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2TiO3 inverse opal photonic crystals
Journal of Alloys and Compounds 471 (2009) 241–243
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Preparation and photonic bandgap properties of Na1/2 Bi1/2 TiO3 inverse opal photonic crystals Zhengwen Yang, Ji Zhou ∗ , Xueguang Huang, Qin Xie, Ming Fu, Bo Li, Longtu Li State Key Lab of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China
a r t i c l e
i n f o
Article history: Received 12 February 2008 Received in revised form 13 March 2008 Accepted 13 March 2008 Available online 6 May 2008 Keywords: Inverse opal photonic crystals Ferroelectrics Na1/2 Bi1/2 TiO3 Self-assembly and sol–gel method
a b s t r a c t The Na1/2 Bi1/2 TiO3 (NBT) inverse opal photonic crystals were prepared by the self-assembly technique in combination with a sol–gel method. In the preparation process, NBT precursors were filled into the interstices of the opal template assembled by monodispersive polystyrene microspheres. The polystyrene template was then removed by calcination at 800 ◦ C for 5 h, meanwhile, a perovskite NBT inverse opal photonic crystal was formed. An optical micrograph shows that the NBT inverse opals reflect green-yellow light strongly. Moreover, a photonic band gap was observed by reflective spectra of NBT sample. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Recently, much attention has been focused on the threedimensional (3D) photonic crystals since the concept was proposed by Yablonovitch and John [1,2] for application potential in an area of photonics, including near-zero threshold lasers, sensors, waveguide, photonic crystal fibers, etc. [3–6]. Photonic crystals with various 3D periodical structures, such as opal, inverse opal, woodpile, diamond structure, etc., have been fabricated [7–10]. The inverse opals are comprised of air spheres closely packed in a highly ordered three-dimensional array, which has been proved to be a promising structure for complete photonic band gap and practical applications. The inverse opals based on different materials such as metal [11], polymer [12], semiconductor [13] and insulator [14–18] have been prepared by infiltration of the interstices of the opal template. The ferroelectrics is a class of important dielectric material, which has been widely investigated for application in many optical devices and high-performance capacitor. Ferroelectric photonic crystals based on BaTiO3 or Pb0.91 La0.09 (Zr0.65 ,Ti0.35 )O3 have been reported by many researchers, and a tunability in photonic bandgap was shown in these photonic crystals [15,18]. Na1/2 Bi1/2 TiO3 (NBT) is a newly developed ferroelectric oxide with remarkable piezoelectric properties and friendly to environment. As we know, there has been no report about the NBT inverse opals.
∗ Corresponding author. Tel.: +86 10 62772975; fax: +86 10 62772975. E-mail address: [email protected] (J. Zhou). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.03.068
A wide variety of methods have been developed for the preparation of three-dimensional photonic crystals, including colloidal self-assembly method, the microfabrication techniques, holographic patterning using multiple laser beams, etc. [7,19,20]. Compared with the other approaches, the colloidal self-assembly provides a much simpler and less-expensive process to prepare photonic crystals. In the present work, NBT inverse opal photonic crystals were prepared by the self-assembly technique in combination with a sol–gel method. 2. Experimental procedure The commercial monodispersive polystyrene microsphere colloidal suspension (10 vol% solid content, Bangs Laboratories Inc., Fishers, IN) with an average diameter of 430 nm was used. Size deviation of microspheres is less than 5%, and the solvent of the polystyrene colloidal suspension is water. The opal templates were assembled by vertical deposition process. 500 l polystyrene microspheres suspension was added into a glass container filled with the 10 ml water. Then a quartz substrate was vertically suspended the glass container and placed in a 50 ◦ C oven for a week. After the water in container was evaporated, highly ordered colloidal arrays were formed on the quartz substrate. The 0.1 M NBT precursor sol was prepared according to the formula Na0.5 Bi0.5 TiO3 by using titanium butoxide (Ti(OC4 H9 )4 ), bismuth nitrate and sodium carbonate as raw materials. The bismuth nitrate and sodium carbonate was dissolved in a mixture of glycol and acetic acid, in which titanium butoxide were added. The mixture was stirred for 1 h to form a homogeneous NBT solution. The prepared NBT precursor solutions were used to infiltrate into the voids of the opal template through capillary force. After infiltration, the opals were calcined at different temperature for 5 h in an air furnace with a heating rate of 50 ◦ C/h. The reflective spectra of the sample were recorded by microregion UV–visible spectroscopy. The microstructures of the opal template and NBT inverse opals were observed by both optical microscope and scanning electron microscope (SEM; FEI QUANTA 200F). XRD data of the pow-
242
Z. Yang et al. / Journal of Alloys and Compounds 471 (2009) 241–243
Fig. 1. The SEM micrograph of the polystyrene opal template.
der sample were obtained on 2500 diffractometer (Japan) using Cu K␣ radiation ˚ ( = 1.5418 A).
3. Result and discussion Fig. 1 shows the SEM micrograph of the opal colloidal crystal template prepared by the self-assembly technique, demonstrating a highly order degree. The packed microspheres form into a face-centered cubic (fcc) structure with (1 1 1) plane parallel to the surface of the quartz substrate. Fig. 2 shows the XRD patterns of the NBT gel and inverse opal photonic crystals, demonstrating that an amorphous phase is formed in the NBT inverse opal samples sintered below 550 ◦ C, while the perovskite phase NBT can be obtained when sintered at 800 ◦ C (JCPD card: 89–3109). The SEM images of NBT inverse opals sintered at 800 ◦ C are shown in Fig. 3, in which (a) and (b) are under a low magnification and high magnification, respectively. The lighter regions and the darker circles in the SEM images represent the walls of inverse
Fig. 2. XRD patterns of the NBT inverse opal sintered at different temperature (a) gel, (b) 550 ◦ C and (c) 800 ◦ C.
Fig. 3. The SEM micrograph of NBT inverse opals.
opals and the air spheres previously occupied by polystyrene microspheres, respectively. It can be clearly seen that air spheres are very well ordered hexagonal domains, which suggests that sintering process does not destroy the ordered opal template. Inside each hollow region are dark regions, which correspond to the air spheres of the sub-layer. The center-to-center distance between the air spheres is about 285 nm, which is about 34% smaller than 430 nm polystyrene microspheres used to form template. Thus it can be concluded that considerable shrinkage occurs during calcinations. Based on the structure of inverse opals and the size data measured from SEM images, we calculated that the volume fraction of NBT materials in the inverse photonic crystals is 17%. The ordered NBT inverse opals display green-yellow regions and the light is easily observed with the naked eye. The observed bright green-yellow color corresponds to Bragg reflections from the ordered porous structure. The reflective spectra and an optical micrograph of the NBT inverse opal photonic crystals are shown in Fig. 4(a) and (b), respectively. The central wavelength of the vale is at 578 nm in accordance with that for the green-yellow light
Z. Yang et al. / Journal of Alloys and Compounds 471 (2009) 241–243
243
Fig. 4. The optical micrograph and the reflectivity spectra of NBT inverse opal photonic crystals.
so an agreement was found between two results obtained from both the reflective spectra and the optical micrograph. The optical micrograph shows that there are many cracking in the NBT inverse opals, and the domain size for uniform structures is several square millimeters. There are two factors for the cracks. One is the presence of defect and cracking in the opal template. Another is the sample shrinkage after removal of the template by calcination [21]. The band gap of NBT inverse opal photonic crystals were calculated by the modified form of Bragg’s law: 1/2
= 2d( n2eff − sin2 ) n2eff = n2NBT fNBT + n2air (1 − fNBT ) where , d, , and f denote the wavelength of reflect light, the plane spacing, the angle between the incidence light and the normal line of plane and the volume fraction of NBT ceramic (17%), respectively. neff, nair (=1) and nNBT (=2.3) represent average refractive indexes of the inverse opals, air and NBT ceramics, respectively. The calculated band gap is 580 nm, which is consistent with that of sample measured. 4. Conclusion
Acknowledgments This work was supported by National Natural Science Foundation of China under grants of 50425204, 50572043, 60608016 and 10774087, and Ministry of Education of China through Seeding Foundation of Major Projects. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
The perovskite BNT inverse opal photonic crystals were prepared through filling voids in 430 nm polystyrene microspheres colloidal crystals by sol–gel method. The optical micrograph shows that the inverse opal samples reflect green-yellow light strongly. The 578 nm band gap was verified by the reflective spectra. Such NBT inverse opal photonic crystals would be of importance in device applications.
[16] [17] [18] [19] [20] [21]
E. Yablonovitch, Phys. Rev. Lett. 58 (1987) 2059–2062. S. John, Phys. Rev. Lett. 58 (1987) 2486–2489. W.M. Lee, S.A. Pruzinsky, P.V. Braun, Adv. Mater. 14 (2002) 271–274. R.A. Barry, P. Wiltzius, Langmuir 22 (2006) 1369–1374. O. Painte, R.K. Lee, A. Scherer, A. Yariv, J.D. O’Brien, P.D. Dapkus, et al., Science 284 (1999) 1819–1821. P. Russell, Science 299 (2003) 358–362. Y.N. Xia, B. Gates, Z.Y. Li, Adv. Mater. 13 (2001) 409–513. J.J. Wang, Q. Li, W. Knoll, U. Jonas, J. Am. Chem. Soc. 128 (2006) 15606–15607. H.S. Sozuer, J.P. Dowling, J. Mod. Opt. 41 (1994) 231–239. K.M. Ho, C.T. Chan, C.M. Soukoulis, Phys. Rev. Lett. 65 (1990) 3152–3155. Y.L. Wang, M. Ibisate, Z.Y. Li, Y.N. Xiao, Adv. Mater. 18 (2006) 471–476. A.C. Arsenault, J. Clark, G.V. Fretnann, L. Cademartiri, R. Sapienza, J. Bertolotti, et al., Nat. Mater. 5 (2006) 179–184. C. Paquet, F. Yoshino, L. Levina, I. Gourevich, E. Sargent, E. Kumacheva, Adv. Funct. Mater. 16 (2006) 1892–1896. P.C. Schroden, A.M. Daous, C.F. Blanford, A. Stein, Chem. Mater. 14 (2002) 3305–3315. I. Soten, H. Miguez, S.M. Yang, S. Petrov, N. Coombs, N. Tetreault, et al., Adv. Funct. Mater. 12 (2002) 71–77. B. Li, J. Zhou, Q. Li, L.T. Li, Z.L. Gui, J. Am. Ceram. Soc. 86 (2006) 867–869. D.Y. Wang, F. Caruso, Adv. Mater. 15 (2003) 205–209. B. Li, J. Zhou, R.L. Zong, M. Fu, Y. Bai, L.T. Li, et al., J. Am. Ceram. Soc. 89 (2003) 2298–2300. ¨ E. ozbay, E. Michel, G. Tuttle, R. Biswas, H. Km, J. Bostak, et al., Appl. Phys. Lett. 64 (1994) 2059–2061. S. Noda, A. Chutinan, M. Imada, Nature 407 (2000) 608–610. Q.B. Meng, Z.Z. Gu, O. Sato, A. Fujishima, Appl. Phys. Lett. 77 (2000) 4313–4315.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Preparation and photonic bandgap properties of Na1/2 Bi1/2 TiO3 inverse opal photonic crystals Zhengwen Yang, Ji Zhou ∗ , Xueguang Huang, Qin Xie, Ming Fu, Bo Li, Longtu Li State Key Lab of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China
a r t i c l e
i n f o
Article history: Received 12 February 2008 Received in revised form 13 March 2008 Accepted 13 March 2008 Available online 6 May 2008 Keywords: Inverse opal photonic crystals Ferroelectrics Na1/2 Bi1/2 TiO3 Self-assembly and sol–gel method
a b s t r a c t The Na1/2 Bi1/2 TiO3 (NBT) inverse opal photonic crystals were prepared by the self-assembly technique in combination with a sol–gel method. In the preparation process, NBT precursors were filled into the interstices of the opal template assembled by monodispersive polystyrene microspheres. The polystyrene template was then removed by calcination at 800 ◦ C for 5 h, meanwhile, a perovskite NBT inverse opal photonic crystal was formed. An optical micrograph shows that the NBT inverse opals reflect green-yellow light strongly. Moreover, a photonic band gap was observed by reflective spectra of NBT sample. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Recently, much attention has been focused on the threedimensional (3D) photonic crystals since the concept was proposed by Yablonovitch and John [1,2] for application potential in an area of photonics, including near-zero threshold lasers, sensors, waveguide, photonic crystal fibers, etc. [3–6]. Photonic crystals with various 3D periodical structures, such as opal, inverse opal, woodpile, diamond structure, etc., have been fabricated [7–10]. The inverse opals are comprised of air spheres closely packed in a highly ordered three-dimensional array, which has been proved to be a promising structure for complete photonic band gap and practical applications. The inverse opals based on different materials such as metal [11], polymer [12], semiconductor [13] and insulator [14–18] have been prepared by infiltration of the interstices of the opal template. The ferroelectrics is a class of important dielectric material, which has been widely investigated for application in many optical devices and high-performance capacitor. Ferroelectric photonic crystals based on BaTiO3 or Pb0.91 La0.09 (Zr0.65 ,Ti0.35 )O3 have been reported by many researchers, and a tunability in photonic bandgap was shown in these photonic crystals [15,18]. Na1/2 Bi1/2 TiO3 (NBT) is a newly developed ferroelectric oxide with remarkable piezoelectric properties and friendly to environment. As we know, there has been no report about the NBT inverse opals.
∗ Corresponding author. Tel.: +86 10 62772975; fax: +86 10 62772975. E-mail address: [email protected] (J. Zhou). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.03.068
A wide variety of methods have been developed for the preparation of three-dimensional photonic crystals, including colloidal self-assembly method, the microfabrication techniques, holographic patterning using multiple laser beams, etc. [7,19,20]. Compared with the other approaches, the colloidal self-assembly provides a much simpler and less-expensive process to prepare photonic crystals. In the present work, NBT inverse opal photonic crystals were prepared by the self-assembly technique in combination with a sol–gel method. 2. Experimental procedure The commercial monodispersive polystyrene microsphere colloidal suspension (10 vol% solid content, Bangs Laboratories Inc., Fishers, IN) with an average diameter of 430 nm was used. Size deviation of microspheres is less than 5%, and the solvent of the polystyrene colloidal suspension is water. The opal templates were assembled by vertical deposition process. 500 l polystyrene microspheres suspension was added into a glass container filled with the 10 ml water. Then a quartz substrate was vertically suspended the glass container and placed in a 50 ◦ C oven for a week. After the water in container was evaporated, highly ordered colloidal arrays were formed on the quartz substrate. The 0.1 M NBT precursor sol was prepared according to the formula Na0.5 Bi0.5 TiO3 by using titanium butoxide (Ti(OC4 H9 )4 ), bismuth nitrate and sodium carbonate as raw materials. The bismuth nitrate and sodium carbonate was dissolved in a mixture of glycol and acetic acid, in which titanium butoxide were added. The mixture was stirred for 1 h to form a homogeneous NBT solution. The prepared NBT precursor solutions were used to infiltrate into the voids of the opal template through capillary force. After infiltration, the opals were calcined at different temperature for 5 h in an air furnace with a heating rate of 50 ◦ C/h. The reflective spectra of the sample were recorded by microregion UV–visible spectroscopy. The microstructures of the opal template and NBT inverse opals were observed by both optical microscope and scanning electron microscope (SEM; FEI QUANTA 200F). XRD data of the pow-
242
Z. Yang et al. / Journal of Alloys and Compounds 471 (2009) 241–243
Fig. 1. The SEM micrograph of the polystyrene opal template.
der sample were obtained on 2500 diffractometer (Japan) using Cu K␣ radiation ˚ ( = 1.5418 A).
3. Result and discussion Fig. 1 shows the SEM micrograph of the opal colloidal crystal template prepared by the self-assembly technique, demonstrating a highly order degree. The packed microspheres form into a face-centered cubic (fcc) structure with (1 1 1) plane parallel to the surface of the quartz substrate. Fig. 2 shows the XRD patterns of the NBT gel and inverse opal photonic crystals, demonstrating that an amorphous phase is formed in the NBT inverse opal samples sintered below 550 ◦ C, while the perovskite phase NBT can be obtained when sintered at 800 ◦ C (JCPD card: 89–3109). The SEM images of NBT inverse opals sintered at 800 ◦ C are shown in Fig. 3, in which (a) and (b) are under a low magnification and high magnification, respectively. The lighter regions and the darker circles in the SEM images represent the walls of inverse
Fig. 2. XRD patterns of the NBT inverse opal sintered at different temperature (a) gel, (b) 550 ◦ C and (c) 800 ◦ C.
Fig. 3. The SEM micrograph of NBT inverse opals.
opals and the air spheres previously occupied by polystyrene microspheres, respectively. It can be clearly seen that air spheres are very well ordered hexagonal domains, which suggests that sintering process does not destroy the ordered opal template. Inside each hollow region are dark regions, which correspond to the air spheres of the sub-layer. The center-to-center distance between the air spheres is about 285 nm, which is about 34% smaller than 430 nm polystyrene microspheres used to form template. Thus it can be concluded that considerable shrinkage occurs during calcinations. Based on the structure of inverse opals and the size data measured from SEM images, we calculated that the volume fraction of NBT materials in the inverse photonic crystals is 17%. The ordered NBT inverse opals display green-yellow regions and the light is easily observed with the naked eye. The observed bright green-yellow color corresponds to Bragg reflections from the ordered porous structure. The reflective spectra and an optical micrograph of the NBT inverse opal photonic crystals are shown in Fig. 4(a) and (b), respectively. The central wavelength of the vale is at 578 nm in accordance with that for the green-yellow light
Z. Yang et al. / Journal of Alloys and Compounds 471 (2009) 241–243
243
Fig. 4. The optical micrograph and the reflectivity spectra of NBT inverse opal photonic crystals.
so an agreement was found between two results obtained from both the reflective spectra and the optical micrograph. The optical micrograph shows that there are many cracking in the NBT inverse opals, and the domain size for uniform structures is several square millimeters. There are two factors for the cracks. One is the presence of defect and cracking in the opal template. Another is the sample shrinkage after removal of the template by calcination [21]. The band gap of NBT inverse opal photonic crystals were calculated by the modified form of Bragg’s law: 1/2
= 2d( n2eff − sin2 ) n2eff = n2NBT fNBT + n2air (1 − fNBT ) where , d, , and f denote the wavelength of reflect light, the plane spacing, the angle between the incidence light and the normal line of plane and the volume fraction of NBT ceramic (17%), respectively. neff, nair (=1) and nNBT (=2.3) represent average refractive indexes of the inverse opals, air and NBT ceramics, respectively. The calculated band gap is 580 nm, which is consistent with that of sample measured. 4. Conclusion
Acknowledgments This work was supported by National Natural Science Foundation of China under grants of 50425204, 50572043, 60608016 and 10774087, and Ministry of Education of China through Seeding Foundation of Major Projects. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
The perovskite BNT inverse opal photonic crystals were prepared through filling voids in 430 nm polystyrene microspheres colloidal crystals by sol–gel method. The optical micrograph shows that the inverse opal samples reflect green-yellow light strongly. The 578 nm band gap was verified by the reflective spectra. Such NBT inverse opal photonic crystals would be of importance in device applications.
[16] [17] [18] [19] [20] [21]
E. Yablonovitch, Phys. Rev. Lett. 58 (1987) 2059–2062. S. John, Phys. Rev. Lett. 58 (1987) 2486–2489. W.M. Lee, S.A. Pruzinsky, P.V. Braun, Adv. Mater. 14 (2002) 271–274. R.A. Barry, P. Wiltzius, Langmuir 22 (2006) 1369–1374. O. Painte, R.K. Lee, A. Scherer, A. Yariv, J.D. O’Brien, P.D. Dapkus, et al., Science 284 (1999) 1819–1821. P. Russell, Science 299 (2003) 358–362. Y.N. Xia, B. Gates, Z.Y. Li, Adv. Mater. 13 (2001) 409–513. J.J. Wang, Q. Li, W. Knoll, U. Jonas, J. Am. Chem. Soc. 128 (2006) 15606–15607. H.S. Sozuer, J.P. Dowling, J. Mod. Opt. 41 (1994) 231–239. K.M. Ho, C.T. Chan, C.M. Soukoulis, Phys. Rev. Lett. 65 (1990) 3152–3155. Y.L. Wang, M. Ibisate, Z.Y. Li, Y.N. Xiao, Adv. Mater. 18 (2006) 471–476. A.C. Arsenault, J. Clark, G.V. Fretnann, L. Cademartiri, R. Sapienza, J. Bertolotti, et al., Nat. Mater. 5 (2006) 179–184. C. Paquet, F. Yoshino, L. Levina, I. Gourevich, E. Sargent, E. Kumacheva, Adv. Funct. Mater. 16 (2006) 1892–1896. P.C. Schroden, A.M. Daous, C.F. Blanford, A. Stein, Chem. Mater. 14 (2002) 3305–3315. I. Soten, H. Miguez, S.M. Yang, S. Petrov, N. Coombs, N. Tetreault, et al., Adv. Funct. Mater. 12 (2002) 71–77. B. Li, J. Zhou, Q. Li, L.T. Li, Z.L. Gui, J. Am. Ceram. Soc. 86 (2006) 867–869. D.Y. Wang, F. Caruso, Adv. Mater. 15 (2003) 205–209. B. Li, J. Zhou, R.L. Zong, M. Fu, Y. Bai, L.T. Li, et al., J. Am. Ceram. Soc. 89 (2003) 2298–2300. ¨ E. ozbay, E. Michel, G. Tuttle, R. Biswas, H. Km, J. Bostak, et al., Appl. Phys. Lett. 64 (1994) 2059–2061. S. Noda, A. Chutinan, M. Imada, Nature 407 (2000) 608–610. Q.B. Meng, Z.Z. Gu, O. Sato, A. Fujishima, Appl. Phys. Lett. 77 (2000) 4313–4315.