Three dimensional silicon-air photonic crystals with controlled defects ...
APPLIED PHYSICS LETTERS 92, 173304 共2008兲
Three dimensional silicon-air photonic crystals with controlled defects using interference lithography V. Ramanan,a兲 E. Nelson,a兲 A. Brzezinski,a兲 P. V. Braun,a兲 and P. Wiltziusb兲 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
共Received 11 February 2008; accepted 1 April 2008; published online 1 May 2008兲 Interference lithography is an attractive technique for the creation of three dimensional photonic crystals. Structures with potential for photonic applications are fabricated in a photoresist through concurrent exposure with four coherent beams of laser radiation. The polymer-air templates are used to create higher refractive index contrast photonic crystals by infilling using atomic layer deposition followed by chemical vapor deposition. These photonic crystals exhibit excellent optical properties with strong reflectance peaks at the calculated band gap frequencies. Two-photon polymerization is used to demonstrate the ability to create designed defect structures such as waveguides in silicon-air photonic crystals. © 2008 American Institute of Physics. 关DOI: 10.1063/1.2919523兴 The area of optical communication has seen rapid growth in the past few years. Considerable study has been devoted to the control of optical properties of materials through the use of photonic crystals,1–4 materials with a periodic arrangement of dielectric medium in one, two or three dimensions, with periodicities on the order of the wavelength of the light being manipulated. Photonic crystals can exhibit photonic band gaps 共PBGs兲 where all frequencies within the gap are forbidden to propagate within the crystal. A PBG is a function of the geometry and refractive index contrast of the photonic crystal, with the phenomenon of a complete PBG only observed in high dielectric contrast three dimensional 共3D兲 photonic crystals.5 There has been great interest in developing fabrication techniques for 3D photonic crystals. These include phasemask lithography,6,7 colloidal self-assembly,8 two-photon polymerization,9 and direct writing.10 This paper will focus on a versatile method of creating wide area defect free crystals based on interference lithography.11–16 This technique involves splitting a monochromatic plane wave from a laser into multiple beams and recombining them inside a photoresist. The lattice symmetry of the resultant structures depends on the wave vector, polarization, phase, and intensity of each beam. Integration of photonic crystals into optical components requires both high refractive index contrast5 and, for many applications, the ability to place designed defects in a precise manner within the crystal structure. Typical photonic crystals fabricated by interference lithography start out as polymerair structures and have a low refractive index contrast. This paper demonstrates the fabrication of high quality, high refractive index contrast silicon-air photonic crystals using interference lithography while simultaneously writing controlled defects and discusses their optical properties. Face centered cubic 共fcc兲-like structures, with lattices elongated perpendicular to the 具111典 direction, were fabricated by concurrent exposure with four noncoplanar coherent
laser beams 共Coherent Ar-ion laser, 351 nm兲 in an umbrella configuration.11,12 This configuration has one central beam and three symmetrically placed beams around it, each making an angle of 34° with the central beam in the resist. The projections of the polarizations of all the beams on the plane of the sample, which is placed perpendicular to the central beam, are parallel 关Fig. 1共a兲, inset兴. The interference pattern created was aligned to be within the resin-based negative photoresist SU8 共MicroChem SU8-2000 series兲 which crosslinks in the high intensity regions when exposed to 351 nm radiation. The substrate was a glass cover slip coated with a 0.5 m layer of crosslinked photoresist to promote adhesion. A 10 m active SU8 layer was then spun on the substrate and prebaked for 5 min at 65 ° C and 10 min at 95 ° C to remove the solvent. After laser exposure, the sample was postbaked for 40 min at 60 ° C to crosslink the high intensity regions. Unexposed polymer was removed using propylene glycol monomethyl ether acetate. The sample was supercriti-
a兲
Also at Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. b兲 Also at Department of Physics, University of Illinois at UrbanaChampaign, Urbana, Illinois 61801, USA. Electronic mail: [email protected].
FIG. 1. 共a兲 SEM top view and 共b兲 SEM cross section of a polymer-air photonic crystal fabricated using 共inset兲 umbrella beam geometry, 共c兲 SEM top view, and 共d兲 cross section exposed using FIB, of an air-silicon photonic crystal.
0003-6951/2008/92共17兲/173304/3/$23.00 92, 173304-1 © 2008 American Institute of Physics Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
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Appl. Phys. Lett. 92, 173304 共2008兲
Ramanan et al.
cally dried from isopropanol, helping maintain the structural integrity of the polymer-air photonic crystal. Following this approach, defect free crystals 关Figs. 1共a兲 and 1共b兲兴 of 5 mm diameter were reproducibly fabricated. The patterned photoresist contracts roughly 20% perpendicular to the substrate during processing. A single inversion procedure was devised to convert polymer-air templates to silicon-air structures. Atomic layer deposition was used to deposit a 30 nm conformal layer of alumina at 90 ° C on the polymer-air photonic crystals, enabling them to withstand temperatures as high as 330 ° C without damage. The alumina coated photonic crystals were filled with amorphous silicon using low temperature static chemical vapor deposition 共CVD兲.17 Samples were loaded into a chamber which was evacuated and charged with ⬃400 mbar of disilane and held at 325 ° C for 15 h, resulting in the deposition of approximately 28 nm of Si. Complete infilling was achieved after 3 cycles. An overlayer of silicon on the sample, indicating that all accessible pore volumes were filled, was removed by subjecting the sample to Si reactive ion etching for 1 min under 20 SCCM 共SCCM denotes cubic centimeter per minute at STP兲 SF6 / O2 with a pressure of 100 mTorr and a power of 70 W. A drop of diluted HF 共5% HF in 50/ 50 ethanol/water mixture兲 was put on the sample for 2 min to remove the alumina and expose the polymer network to air. This was found to limit crack formation during removal of the SU8 polymer at 410 ° C for 4 h. The resultant structure was an inverse silicon-air photonic crystal. The filling fraction of silicon could be controlled either by depositing more alumina before Si CVD to reduce the final amount of Si or by subjecting the silicon-air structure to further CVD to increase the silicon volume fraction. It is important to note that due to the conformal nature of the CVD process, it is not possible to completely fill the pores of the polymer-air template. Scanning electron microscope 共SEM兲 images depicting the top and the cross section of the final structures, exposed using focused ion beam 共FIB兲 milling, are shown in Figs. 1共c兲 and 1共d兲. These crystals are 5 mm in diameter and exhibit no delamination. Having a reproducible technique to create high quality silicon-air crystals is essential for fabricating crystals with embedded defect structures. Polymer-air crystals, fabricated using the method described above, were infiltrated with a mixture of Trimethylol propane triacrylate 共TMPTA兲 monomer and a two-photon sensitive photoinitiator 共0.1 wt % AF-350兲.17,18 The twophoton initiator was excited using a Ti:sapphire laser 共Spectra-Physics Tsunami兲 operating at 780 nm at 50 mW. The mixture also contained a dye 共10−5M BODIPY 630/ 650-⫻, SE from Invitrogen兲 that excites at 625 nm and emits at 640 nm, which enabled fluorescence imaging of the structure in the confocal microscope 共Leica SP2 MultiPhoton Confocal Microscope兲. Concurrent imaging and writing of defects allowed for alignment of the defects to specific crystalline directions. Block features through the thickness of the crystal and embedded channels were written to demonstrate the flexibility of the process. After removal of unpolymerized TMPTA using ethanol, the sample is subjected to the inversion process previously described, resulting in a silicon-air photonic crystal with embedded defects 共Fig. 2兲.
FIG. 2. Fluorescence confocal micrograph of 共a兲 the crystal parallel to the substrate showing embedded channels between darker block features, 共b兲 the crystal perpendicular to the substrate showing the channels are in fact embedded, 共c兲 SEM of a 4 m block feature, SEM of a FIB exposed cross section of 共d兲 a 1 m embedded channel, and 共e兲 a 0.5 m embedded channel. All SEM images depict silicon-air crystals.
The fcc-like silicon-air photonic crystals possess a calculated complete PBG between the second and third bands, assuming complete infilling with silicon. In practice, the conformal CVD process results in a silicon-air structure containing pinched off air voids and a partial PBG.19,20 The reflectance spectrum from the photonic crystals was collected at normal incidence 共具111典 direction兲 in the near infrared region after each processing step using a Fourier transform infrared microscope 共Fig. 3兲. The filling fraction of polymer and alumina in the polymer-alumina-air crystal with an effective refractive index neff = 1.489 共as calculated from SEM and Fabry–Perot fringes兲 is f = 0.78, computed from an effective medium relationship. neff = 冑 fn21 + 共1 − f兲n22 .
共1兲
The refractive indices of SU8 and alumina and silicon are 1.67, 1.6, and 3.6. We can consider the crystal to be a periodic multilayer dielectric stack with a z spacing of
FIG. 3. 共a兲 Spectra showing strong reflectance peak of SU8-air crystal. 共b兲 Peak shift observed upon removal of alumina and SU8. The resonance peak at 1.18 m disappears when Si overlayer on surface is removed. Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
173304-3
d = 0.40 m 共from SEM兲. The reflectance peak is expected to be at = 2neffd. The redshift of the peak upon consecutive deposition of alumina, and silicon then allows us to calculate the filling fractions of SU8, alumina, and silicon to be 0.64, 0.14, and 0.145, respectively. These filling fractions do not add up to 1 due to the conformal nature of the CVD process. Knowledge of the amount of silicon in the air-silicon crystal gives us a calculated reflectance peak at = 2neffd = 1.32 m which is in agreement with the data. The structures exhibited strong reflectance peaks over large areas affirming the high quality of the crystal. The peak reflectance of about 40% for the polymer-air crystal is higher than previously reported values of around 30%.16,19,21 Optical data collected from various samples established the fabrication process to be highly reproducible. Another interesting feature observed is the strong high-energy peak at 1.18 m in the polymer-alumina-silicon crystal, which still has a layer of silicon over the completely filled photonic crystal template. This is indicative of a surface resonance phenomenon that has been observed in similarly filled colloidal crystal templates.22 In conclusion, we have demonstrated a technique to fabricate 3D silicon-air photonic crystals with controlled defect structures incorporated into them. These crystals have uniform, periodic structures over large areas and display excellent optical properties. This provides an important step toward the development of functional optical devices using photonic crystals. J. D. Joannopoulos, P. R. Villeneuve, and S. Fan, Nature 共London兲 386, 143 共1997兲. E. Yablonovitch and T. J. Gmitter, Phys. Rev. Lett. 67, 3380 共1991兲. 3 A. Mekis, J. C. Chen, I. Kurland, S. Fan, P. R. Villeneuve, and J. D. 1
2
Appl. Phys. Lett. 92, 173304 共2008兲
Ramanan et al.
Joannopoulos, Phys. Rev. Lett. 77, 3787 共1996兲. M. Soljacic, C. Luo, J. D. Joannopoulos, and S. Fan, Opt. Lett. 28, 637 共2003兲. 5 M. Maldovan, A. M. Urbas, N. Yufa, W. C. Carter, and E. L. Thomas, Phys. Rev. B 65, 165123 共2002兲. 6 S. Jeon, E. Menard, M. Meitl, and J. A. Rogers, Adv. Mater. 共Weinheim, Ger.兲 16, 1369 共2004兲. 7 T. Y. M. Chan, O. Toader, and S. John, Phys. Rev. E 73, 046610 共2006兲. 8 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, and H. M. van Driel, Nature 共London兲 405, 437 共2000兲. 9 B. H. Cumpston, S. P. Ananthavel, S. R. Marder, and J. W. Perry, Nature 共London兲 398, 51 共1999兲. 10 G. M. Gratson, M. Xu, and J. A. Lewis, Nature 共London兲 428, 386 共2004兲. 11 M. Campbell, D. N. Sharp, M. T. Harrison, R. G. Denning, and A. J. Turberfield, Nature 共London兲 404, 53 共2000兲. 12 S. Yang, M. Megens, J. Aizenberg, P. Wiltzius, P. M. Chaikin, and W. B. Russel, Chem. Mater. 14, 2831 共2002兲. 13 C. K. Ullal, M. Maldovan, E. L. Thomas, G. Chen, Y. J. Han, and S. Yang, Appl. Phys. Lett. 84, 5434 共2004兲. 14 J. H. Moon, S. Yang, W. Dong, J. W. Perry, A. Adibi, and Seung-Man Yang, Opt. Express 14, 6297 共2006兲. 15 N. Tétreault, G. von Freymann, M. Deubel, M. Hermatschweiler, F. PérezWillard, S. John, M. Wegener, and G. A. Ozin, Adv. Mater. 共Weinheim, Ger.兲 18, 457 共2006兲. 16 J. Scrimgeour, D. N. Sharp, C. F. Blanford, O. M. Roche, R. G. Denning, and A. J. Turberfield, Adv. Mater. 共Weinheim, Ger.兲 18, 1557 共2006兲. 17 S. A. Rinne, F. Garcia-Santamaria, and P. V. Braun, Nat. Photonics 2, 52 共2008兲. 18 S. A. Pruzinsky and P. V. Braun, Adv. Funct. Mater. 15, 1995 共2005兲. 19 J. H. Moon, W. Dong, J. W. Perry, A. Adibi, S. M. Yang, and S. Yang, Opt. Express 14, 6297 共2006兲. 20 J. H. Moon, Y. Xu, Y. Dan, S. M. Yang, A. T. Johnson, and S. Yang, Adv. Mater. 共Weinheim, Ger.兲 19, 1510 共2007兲. 21 J. Q. Chen, J. Q. Jiang, X. N. Chen, L. Wang, S. S. Zhang, and R. T. Chen, Appl. Phys. Lett. 90, 093102 共2007兲. 22 F. Garcia-Santamaria, E. C. Nelson, and P. V. Braun, Phys. Rev. B 76, 075132 共2007兲. 4
Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
Three dimensional silicon-air photonic crystals with controlled defects using interference lithography V. Ramanan,a兲 E. Nelson,a兲 A. Brzezinski,a兲 P. V. Braun,a兲 and P. Wiltziusb兲 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
共Received 11 February 2008; accepted 1 April 2008; published online 1 May 2008兲 Interference lithography is an attractive technique for the creation of three dimensional photonic crystals. Structures with potential for photonic applications are fabricated in a photoresist through concurrent exposure with four coherent beams of laser radiation. The polymer-air templates are used to create higher refractive index contrast photonic crystals by infilling using atomic layer deposition followed by chemical vapor deposition. These photonic crystals exhibit excellent optical properties with strong reflectance peaks at the calculated band gap frequencies. Two-photon polymerization is used to demonstrate the ability to create designed defect structures such as waveguides in silicon-air photonic crystals. © 2008 American Institute of Physics. 关DOI: 10.1063/1.2919523兴 The area of optical communication has seen rapid growth in the past few years. Considerable study has been devoted to the control of optical properties of materials through the use of photonic crystals,1–4 materials with a periodic arrangement of dielectric medium in one, two or three dimensions, with periodicities on the order of the wavelength of the light being manipulated. Photonic crystals can exhibit photonic band gaps 共PBGs兲 where all frequencies within the gap are forbidden to propagate within the crystal. A PBG is a function of the geometry and refractive index contrast of the photonic crystal, with the phenomenon of a complete PBG only observed in high dielectric contrast three dimensional 共3D兲 photonic crystals.5 There has been great interest in developing fabrication techniques for 3D photonic crystals. These include phasemask lithography,6,7 colloidal self-assembly,8 two-photon polymerization,9 and direct writing.10 This paper will focus on a versatile method of creating wide area defect free crystals based on interference lithography.11–16 This technique involves splitting a monochromatic plane wave from a laser into multiple beams and recombining them inside a photoresist. The lattice symmetry of the resultant structures depends on the wave vector, polarization, phase, and intensity of each beam. Integration of photonic crystals into optical components requires both high refractive index contrast5 and, for many applications, the ability to place designed defects in a precise manner within the crystal structure. Typical photonic crystals fabricated by interference lithography start out as polymerair structures and have a low refractive index contrast. This paper demonstrates the fabrication of high quality, high refractive index contrast silicon-air photonic crystals using interference lithography while simultaneously writing controlled defects and discusses their optical properties. Face centered cubic 共fcc兲-like structures, with lattices elongated perpendicular to the 具111典 direction, were fabricated by concurrent exposure with four noncoplanar coherent
laser beams 共Coherent Ar-ion laser, 351 nm兲 in an umbrella configuration.11,12 This configuration has one central beam and three symmetrically placed beams around it, each making an angle of 34° with the central beam in the resist. The projections of the polarizations of all the beams on the plane of the sample, which is placed perpendicular to the central beam, are parallel 关Fig. 1共a兲, inset兴. The interference pattern created was aligned to be within the resin-based negative photoresist SU8 共MicroChem SU8-2000 series兲 which crosslinks in the high intensity regions when exposed to 351 nm radiation. The substrate was a glass cover slip coated with a 0.5 m layer of crosslinked photoresist to promote adhesion. A 10 m active SU8 layer was then spun on the substrate and prebaked for 5 min at 65 ° C and 10 min at 95 ° C to remove the solvent. After laser exposure, the sample was postbaked for 40 min at 60 ° C to crosslink the high intensity regions. Unexposed polymer was removed using propylene glycol monomethyl ether acetate. The sample was supercriti-
a兲
Also at Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. b兲 Also at Department of Physics, University of Illinois at UrbanaChampaign, Urbana, Illinois 61801, USA. Electronic mail: [email protected].
FIG. 1. 共a兲 SEM top view and 共b兲 SEM cross section of a polymer-air photonic crystal fabricated using 共inset兲 umbrella beam geometry, 共c兲 SEM top view, and 共d兲 cross section exposed using FIB, of an air-silicon photonic crystal.
0003-6951/2008/92共17兲/173304/3/$23.00 92, 173304-1 © 2008 American Institute of Physics Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
173304-2
Appl. Phys. Lett. 92, 173304 共2008兲
Ramanan et al.
cally dried from isopropanol, helping maintain the structural integrity of the polymer-air photonic crystal. Following this approach, defect free crystals 关Figs. 1共a兲 and 1共b兲兴 of 5 mm diameter were reproducibly fabricated. The patterned photoresist contracts roughly 20% perpendicular to the substrate during processing. A single inversion procedure was devised to convert polymer-air templates to silicon-air structures. Atomic layer deposition was used to deposit a 30 nm conformal layer of alumina at 90 ° C on the polymer-air photonic crystals, enabling them to withstand temperatures as high as 330 ° C without damage. The alumina coated photonic crystals were filled with amorphous silicon using low temperature static chemical vapor deposition 共CVD兲.17 Samples were loaded into a chamber which was evacuated and charged with ⬃400 mbar of disilane and held at 325 ° C for 15 h, resulting in the deposition of approximately 28 nm of Si. Complete infilling was achieved after 3 cycles. An overlayer of silicon on the sample, indicating that all accessible pore volumes were filled, was removed by subjecting the sample to Si reactive ion etching for 1 min under 20 SCCM 共SCCM denotes cubic centimeter per minute at STP兲 SF6 / O2 with a pressure of 100 mTorr and a power of 70 W. A drop of diluted HF 共5% HF in 50/ 50 ethanol/water mixture兲 was put on the sample for 2 min to remove the alumina and expose the polymer network to air. This was found to limit crack formation during removal of the SU8 polymer at 410 ° C for 4 h. The resultant structure was an inverse silicon-air photonic crystal. The filling fraction of silicon could be controlled either by depositing more alumina before Si CVD to reduce the final amount of Si or by subjecting the silicon-air structure to further CVD to increase the silicon volume fraction. It is important to note that due to the conformal nature of the CVD process, it is not possible to completely fill the pores of the polymer-air template. Scanning electron microscope 共SEM兲 images depicting the top and the cross section of the final structures, exposed using focused ion beam 共FIB兲 milling, are shown in Figs. 1共c兲 and 1共d兲. These crystals are 5 mm in diameter and exhibit no delamination. Having a reproducible technique to create high quality silicon-air crystals is essential for fabricating crystals with embedded defect structures. Polymer-air crystals, fabricated using the method described above, were infiltrated with a mixture of Trimethylol propane triacrylate 共TMPTA兲 monomer and a two-photon sensitive photoinitiator 共0.1 wt % AF-350兲.17,18 The twophoton initiator was excited using a Ti:sapphire laser 共Spectra-Physics Tsunami兲 operating at 780 nm at 50 mW. The mixture also contained a dye 共10−5M BODIPY 630/ 650-⫻, SE from Invitrogen兲 that excites at 625 nm and emits at 640 nm, which enabled fluorescence imaging of the structure in the confocal microscope 共Leica SP2 MultiPhoton Confocal Microscope兲. Concurrent imaging and writing of defects allowed for alignment of the defects to specific crystalline directions. Block features through the thickness of the crystal and embedded channels were written to demonstrate the flexibility of the process. After removal of unpolymerized TMPTA using ethanol, the sample is subjected to the inversion process previously described, resulting in a silicon-air photonic crystal with embedded defects 共Fig. 2兲.
FIG. 2. Fluorescence confocal micrograph of 共a兲 the crystal parallel to the substrate showing embedded channels between darker block features, 共b兲 the crystal perpendicular to the substrate showing the channels are in fact embedded, 共c兲 SEM of a 4 m block feature, SEM of a FIB exposed cross section of 共d兲 a 1 m embedded channel, and 共e兲 a 0.5 m embedded channel. All SEM images depict silicon-air crystals.
The fcc-like silicon-air photonic crystals possess a calculated complete PBG between the second and third bands, assuming complete infilling with silicon. In practice, the conformal CVD process results in a silicon-air structure containing pinched off air voids and a partial PBG.19,20 The reflectance spectrum from the photonic crystals was collected at normal incidence 共具111典 direction兲 in the near infrared region after each processing step using a Fourier transform infrared microscope 共Fig. 3兲. The filling fraction of polymer and alumina in the polymer-alumina-air crystal with an effective refractive index neff = 1.489 共as calculated from SEM and Fabry–Perot fringes兲 is f = 0.78, computed from an effective medium relationship. neff = 冑 fn21 + 共1 − f兲n22 .
共1兲
The refractive indices of SU8 and alumina and silicon are 1.67, 1.6, and 3.6. We can consider the crystal to be a periodic multilayer dielectric stack with a z spacing of
FIG. 3. 共a兲 Spectra showing strong reflectance peak of SU8-air crystal. 共b兲 Peak shift observed upon removal of alumina and SU8. The resonance peak at 1.18 m disappears when Si overlayer on surface is removed. Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
173304-3
d = 0.40 m 共from SEM兲. The reflectance peak is expected to be at = 2neffd. The redshift of the peak upon consecutive deposition of alumina, and silicon then allows us to calculate the filling fractions of SU8, alumina, and silicon to be 0.64, 0.14, and 0.145, respectively. These filling fractions do not add up to 1 due to the conformal nature of the CVD process. Knowledge of the amount of silicon in the air-silicon crystal gives us a calculated reflectance peak at = 2neffd = 1.32 m which is in agreement with the data. The structures exhibited strong reflectance peaks over large areas affirming the high quality of the crystal. The peak reflectance of about 40% for the polymer-air crystal is higher than previously reported values of around 30%.16,19,21 Optical data collected from various samples established the fabrication process to be highly reproducible. Another interesting feature observed is the strong high-energy peak at 1.18 m in the polymer-alumina-silicon crystal, which still has a layer of silicon over the completely filled photonic crystal template. This is indicative of a surface resonance phenomenon that has been observed in similarly filled colloidal crystal templates.22 In conclusion, we have demonstrated a technique to fabricate 3D silicon-air photonic crystals with controlled defect structures incorporated into them. These crystals have uniform, periodic structures over large areas and display excellent optical properties. This provides an important step toward the development of functional optical devices using photonic crystals. J. D. Joannopoulos, P. R. Villeneuve, and S. Fan, Nature 共London兲 386, 143 共1997兲. E. Yablonovitch and T. J. Gmitter, Phys. Rev. Lett. 67, 3380 共1991兲. 3 A. Mekis, J. C. Chen, I. Kurland, S. Fan, P. R. Villeneuve, and J. D. 1
2
Appl. Phys. Lett. 92, 173304 共2008兲
Ramanan et al.
Joannopoulos, Phys. Rev. Lett. 77, 3787 共1996兲. M. Soljacic, C. Luo, J. D. Joannopoulos, and S. Fan, Opt. Lett. 28, 637 共2003兲. 5 M. Maldovan, A. M. Urbas, N. Yufa, W. C. Carter, and E. L. Thomas, Phys. Rev. B 65, 165123 共2002兲. 6 S. Jeon, E. Menard, M. Meitl, and J. A. Rogers, Adv. Mater. 共Weinheim, Ger.兲 16, 1369 共2004兲. 7 T. Y. M. Chan, O. Toader, and S. John, Phys. Rev. E 73, 046610 共2006兲. 8 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, and H. M. van Driel, Nature 共London兲 405, 437 共2000兲. 9 B. H. Cumpston, S. P. Ananthavel, S. R. Marder, and J. W. Perry, Nature 共London兲 398, 51 共1999兲. 10 G. M. Gratson, M. Xu, and J. A. Lewis, Nature 共London兲 428, 386 共2004兲. 11 M. Campbell, D. N. Sharp, M. T. Harrison, R. G. Denning, and A. J. Turberfield, Nature 共London兲 404, 53 共2000兲. 12 S. Yang, M. Megens, J. Aizenberg, P. Wiltzius, P. M. Chaikin, and W. B. Russel, Chem. Mater. 14, 2831 共2002兲. 13 C. K. Ullal, M. Maldovan, E. L. Thomas, G. Chen, Y. J. Han, and S. Yang, Appl. Phys. Lett. 84, 5434 共2004兲. 14 J. H. Moon, S. Yang, W. Dong, J. W. Perry, A. Adibi, and Seung-Man Yang, Opt. Express 14, 6297 共2006兲. 15 N. Tétreault, G. von Freymann, M. Deubel, M. Hermatschweiler, F. PérezWillard, S. John, M. Wegener, and G. A. Ozin, Adv. Mater. 共Weinheim, Ger.兲 18, 457 共2006兲. 16 J. Scrimgeour, D. N. Sharp, C. F. Blanford, O. M. Roche, R. G. Denning, and A. J. Turberfield, Adv. Mater. 共Weinheim, Ger.兲 18, 1557 共2006兲. 17 S. A. Rinne, F. Garcia-Santamaria, and P. V. Braun, Nat. Photonics 2, 52 共2008兲. 18 S. A. Pruzinsky and P. V. Braun, Adv. Funct. Mater. 15, 1995 共2005兲. 19 J. H. Moon, W. Dong, J. W. Perry, A. Adibi, S. M. Yang, and S. Yang, Opt. Express 14, 6297 共2006兲. 20 J. H. Moon, Y. Xu, Y. Dan, S. M. Yang, A. T. Johnson, and S. Yang, Adv. Mater. 共Weinheim, Ger.兲 19, 1510 共2007兲. 21 J. Q. Chen, J. Q. Jiang, X. N. Chen, L. Wang, S. S. Zhang, and R. T. Chen, Appl. Phys. Lett. 90, 093102 共2007兲. 22 F. Garcia-Santamaria, E. C. Nelson, and P. V. Braun, Phys. Rev. B 76, 075132 共2007兲. 4
Downloaded 06 May 2008 to 128.174.228.144. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp
