which the water, solvent, by-products and the like contained in the oxide particles are evaporated or decomposed to remove them from the oxide particles. The spherical oxide particles obtained by treatment through the treatment method according to the present invention exhibit one or more of the following properties.

(1) The weight loss after heat treatment at 550 DEG C or higher is 12% by weight or less, preferably 10% or less, most preferably 9% or less.

(2) The specific surface area increase rate after heat treatment of 550 DEG C or higher is 9% or less, preferably 8% or less, most preferably 7% or less.

(3) The size shrinkage (based on average diameter change) after heat treatment of 550 DEG C or higher is 1.5% or less, preferably 1.3% or less, and most preferably 1.2% or less.

(4) Transmittance at 960 cm ^-1 is 9% or less, preferably 8% or less, and most preferably 7% or less when compared to the transmittance at 1100 cm ^-1 when measuring infrared spectroscopic spectra in a powder state.

(5) Incidence scattering in powder form after heat treatment of 550 ° C. or higher, the inclination increase value in the Q = 0.7 to 2 nm ⁻¹ region is 8% or less, preferably 7% or less, most preferably, before the heat treatment. Less than 6%.

The present invention also relates to the use of the spherical oxide particles described above, wherein the spherical oxide particles of the present invention are regularly arranged. It relates to an optical element such as a coating agent.

In a preferred embodiment of the present invention, the monodisperse silica particles synthesized by the sol-gel method are heat-treated to remove or remove moisture and organic matter contained in the surface and the interior, and to change the internal and surface structural changes that may occur at high temperature in advance. By inducing, it is possible to perform stable arrangements without generating defects over a wide range by not causing geometrical changes (changes in size and shape) even when the particles are arranged or when the arranged particles are exposed to a dry atmosphere or a high temperature environment.

Since there is no change in size and shape when the heated silica particles are dispersed in a liquid medium to induce a regular arrangement, it is possible to minimize the occurrence of bonding due to shrinkage or shape change of the silica particles during or after drying. . Therefore, silica particles can be regularly arranged in a large area, and three-dimensional large crystals can be produced. In addition, since the stability of the silica particles is greatly increased by the heat treatment, the process time can be increased, and the process temperature can be selected from room temperature to several hundred degrees Celsius.

1 is a thermogravimetric analysis result of the silica powder (a) and the unheated silica powder (b) prepared in Example 1,
In Figure 2, a) is a scanning micrograph of the silica powder heat-treated in Example 1, (b) is a scanning micrograph of the powder not heat-treated.
3 is infrared spectral spectra of silica powder, (a) shows a silica powder heat treated in Example 1, and (b) shows a powder not heat treated.
4 is an image of silica particles observed with a transmission electron microscope, (a) and (b) shows the silica powder heat-treated in Example 1, (c) and (d) shows the powder not heat-treated.
Fig. 5 (a) is an incineration scattering X-ray analysis spectrum of silica powder, in which the dotted line shows the silica powder heated in Example 1, and the solid line shows the powder without heat treatment.
5 (b) shows incineration scattering X-ray spectra of powders 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.
6 is a transmission electron microscope photograph of silica particles heated at 1000 ° C. FIG.
7 is a scanning electron micrograph ((a) and (b) enlarged by 1,000 times and (c) and (d) enlarged by 5,000 times) of silica particles after heat treatment arranged on a silicon wafer substrate.
8 is a scanning electron micrograph ((a) and (b) of 1,000 times observed and (c) and (d) of 5,000 times observed) of unheated silica particles arranged on a silicon wafer substrate. .

Hereinafter, the present invention will be described in detail with reference to the following examples, which do not limit the scope of the present invention.

Example 1 Heat Treatment of Silica Particles

Monodisperse spherical silica particles (each having a diameter of 230 nm (manufactured by Stubber synthesis), 450 nm (manufactured by Stubber synthesis), and 980 nm (purchased from Polysciences, Inc.) at room temperature for 24 hours And heated to 550 ° C. in air at a rate of 2 ° C./min. The temperature was lowered to 25 ° C. over 30 minutes after maintaining the temperature at 550 ° C. for 4 hours.

In order to qualitatively compare the change of the silica powder during the heat treatment, the mass change of the heat treated silica powder was measured using a thermogravimetric analyzer (Q600 SDT from TA Instruments, Inc.). The measurement results are shown in FIG. 1 together with the results obtained on unheated silica powder. After the heat treatment, the silica powder (a) showed only a decrease of about 2.1 wt% in the range of 210 to 280 ° C., while the unheated silica powder (b) showed a weight loss of 9.2 wt% in the same temperature range. In addition, when heated to more than 280 ℃, unheated silica powder continued to reduce the mass, at 550 ℃ total weight loss of 11.6% by weight. On the other hand, the heat treated silica powder showed a total weight loss of only 2.1 wt% without changing the weight at a temperature of 280 ° C. or higher. The difference in the weight change behavior means that a considerable amount of moisture contained in the surface and interior of silica and organic matter or by-products remaining after synthesis are removed during the heat treatment of the silica particles. The weight loss of 2.1% by weight at temperatures below 210 ° C. at the beginning of heating can be seen as the amount indicated by the removal of moisture adsorbed on the surface of the silica particles or the pore walls open to the surface during the storage of the silica particles.

In this regard, the specific surface area of the silica powder before and after the heat treatment was measured. The specific surface area was measured using a surface area analyzer device of BEL Japan, Inc., model name: BELSORP-max, and the surface area was measured in a nitrogen atmosphere after 1 hour heat treatment in a vacuum atmosphere at 100 ° C. In the case of silica powder having an average diameter of 230 nm, the specific surface area of the heat treated 20.35 m 2 / g and the unheated 18.62 m 2 / g were respectively shown. This means that the moisture and organic matter remaining on the surface of the silica particles and the pore walls were removed during the heating process, thereby increasing the specific surface area by about 9%.

The change in the size of the silica particles along with the mass loss during the heat treatment was observed through a scanning electron microscope (SEM, ESEM equipment of FEI, model name: XL-30 FEG, measured in Environmental SEM mode without coating). Shown in The diameter was measured from the vertical observation image (a) of 196 heat-treated silica powder particles, and the average value was obtained. For comparison, the average diameter was determined by the same method from the vertical observation image (b) of 189 silica powder particles not heated by the same method. As a result of the heat treatment, the average diameter was 960 nm, and the heat treatment did not show the average diameter of 980 nm, indicating that the diameter decreased by about 2% during the heat treatment.

3 is an infrared spectral curve measured by making a KBr pellet using a silica powder (a) heat-treated in Example 1 using Mattson's FT-IR spectrometer, model name: IR300, and the silica powder without heat treatment ( Shown in comparison with b). Silica powder from Figure 3 is significantly decreased in the amount of water appearing in the 3100 ~ 3700 ㎝ ^-1 after the heat treatment, decreased from the silicon hydroxyl groups (Si-OH) instead of 1100 ㎝ ^-1 and 820 ㎝ ^-1 it appears at 960 ㎝ ^-1 The silicon-oxide group (Si-O-Si) which appeared appeared to increase. This shows that water is removed during the heat treatment described in FIG. 1, and it can be interpreted that condensation reaction occurs between silicon atoms due to removal of hydroxyl groups on the surface of silica particles, thereby increasing silicon oxide groups.

FIG. 4 is an image [(a) and (b)] of the silica particles heat-treated in Example 1 using a transmission electron microscope (TEM, FEI company, model name: Tecnai G2). Compared with [(c) and (d)], the surface of the particle is considerably smoother. As described in FIG. 3, it can be seen that the surface is flattened in the process of changing the silicon oxide group through the condensation reaction of moisture and organic matter on the surface during the heat treatment and the condensation reaction of the silicon hydroxyl group.

Small-angle X-ray scattering (small angle X-ray scattering, SAXS, Anton Paar, model name SAXSess mc ² , measured in solid state) was used to determine the change of silica particle size and pore surface roughness by heat treatment. Measured. The heat treated silica powder (dotted line) is shown in Fig. 5 (a) as compared with the unheated one (solid line). In FIG. 5, the low Q value portion (Q <0.4 nm ⁻¹ ) is called a Guinier region and the high Q value portion (0.7 <Q <2 nm ⁻¹ ) is called a Porod region. The part between the two regions is the Fractal region, where the transition between the two regions is observed, which is related to the particle size. The unheated silica powder (solid line) in FIG. 5 (a) shows the transition at 0.46 nm ⁻¹ and the heat treated (dashed line) at 0.54 nm ⁻¹ . This increase in transition is a result of the size of the powder becoming smaller after heat treatment. In addition, it is possible to determine the roughness of the surface through the slope in the section showing the negative slope corresponding to the Porod region, in which the silica powder (dotted line) heated in FIG. 5 (a) is not heated (solid line). Shows an increase in the slope. This means that the pore surface of the heat treated silica particles is smoother than when not heat treated.

Incineration scattering X-ray analysis of the temperature-treated silica powders were observed. Incineration scattering X-ray analysis of powders 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, is shown in FIG. 5 (b). . The powder size and surface roughness of the powder gradually change up to 800 ° C., but suddenly change at a higher temperature, which is a result of agglomeration of particles through phase change at 800 ° C. or higher. In this regard, the image of the silica powder heat-treated at 1000 ° C. was also observed in a transmission electron microscope. The shape of each particle is unknown and shows that they are agglomerated and present in large chunks.

Example 2 Planar Arrangement by Self-Assembly of Silica Particles

Some of the silica particles heated in Example 1 were taken to form 20 ml of a 1 wt% aqueous solution, and the particles were dispersed by an ultrasonic bath for 1 hour. After immersing the silicon wafer substrate of 1 × 5 cm 2 size vertically in a white colloidal aqueous solution in which silica particles were dispersed, silica particles were arranged on the substrate surface while slowly evaporating moisture for 18 hours in an oven maintained at 60 ° C. The substrate on which the silica particles were arranged was separated from the solution, dried at room temperature for 1 hour, and then dried at 60 ° C. in an oven for 24 hours.

As a control, silica particles not heat-treated in the same manner were arranged on a silicon wafer and then dried.

In order to compare the degree of arrangement of the silica particles arranged on the surface of the silicon substrate, each image observed with a scanning electron microscope is shown in FIGS. 7 (when the heat-treated silica particles are arranged) and FIG. 8 (the heat-treated silica particles are arranged In one case). In comparison with FIG. 7 and FIG. 8, in the case of the silica particles according to the present invention, the arrangement is stable and almost no cracking is observed, whereas in the case of the silica particles without the heat treatment, the particle size is smaller than 0.5 on the arrangement surface. Folds, up to fifteen times, were observed. Thus, it can be seen that the particles treated through the treatment method according to the invention are arranged without defects.

Photonic crystals composed of silica particles arranged regularly without cracking can be applied to many areas. In particular, it can be used as an optical waveguide, a distributed Bragg reflector (DBR) required in the optical communication field, and other materials such as photonic crystal (eg, opal), optical coating, discharge film, and sensor. It can be used as.

Claims (8)

A method of producing a spherical oxide particle that satisfies one or more of the following properties, including heating the spherical oxide particle at a temperature higher than room temperature.
(1) The weight loss after heat treatment of 550 DEG C or higher is 12% by weight or less.
(2) The specific surface area increase rate is 9% or less after heat treatment of 550 ° C. or higher.
(3) The size shrinkage (based on average diameter change) after heat treatment of 550 DEG C or higher is 2% or less.
(4) Transmittance at 960 cm ^-1 was 9% or less compared to the transmittance at 1100 cm ^-1 in the infrared spectroscopy measurement in the powder state.
(5) Incineration scattering X-ray analysis in powder state after heat treatment of 550 ° C. or higher, the inclination increase value in the region of Q = 0.7˜2 nm ⁻¹ is 8% or less than before heat treatment. The method of claim 1, wherein the temperature higher than the room temperature is a temperature higher than room temperature to 900 ℃. The method of claim 1, wherein the heat treatment is continued until substantially no weight loss of the spherical oxide particles occurs. The method of claim 1, wherein the spherical oxide particles have a monodisperse distribution. Spherical oxide particles produced by the method according to claim 1. Spherical oxide particles according to claim 5, which are spherical silica particles. A photonic crystal in which the spherical oxide particles according to claim 5 are arranged regularly. A coating agent in which the spherical oxide particles according to claim 5 are arranged regularly.

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