WO2009128591A1 - Method for patterning of hemispherical photonic crystallines and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions - Google Patents

Method for patterning of hemispherical photonic crystallines and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions Download PDF

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Publication number
WO2009128591A1
WO2009128591A1 PCT/KR2008/004940 KR2008004940W WO2009128591A1 WO 2009128591 A1 WO2009128591 A1 WO 2009128591A1 KR 2008004940 W KR2008004940 W KR 2008004940W WO 2009128591 A1 WO2009128591 A1 WO 2009128591A1
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Prior art keywords
photonic crystals
colloidal
hemispherical
frame
photonic
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PCT/KR2008/004940
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French (fr)
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Seung-Man Yang
Shin-Hyun Kim
Jong-Min Lim
Woong-Chan Jeong
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Korea Advanced Institute Of Science And Technology
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Publication of WO2009128591A1 publication Critical patent/WO2009128591A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/0045—Photosensitive materials with organic non-macromolecular light-sensitive compounds not otherwise provided for, e.g. dissolution inhibitors
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/0047—Photosensitive materials characterised by additives for obtaining a metallic or ceramic pattern, e.g. by firing
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/1213—Constructional arrangements comprising photonic band-gap structures or photonic lattices

Definitions

  • the present invention relates to a method for patterning of hemispherical photonic crystallines and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions, colloidal photonic crystals formed by the same method, and a porous polymer structure fabricated using the same method. More particularly, the present invention relates to a method for fabrication of a structure having a uniform array of colloidal particles by introducing a photocurable colloidal suspension into a molding frame (abbreviated to "frame”) having different shapes.
  • frame molding frame
  • a photonic crystal means a material having a periodical variation in dielectric constants and a photonic band gap similar to those of semiconductors, in which light with specific energy levels cannot exist. Accordingly, by uniformly aligning colloidal particles, a structure for selectively reflecting light at specific wavelengths may be fabricated.
  • reflective wavelengths are typically defined based on refractive index, structure of a crystal, particle size, and a gap between particles, etc. and, if controlling such parameters, colloidal photonic crystals at desired reflective wavelengths may be obtained.
  • the present invention suggests control of direction and/or photonic characteristics of photonic crystals by forming colloidal photonic crystals having a variety of shapes such as hemispherical, film shape, linear pattern, pyramid form, and/or cylindrical forms.
  • colloidal photonic crystals having a variety of shapes such as hemispherical, film shape, linear pattern, pyramid form, and/or cylindrical forms.
  • a film type photonic crystal is mostly formed through a vertical coating method and/or a spin coating method.
  • the vertical coating method disclosed in a research paper (see, P. Jiang, J. F. Bertone, K. S. Hwang and V. L. Colvin, "Single-crystal colloidal multilayers of controlled thickness” Chemistry of Materials, 11, 2132-2140 (1999)) is effective to produce a thick film having a high reflectivity.
  • this is based on evaporation requiring a long processing time and has difficulty in practical applications due to increased cracks in the film.
  • the spin coating method described in US Laid-Open Patent Application No. 2005/0095471 also see, Journal of American Chemical Society, 126, 13778-13786 (2006)) allows rapid production of crystals, however, this has also a problem in formation of thick crystals having high reflectivity.
  • the conventional method for production of hemispherical photonic crystals through evaporation from colloidal suspension droplets formed using an ink-jet printing process requires a long processing time, and often has a problem of nozzle clogging and a fundamental restriction in production of hemispheres having high density.
  • the spin coating method is preferably used in rapid production of crystals, however, has a problem in formation of thick crystals having high reflectivity.
  • other known processes for formation of colloidal crystal patterns or structures with a variety of shapes have problems in mass production and/or mechanical strength of a structure, thus causing difficulty in being used in industrial applications.
  • the present invention is directed to solve the problems described above in regard to conventional methods and an object of the present invention is to provide a method for patterning of hemispherical photonic crystals by using a photocurable monomer solution containing high concentration colloidal particles to form a uniform pattern on a lipophilic surface of a substrate having high contact angle to liquid droplets, and then, curing the patterned particles to fabricate a pattern of hemispherical photonic crystals and a method for fabrication of photonic crystals with various shapes by introducing a colloidal suspension into a frame having various forms such as microfine tubes.
  • a photocurable monomer solution containing high concentration colloidal particles to form a uniform pattern on a lipophilic surface of a substrate having high contact angle to liquid droplets
  • a method for fabrication of colloidal and/or porous photonic crystals having different shapes comprising: (a) dispersing colloidal particles in a photocurable monomer solution and introducing the dispersed solution (which is defined as a "colloidal suspension") into a frame with a desired shape; (b) UV irradiating the colloidal suspension in the frame to fabricate photonic crystals; and (c) if desired, releasing the photonic crystals from the frame to selectively remove the colloidal particles.
  • the patterning method using a photocurable colloidal suspension according to the present invention may result in patterning of hemispherical colloidal photonic crystals, thus ensuring a wide photo-viewing angle of a reflective display.
  • the method for fabrication of photonic crystals using a photo- polymerizable colloidal suspension according to the present invention may fabricate colloidal photonic crystals or porous photonic crystals in various shapes such as a film shape, a cylindrical shape, a linear patterned shape, a pyramidal shape, etc., thus favorably being used in mass production of photonic crystals in a number of applications.
  • Fig. 1 is a schematic view showing a process for forming a multi-color pattern of mono-colored hemispherical photonic crystals and a pattern of multi-colored hemispherical photonic crystals according to the present invention
  • Fig. 2 is photographs showing a pattern of the mono-colored hemispherical photonic crystals with red, green and blue colors, prepared according to Example 1 ;
  • Fig. 3 is optical microscope photographs showing the mono-colored hemispherical photonic crystals with red, green and blue colors, respectively, prepared according to Example 1 and reflectance spectra thereof;
  • Fig. 4 is optical microscope photographs showing isotropic property of reflected color of the red color hemispherical photonic crystals prepared according to Example 1 and reflectance spectra thereof;
  • Fig. 5 is a photograph showing a pattern of the mono-colored hemispherical photonic crystals having high density with red, green and blue colors, respectively, prepared according to Example 1 ;
  • Fig. 6 is photographs showing the mono-colored porous hemispherical photonic crystals patterned on the soft polymer film prepared according to Example 2 and electron microscope photographs showing an inner part of a hemisphere of the crystal;
  • Fig. 7 is photographs showing patterns of the multi-colored hemispherical photonic crystals prepared according to Example 3.
  • Fig. 8 is optical microscope photographs and scanning electron microscope photographs showing both the colloidal photonic crystal film and the porous photonic crystal film prepared according to Example 4, and reflectance spectra thereof;
  • Fig. 9 is optical microscope photographs and scanning electron microscope photographs showing both the linear pattern colloidal photonic crystals and the porous photonic crystals prepared according to Example 5;
  • Fig. 10 is optical microscope photographs and scanning electron microscope photographs showing pyramid-shaped photonic crystals prepared according to Example 6.
  • Fig. 11 is optical microscope photographs and scanning electron microscope photographs showing the cylindrical photonic crystals prepared according to Example 7. [Best Mode]
  • the present invention discloses a method of fabricating hemispherical photonic crystals.
  • the method of fabricating hemispherical photonic crystals according to the present invention comprises: dispersing colloidal particles in a UV curable polymer solution to form hemispherical colloidal suspension droplets on a substrate; and UV irradiating the colloidal suspension droplets to cure the same.
  • the substrate may be a substrate coated with a lipophilic material such as Teflon or made of the lipophilic material.
  • the substrate may be a soft polymer film substrate having flexible properties.
  • the method of the present invention may further comprise patterning of colloidal or porous mono-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals without coalescence of the colloidal suspension droplets.
  • the method of the present invention may further comprise patterning of colloidal or porous multi-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals through coalescence of the colloidal suspension droplets.
  • a mechanical injection using a dispenser or an ink-jet printing method may be adapted to perform patterning of the colloidal suspension droplets.
  • the present invention may further comprise selectively removing the colloidal particles from the fabricated colloidal hemispherical photonic crystals to obtain the porous hemispherical photonic crystals.
  • each of the colloidal hemispherical photonic crystals may have a size of several micrometers to several millimeters while a contact angle of the photonic crystal to the substrate may range from 20 to 160°.
  • the colloids may be photocurable monomer solution containing colloidal particles in an amount of 5 to 50% by volume (v/v).
  • the present invention also discloses a method of fabricating colloidal and/or porous photonic crystals comprising: dispersing colloidal particles in a UV curable polymer solution and introducing the dispersed solution as a colloidal suspension into a frame; and UV irradiating the dispersed colloidal suspension in the frame to cure the same.
  • the photonic crystals may be formed in a film shape by using a space defined between two plates as the frame.
  • the photonic crystals may be formed in a shape of microfine tube by using a microfine tube as the frame.
  • the photonic crystals may be formed in a cylindrical shape by using a cylindrical microfine tube as the frame.
  • the frame may be a polymer linear patterned frame.
  • the frame may be a pyramid-shaped frame.
  • the present invention may further comprise selectively removing colloidal particles from the fabricated colloidal photonic crystals.
  • the colloids may be photocurable monomer solution containing colloidal particles in an amount of 5 to 50% by volume (v/v).
  • the colloidal particles may have a size of 150 to 100,000nm.
  • the present invention discloses a method for fabrication of colloidal and/or porous photonic crystals having different shapes, comprising: (a) dispersing colloidal particles in a photo-polymerizable monomer solution and introducing the dispersed solution into a frame with a desired shape; (b) UV irradiating the dispersed solution in the frame to fabricate photonic crystals; and (c) if desired, selectively removing the colloidal particles after releasing the photonic crystals from the frame.
  • the monomer solution used in step (a) is substantially defined as a monomer suspension and contains colloidal particles in an amount of 5 to 40% by volume (“v/v”), and preferably 10 to 30% (v/v).
  • Each of the colloidal particles may have a size ranging from 100 to 100,000nm, preferably 150 to 3,000nm.
  • the polymer is preferably at least one or two or more selected from photocurable polymers having acrylate groups, however, is not particularly limited thereto so long as it may be cured by UV rays.
  • the frame used in step (a) may be any structure having surfaces with characteristic length in a range of several micrometers to several millimeters, and typically comprise any one selected from liquid droplets having a high contact angle, a space between two flat plates, a microfine tube, a film having pyramid type pits, a structure having a linear channel and the like.
  • UV irradiation in step (b) is often performed at a light intensity of about 40mW/cm for 1 to 10 seconds, however, light intensity and/or UV irradiation time is not particularly restricted thereto if a combination of the light intensity and the UV irradiation time is sufficient to complete photo-curing of monomers.
  • Removal of colloid particles in step (c) is mostly performed by a wet etching process and the present invention may use fluoric acid to remove silica particles.
  • the colloidal particles may be selectively removed by any commonly known method without particular limitation thereof.
  • the photonic crystal fabricated according to the present invention forms a hexagonal close-packed face having the highest planar density of a face-centered cubic structure along a surface of the frame, therefore, exhibits reflected light always having the same wavelength to light incident normally on any surface of the frame. Adjusting a size and/or volume fraction of the colloidal particles may control a reflective wavelength of the colloidal particles to a desired range.
  • the reflective wavelength moves to a range of shorter wavelengths while the crystal shows higher reflectivity, because of a decrease in effective refractive index and an increase in refractive index contrast.
  • the fabricated porous photonic crystals are noticeably useful for various applications requiring high reflectivity.
  • the present invention proposes a method for fabrication of colloidal and/or porous photonic crystals with various shapes without an alternative evaporation process, compared to existing methods in the art.
  • the method for fabrication of photonic crystals according to the present invention does not employ an evaporation process but make a high concentration of particles align themselves in a photocurable monomer solution, followed by UV irradiation for several seconds to cure the aligned particles.
  • a fabrication time is decreased while simplifying processes for the fabrication of photonic crystals.
  • the fabricated crystals have a considerably increased mechanical strength.
  • a range of reflective wavelengths may be expected by the following equation 1 :
  • n refractive index of a substance
  • v volume fraction of colloidal particles
  • D diameter of a colloidal particle
  • a mechanically driven dispenser apparatus is used. Introducing a colloidal suspension into an injector then fitting the injector to the apparatus, a dispenser of the apparatus may apply the suspension in the form of liquid droplets and in an accurately controlled amount to a substrate.
  • a dispenser of the apparatus may apply the suspension in the form of liquid droplets and in an accurately controlled amount to a substrate.
  • each of the liquid droplets has a high contact angle to the substrate, so as to form a hemispherical drop. Since colloidal particles are aligned along a surface of the liquid droplet, photo-curing of the colloidal particles may produce hemispherical colloidal crystals irradiating the same reflected wavelength regardless of position on the surface of the liquid droplet.
  • photonic crystals in any form of film shapes, cylinder forms, linear patterns, pyramid forms, etc. may be fabricated by introducing a colloidal suspension into a frame through capillary force and photo-polymerizing the same.
  • a film type photonic crystal interposing a spacer between two glass plates may fabricate a frame.
  • a cylindrical photonic crystal a glass or plastic tube may be used.
  • a linear pattern frame may be fabricated by soft lithography (as a well known process that introduces a polymer material such as a polydimethylsiloxane (PDMS) to a linear pattern of photosensitive polymer obtained through photolithography and releases the applied polymer material to form a pattern).
  • PDMS polydimethylsiloxane
  • a pyramid form frame may be fabricated by anisotropic etching of a silicon wafer.
  • the monomer solution used in the present invention may be ethoxylated trimethylolpropane triacrylate monomer ETPTA (MW 428, viscosity 60 cps, SR 454) which is curable by UV.
  • ETPTA ethoxylated trimethylolpropane triacrylate monomer
  • the monomer solution is not particularly restricted thereto if it is selected from materials cured when exposed to UV and, at the same, spontaneously forms crystals when colloidal particles are dispersed in the monomer solution.
  • the colloidal particle used in the present invention may be a silica particle produced using a so-called Stober-Fink-Bohn method, however, the colloidal particle is not particularly restricted thereto.
  • porous photonic crystals may also be fabricated using the same system as for the colloidal photonic crystals having different shapes. More particularly, these porous photonic crystals may be fabricated by selectively removing silica particles from the formed colloidal photonic crystals that consist of particles and cured ETPTA.
  • the silica particles are substantially removed using a specific material such as a sodium hydroxide solution or fluoric acid and the remaining ETPTA in a cured form may continuously maintain the structure of the crystal.
  • Silica particles having uniform sizes of 195nm, 150nm and 145nm prepared using the Stober-Fink-Bohn method were dispersed in ETPTA in volume ratios of 1 :2, 1:3 and 1:2, respectively.
  • route 1 in Fig. 1 mono-colored hemispherical liquid droplets having red, green and blue colors, respectively, were used in patterning.
  • the liquid droplets were patterned on a Teflon coated glass plate at a contact angle of 80°.
  • the glass plate was a substrate coated with lipophilic material such as Teflon and/or made of the same material, which is preferable for patterning.
  • the substrate is not particularly restricted to Teflon coated plates but includes any substrate having a contact angle of at least 40°.
  • treatment of a self-assembled monolayer (SAM) on a glass plate or a wafer may induce a high contact angle, which is useable in patterning according to the present invention.
  • SAM self-assembled monolayer
  • a distance between two hemispheres having the same color was maintained at lmm, while controlling each of the hemispheres to have a diameter of 293 ⁇ m corresponding to a volume of 5 nanoliters.
  • the prepared liquid droplets were exposed to UV irradiation at a light intensity of 40mW/cm 2 for 10 seconds using a mercury arc lamp, thus curing the hemispherical liquid crystals.
  • Fig. 2 is photographs showing a pattern of the mono-colored hemispherical photonic crystals with red, green and blue colors. Especially, Fig. 2A is a photograph at a low magnification while Fig. 2B is another photograph at a high magnification.
  • Fig. 3 is optical microscope photographs showing the mono-colored hemispherical photonic crystals with red, green and blue colors, respectively, and reflectance spectra thereof.
  • optical microscope photographs were taken at different light incident angles and reflectance spectra of the crystal were measured.
  • Fig. 4 is optical microscope photographs showing the same reflected color of a mono-colored hemispherical photonic crystal at different light incident angles and reflectance spectra thereof at the light incident angles.
  • a diameter of a liquid droplet increased to 375 ⁇ m corresponding to a volume of 10 nanoliters of the droplet while maintaining a distance between two hemispheres at lmm.
  • the density of the pattern increased from 20% to 33%.
  • Fig. 5 is a photograph showing a three-color pattern of the mono-colored hemispherical photonic crystals having increased density.
  • EXAMPLE 2 Formation of multi-color pattern of mono-colored hemispherical photonic crystals on soft polymer film
  • Patterning of liquid droplets was performed by the same procedure described in Example 1, except that a soft substrate made of PDMS polymer film having a thickness of 3mm was used.
  • the substrate had a contact angle of 50 ° and the liquid droplets were cured by the same method as described in Example 1.
  • the formed pattern was immersed in a 5wt% fluoric acid solution for 5 minutes to selectively remove silica particles, resulting in porous hemispherical photonic crystals.
  • the produced photonic crystals had shorter reflective wavelength caused by a decrease in effective refractive index and exhibited brighter colors owing to an increase in refractive index contrast, compared to before the silica particles were removed.
  • Fig. 6A is a photograph showing a three-color pattern of mono-colored porous hemispherical photonic crystals formed on a soft polymer film
  • Fig. 6B is a scanning electron microscope photograph showing an inner part of a hemispherical photonic crystal
  • Figs. 6C, 6D and 6E are optical microscope photographs showing porous hemispherical photonic crystals obtained after removing colloidal particles from the mono-colored hemispherical colloidal photonic crystals with blue, green and red colors, respectively.
  • EXAMPLE 3 Formation of pattern of multi-colored hemispherical photonic crystals
  • Spherical photonic crystals were prepared by the same procedure described in Example 1, except that a position of dropping liquid droplets was adjusted to induce coalescence with existing liquid droplets during second and/or third patterning of the liquid droplets, which corresponds to route 2 illustrated in Fig. 1. As a result, multicolored hemispherical photonic crystals were obtained, each of the hemispherical photonic crystals of which showed a plurality of reflected colors.
  • Fig. 7A is a photograph showing a pattern of multi-colored hemispherical photonic crystals with a combination of red and blue colors while Fig. 7B is an optical microscope photograph showing one of the multi-colored hemispherical photonic crystals.
  • This crystal had a diameter of 375//m (corresponding to a volume of 10 nanoliters) and was prepared by combining 5 nanoliters of red colloidal suspension and 5 nanoliters of blue colloidal suspension.
  • Fig. 7C is a photograph showing a pattern of multi-colored hemispherical photonic crystals with a combination of red, green and blue colors while Fig. 7D is an optical microscope photograph showing one of the multi-colored hemispherical photonic crystals.
  • This crystal had a diameter of 510 ⁇ m (corresponding to a volume of 25 nanoliters) and was prepared by combining 10 nanoliters of red colloidal suspension, 10 nanoliters of green colloidal suspension and 5 nanoliters of blue colloidal suspension.
  • EXAMPLE 4 Fabrication of photonic crystal film
  • a spacer having a thickness of 50 ⁇ m was inserted between two glass plates to ensure an inner space, followed by filling the space with a suspension containing 195nm silica particles in ETPTA with volume ratio of 1 :2 through capillary force.
  • the suspension was photo-cured according to the same procedure as described in Example 1 and a cured colloid photonic crystal film was separated from both the glass plates.
  • the prepared film showed a reflectivity of about 30%.
  • the film was immersed in a 5wt.% fluoric acid solution for 12 hours to remove silica particles from the film, thus obtaining a porous photonic crystal film.
  • this film Compared to colloidal photonic crystals, this film exhibited reflectance peak at shorter wavelength, had high reflectivity of about 70% and a considerable increase in widths of reflectance peak. It was believed that these resulted from a decrease in effective refractive index and an increase in refractive index contrast because of silica particle removal.
  • Fig. 8A is optical microscope photographs showing a colloidal photonic crystal film and a porous photonic crystal film, as well as reflectance spectra thereof.
  • Figs. 8B and 8C are scanning electron microscope photographs showing cross sections of the colloidal photonic crystal film and the porous photonic crystal film, respectively.
  • EXAMPLE 5 Formation of photonic crystal linear pattern
  • the colloidal suspension used in Example 4 was introduced into a linear pattern frame made of PDMS polymer by soft lithography, through capillary force.
  • the linear pattern had a width of 25 ⁇ m and a depth of 30//m.
  • the colloidal suspension was introduced thereto so as to form the linear pattern frame.
  • the suspension filled in the frame was photo-cured according to the same procedure described in Example 1 and a cured linear pattern having red color was released from the frame. Removing silica particles according to the same procedure as described in Example 4 resulted in a linear pattern having green color.
  • Figs. 9A and 9B are optical microscope photographs showing a colloidal photonic crystal linear pattern and a porous photonic crystal linear pattern
  • Figs. 9C and 9D are scanning electron microscope photographs showing cross sections of the colloidal photonic crystal linear pattern and the porous photonic crystal linear pattern, respectively.
  • EXAMPLE 6 Formation of pyramid-shaped photonic crystal pattern
  • the colloidal suspension used in Example 4 was introduced into a pyramid- shaped frame made of PDMS polymer, followed by photo-curing the same to prepare a pyramid-shaped photonic crystal pattern.
  • the pyramid-shaped frame made of PDMS polymer was prepared by double transfer molding of pyramid pattern formed by anisotropic wet etching of silicon.
  • Figs. 1OA and 1OB are optical microscope photographs showing a lateral side and a front side of a red pyramid pattern
  • Figs. 1OC and 1OD are scanning electron microscope photographs at low and high magnifications showing a surface near a peak of the pyramid form, respectively.
  • EXAMPLE 7 Fabrication of cylindrical photonic crystals
  • Example 1 Blue, green and red color colloidal suspensions used in Example 1 were fed into a glass tube having an inner diameter of 1.1mm in this order, followed by photo- curing the same. A cured cylindrical photonic crystal having three colors therein was released from the glass tube.
  • Fig. HA is a photograph showing a cylindrical photonic crystal having three colors
  • Fig. HB is a scanning electron microscope photograph showing a cross section of the cylindrical photonic crystal
  • Figs. HC, HD and HE are optical microscope photographs showing red, green and blue colored parts of the cylindrical photonic crystal, respectively.
  • the method for fabrication of photonic crystals according to the present invention can very rapidly form photonic crystals using a UV curable colloidal suspension without alternative evaporation processes, therefore, has an advantage in that a wide range of photonic crystals with various shapes can be produced.
  • the inventive method is remarkably useful for patterning of photonic crystals, thus being preferably applied in manufacturing pixels of reflection type displays.
  • a film type photonic crystal having excellent reflection and high crystallinity may vary photoluminescence spectra of fluorescent molecules or quantum dots, thereby being utilized in lasing.

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Abstract

Disclosed are a method for patterning of hemispherical photonic crystals and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions. More particularly, the present invention discloses a method for patterning of hemispherical photonic crystals by using a photocurable monomer solution containing high concentration colloidal particles to form a uniform pattern on a lipophilic surface of a substrate with high contact angle to liquid droplets, and then, curing the patterned surface to produce a pattern of the hemispherical photonic crystals, and a method for fabrication of photonic crystals with various shapes by introducing a colloidal solution into a frame having various forms such as microfine tubes. The photonic crystals fabricated using colloidal suspensions may be effectively used in a number of applications including, for example, pixels of a reflective display.

Description

METHOD FOR PATTERNING OF HEMISPHERICAL PHOTONIC CRYSTALLINES AND FABRICATION OF PHOTONIC CRYSTALS WITH VARIOUS SHAPES USING PHOTOCURABLE COLLOIDAL SUSPENSIONS
[Technical Field]
The present invention relates to a method for patterning of hemispherical photonic crystallines and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions, colloidal photonic crystals formed by the same method, and a porous polymer structure fabricated using the same method. More particularly, the present invention relates to a method for fabrication of a structure having a uniform array of colloidal particles by introducing a photocurable colloidal suspension into a molding frame (abbreviated to "frame") having different shapes.
[Background Art]
It is well known that a uniform array of colloidal particles exhibits photonic band gap characteristics of photonic crystals at half the level of respective light wavelengths. A photonic crystal means a material having a periodical variation in dielectric constants and a photonic band gap similar to those of semiconductors, in which light with specific energy levels cannot exist. Accordingly, by uniformly aligning colloidal particles, a structure for selectively reflecting light at specific wavelengths may be fabricated. In this regard, reflective wavelengths are typically defined based on refractive index, structure of a crystal, particle size, and a gap between particles, etc. and, if controlling such parameters, colloidal photonic crystals at desired reflective wavelengths may be obtained. The present invention suggests control of direction and/or photonic characteristics of photonic crystals by forming colloidal photonic crystals having a variety of shapes such as hemispherical, film shape, linear pattern, pyramid form, and/or cylindrical forms. There have been many studies and investigations in regard to a method for fabrication of a colloidal photonic crystal in a hemispherical form. According to a previous document disclosed in "Chemistry of Materials" as one of famous journals well known in applications of materials (see, Hwa- Young Ko, Jungho Park, Hyunjung Shin, Jooho Moon, "Rapid self-assembly of monodisperse colloidal spheres in an ink-jet printed droplet," Chemistry of Materials, 16, 4212-4215 (2004)), it was reported that evaporation of liquid droplets of a colloidal suspension formed through ink-jet printing produces hemispherical photonic crystals. However, this method requires extended time owing to an evaporation process and often has a problem of nozzle clogging, as well as a fundamental restriction in formation of hemispheres with high density.
A research paper published in Langmuir as one of famous journals in applications of colloids (see, Jun Hyuk Moon, Sarah Kim, Gi-Ra Yi, Yong-Hee Lee, and Seung-Man Yang, "Fabrication of ordered macroporous cylinders by colloidal templating in microcapillaries" Langmuir, 20, 2033-2035 (2004)) reported a photonic crystal in a cylindrical form. However, this approach also has a drawback of requiring a long processing time due to an evaporation process.
A film type photonic crystal is mostly formed through a vertical coating method and/or a spin coating method. The vertical coating method disclosed in a research paper (see, P. Jiang, J. F. Bertone, K. S. Hwang and V. L. Colvin, "Single-crystal colloidal multilayers of controlled thickness" Chemistry of Materials, 11, 2132-2140 (1999)) is effective to produce a thick film having a high reflectivity. However, this is based on evaporation requiring a long processing time and has difficulty in practical applications due to increased cracks in the film. Alternatively, the spin coating method described in US Laid-Open Patent Application No. 2005/0095471 (also see, Journal of American Chemical Society, 126, 13778-13786 (2006)) allows rapid production of crystals, however, this has also a problem in formation of thick crystals having high reflectivity.
Additionally, although a number of approaches or processes for fabrication of colloidal crystal patterns or structures having a variety of shapes have been disclosed, these are mostly based on evaporation processes, leading to problems in mass production and/or mechanical strength of a structure, thus causing difficulty in being used in industrial applications.
As described above, the conventional method for production of hemispherical photonic crystals through evaporation from colloidal suspension droplets formed using an ink-jet printing process requires a long processing time, and often has a problem of nozzle clogging and a fundamental restriction in production of hemispheres having high density. The spin coating method is preferably used in rapid production of crystals, however, has a problem in formation of thick crystals having high reflectivity. Additionally, other known processes for formation of colloidal crystal patterns or structures with a variety of shapes have problems in mass production and/or mechanical strength of a structure, thus causing difficulty in being used in industrial applications.
[Disclosure]
[Technical Problem]
Accordingly, the present invention is directed to solve the problems described above in regard to conventional methods and an object of the present invention is to provide a method for patterning of hemispherical photonic crystals by using a photocurable monomer solution containing high concentration colloidal particles to form a uniform pattern on a lipophilic surface of a substrate having high contact angle to liquid droplets, and then, curing the patterned particles to fabricate a pattern of hemispherical photonic crystals and a method for fabrication of photonic crystals with various shapes by introducing a colloidal suspension into a frame having various forms such as microfine tubes. [Technical Solution]
In accordance with the present invention, there is provided a method for fabrication of colloidal and/or porous photonic crystals having different shapes, comprising: (a) dispersing colloidal particles in a photocurable monomer solution and introducing the dispersed solution (which is defined as a "colloidal suspension") into a frame with a desired shape; (b) UV irradiating the colloidal suspension in the frame to fabricate photonic crystals; and (c) if desired, releasing the photonic crystals from the frame to selectively remove the colloidal particles.
[Advantageous Effects]
As is apparent from the above, the patterning method using a photocurable colloidal suspension according to the present invention may result in patterning of hemispherical colloidal photonic crystals, thus ensuring a wide photo-viewing angle of a reflective display. Also, the method for fabrication of photonic crystals using a photo- polymerizable colloidal suspension according to the present invention may fabricate colloidal photonic crystals or porous photonic crystals in various shapes such as a film shape, a cylindrical shape, a linear patterned shape, a pyramidal shape, etc., thus favorably being used in mass production of photonic crystals in a number of applications. [Description of Drawings]
The above objects, features and advantages of the present invention will become more apparent to those skilled in the related art in conjunction with the accompanying drawings. In the drawings:
Fig. 1 is a schematic view showing a process for forming a multi-color pattern of mono-colored hemispherical photonic crystals and a pattern of multi-colored hemispherical photonic crystals according to the present invention;
Fig. 2 is photographs showing a pattern of the mono-colored hemispherical photonic crystals with red, green and blue colors, prepared according to Example 1 ;
Fig. 3 is optical microscope photographs showing the mono-colored hemispherical photonic crystals with red, green and blue colors, respectively, prepared according to Example 1 and reflectance spectra thereof;
Fig. 4 is optical microscope photographs showing isotropic property of reflected color of the red color hemispherical photonic crystals prepared according to Example 1 and reflectance spectra thereof; Fig. 5 is a photograph showing a pattern of the mono-colored hemispherical photonic crystals having high density with red, green and blue colors, respectively, prepared according to Example 1 ;
Fig. 6 is photographs showing the mono-colored porous hemispherical photonic crystals patterned on the soft polymer film prepared according to Example 2 and electron microscope photographs showing an inner part of a hemisphere of the crystal;
Fig. 7 is photographs showing patterns of the multi-colored hemispherical photonic crystals prepared according to Example 3;
Fig. 8 is optical microscope photographs and scanning electron microscope photographs showing both the colloidal photonic crystal film and the porous photonic crystal film prepared according to Example 4, and reflectance spectra thereof;
Fig. 9 is optical microscope photographs and scanning electron microscope photographs showing both the linear pattern colloidal photonic crystals and the porous photonic crystals prepared according to Example 5;
Fig. 10 is optical microscope photographs and scanning electron microscope photographs showing pyramid-shaped photonic crystals prepared according to Example 6; and
Fig. 11 is optical microscope photographs and scanning electron microscope photographs showing the cylindrical photonic crystals prepared according to Example 7. [Best Mode]
The present invention discloses a method of fabricating hemispherical photonic crystals.
The method of fabricating hemispherical photonic crystals according to the present invention comprises: dispersing colloidal particles in a UV curable polymer solution to form hemispherical colloidal suspension droplets on a substrate; and UV irradiating the colloidal suspension droplets to cure the same.
In the present invention, the substrate may be a substrate coated with a lipophilic material such as Teflon or made of the lipophilic material.
In the present invention, the substrate may be a soft polymer film substrate having flexible properties.
Here, the method of the present invention may further comprise patterning of colloidal or porous mono-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals without coalescence of the colloidal suspension droplets.
Also, the method of the present invention may further comprise patterning of colloidal or porous multi-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals through coalescence of the colloidal suspension droplets.
In the present invention, a mechanical injection using a dispenser or an ink-jet printing method may be adapted to perform patterning of the colloidal suspension droplets.
The present invention may further comprise selectively removing the colloidal particles from the fabricated colloidal hemispherical photonic crystals to obtain the porous hemispherical photonic crystals.
In the present invention, each of the colloidal hemispherical photonic crystals may have a size of several micrometers to several millimeters while a contact angle of the photonic crystal to the substrate may range from 20 to 160°.
In the present invention, the colloids may be photocurable monomer solution containing colloidal particles in an amount of 5 to 50% by volume (v/v).
The present invention also discloses a method of fabricating colloidal and/or porous photonic crystals comprising: dispersing colloidal particles in a UV curable polymer solution and introducing the dispersed solution as a colloidal suspension into a frame; and UV irradiating the dispersed colloidal suspension in the frame to cure the same.
In the present invention, the photonic crystals may be formed in a film shape by using a space defined between two plates as the frame.
In the present invention, the photonic crystals may be formed in a shape of microfine tube by using a microfine tube as the frame.
In the present invention, the photonic crystals may be formed in a cylindrical shape by using a cylindrical microfine tube as the frame.
In the present invention, the frame may be a polymer linear patterned frame.
In the present invention, the frame may be a pyramid-shaped frame.
The present invention may further comprise selectively removing colloidal particles from the fabricated colloidal photonic crystals.
In the present invention, the colloids may be photocurable monomer solution containing colloidal particles in an amount of 5 to 50% by volume (v/v). Here, the colloidal particles may have a size of 150 to 100,000nm.
The present invention will be more apparent from the following detailed description.
The present invention discloses a method for fabrication of colloidal and/or porous photonic crystals having different shapes, comprising: (a) dispersing colloidal particles in a photo-polymerizable monomer solution and introducing the dispersed solution into a frame with a desired shape; (b) UV irradiating the dispersed solution in the frame to fabricate photonic crystals; and (c) if desired, selectively removing the colloidal particles after releasing the photonic crystals from the frame. The monomer solution used in step (a) is substantially defined as a monomer suspension and contains colloidal particles in an amount of 5 to 40% by volume ("v/v"), and preferably 10 to 30% (v/v). Each of the colloidal particles may have a size ranging from 100 to 100,000nm, preferably 150 to 3,000nm. In case of a UV curable polymer, the polymer is preferably at least one or two or more selected from photocurable polymers having acrylate groups, however, is not particularly limited thereto so long as it may be cured by UV rays.
The frame used in step (a) may be any structure having surfaces with characteristic length in a range of several micrometers to several millimeters, and typically comprise any one selected from liquid droplets having a high contact angle, a space between two flat plates, a microfine tube, a film having pyramid type pits, a structure having a linear channel and the like.
UV irradiation in step (b) is often performed at a light intensity of about 40mW/cm for 1 to 10 seconds, however, light intensity and/or UV irradiation time is not particularly restricted thereto if a combination of the light intensity and the UV irradiation time is sufficient to complete photo-curing of monomers.
Removal of colloid particles in step (c) is mostly performed by a wet etching process and the present invention may use fluoric acid to remove silica particles. However, according to the present invention, the colloidal particles may be selectively removed by any commonly known method without particular limitation thereof.
The photonic crystal fabricated according to the present invention forms a hexagonal close-packed face having the highest planar density of a face-centered cubic structure along a surface of the frame, therefore, exhibits reflected light always having the same wavelength to light incident normally on any surface of the frame. Adjusting a size and/or volume fraction of the colloidal particles may control a reflective wavelength of the colloidal particles to a desired range.
As to fabrication of the porous photonic crystals by removing colloidal particles from the formed colloidal photonic crystals, the reflective wavelength moves to a range of shorter wavelengths while the crystal shows higher reflectivity, because of a decrease in effective refractive index and an increase in refractive index contrast. The fabricated porous photonic crystals are noticeably useful for various applications requiring high reflectivity.
Hereinafter, the present invention will be apparent from the following detailed description with reference to the accompanying drawings.
The present invention proposes a method for fabrication of colloidal and/or porous photonic crystals with various shapes without an alternative evaporation process, compared to existing methods in the art.
According to any conventional process, a solvent was very slowly removed so as to produce colloidal crystals in a dry state. However, this process demands a long processing time and a very complicated process, which in turn, leads to unfavorable conditions for industrial mass production of colloidal crystals. In addition, the dried colloidal crystal has a considerably weak structure and is substantially impossible to be used in practical applications.
On the other hand, the method for fabrication of photonic crystals according to the present invention does not employ an evaporation process but make a high concentration of particles align themselves in a photocurable monomer solution, followed by UV irradiation for several seconds to cure the aligned particles. As a result, a fabrication time is decreased while simplifying processes for the fabrication of photonic crystals. Also the fabricated crystals have a considerably increased mechanical strength. As for the colloidal photonic crystals fabricated by the above method, a range of reflective wavelengths may be expected by the following equation 1 :
(Equation 1)
1/3 £ 1/2 λ=2ΛV=( ^|7) ( y) IKnfa+nlV-vJΫ12
Wherein n is refractive index of a substance, v is volume fraction of colloidal particles and D is diameter of a colloidal particle.
As to the method for fabrication of hemispherical photonic crystals according to the present invention, a mechanically driven dispenser apparatus is used. Introducing a colloidal suspension into an injector then fitting the injector to the apparatus, a dispenser of the apparatus may apply the suspension in the form of liquid droplets and in an accurately controlled amount to a substrate. In case of the substrate having a lipophilic surface, each of the liquid droplets has a high contact angle to the substrate, so as to form a hemispherical drop. Since colloidal particles are aligned along a surface of the liquid droplet, photo-curing of the colloidal particles may produce hemispherical colloidal crystals irradiating the same reflected wavelength regardless of position on the surface of the liquid droplet. Meanwhile, when using colloidal suspensions irradiating reflected light with different colors in patterning of photonic crystals without coalescence between adjacent colloidal suspension droplets, mono-colored hemispherical photonic crystals can produce a multi-color pattern. On the other hand, with coalescence of the colloidal suspension droplets, a pattern having multiple colors on each part of the hemispherical photonic crystals can be attained.
Additionally, other photonic crystals in any form of film shapes, cylinder forms, linear patterns, pyramid forms, etc. may be fabricated by introducing a colloidal suspension into a frame through capillary force and photo-polymerizing the same. For a film type photonic crystal, interposing a spacer between two glass plates may fabricate a frame. For a cylindrical photonic crystal, a glass or plastic tube may be used. Also, a linear pattern frame may be fabricated by soft lithography (as a well known process that introduces a polymer material such as a polydimethylsiloxane (PDMS) to a linear pattern of photosensitive polymer obtained through photolithography and releases the applied polymer material to form a pattern). Lastly, a pyramid form frame may be fabricated by anisotropic etching of a silicon wafer.
The monomer solution used in the present invention may be ethoxylated trimethylolpropane triacrylate monomer ETPTA (MW 428, viscosity 60 cps, SR 454) which is curable by UV. However, the monomer solution is not particularly restricted thereto if it is selected from materials cured when exposed to UV and, at the same, spontaneously forms crystals when colloidal particles are dispersed in the monomer solution.
The colloidal particle used in the present invention may be a silica particle produced using a so-called Stober-Fink-Bohn method, however, the colloidal particle is not particularly restricted thereto.
According to the present invention, porous photonic crystals may also be fabricated using the same system as for the colloidal photonic crystals having different shapes. More particularly, these porous photonic crystals may be fabricated by selectively removing silica particles from the formed colloidal photonic crystals that consist of particles and cured ETPTA.
Herein, the silica particles are substantially removed using a specific material such as a sodium hydroxide solution or fluoric acid and the remaining ETPTA in a cured form may continuously maintain the structure of the crystal.
Exemplary embodiments of the present invention will be described in more detail in relation to specific examples, which are only given for the purpose of illustration and are not to be construed as limiting the scope of the invention. EXAMPLE 1 : Formation of multi-color pattern of mono-colored hemispherical photonic crystals
Silica particles having uniform sizes of 195nm, 150nm and 145nm prepared using the Stober-Fink-Bohn method were dispersed in ETPTA in volume ratios of 1 :2, 1:3 and 1:2, respectively. According to a procedure illustrated by route 1 in Fig. 1, mono-colored hemispherical liquid droplets having red, green and blue colors, respectively, were used in patterning. Using a mechanical dispenser apparatus, the liquid droplets were patterned on a Teflon coated glass plate at a contact angle of 80°. The glass plate was a substrate coated with lipophilic material such as Teflon and/or made of the same material, which is preferable for patterning. However, the substrate is not particularly restricted to Teflon coated plates but includes any substrate having a contact angle of at least 40°. For instance, treatment of a self-assembled monolayer (SAM) on a glass plate or a wafer may induce a high contact angle, which is useable in patterning according to the present invention.
Herein, a distance between two hemispheres having the same color was maintained at lmm, while controlling each of the hemispheres to have a diameter of 293μm corresponding to a volume of 5 nanoliters. The prepared liquid droplets were exposed to UV irradiation at a light intensity of 40mW/cm2 for 10 seconds using a mercury arc lamp, thus curing the hemispherical liquid crystals.
Fig. 2 is photographs showing a pattern of the mono-colored hemispherical photonic crystals with red, green and blue colors. Especially, Fig. 2A is a photograph at a low magnification while Fig. 2B is another photograph at a high magnification.
Fig. 3 is optical microscope photographs showing the mono-colored hemispherical photonic crystals with red, green and blue colors, respectively, and reflectance spectra thereof.
In order to determine optical isotropy of a mono-colored hemispherical photonic crystal having no variation in reflected waves along a surface of the crystal, optical microscope photographs were taken at different light incident angles and reflectance spectra of the crystal were measured.
Fig. 4 is optical microscope photographs showing the same reflected color of a mono-colored hemispherical photonic crystal at different light incident angles and reflectance spectra thereof at the light incident angles.
In order to produce a pattern with high density, a diameter of a liquid droplet increased to 375μm corresponding to a volume of 10 nanoliters of the droplet while maintaining a distance between two hemispheres at lmm. As a result, the density of the pattern increased from 20% to 33%.
Fig. 5 is a photograph showing a three-color pattern of the mono-colored hemispherical photonic crystals having increased density.
EXAMPLE 2 : Formation of multi-color pattern of mono-colored hemispherical photonic crystals on soft polymer film
Patterning of liquid droplets was performed by the same procedure described in Example 1, except that a soft substrate made of PDMS polymer film having a thickness of 3mm was used. The substrate had a contact angle of 50° and the liquid droplets were cured by the same method as described in Example 1. The formed pattern was immersed in a 5wt% fluoric acid solution for 5 minutes to selectively remove silica particles, resulting in porous hemispherical photonic crystals. The produced photonic crystals had shorter reflective wavelength caused by a decrease in effective refractive index and exhibited brighter colors owing to an increase in refractive index contrast, compared to before the silica particles were removed.
Fig. 6A is a photograph showing a three-color pattern of mono-colored porous hemispherical photonic crystals formed on a soft polymer film, while Fig. 6B is a scanning electron microscope photograph showing an inner part of a hemispherical photonic crystal. Figs. 6C, 6D and 6E are optical microscope photographs showing porous hemispherical photonic crystals obtained after removing colloidal particles from the mono-colored hemispherical colloidal photonic crystals with blue, green and red colors, respectively. EXAMPLE 3 : Formation of pattern of multi-colored hemispherical photonic crystals
Spherical photonic crystals were prepared by the same procedure described in Example 1, except that a position of dropping liquid droplets was adjusted to induce coalescence with existing liquid droplets during second and/or third patterning of the liquid droplets, which corresponds to route 2 illustrated in Fig. 1. As a result, multicolored hemispherical photonic crystals were obtained, each of the hemispherical photonic crystals of which showed a plurality of reflected colors.
Fig. 7A is a photograph showing a pattern of multi-colored hemispherical photonic crystals with a combination of red and blue colors while Fig. 7B is an optical microscope photograph showing one of the multi-colored hemispherical photonic crystals. This crystal had a diameter of 375//m (corresponding to a volume of 10 nanoliters) and was prepared by combining 5 nanoliters of red colloidal suspension and 5 nanoliters of blue colloidal suspension.
Fig. 7C is a photograph showing a pattern of multi-colored hemispherical photonic crystals with a combination of red, green and blue colors while Fig. 7D is an optical microscope photograph showing one of the multi-colored hemispherical photonic crystals. This crystal had a diameter of 510μm (corresponding to a volume of 25 nanoliters) and was prepared by combining 10 nanoliters of red colloidal suspension, 10 nanoliters of green colloidal suspension and 5 nanoliters of blue colloidal suspension. EXAMPLE 4 : Fabrication of photonic crystal film
A spacer having a thickness of 50μm was inserted between two glass plates to ensure an inner space, followed by filling the space with a suspension containing 195nm silica particles in ETPTA with volume ratio of 1 :2 through capillary force. Next, the suspension was photo-cured according to the same procedure as described in Example 1 and a cured colloid photonic crystal film was separated from both the glass plates. The prepared film showed a reflectivity of about 30%. The film was immersed in a 5wt.% fluoric acid solution for 12 hours to remove silica particles from the film, thus obtaining a porous photonic crystal film. Compared to colloidal photonic crystals, this film exhibited reflectance peak at shorter wavelength, had high reflectivity of about 70% and a considerable increase in widths of reflectance peak. It was believed that these resulted from a decrease in effective refractive index and an increase in refractive index contrast because of silica particle removal.
Fig. 8A is optical microscope photographs showing a colloidal photonic crystal film and a porous photonic crystal film, as well as reflectance spectra thereof. Figs. 8B and 8C are scanning electron microscope photographs showing cross sections of the colloidal photonic crystal film and the porous photonic crystal film, respectively. EXAMPLE 5 : Formation of photonic crystal linear pattern
The colloidal suspension used in Example 4 was introduced into a linear pattern frame made of PDMS polymer by soft lithography, through capillary force. The linear pattern had a width of 25μm and a depth of 30//m. After the linear pattern was attached to a glass plate, the colloidal suspension was introduced thereto so as to form the linear pattern frame. Next, the suspension filled in the frame was photo-cured according to the same procedure described in Example 1 and a cured linear pattern having red color was released from the frame. Removing silica particles according to the same procedure as described in Example 4 resulted in a linear pattern having green color.
Figs. 9A and 9B are optical microscope photographs showing a colloidal photonic crystal linear pattern and a porous photonic crystal linear pattern, while Figs. 9C and 9D are scanning electron microscope photographs showing cross sections of the colloidal photonic crystal linear pattern and the porous photonic crystal linear pattern, respectively. EXAMPLE 6 : Formation of pyramid-shaped photonic crystal pattern
The colloidal suspension used in Example 4 was introduced into a pyramid- shaped frame made of PDMS polymer, followed by photo-curing the same to prepare a pyramid-shaped photonic crystal pattern. The pyramid-shaped frame made of PDMS polymer was prepared by double transfer molding of pyramid pattern formed by anisotropic wet etching of silicon.
Figs. 1OA and 1OB are optical microscope photographs showing a lateral side and a front side of a red pyramid pattern, while Figs. 1OC and 1OD are scanning electron microscope photographs at low and high magnifications showing a surface near a peak of the pyramid form, respectively. EXAMPLE 7 : Fabrication of cylindrical photonic crystals
Blue, green and red color colloidal suspensions used in Example 1 were fed into a glass tube having an inner diameter of 1.1mm in this order, followed by photo- curing the same. A cured cylindrical photonic crystal having three colors therein was released from the glass tube.
Fig. HA is a photograph showing a cylindrical photonic crystal having three colors, Fig. HB is a scanning electron microscope photograph showing a cross section of the cylindrical photonic crystal, while Figs. HC, HD and HE are optical microscope photographs showing red, green and blue colored parts of the cylindrical photonic crystal, respectively. [INDUSTRIAL APPLICABILITY]
As is apparent from the description disclosed above, the method for fabrication of photonic crystals according to the present invention can very rapidly form photonic crystals using a UV curable colloidal suspension without alternative evaporation processes, therefore, has an advantage in that a wide range of photonic crystals with various shapes can be produced. Especially, the inventive method is remarkably useful for patterning of photonic crystals, thus being preferably applied in manufacturing pixels of reflection type displays. In addition, a film type photonic crystal having excellent reflection and high crystallinity may vary photoluminescence spectra of fluorescent molecules or quantum dots, thereby being utilized in lasing.
Although the present invention has been described in connection with the exemplary embodiments illustrated in the drawings, it is only illustrative. It will be understood by those skilled in the art that various modifications and equivalents can be made to the present invention. Therefore, the true technical scope of the present invention should be defined by the appended claims.

Claims

[CLAIMS] [Claim 1 ]
A method of fabricating hemispherical photonic crystals comprising: dispersing colloidal particles in a UV curable polymer solution to form hemispherical colloidal suspension droplets on a substrate; and
UV irradiating the colloidal suspension droplets to cure the same. [Claim 2]
The method according to claim 1, wherein the substrate is a substrate coated with a lipophilic material such as Teflon or made of the lipophilic material. [Claim 3]
The method according to claim 1 , wherein the substrate is a soft polymer film substrate having flexible properties. [Claim 4]
The method according to claim 1 , further comprising patterning of colloidal or porous mono-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals without coalescence of the colloidal suspension droplets. [Claim 5]
The method according to claim 1 , further comprising patterning of colloidal or porous multi-colored hemispherical photonic crystals to produce a pattern having multiple colors on the photonic crystals through coalescence of the colloidal suspension droplets. [Claim 6]
The method according to claim 1, wherein a mechanical injection using a dispenser or an ink-jet printing method is adapted to perform patterning of the colloidal suspension droplets. [Claim 7]
The method according to claim 1, further comprising selectively removing the colloidal particles from the fabricated colloidal hemispherical photonic crystals to obtain the porous hemispherical photonic crystals. [Claim 8]
The method according to claim 1 , wherein each of the colloidal hemispherical photonic crystals has a size of several micrometers to several millimeters while a contact angle of the photonic crystal to the substrate ranges from 20 to 160°. [Claim 9]
A method of fabricating colloidal and/or porous photonic crystals comprising: dispersing colloidal particles in a UV curable polymer solution and introducing the dispersed solution into a frame; and
UV irradiating the dispersed solution in the frame to cure the same. [Claim 10]
The method according to claim 9, wherein the photonic crystals are formed in a film shape by using a space defined between two plates is used as the frame. [Claim 11 ]
The method according to claim 9, wherein the photonic crystals are formed in a cylindrical shape by using a microfine tube as the frame. [Claim 12]
The method according to claim 9, wherein the frame is a polymer linear patterned frame. [Claim 13]
The method according to claim 9, wherein the frame is a pyramid-shaped frame. [Claim 14]
The method according to claim 9, further comprising selectively removing colloidal particles from the fabricated colloidal photonic crystals. [Claim 15]
The method according to claim 9, wherein the colloids are photocurable monomer solution containing colloidal particles in an amount of 5 to 50% by volume (v/v). [Claim 16]
The method according to claim 15, wherein the colloidal particles have a size of 150 to 100,000 nm.
PCT/KR2008/004940 2008-04-14 2008-08-25 Method for patterning of hemispherical photonic crystallines and fabrication of photonic crystals with various shapes using photocurable colloidal suspensions WO2009128591A1 (en)

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