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Formation of 2D colloidal crystals by the Langmuir–Blodgett technique monitored in situ by Brewster angle microscopy
Journal of Colloid and Interface Science 307 (2007) 304–307 www.elsevier.com/locate/jcis
Note
Formation of 2D colloidal crystals by the Langmuir–Blodgett technique monitored in situ by Brewster angle microscopy Alvaro Gil ∗ , Francisco Guitián Instituto de Cerámica, University of Santiago de Compostela, Santiago de Compostela 15782, Spain Received 5 July 2006; accepted 29 November 2006 Available online 2 December 2006
Abstract We report a method that combines Brewster angle microscopy and Langmuir–Blodgett films technique to obtain highly ordered 2D colloidal crystals of nanospheres. The deposition of Langmuir–Blodgett films of silica spheres monitored by Brewster angle microscopy allows to determine with accuracy the best physical conditions to transfer highly ordered monolayers of nanoparticles. © 2006 Elsevier Inc. All rights reserved. Keywords: Colloidal crystals; Langmuir–Blodgett; Nanospheres; Photonic crystals
1. Introduction Photonic crystals [1–3] are ordered nanostructures with two dielectric media and different refractive index where diffraction can cause photon localization. By colloidal self-assembly it is possible to produce photonic crystals by close-packing of monodisperse spheres [4–7] forming a face-centered cubic (fcc) lattice. The most interesting photonic crystals are those with a complete photonic bandgap (PBG) in the optical and infrared range. In that case, for a crystal with a complete PGB the refractive index contrast must be larger than 2.8 for a fcc lattice. Common colloidal crystals of close-packing of monodisperse sphere have low refractive index contrast, in this case they must be used as templates to infiltrate materials with high refraction index. It is of extreme importance to be able to introduce controlled defects [8,9] in the colloidal crystals in order to direct the flux of light inside the photonic crystal. In addition, colloidal crystals of nanospheres are needed in a pure and highly crystalline form in order to use them as templates to obtain photonic crystals [10] with a complete PGB and with a level of flaws acceptable in optical telecommunication applications [11–15]. Herein we use a technique involving Brewster angle microscopy [16] and * Corresponding author. Fax: +34 981564242.
E-mail address: [email protected] (A. Gil). 0021-9797/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.11.045
Langmuir–Blodgett [17–19] (LB) film method to improve the technique to prepare 2D colloidal crystals. Previous methods of synthesis have been efficient enough to prepare colloidal crystals with high order and quality [7,20]. Nevertheless, it remains a challenge the formation of those crystals with controlled size, shape, and controlled defects [14]. LB film technique enables to assemble the colloidal crystals, transferring monolayers of functionalized spherical particles from the air–water interface onto solid substrates. Simultaneously, this technique provides the possibility to insert monolayers with different diameters of the spheres to introduce extrinsic defects in the crystal [21,22]. 2. Materials and methods Chloroform (Baker, 99.8%, HPLC grade), ethanol (Merck, 99.9%, absolute grade), ammonia (Merck, 25.0% NH3 solution in water), allyltrimethoxysilane (ABCR GmbH & Co, 50% methanolic solution) were used as received. Tetraethyl orthosilicate (Fluka, 99.0%) was vacuum distilled before use for particles synthesis. Water was purified in a Milli-Q filtration unit from Millipore Co., with a resistivity of 18 M cm. Monodisperse silica particles were prepared by the method of Stöber [23]. In a 500 ml conical flask, a mixture containing 1 M NH3 , 8 M H2 O, and 80 vol% ethanol was stirred at room temperature. The mixture was homogenized at room tempera-
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
ture and 0.17 M tetraethyl orthosilicate was added in one step, the mixture then being stirred for 24 h. The resulting silica suspension was centrifuged at 3000 rpm for 30 min and washed by repeating redispersion three times in pure ethanol and three times in deionized water. The final precipitate was dried out overnight at 120 ◦ C. The diameter of the silica spheres was determined by scanning electron microscopy (SEM). The mean diameter of the particles was 439 nm. Allyltrimethoxysilane [24,25] was added to a suspension of silica spheres in ethanol. The mixture was stirred 12 h at 80 ◦ C. The remaining reagents where eliminated by washing the suspension several times with deionized water. The resulting suspension was dialyzed against water. The treated silica spheres were centrifuged and dried at 60 ◦ C. Surface pressure–area and surface potential–area isotherms were measured in a rectangular trough made from poly(tetrafluoroethylene) with the dimensions 36 cm (length), 11 cm (width), and 1 cm (depth). The trough was thermostated at 20 ◦ C and enclosed in a box. A Wilhelmy balance provided with a 20 mm wide filter paper as a plate was used for the measurement of the surface pressure. The barrier is moved gradually decreasing the area at constant speed. The surface potential was measured with a vibrating plate condensor as the counter electrode, a quadratic Pt plate of length 3 cm was placed at the bottom of the trough. 251 mg of functionalized silica particles were suspended in 10 ml of a mixture 80/20 (v/v) chloroform/ethanol. The suspension was sonicated for 20 min before spreading. Volumes of 200 µl of suspensions of ca. 25.1 mg/ml concentration were spread onto the initial surface of 352 cm2 . After about 10 min of relaxation, the monolayers were compressed at an average speed of 16.2 cm2 /min until the selected surface pressure. The films were transferred to glass at the surface pressure of 5.5 mN/m by using the vertical dipping technique with a lifting speed of 5 mm/min. The transfer ratio was close to unity in all cases. Brewster angle microscope images were taken during compression with a MiniBAM from Nanofilm Technologie NFT, Göttingen, Germany. The wavelength of the laser diode emission of this instrument was 660 nm. Scanning electron micrographs images were taken on a JEOL 6400 electronic scan microscope at 10.0 kV. The surface of a sample was coated with gold (∼200 Å thick) prior to imaging. 3. Results and discussion During the deposition of the monolayer on a solid substrate by the LB method the pressure should be set constant. Classic method to identify the adequate pressure to transfer the monolayers onto solid substrates by the LB method relies on the analysis of the pressure–area (π–A) and surface potential– area (V –A) isotherms of the spread monolayers [17]. This analysis provides the appropriate pressure and area values at which the monolayer is condensed enough to be transferred to the solid substrate. However, due to the low compressibility of solid silica particles, the π–A isotherm is very steep. In consequence, the analysis of the π–A and V –A isotherms is not enough to determine accurately the pressure at which the water
305
Fig. 1. Isotherms (a) pressure–area and (b) potential–area. The strong steep in the π –A isotherm from 0.8 to 8.9 mN/m indicates the gap area where the monolayer can be transferred.
surface is homogeneously covered with particles aggregated in a compact monolayer. Herein, we introduce the Brewster angle microscopy (BAM) technique to observe the spheres monolayer simultaneously to the π–A and V –A determinations. BAM allows us to visualize and monitored in situ the evolution of the particle aggregation and the density of the spheres monolayer throughout the process of monolayer compression. In doing so, we can determine accurately the surface pressure to transfer the monolayer to the solid substrate maintaining spheres highly ordered. As allyltrimethoxysilane (ATS) confers to the particles the suitable hydrophobic–hydrophilic balance to form the air–water monolayer, we functionalized them with ATS before spreading them on the interface [24,25]. The continuous π–A isotherm (Fig. 1) shows a strong steep between 0.8 and 8.9 mN/m corresponding to the condensed monolayer. The combination of the information provided by BAM images and the isotherms allows to know the pressure and area where the surface is completely covered with the particles in the range 0.8–8.9 mN/m. BAM images provide clear information regarding the homogeneity of the particles monolayer. In Brewster angle microscopy the p-polarized light incident at the Brewster angle of the pure subphase is reflected due to the presence of the monolayer [16]. With constant angle of incidence, the formation of a monolayer on the water surface modifies the Brewster angle condition, and light reflection is observed. No light is reflected from the air–water interface under Brewster angle if p-polarized light is used. Fig. 2 shows BAM micrographs of the monolayer at different π–A, captured from the recorded movie of the monolayer compression. The pictures show the different domains of the sample. Bright areas represent tightly packed particles, whereas black areas correspond to the water surface and disperse particles. Fig. 2a, at 0.5 mN/m, shows the surface of the monolayer (bright domains) and water without spheres (black areas). The presence of isolated particle domains indicates that the monolayer is inhomogeneous, the spheres are not uniformly packed and, in consequence, the surface is not completely covered with particles. In contrast, in Fig. 2b at 5.5 mN/m the brightness is homogeneous
306
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
Fig. 3. Transferred monolayer of silica spheres. Scanning electron microscopy micrograph of ordered silica spheres of 439 nm display in hexagonal packing.
4. Conclusions In summary, we have reported a new methodology to prepare colloidal crystals that combines Brewster angle microscopy and the Langmuir–Blodgett method. BAM allows to determine the optimal pressure–area to transfer ordered monolayers of silica particles to solid substrates. Our findings open the way to a new, easy and practical method to obtain highly ordered 2D colloidal crystals of nanospheres. The accuracy of the method to select the parameters to transfer the spheres monolayer to solid substrates will make possible to build ordered colloidal crystals as precursors of photonic crystals. We plan to use this novel approach to prepare photonic crystals with controlled defects. Acknowledgment A.G. expresses gratitude for support from the Ministry of Innovation and Industry of the Galician Government under the program “Isidro Parga Pondal.” Fig. 2. Brewster angle microscopy micrographs of a monolayer of silica spheres at different pressure–area. (a) Before the formation of the rigid monolayer (0.5 mN/m). (b) The monolayer is homogeneously covered with particles (5.5 mN/m). In these conditions the monolayer is perfectly suitable to be transferred. (c) Broken-down monolayer when the monolayer has been decompressed.
in the entire micrograph. It implies that the surface is homogeneously covered with packed particles. As a result, 5.5 mN/m is selected as the most suitable surface pressure to deposit the LB films. Fig. 2c is made when the monolayer has been decompressed. The appearance of cracks evidences the breaking of the monolayer. The presence of some blocks of aggregated particles remaining in the air–water interface shows the rigidity of the film and the strong forces of cohesion between the particles. The transferred LB film attached to a glass substrate shows all the colors of the visible spectrum depending on the angles. The resulting crystal lattice of spheres causes opalescent colors due to Bragg diffraction of visible light. The reflection of light shifts as expected, changing the angle of the incident light. This phenomenon proves the order of the spheres and the optical quality of the film [26]. The order of the spheres can be checked if the same sample is observed by scanning electron microscopy (SEM) (Fig. 3).
References [1] [2] [3] [4] [5] [6] [7] [8]
[9] [10]
[11] [12] [13] [14] [15]
E. Yablonovitch, Phys. Rev. Lett. 58 (1987) 2059. S. John, Phys. Rev. Lett. 58 (1987) 2486. J.D. Joannopoulos, P.R. Villeneuve, S. Fan, Nature 386 (1997) 143. S.M. Yang, H. Míguez, D.A. Ozin, Adv. Funct. Mater. 12 (2002) 425. P. Jiang, J.F. Bertone, K.S. Hwang, V.L. Colvin, Chem. Mater. 11 (1999) 2132. K. Wostyn, Y. Zhao, B. Yee, K. Clays, A.J. Persoons, Chem. Phys. 118 (2003) 4465. S. Wong, V. Kitaev, G.A. Ozin, J. Am. Chem. Soc. 125 (2003) 15,589. A. Blanco, E. Chomski, S. Grabtchak, M. Ibisate, S. John, S.W. Leonard, C. Lopez, F. Meseguer, H. Miguez, J.P. Mondia, G.A. Ozin, O. Toader, H.M. van Driel, Nature 405 (2000) 437. P. Lodahl, A.F. van Driel, I.S. Nikolaev, A. Irman, K. Overgaag, D. Vanmaekelbergh, W.L. Vos, Nature 430 (2004) 654. A. Arsenault, S. Fournier-Bidoz, B. Hatton, H. Miguez, N. Tétreault, E. Verkis, S. Wong, S.M. Yang, V. Kitaev, G.A. Ozin, J. Mater. Chem. 14 (2004) 781. P. Russell, Science 299 (2003) 358. C.M. Smith, N. Venkataraman, M.T. Gallagher, D. Müller, J.A. West, M.F. Borelli, D.C. Allan, K.W. Koch, Nature 424 (2003) 657. R.F. Cregan, B.J. Mangan, J.C. Knight, T.A. Birks, P.St.J. Russell, P.J. Roberts, D.C. Allan, Science 285 (1999) 1537. N. Tétreault, H. Míguez, S.M. Yang, V. Kitaev, G.A. Ozin, Adv. Mater. 15 (2003) 1167. E. Vekris, V. Kitaev, G. von Freymann, D. Perovic, J.S. Aitchison, G.A. Ozin, Adv. Mater. 17 (2005) 1269.
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
[16] D. Hönig, D. Möbius, Thin Solid Films 210–211 (1992) 64. [17] H. Kuhn, D. Möbius, Monolayer Assemblies. Investigations of Surfaces and Interfaces, second ed., Wiley, New York, 1993. [18] B. van Duffel, R.H.A. Ras, F.C. De Schryver, R.A. Schoonheydt, J. Mater. Chem. 11 (2001) 3333. [19] I. Dékány, J. Nëmeth, M. Szekeres, R. Schoonheydt, Colloid Polym. Sci. 282 (2003) 1. [20] Y.A. Vlasov, X.Z. Bo, J.C. Sturm, D.J. Norris, Nature 414 (2001) 289.
307
[21] P. Massé, S. Reculusa, K. Clays, S. Ravaine, Chem. Phys. Lett. 422 (2006) 251. [22] K. Wostyn, Y. Zhao, G. de Schaetzen, L. Hellemans, N. Matsuda, K. Clays, A. Persoons, Langmuir 19 (2003) 4465. [23] W. Stöber, A. Fink, E.J. Bohn, Colloid Interface Science 26 (1968) 62. [24] S. Reculusa, S. Ravaine, Chem. Mater. 15 (2003) 598. [25] S. Reculusa, S. Ravaine, Appl. Surf. Sci. 246 (2005) 409. [26] M. Egen, R. Zentel, Macromol. Chem. Phys. 205 (2004) 1479.
Note
Formation of 2D colloidal crystals by the Langmuir–Blodgett technique monitored in situ by Brewster angle microscopy Alvaro Gil ∗ , Francisco Guitián Instituto de Cerámica, University of Santiago de Compostela, Santiago de Compostela 15782, Spain Received 5 July 2006; accepted 29 November 2006 Available online 2 December 2006
Abstract We report a method that combines Brewster angle microscopy and Langmuir–Blodgett films technique to obtain highly ordered 2D colloidal crystals of nanospheres. The deposition of Langmuir–Blodgett films of silica spheres monitored by Brewster angle microscopy allows to determine with accuracy the best physical conditions to transfer highly ordered monolayers of nanoparticles. © 2006 Elsevier Inc. All rights reserved. Keywords: Colloidal crystals; Langmuir–Blodgett; Nanospheres; Photonic crystals
1. Introduction Photonic crystals [1–3] are ordered nanostructures with two dielectric media and different refractive index where diffraction can cause photon localization. By colloidal self-assembly it is possible to produce photonic crystals by close-packing of monodisperse spheres [4–7] forming a face-centered cubic (fcc) lattice. The most interesting photonic crystals are those with a complete photonic bandgap (PBG) in the optical and infrared range. In that case, for a crystal with a complete PGB the refractive index contrast must be larger than 2.8 for a fcc lattice. Common colloidal crystals of close-packing of monodisperse sphere have low refractive index contrast, in this case they must be used as templates to infiltrate materials with high refraction index. It is of extreme importance to be able to introduce controlled defects [8,9] in the colloidal crystals in order to direct the flux of light inside the photonic crystal. In addition, colloidal crystals of nanospheres are needed in a pure and highly crystalline form in order to use them as templates to obtain photonic crystals [10] with a complete PGB and with a level of flaws acceptable in optical telecommunication applications [11–15]. Herein we use a technique involving Brewster angle microscopy [16] and * Corresponding author. Fax: +34 981564242.
E-mail address: [email protected] (A. Gil). 0021-9797/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.11.045
Langmuir–Blodgett [17–19] (LB) film method to improve the technique to prepare 2D colloidal crystals. Previous methods of synthesis have been efficient enough to prepare colloidal crystals with high order and quality [7,20]. Nevertheless, it remains a challenge the formation of those crystals with controlled size, shape, and controlled defects [14]. LB film technique enables to assemble the colloidal crystals, transferring monolayers of functionalized spherical particles from the air–water interface onto solid substrates. Simultaneously, this technique provides the possibility to insert monolayers with different diameters of the spheres to introduce extrinsic defects in the crystal [21,22]. 2. Materials and methods Chloroform (Baker, 99.8%, HPLC grade), ethanol (Merck, 99.9%, absolute grade), ammonia (Merck, 25.0% NH3 solution in water), allyltrimethoxysilane (ABCR GmbH & Co, 50% methanolic solution) were used as received. Tetraethyl orthosilicate (Fluka, 99.0%) was vacuum distilled before use for particles synthesis. Water was purified in a Milli-Q filtration unit from Millipore Co., with a resistivity of 18 M cm. Monodisperse silica particles were prepared by the method of Stöber [23]. In a 500 ml conical flask, a mixture containing 1 M NH3 , 8 M H2 O, and 80 vol% ethanol was stirred at room temperature. The mixture was homogenized at room tempera-
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
ture and 0.17 M tetraethyl orthosilicate was added in one step, the mixture then being stirred for 24 h. The resulting silica suspension was centrifuged at 3000 rpm for 30 min and washed by repeating redispersion three times in pure ethanol and three times in deionized water. The final precipitate was dried out overnight at 120 ◦ C. The diameter of the silica spheres was determined by scanning electron microscopy (SEM). The mean diameter of the particles was 439 nm. Allyltrimethoxysilane [24,25] was added to a suspension of silica spheres in ethanol. The mixture was stirred 12 h at 80 ◦ C. The remaining reagents where eliminated by washing the suspension several times with deionized water. The resulting suspension was dialyzed against water. The treated silica spheres were centrifuged and dried at 60 ◦ C. Surface pressure–area and surface potential–area isotherms were measured in a rectangular trough made from poly(tetrafluoroethylene) with the dimensions 36 cm (length), 11 cm (width), and 1 cm (depth). The trough was thermostated at 20 ◦ C and enclosed in a box. A Wilhelmy balance provided with a 20 mm wide filter paper as a plate was used for the measurement of the surface pressure. The barrier is moved gradually decreasing the area at constant speed. The surface potential was measured with a vibrating plate condensor as the counter electrode, a quadratic Pt plate of length 3 cm was placed at the bottom of the trough. 251 mg of functionalized silica particles were suspended in 10 ml of a mixture 80/20 (v/v) chloroform/ethanol. The suspension was sonicated for 20 min before spreading. Volumes of 200 µl of suspensions of ca. 25.1 mg/ml concentration were spread onto the initial surface of 352 cm2 . After about 10 min of relaxation, the monolayers were compressed at an average speed of 16.2 cm2 /min until the selected surface pressure. The films were transferred to glass at the surface pressure of 5.5 mN/m by using the vertical dipping technique with a lifting speed of 5 mm/min. The transfer ratio was close to unity in all cases. Brewster angle microscope images were taken during compression with a MiniBAM from Nanofilm Technologie NFT, Göttingen, Germany. The wavelength of the laser diode emission of this instrument was 660 nm. Scanning electron micrographs images were taken on a JEOL 6400 electronic scan microscope at 10.0 kV. The surface of a sample was coated with gold (∼200 Å thick) prior to imaging. 3. Results and discussion During the deposition of the monolayer on a solid substrate by the LB method the pressure should be set constant. Classic method to identify the adequate pressure to transfer the monolayers onto solid substrates by the LB method relies on the analysis of the pressure–area (π–A) and surface potential– area (V –A) isotherms of the spread monolayers [17]. This analysis provides the appropriate pressure and area values at which the monolayer is condensed enough to be transferred to the solid substrate. However, due to the low compressibility of solid silica particles, the π–A isotherm is very steep. In consequence, the analysis of the π–A and V –A isotherms is not enough to determine accurately the pressure at which the water
305
Fig. 1. Isotherms (a) pressure–area and (b) potential–area. The strong steep in the π –A isotherm from 0.8 to 8.9 mN/m indicates the gap area where the monolayer can be transferred.
surface is homogeneously covered with particles aggregated in a compact monolayer. Herein, we introduce the Brewster angle microscopy (BAM) technique to observe the spheres monolayer simultaneously to the π–A and V –A determinations. BAM allows us to visualize and monitored in situ the evolution of the particle aggregation and the density of the spheres monolayer throughout the process of monolayer compression. In doing so, we can determine accurately the surface pressure to transfer the monolayer to the solid substrate maintaining spheres highly ordered. As allyltrimethoxysilane (ATS) confers to the particles the suitable hydrophobic–hydrophilic balance to form the air–water monolayer, we functionalized them with ATS before spreading them on the interface [24,25]. The continuous π–A isotherm (Fig. 1) shows a strong steep between 0.8 and 8.9 mN/m corresponding to the condensed monolayer. The combination of the information provided by BAM images and the isotherms allows to know the pressure and area where the surface is completely covered with the particles in the range 0.8–8.9 mN/m. BAM images provide clear information regarding the homogeneity of the particles monolayer. In Brewster angle microscopy the p-polarized light incident at the Brewster angle of the pure subphase is reflected due to the presence of the monolayer [16]. With constant angle of incidence, the formation of a monolayer on the water surface modifies the Brewster angle condition, and light reflection is observed. No light is reflected from the air–water interface under Brewster angle if p-polarized light is used. Fig. 2 shows BAM micrographs of the monolayer at different π–A, captured from the recorded movie of the monolayer compression. The pictures show the different domains of the sample. Bright areas represent tightly packed particles, whereas black areas correspond to the water surface and disperse particles. Fig. 2a, at 0.5 mN/m, shows the surface of the monolayer (bright domains) and water without spheres (black areas). The presence of isolated particle domains indicates that the monolayer is inhomogeneous, the spheres are not uniformly packed and, in consequence, the surface is not completely covered with particles. In contrast, in Fig. 2b at 5.5 mN/m the brightness is homogeneous
306
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
Fig. 3. Transferred monolayer of silica spheres. Scanning electron microscopy micrograph of ordered silica spheres of 439 nm display in hexagonal packing.
4. Conclusions In summary, we have reported a new methodology to prepare colloidal crystals that combines Brewster angle microscopy and the Langmuir–Blodgett method. BAM allows to determine the optimal pressure–area to transfer ordered monolayers of silica particles to solid substrates. Our findings open the way to a new, easy and practical method to obtain highly ordered 2D colloidal crystals of nanospheres. The accuracy of the method to select the parameters to transfer the spheres monolayer to solid substrates will make possible to build ordered colloidal crystals as precursors of photonic crystals. We plan to use this novel approach to prepare photonic crystals with controlled defects. Acknowledgment A.G. expresses gratitude for support from the Ministry of Innovation and Industry of the Galician Government under the program “Isidro Parga Pondal.” Fig. 2. Brewster angle microscopy micrographs of a monolayer of silica spheres at different pressure–area. (a) Before the formation of the rigid monolayer (0.5 mN/m). (b) The monolayer is homogeneously covered with particles (5.5 mN/m). In these conditions the monolayer is perfectly suitable to be transferred. (c) Broken-down monolayer when the monolayer has been decompressed.
in the entire micrograph. It implies that the surface is homogeneously covered with packed particles. As a result, 5.5 mN/m is selected as the most suitable surface pressure to deposit the LB films. Fig. 2c is made when the monolayer has been decompressed. The appearance of cracks evidences the breaking of the monolayer. The presence of some blocks of aggregated particles remaining in the air–water interface shows the rigidity of the film and the strong forces of cohesion between the particles. The transferred LB film attached to a glass substrate shows all the colors of the visible spectrum depending on the angles. The resulting crystal lattice of spheres causes opalescent colors due to Bragg diffraction of visible light. The reflection of light shifts as expected, changing the angle of the incident light. This phenomenon proves the order of the spheres and the optical quality of the film [26]. The order of the spheres can be checked if the same sample is observed by scanning electron microscopy (SEM) (Fig. 3).
References [1] [2] [3] [4] [5] [6] [7] [8]
[9] [10]
[11] [12] [13] [14] [15]
E. Yablonovitch, Phys. Rev. Lett. 58 (1987) 2059. S. John, Phys. Rev. Lett. 58 (1987) 2486. J.D. Joannopoulos, P.R. Villeneuve, S. Fan, Nature 386 (1997) 143. S.M. Yang, H. Míguez, D.A. Ozin, Adv. Funct. Mater. 12 (2002) 425. P. Jiang, J.F. Bertone, K.S. Hwang, V.L. Colvin, Chem. Mater. 11 (1999) 2132. K. Wostyn, Y. Zhao, B. Yee, K. Clays, A.J. Persoons, Chem. Phys. 118 (2003) 4465. S. Wong, V. Kitaev, G.A. Ozin, J. Am. Chem. Soc. 125 (2003) 15,589. A. Blanco, E. Chomski, S. Grabtchak, M. Ibisate, S. John, S.W. Leonard, C. Lopez, F. Meseguer, H. Miguez, J.P. Mondia, G.A. Ozin, O. Toader, H.M. van Driel, Nature 405 (2000) 437. P. Lodahl, A.F. van Driel, I.S. Nikolaev, A. Irman, K. Overgaag, D. Vanmaekelbergh, W.L. Vos, Nature 430 (2004) 654. A. Arsenault, S. Fournier-Bidoz, B. Hatton, H. Miguez, N. Tétreault, E. Verkis, S. Wong, S.M. Yang, V. Kitaev, G.A. Ozin, J. Mater. Chem. 14 (2004) 781. P. Russell, Science 299 (2003) 358. C.M. Smith, N. Venkataraman, M.T. Gallagher, D. Müller, J.A. West, M.F. Borelli, D.C. Allan, K.W. Koch, Nature 424 (2003) 657. R.F. Cregan, B.J. Mangan, J.C. Knight, T.A. Birks, P.St.J. Russell, P.J. Roberts, D.C. Allan, Science 285 (1999) 1537. N. Tétreault, H. Míguez, S.M. Yang, V. Kitaev, G.A. Ozin, Adv. Mater. 15 (2003) 1167. E. Vekris, V. Kitaev, G. von Freymann, D. Perovic, J.S. Aitchison, G.A. Ozin, Adv. Mater. 17 (2005) 1269.
A. Gil, F. Guitián / Journal of Colloid and Interface Science 307 (2007) 304–307
[16] D. Hönig, D. Möbius, Thin Solid Films 210–211 (1992) 64. [17] H. Kuhn, D. Möbius, Monolayer Assemblies. Investigations of Surfaces and Interfaces, second ed., Wiley, New York, 1993. [18] B. van Duffel, R.H.A. Ras, F.C. De Schryver, R.A. Schoonheydt, J. Mater. Chem. 11 (2001) 3333. [19] I. Dékány, J. Nëmeth, M. Szekeres, R. Schoonheydt, Colloid Polym. Sci. 282 (2003) 1. [20] Y.A. Vlasov, X.Z. Bo, J.C. Sturm, D.J. Norris, Nature 414 (2001) 289.
307
[21] P. Massé, S. Reculusa, K. Clays, S. Ravaine, Chem. Phys. Lett. 422 (2006) 251. [22] K. Wostyn, Y. Zhao, G. de Schaetzen, L. Hellemans, N. Matsuda, K. Clays, A. Persoons, Langmuir 19 (2003) 4465. [23] W. Stöber, A. Fink, E.J. Bohn, Colloid Interface Science 26 (1968) 62. [24] S. Reculusa, S. Ravaine, Chem. Mater. 15 (2003) 598. [25] S. Reculusa, S. Ravaine, Appl. Surf. Sci. 246 (2005) 409. [26] M. Egen, R. Zentel, Macromol. Chem. Phys. 205 (2004) 1479.