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Fabrication and properties of inverse opal photonic crystal films of La-doped bismuth titanate
ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470 www.elsevier.com/locate/jpcs
Fabrication and properties of inverse opal photonic crystal films of La-doped bismuth titanate Jong Kuk Kim, Chun Mao, Jinheung Kim Department of Chemistry, Division of Nano Sciences, Ewha Womans University, Seoul 120-750, Republic of Korea
Abstract Colloidal crystal-templating methods have been used to prepare inverse opal photonic crystal films of La-doped bismuth titanate, Bi3.25La0.75Ti3O12 (BLT). Ordered arrays of uniformly sized polymer spheres were deposited on glass substrates by a unidirectional deposition method. By carefully controlling the synthetic procedures, macroporous films exhibiting photonic crystal properties were obtained. Bragg diffractions from the planes produced photonic stop bands in the visible spectra of these films. r 2007 Published by Elsevier Ltd.
1. Introduction Macroporous materials with regular periodicity comparable to the wavelength of electromagnetic waves have received intense attention as they enable the manipulation of light transmission by localizing light and controlling spontaneous emission [1–5]. Such ordered macroporous materials are also attractive in many areas including catalysis, thermal and acoustic insulators, chemical sensors, and supports for catalysts [6–8]. The self-assembled template replication process named inverse opal (IO) has proven to be a promising approach for the fabrication of three-dimensionally (3-D), highly ordered macroporous materials, which are composed of air spheres and dielectric materials [9–13]. For preparing IO materials from silica or polymer sphere templates, monodisperse colloids are formed as high-quality colloidal crystal films with a controllable thickness and then the voids of colloidal crystal were infiltrated with metal oxide materials. Ferroelectric bismuth titanate (BIT) has attracted much attention for optical memory and electro-optic devices due to their high dielectric constants, excellent ferroelectricity, and electro-optic properties [14,15]. BIT films, by substituting other heavy metal ions for Bi sites, have been very attractive for their large ferroelctricity and good fatigue resistance [16,17]. Recently, we also reported the Corresponding author. Tel.: 82 2 3277 4453; fax: +82 2 3277 3419.
E-mail address: [email protected] (J. Kim). 0022-3697/$ - see front matter r 2007 Published by Elsevier Ltd. doi:10.1016/j.jpcs.2007.09.021
preparation and ferroelectric properties of La-, Nb-, and Nd-doped BIT thin films [18–20]. However, a few metal oxide materials such as La0.7Ca0.3MnO3, LiNbO3, and (Pb,Lz)(Zr,Ti)O3 have been used to fabricate macroporous materials [21–23]. In this report, we prepared 3-D macroporous thin films of Bi3.25La0.75Ti3O12 (BLT) by a convective assembly device. IO photonic films, prepared by our fabrication method, exhibit Bragg diffractions from the planesproduced-photonic stop bands in the visible region. 2. Materials and methods Well-ordered thin colloidal templates were fabricated by a unidirectional deposition method using nearly monodisperse polystyrene (PS) spheres (360 nm, 2%, v/v0). In the setup shown in Fig. 1a, the top slide was attached to an electric motor at an angle of ca. 301 relative to the lower slide and moved horizontally at different speeds, varying from 0.1 to 2 mm/s. As the top slide was translated by the electric motor, the meniscus was dragged along the bottom and a thin film of latex particles was deposited. For the fabrication of IO-BLT films, the precursor solution of Bi3.25La0.75Ti4O12 (0.5 M) was infiltrated into PS thin films by a directional wetting method at a speed of 1000 mm/s to achieve complete and even soaking without separation of colloidal spheres (Fig. 1b). After the film was dried for 2 h at 20 1C, the PS colloids were removed by increasing samples at a rate of 1–450 1C/min.
ARTICLE IN PRESS J.K. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470
1469
Electric motor Electric motor
Evaporation
Evaporation BLT solution
PS sphere
Substrate
Substrate
Fig. 1. Schematic of the coating apparatus: (a) thin PS layers were deposited by dragging a PS suspension droplet between two plates. (b) The meniscus of a BLT solution to soak the well-ordered PS film was dragged by an electric motor.
Fig. 2. SEM images of dried PS sphere colloidal crystal films: (a, c) top-down views of PS colloidal crystals; (b) cross section of the film.
3. Results and discussion 0° 5° 10° 15°
Transmittance (%)
Our goal to find conditions leading to uniform crystalline layers of PS was achieved by controlling the deposition speed of latex suspensions. SEM images of representative samples of macroporous thin colloidal films are presented in Fig. 2. Fig. 2a and b shows images of the top surface and cross section of the film, suggesting that the opaline lattice of the film exhibits a cubic-close-packed structure. Decreasing the deposition speed resulted in thicker coating, as reported in the deposition of the films of PS and silica beads [24,25]. The film composed of 10 layers of PS beads was obtained at dragging speed of 0.2 mm/s. A low magnification image shows that the uniform surface of the film can extend to a very large region with some cracks (Fig. 2c). This morphology is similar to that observed in the films of PS spheres and silica nanoparticles fabricated by a similar method [24,25] and the PS opal films by other methods [26,27]. The opaline lattice of PS films exhibits stop bands (Fig. 3). The stop band position (l) was gradually shifted with increasing detection angle, as a result of optical diffractions from the crystal lattice planes. The voids among PS beads in films have been completely filled with the BLT solution. SEM images of IO-BLT films obtained after gelation and calcinations are shown in Fig. 4. The lighter regions in the images represent the solid BLT framework, and the darker circles represent the air spheres that were previously occupied by PS beads. The shrinkage observed from the diameter of the original polymer sphere templates to the spacing between the pores was about 20%. Contact points between neighboring PS beads appear as windows between the macropores. Similar
400
20°
500
600
700 800 Wavelength (nm)
900
1000
1100
Fig. 3. UV–vis transmission spectra of PS films formed with 360 nm PS spheres.
openings have also been observed for other metal oxides of IO materials. The absence of these features, reported in other macroporous materials of metal oxides, suggests that a filling in templates occurred in which the precursor solution completely filled the volume between the spheres [11,28]. Fig. 5 shows the transmission spectrum of the IO photonic crystal of BLT. Diffraction resonance from a stack of a (1 1 1) plane of the BLT layers gave an optical reflection at 510 nm. The spectral position of the stop band of IO-BLT crystal could be calculated in a predictable manner [29].
ARTICLE IN PRESS J.K. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470
1470
Fig. 4. SEM images of macroporous BLT films prepared with 360 nm diameter PS spheres: (a) top-down view of pores; (b) cross section of the film.
60
Transmittance (%)
50
40
30
20
10
0 300
400
500
600
700
800
900
Wavelength (nm)
Fig. 5. UV–vis transmission spectrum of a photonic crystal film of BLT.
In summary, using a template prepared by assembling close-packed arrays of PS beads, highly ordered macroporous thin films of BLT were deposited by synthetic methods of a unidirectional deposition procedure. The spectral position of the optical stop band of macroporous BLT films was found to be in agreement with theoretical predictions based on Bragg diffraction, and confirmed that the pores were arranged in a fcc structure. The periodicity introduced into the wall structure by the colloidal crystal templates was in the order of optical wavelengths. Acknowledgments This work was supported by Seoul R&BD program (2006–2007) and Ministry of Environment, Republic of Korea (Grant no. 022-061-023). References [1] P. Ni, B. Cheng, D. Zhang, Appl. Phys. Lett. 80 (2002) 1879.
[2] A. Richel, N.P. Johnson, D.W. McComb, Appl. Phys. Lett. 76 (2000) 1816. [3] J.E.G. Wijnhoven, L. Bechger, W.L. Vos, Chem. Mater. 13 (2001) 4486. [4] G. Subramanian, V.N. Manoharan, J.D. Thorne, D.J. Pine, Adv. Mater. 11 (1999) 1261. [5] B.G. Kim, K.S. Parikh, G. Ussery, A. Zakhidov, R.H. Baughman, E. Yablonobitch, B.S. Dunn, Appl. Phys. Lett. 81 (2002) 4440. [6] C. Lopez, Adv. Mater. 15 (2003) 1679. [7] Y. Yin, Y. Lu, B. Gates, Y. Xia, Chem. Mater. 13 (2001) 1146. [8] L. Xu, L.D. Tung, L. Spinu, A.A. Zakhidov, R.H. Baughman, J.B. Wiley, Adv. Mater. 15 (2003) 1562. [9] P.N. Bartlett, J.J. Baumberg, P.R. Birkin, M.A. Ghanem, M.C. Netti, Chem. Mater. 14 (2002) 2199. [10] P. Ni, P. Dong, B. Cheng, X. Li, D. Zhang, Adv. Mater. 13 (2001) 437. [11] Z. Zhong, Y. Yin, B. Gates, Y. Xia, Adv. Mater. 12 (2000) 206. [12] M.E. Turner, T.J. Trentler, V.L. Colvin, Adv. Mater. 13 (2001) 180. [13] J.F. Bertone, P. Jiang, K.S. Hwang, D.M. Mittleman, V.L. Colvin, Phys. Rev. Lett. 83 (1999) 300. [14] Z. Hu, G. Wang, Z. Huang, J. Chu, J. Appl. Phys. 93 (2003) 3811. [15] M. Yamaguchi, T. Nagamoto, O. Omoto, Thin Solid Films 300 (1997) 299. [16] U. Chon, H.M. Jang, M.G. Kim, C.H. Chang, Phys. Rev. Lett. 89 (2002) 601. [17] B.H. Park, B.S. Kang, S.D. Bu, T.W. Noh, J. Lee, W. Jo, Nature 401 (1999) 682. [18] J.K. Kim, S.S. Kim, J. Kim, J. Mater. Res. 18 (2003) 1884–1888. [19] J.K. Kim, J. Kim, T.K. Song, S.S. Kim, Thin Solid Films 419 (2002) 225–229. [20] J. Kim, J.K. Kim, S. Heo, H.S. Lee, Thin Solid Films 503 (2006) 60–63. [21] E.O. Chi, Y.N. Kim, J.C. Kim, N.H. Hur, Chem. Mater. 15 (2003) 1929. [22] D. Wang, F. Caruso, Adv. Mater. 15 (2003) 205. [23] B. Li, J. Zhou, L. Hao, W. Hu, R. Zong, M. Cai, M. Fu, Z. Gui, L. Li, Q. Li, Appl. Phys. Lett. 82 (2003) 3617. [24] N.H. Finkel, B.G. Prevo, O.D. Velev, L. He, Anal. Chem. 77 (2005) 1088–1095. [25] B.G. Prevo, O.D. Velev, Langmuir 20 (2004) 2099–2107. [26] Z.-Z. Gu, A. Fujishima, O. Sato, Chem. Mater. 14 (2002) 760. [27] P. Jiang, J.F. Bertone, K.S. Hwang, V.L. Colvin, Chem. Mater. 11 (1999) 2131. [28] R.C. Schroden, M. Al-Daous, C.F. Blanford, A. Stein, Chem. Mater. 14 (2002) 3305. [29] Calculation based on l ¼ 2dhkl/m[jns+(1j)nv], where m is the order of Bragg diffraction, j is the volume fraction of BLT materials, ns is the refractive index of BLT materials (nBLT ¼ 2.51) [14], and nv is the refractive index of the void space.
Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470 www.elsevier.com/locate/jpcs
Fabrication and properties of inverse opal photonic crystal films of La-doped bismuth titanate Jong Kuk Kim, Chun Mao, Jinheung Kim Department of Chemistry, Division of Nano Sciences, Ewha Womans University, Seoul 120-750, Republic of Korea
Abstract Colloidal crystal-templating methods have been used to prepare inverse opal photonic crystal films of La-doped bismuth titanate, Bi3.25La0.75Ti3O12 (BLT). Ordered arrays of uniformly sized polymer spheres were deposited on glass substrates by a unidirectional deposition method. By carefully controlling the synthetic procedures, macroporous films exhibiting photonic crystal properties were obtained. Bragg diffractions from the planes produced photonic stop bands in the visible spectra of these films. r 2007 Published by Elsevier Ltd.
1. Introduction Macroporous materials with regular periodicity comparable to the wavelength of electromagnetic waves have received intense attention as they enable the manipulation of light transmission by localizing light and controlling spontaneous emission [1–5]. Such ordered macroporous materials are also attractive in many areas including catalysis, thermal and acoustic insulators, chemical sensors, and supports for catalysts [6–8]. The self-assembled template replication process named inverse opal (IO) has proven to be a promising approach for the fabrication of three-dimensionally (3-D), highly ordered macroporous materials, which are composed of air spheres and dielectric materials [9–13]. For preparing IO materials from silica or polymer sphere templates, monodisperse colloids are formed as high-quality colloidal crystal films with a controllable thickness and then the voids of colloidal crystal were infiltrated with metal oxide materials. Ferroelectric bismuth titanate (BIT) has attracted much attention for optical memory and electro-optic devices due to their high dielectric constants, excellent ferroelectricity, and electro-optic properties [14,15]. BIT films, by substituting other heavy metal ions for Bi sites, have been very attractive for their large ferroelctricity and good fatigue resistance [16,17]. Recently, we also reported the Corresponding author. Tel.: 82 2 3277 4453; fax: +82 2 3277 3419.
E-mail address: [email protected] (J. Kim). 0022-3697/$ - see front matter r 2007 Published by Elsevier Ltd. doi:10.1016/j.jpcs.2007.09.021
preparation and ferroelectric properties of La-, Nb-, and Nd-doped BIT thin films [18–20]. However, a few metal oxide materials such as La0.7Ca0.3MnO3, LiNbO3, and (Pb,Lz)(Zr,Ti)O3 have been used to fabricate macroporous materials [21–23]. In this report, we prepared 3-D macroporous thin films of Bi3.25La0.75Ti3O12 (BLT) by a convective assembly device. IO photonic films, prepared by our fabrication method, exhibit Bragg diffractions from the planesproduced-photonic stop bands in the visible region. 2. Materials and methods Well-ordered thin colloidal templates were fabricated by a unidirectional deposition method using nearly monodisperse polystyrene (PS) spheres (360 nm, 2%, v/v0). In the setup shown in Fig. 1a, the top slide was attached to an electric motor at an angle of ca. 301 relative to the lower slide and moved horizontally at different speeds, varying from 0.1 to 2 mm/s. As the top slide was translated by the electric motor, the meniscus was dragged along the bottom and a thin film of latex particles was deposited. For the fabrication of IO-BLT films, the precursor solution of Bi3.25La0.75Ti4O12 (0.5 M) was infiltrated into PS thin films by a directional wetting method at a speed of 1000 mm/s to achieve complete and even soaking without separation of colloidal spheres (Fig. 1b). After the film was dried for 2 h at 20 1C, the PS colloids were removed by increasing samples at a rate of 1–450 1C/min.
ARTICLE IN PRESS J.K. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470
1469
Electric motor Electric motor
Evaporation
Evaporation BLT solution
PS sphere
Substrate
Substrate
Fig. 1. Schematic of the coating apparatus: (a) thin PS layers were deposited by dragging a PS suspension droplet between two plates. (b) The meniscus of a BLT solution to soak the well-ordered PS film was dragged by an electric motor.
Fig. 2. SEM images of dried PS sphere colloidal crystal films: (a, c) top-down views of PS colloidal crystals; (b) cross section of the film.
3. Results and discussion 0° 5° 10° 15°
Transmittance (%)
Our goal to find conditions leading to uniform crystalline layers of PS was achieved by controlling the deposition speed of latex suspensions. SEM images of representative samples of macroporous thin colloidal films are presented in Fig. 2. Fig. 2a and b shows images of the top surface and cross section of the film, suggesting that the opaline lattice of the film exhibits a cubic-close-packed structure. Decreasing the deposition speed resulted in thicker coating, as reported in the deposition of the films of PS and silica beads [24,25]. The film composed of 10 layers of PS beads was obtained at dragging speed of 0.2 mm/s. A low magnification image shows that the uniform surface of the film can extend to a very large region with some cracks (Fig. 2c). This morphology is similar to that observed in the films of PS spheres and silica nanoparticles fabricated by a similar method [24,25] and the PS opal films by other methods [26,27]. The opaline lattice of PS films exhibits stop bands (Fig. 3). The stop band position (l) was gradually shifted with increasing detection angle, as a result of optical diffractions from the crystal lattice planes. The voids among PS beads in films have been completely filled with the BLT solution. SEM images of IO-BLT films obtained after gelation and calcinations are shown in Fig. 4. The lighter regions in the images represent the solid BLT framework, and the darker circles represent the air spheres that were previously occupied by PS beads. The shrinkage observed from the diameter of the original polymer sphere templates to the spacing between the pores was about 20%. Contact points between neighboring PS beads appear as windows between the macropores. Similar
400
20°
500
600
700 800 Wavelength (nm)
900
1000
1100
Fig. 3. UV–vis transmission spectra of PS films formed with 360 nm PS spheres.
openings have also been observed for other metal oxides of IO materials. The absence of these features, reported in other macroporous materials of metal oxides, suggests that a filling in templates occurred in which the precursor solution completely filled the volume between the spheres [11,28]. Fig. 5 shows the transmission spectrum of the IO photonic crystal of BLT. Diffraction resonance from a stack of a (1 1 1) plane of the BLT layers gave an optical reflection at 510 nm. The spectral position of the stop band of IO-BLT crystal could be calculated in a predictable manner [29].
ARTICLE IN PRESS J.K. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1468–1470
1470
Fig. 4. SEM images of macroporous BLT films prepared with 360 nm diameter PS spheres: (a) top-down view of pores; (b) cross section of the film.
60
Transmittance (%)
50
40
30
20
10
0 300
400
500
600
700
800
900
Wavelength (nm)
Fig. 5. UV–vis transmission spectrum of a photonic crystal film of BLT.
In summary, using a template prepared by assembling close-packed arrays of PS beads, highly ordered macroporous thin films of BLT were deposited by synthetic methods of a unidirectional deposition procedure. The spectral position of the optical stop band of macroporous BLT films was found to be in agreement with theoretical predictions based on Bragg diffraction, and confirmed that the pores were arranged in a fcc structure. The periodicity introduced into the wall structure by the colloidal crystal templates was in the order of optical wavelengths. Acknowledgments This work was supported by Seoul R&BD program (2006–2007) and Ministry of Environment, Republic of Korea (Grant no. 022-061-023). References [1] P. Ni, B. Cheng, D. Zhang, Appl. Phys. Lett. 80 (2002) 1879.
[2] A. Richel, N.P. Johnson, D.W. McComb, Appl. Phys. Lett. 76 (2000) 1816. [3] J.E.G. Wijnhoven, L. Bechger, W.L. Vos, Chem. Mater. 13 (2001) 4486. [4] G. Subramanian, V.N. Manoharan, J.D. Thorne, D.J. Pine, Adv. Mater. 11 (1999) 1261. [5] B.G. Kim, K.S. Parikh, G. Ussery, A. Zakhidov, R.H. Baughman, E. Yablonobitch, B.S. Dunn, Appl. Phys. Lett. 81 (2002) 4440. [6] C. Lopez, Adv. Mater. 15 (2003) 1679. [7] Y. Yin, Y. Lu, B. Gates, Y. Xia, Chem. Mater. 13 (2001) 1146. [8] L. Xu, L.D. Tung, L. Spinu, A.A. Zakhidov, R.H. Baughman, J.B. Wiley, Adv. Mater. 15 (2003) 1562. [9] P.N. Bartlett, J.J. Baumberg, P.R. Birkin, M.A. Ghanem, M.C. Netti, Chem. Mater. 14 (2002) 2199. [10] P. Ni, P. Dong, B. Cheng, X. Li, D. Zhang, Adv. Mater. 13 (2001) 437. [11] Z. Zhong, Y. Yin, B. Gates, Y. Xia, Adv. Mater. 12 (2000) 206. [12] M.E. Turner, T.J. Trentler, V.L. Colvin, Adv. Mater. 13 (2001) 180. [13] J.F. Bertone, P. Jiang, K.S. Hwang, D.M. Mittleman, V.L. Colvin, Phys. Rev. Lett. 83 (1999) 300. [14] Z. Hu, G. Wang, Z. Huang, J. Chu, J. Appl. Phys. 93 (2003) 3811. [15] M. Yamaguchi, T. Nagamoto, O. Omoto, Thin Solid Films 300 (1997) 299. [16] U. Chon, H.M. Jang, M.G. Kim, C.H. Chang, Phys. Rev. Lett. 89 (2002) 601. [17] B.H. Park, B.S. Kang, S.D. Bu, T.W. Noh, J. Lee, W. Jo, Nature 401 (1999) 682. [18] J.K. Kim, S.S. Kim, J. Kim, J. Mater. Res. 18 (2003) 1884–1888. [19] J.K. Kim, J. Kim, T.K. Song, S.S. Kim, Thin Solid Films 419 (2002) 225–229. [20] J. Kim, J.K. Kim, S. Heo, H.S. Lee, Thin Solid Films 503 (2006) 60–63. [21] E.O. Chi, Y.N. Kim, J.C. Kim, N.H. Hur, Chem. Mater. 15 (2003) 1929. [22] D. Wang, F. Caruso, Adv. Mater. 15 (2003) 205. [23] B. Li, J. Zhou, L. Hao, W. Hu, R. Zong, M. Cai, M. Fu, Z. Gui, L. Li, Q. Li, Appl. Phys. Lett. 82 (2003) 3617. [24] N.H. Finkel, B.G. Prevo, O.D. Velev, L. He, Anal. Chem. 77 (2005) 1088–1095. [25] B.G. Prevo, O.D. Velev, Langmuir 20 (2004) 2099–2107. [26] Z.-Z. Gu, A. Fujishima, O. Sato, Chem. Mater. 14 (2002) 760. [27] P. Jiang, J.F. Bertone, K.S. Hwang, V.L. Colvin, Chem. Mater. 11 (1999) 2131. [28] R.C. Schroden, M. Al-Daous, C.F. Blanford, A. Stein, Chem. Mater. 14 (2002) 3305. [29] Calculation based on l ¼ 2dhkl/m[jns+(1j)nv], where m is the order of Bragg diffraction, j is the volume fraction of BLT materials, ns is the refractive index of BLT materials (nBLT ¼ 2.51) [14], and nv is the refractive index of the void space.