ABSTRACT Cracking of photonic crystals (PCs) has received considerable attention because of its severe limitation to PC’s applications in high-performance optics devices. Although enormous

efforts have been focused on the understanding and elimination of the uncontrolled cracks in the self-assembly process, no reliable, low cost and scalable methods have been demonstrated for

the fabrication of large (cm or more) crack-free single-crystalline PCs. Herein, we present a facile, reliable approach for the assembly of crack-free single-crystalline PCs on the

centimeter scale by the synergistic effects of substrate deformation and monomer infiltration/polymerization. The co-assembling monomer infiltrates and polymerizes in the interstices of the

single-crystalline PCs will not only prompt the practical applications of PCs in high-performance optics devices, but also have great implications for the fabrication of crack-free thin

films in other fields, such as wet clays, coating and the ceramic industry. SIMILAR CONTENT BEING VIEWED BY OTHERS 3D MICROPRINTING OF INORGANIC POROUS MATERIALS BY CHEMICAL LINKING-INDUCED

SOLIDIFICATION OF NANOCRYSTALS Article Open access 20 December 2023 SIMULTANEOUS MECHANICAL AND CHEMICAL SYNTHESIS OF LONG-RANGE-ORDERED PEROVSKITES Article 22 November 2024 SEMI-CONDUCTING

2D RECTANGLES WITH TUNABLE LENGTH VIA UNIAXIAL LIVING CRYSTALLIZATION-DRIVEN SELF-ASSEMBLY OF HOMOPOLYMER Article Open access 10 May 2021 INTRODUCTION Photonic crystals (PCs) have aroused

worldwide attention because of their special light manipulation properties, which are extensively exploited in integrated optical devices,1, 2, 3 full-color displays4, 5 and

chemical/biological sensors.6, 7, 8 Self-assembly of submicrometer colloidal spheres into PC structures is a promising approach due to its simplicity and low cost, compared with top-down

lithography techniques.9, 10, 11 However, the unintended crack formation in the self-assembly process has severely hindered the fabrication of large-area single crystalline PCs and their

corresponding applications in high-quality optics devices.12, 13, 14 Accordingly, much attention has been focused on the cracking mechanism15, 16 and elimination.17, 18, 19, 20, 21, 22, 23,

24, 25 Generally, cracking is mainly caused by the tensile stress generated in the self-assembly process, which arises from the shrinkage of the colloidal spheres during the final drying

process and the constraint of this shrinkage by the rigid substrate.15, 16 Based on this understanding, various approaches have been devised to eliminate the tensile stress and avoid

cracking.17, 18, 19, 20, 21, 22, 23, 24, 25 Firstly, preventing the colloidal spheres from shrinking by preshrinking them before assembly is an effective approach to eliminate the tensile

stress and avoid cracking.19 Secondly, using the liquid substrate (molten Ga)21 or patterned substrate24 allows the homogeneous shrinkage of the colloidal spheres, thus avoiding the stress

production during the assembly process. Last, but not least, the preferential selection of the low-stacking density crystal structure is favorable for the elimination of cracking as it

releases the stress from the interstices between the lattice faces. As a typical example, Aizenberg _et al._25 prepared large-area crack-free PCs with a low-stacking density (110) lattice

structure. However, the aforementioned approaches are either tedious22 or involve using poisonous21 and costly substrates,24 and the largest single crystalline domain ever-reported is not

more than 200 μm × 200 μm.18 No reliable, low cost, scalable methods have been demonstrated for the fabrication of large (cm or more) crack-free single-crystal PCs. Herein, we present a

facile strategy for large-area crack-free single-crystalline PCs by the combined effects of polymerization-assisted assembly and substrate deformation. The co-assembling monomers infiltrate

and polymerize in the interstices of the colloidal spheres, which could reduce the shrinkage of the colloidal spheres and lower the generated tensile stress. The infiltrated polymer also

strengthens the long range interactions of colloidal spheres based on its elasticity. Otherwise, the timely transformation of the flexible substrate releases the residual stress. Elastic

polymer infiltration and substrate deformation result in an integration of micrometer-sized single-crystal domains into centimeter scale crack-free single-crystalline PCs, which are the

largest ever-reported. The obtained PCs show an improved optical property due to the large-area well-ordered single-crystalline structure. This facile approach to large-area

single-crystalline PCs will be promising for PCs’ practical applications in high-quality optical integrated devices, optical waveguides and so on. MATERIALS AND METHODS MATERIALS Metal foils

with different thickness were obtained from Kaihua Aluminum Company limited, Jiangsu, China. These foils were cleaned in 1:1 absolute ethanol and acetone ultrasonically before use.

Monodisperse latex spheres of poly(styrene–methyl methacrylate–acrylic acid) (poly(St-MMA-AA)) were synthesized via our previous method26, 27, 28 and were directly used without further

treatment. _N_-isopropyl acrylamide (NIPAm) was purchased from Tokyo Chemical Industry Co, Ltd. _N_, _N_′-methylenebisacrylamide (99%) and ammonium persulfate (98%) were purchased from

Sigma-Aldrich (Shanghai, China). All the reagents were purified by re-crystallization before use. METHODS Four percent monomer solution was prepared by mixing 0.64 g monomer, 2.9 g 1% _N_,

_N_′-methylenebisacrylamide, 0.26 g 1% ammonium persulfate into 12.2 g of water. The monomer solution was then mixed with poly(St-MMA-AA) colloidal dispersion with the weight ratios of

monomer/colloid as 0:1, 0.5:1, 1:1, 1.5:1 and 2:1. After dispersing ultrasonically for 30 min, the suspension was divided into vials of 5 ml. Aluminium (Al) foils were vertically positioned

in these vials. Subsequently, the monodispersed poly(St-MMA-AA) colloidal spheres were self-assembled on the Al foils at 60 °C and relative humidity of 60%. During the assembly process, the

monomer infiltrated in the interstices of the poly(St-MMA-AA) colloidal spheres and polymerized with _N_, _N_′-methylenebisacrylamide crosslinker under the initiation of ammonium persulfate,

and upon drying, crack-free composite opal PCs were obtained. Moreover, the inverse opal PCs without cracks were facilely obtained after dissolving the poly(St-MMA-AA) colloidal spheres

with 1,4-dioxane. In these experiments, monomers used are NIPAm, acrylic acid, acrylamide, crotonyl alcohol, trans-2-butenioc acid, 2-hydroxyethyl methacrylate and 2-(dimethylamino)ehyl

methacrylate. CHARACTERIZATION Scanning electronic microscopy (SEM) images were obtained with a field-emission SEM microscope, JSM-6700, JEOL, Ltd (Tokyo, Japan). Ultraviolet-vis spectra

were recorded with an Ocean Optic HR 4000 fiber optic ultraviolet-vis spectrometer (Dunedin, FL, USA), normal to the (hkl, miller indices of a notation system in crystallography for planes

and directions in crystal lattice)=(111) planes of the crystal. Synchrotron small-angle X-ray scattering (SAXS) measurement was performed at the beamline BL16B1 at Shanghai Synchrotron

Radiation Facility, China, using grazing-incidence SAXS (GISAXS) due to the presence of the substrate. The energy of the X-ray radiation was 10 keV, resulting in a wavelength of 0.124 nm.

The size of the primary X-ray beam was 1 × 1.2 mm2 with the incident angle of the X-ray to the sample of _ca_ 2° and the sample-to-detector distance was 5240 mm. The size of the X-ray beam

at the sample position was 28 × 1 mm2 for GISAXS. For SAXS data collection, a Mar165 CCD detector (Diamond Light Source, Oxfordshire, UK) with an average pixel size of 80 × 80 μm2 was used.

The SAXS data were corrected for background scattering and normalized with respect to the primary beam intensity. The yield strength (_R__p0.2_) of metal foils with different thicknesses was

tested at 20 °C using a domestic electronic universal tensile tester (WDW-10E, Time Group, Nanjing, China) controlled by a computer at a tensile test rate of 1.5 mm min−1. The yield point

was determined by the 0.2% offset technique. Thermal characteristics were measured using a differential scanning calorimeter (differential scanning calorimetry, TA Instruments, Q2000, 45,

New Castle, DE, USA). RESULTS AND DISCUSSIONS CHARACTERIZATION OF LARGE-AREA CRACK-FREE SINGLE-CRYSTALLINE PCS The fabrication of large-area crack-free single-crystalline PCs is shown in

Scheme 1. Monodisperse colloidal spheres of poly(St-MMA-AA) are co-assembled with a water-soluble monomer (NIPAm for instance) on metal foils. While the colloidal spheres self-assemble into

well-ordered periodic structures, the monomer infiltrates and polymerizes in the interstices of the colloidal spheres to form a crosslinked elastic polymer network. The crosslinked polymer

network can fix the perfectly-ordered latex arrangement in the saturated dispersion, favoring the achievement of large-area crack-free single crystalline PCs. Meanwhile, the used flexible

substrate of metal foils can be deformed to release the residual stress. The synergetic effects of elastic polymer infiltration and the substrate deformation allow the achievement of

large-area crack-free composite opal and inverse opal PCs. The colloidal spheres of poly(St-MMA-AA) synthesized in our lab were chosen because they are favorable for the fabrication of large

area crack-free single crystalline PCs. Firstly, the colloidal sphere of poly(St-MMA-AA) has good monodispersity with a polydispersity index of 0.005. The excellent monodispersity is

beneficial for the large-scale assembly of uniform PCs. Secondly, the colloidal spheres have a special core-shell structure with a hydrophilic PAA shell and a hydrophobic PS core. The

hydrogen bonding among carboxyl groups of the hydrophilic shell is beneficial for the well-ordered colloidal assembly. Thirdly, the hydrophilic shell is helpful for the infiltration of the

hydrophilic co-assembling monomer, such as NIPAm or acrylamide, into the interstices of the colloidal particles, favoring their homogeneous infiltration. Figures 1a and b present the SEM

images of as-prepared poly-NIPAm (PNIPAm)-poly(St-MMA-AA) composite opal PCs assembled on 20-μm-thick Al foil. Clearly, PCs with an area of 1.5 × 2 cm2 (Figures 1a and b, Supplementary

Figure S1 and Supplementary Figure S2) are devoid of cracks. As-prepared composite opal PCs are highly periodic over the whole sample with (111) close-packed faces parallel to the substrates

(Figure 1b). Obviously, the interstices of poly(St-MMA-AA) colloidal spheres have been fully and uniformly infiltrated, as is observed in the magnified SEM image inserted in Figure 1b.

PNIPAm infiltration reduces the shrinkage of the colloidal spheres and strengthens the interaction of the colloidal spheres, which favors the crack elimination20 and the integration of

micrometer sized single-crystalline domains into centimeter-scale single-crystalline PCs. The large area crack-free PCs were assembled with latex diameters of 320, 180, 230 and 260 nm

(Figure 1b and Supplementary Figure S2). Furthermore, after selectively dissolving the colloidal spheres with 1, 4-dioxane, crack-free PNIPAm inverse opal PCs are also obtained, as shown in

Figures 1d and e. The absence of cracks in the (111) plane, which is most prone to cracking,29 implies the complete elimination of cracks in the as-prepared PCs. Expectedly, the obtained

large-area crack-free PNIPAm-poly(St-MMA-AA) composite opal PCs show a single-crystalline property determined by GISAXS, which is a nondestructive tool to characterize the macroscopic single

crystal structure of PCs.30, 31, 32, 33 Figure 2 (Supplementary Figures S3a, b) presents the GISAXS result of the as-prepared large-area crack-free PCs. The incident beam was parallel to

the (111) plane, and thus the collected data were from <110> or zones. The data exhibit typical lattice diffraction features in accordance with the simulated pattern of the zone in

Supplementary Figure S3b, indicating a single-crystalline structure.30, 31, 32, 33As the size of the primary X-ray beam at the sample position was _ca_ 28 mm × 1 mm for the GISAXS

experiment, it could be assumed that the single crystal array in Figure 2b reveals macroscopic single-crystal domains on the centimeter scale.33 The spacing of d200 and d100 is obtained from

the diffraction data: d200=2π/q(200)=261.7 nmd100=2d200=523.4 nm. Thus, a center-to-center distance (_R_) between two adjacent particles is calculated through: . The calculated value is

50.2 nm higher than the latex diameter of _ca_ 320 nm observed by SEM in Figure 1b. The increase by 50.2 nm could result from the infiltration of elastic polymer into the interstice of latex

particles, which is close to the average wall thickness (_ca_ 45 nm) of the inverse opal. The characterization of large scale single-crystalline domain is in consistence with the long-rang

well-ordered crystal structure of the crack-free PCs in Figure 1b. The homogeneous PNIPAm infiltration in the interstices of the latex spheres (inserted image in Figure 1b) produces an

interconnected network among latex particles and strengthens the interactions of the latex spheres. The centimeter scale crack-free single-crystalline domain resulted in the optical

improvement in Figures 1c and f (Supplementary Figure S2d). The full-width-at-half-maximum of the reflectance spectra (Figures 1c and f and Supplementary Figure S2d) of the crack-free PCs

(_ca_ 48 nm) is significantly narrower (30%) than that of the corresponding cracked PCs (_ca_ 70 nm). The much narrower stopband may be due to the elimination of scattering effects caused by

the cracks.22 This largest crack-free single-crystalline PCs ever-reported with improved optical properties will have potential applications in full optical circuit, next-generation

displays and so forth. EFFECT OF MONOMER INFILTRATION/POLYMERIZATION ON THE FABRICATION OF LARGE-AREA CRACK-FREE SINGLE CRYSTALLINE PCS Proper selection of co-assembling monomer is crucial

for the fabrication of large-area crack-free single-crystal PCs. Firstly, the monomer is aqueous and could easily be dispersed in the latex suspension without affecting the system’s

stability. Secondly, the as-formed polymer is elastic, which could undergo reversible expansion/contraction to absorb the stress during the assembling process. Thirdly, the polymerization

rate of the monomer must be slower than the assembly rate of latex particles, which ensures the well-ordered latex assembly and the homogeneous infiltration of the polymer into the

interstice of the latex particles. Too rapid monomer polymerization will cause the viscosity growth of the system and affect the well-ordered latex assembly. Based on these considerations,

aqueous monomers, such as acrylic acid, acrylamide, crotonyl alcohol, trans-2-butenioc acid, 2-hydroxyethyl methacrylate and 2-(dimethylamino)ehyl methacrylate, were used to fabricate the

corresponding composite opal PCs (Supplementary Figure S4). It was found that NIPAm, acrylic acid and acrylamide were the optimal choice as infiltrating monomers. In particularly, the

as-prepared crack-free PNIPAm composite PCs demonstrated the best well-ordered latex arrangement. In this case, the NIPAm polymerizes to form PNIPAm, which precipitates from the latex system

because the assembly temperature is over 33 °C (the lower critical solution temperature of PNIPAm).34 The precipitation of PNIPAm effectively avoids the viscosity growth of the system,

favoring the well-ordered latex assembly. Importantly, the infiltration of PNIPAm among the latex interstice fixes the perfectly-ordered latex arrangement in the saturated dispersion15 and

strengthens the latex interactions, which contributes to the large-area single crystalline PCs (Figure 2). In contrast, composite PCs from other monomers show relatively poor periodic

structure although the cracks are completely eliminated. The relatively poor periodic structure could be attributed to the dramatic viscosity growth resulting from the rapid monomer

polymerization, which would disturb the assembly process. To determine an optimal monomer infiltration amount, a series of PCs were prepared on 20-μm-thick Al foils with varying weight

ratios of monomer/colloid in the co-assembling system from 0:1 to 2:1. Taking NIPAm as an example, the crack width of as-prepared PCs decreases from _ca_ 3 to 0.5 to 0.4 μm (Figures 3a–c),

as the ratios of NIPAm/colloid increase from 0:1 to 0.5:1 to 1:1, respectively. The optimal NIPAm/colloid ratio for crack-free PCs is 1.5:1 (Figure 3d), and an overlayer of PNIPAm occurs

upon the PCs’ surface (Figure 3e) when the ratio of NIPAm/colloid approaches 2:1. Meantime, an obvious red shift of the stopband of the PCs is observed with the PNIPAm/colloid ratios

increasing from 0:1 to 0.5:1 to 1:1 (Supplementary Figure S5). The phenomenon implies that PNIPAm is evenly infiltrated into the interstices of the colloidal spheres, which results in a

continuous growth of the refractive index and of the center-to-center distance (_R_) between two adjacent particles (insert image in Figure 1b). In comparison, the shift of the stopband

position becomes inconspicuous when the ratio of NIPAm/colloid is over 1:1 (Supplementary Figure S5b), which means that the interstice of the colloidal spheres is almost fully infiltrated.

Accordingly, it is concluded that the critical monomer/colloid ratio for large-area crack-free PCs should be about 1:1, over which crack-free PCs could be achieved. The value is a little

higher than the theoretical value of 0.85:1 (Supplementary Figure S6), which may result from the volume shrinkage as the monomer polymerizes during the assembly process. EFFECT OF THE USED

SUBSTRATE ON LARGE-AREA CRACK-FREE SINGLE CRYSTALLINE PCS A proper substrate is necessary for the fabrication of large-area single-crystal PCs. Large cracks are still found in PNIPAm/colloid

composite opal PCs assembled on a glass substrate (Figure 3f) even at the optimized infiltration ratio of 1.5:1. To further assess the specific requirements of the substrate for fabrication

of crack-free PCs, a series of PNIPAm/colloid composite opal PCs were assembled on Al foils with different thickness at fixed NIPAm/colloid ratio of 1.5:1 and a fixed latex concentration of

0.2 wt% (Figure 4). Clearly, crack-free composite opal PCs were obtained on Al foils with thickness ⩽100 μm (that is, 20, 65 and 100 μm) (Figures 4a–c), while cracks occurred in the PC

films on Al foils with thicknesses>100 μm, such as 130, 180 and 280 μm (Figures 4d–f). This could be attributed to the distinct deformation behavior of Al foils determined by their

thickness.35 The thin Al foil deforms easily, which favors the timely release of the tensile stress generated during the assembly process.35 The intrinsic deformation behavior is based on

the _R__p0.2_ of different Al foils (in Supplementary Figure S7a). The thinner the Al foils, the lower their _R__p0.2_ and the easier for the deformation of Al foils; consequently, the

stress is easily released, which contributes to the large-area crack-free PCs (Figures 4a–c). Vice versa, the thicker Al foils show higher _R__p0.2_, which results in a greater difficulty

for their deformation and the release of the stress, leading to the cracked PCs (Figures 4d–f). In our experiment, other metal substrates, such as Cu, Ti and Ni foils (Supplementary Figure

S8), were also applied for the fabrication of crack-free PCs. Besides Al foils, the critical thickness for fabrication of crack-free PCs with fixed latex concentration of 0.2% was also

determined: Ti foil with thickness ⩽35 μm, Cu foil with thickness⩽105 μm and Ni foil with thickness⩽55 μm (Supplementary Figure S8). Subsequently, at a fixed metal foil thickness (100 

μm-thick-Al-foil for instance), PCs with different thickness were assembled by varying the latex concentration and the critical crack-free PC thicknesses were determined. In the case of Al

foil with a thickness of 100 μm, the critical crack-free PC thickness is ∼5.6 μm assembled with a latex concentration of 0.2% (Supplementary Figure S9 and Supplementary Figure S7b). The

relationship of PC thickness (cracking or not) and substrate compliance are summarized in Figure 5. The _R__p0.2_ of the substrate and the critical crack-free PC thickness demonstrates

typical reciprocal relation, which is in good agreement with the theoretical relationship between the critical stresses for nucleation of a crack in a film of identical elastic spheres and

the critical film thickness predicted based on Griffith’s energy balance concept.15 From Figure 5, the thickest crack-free PC that can be fabricated herein is ∼5.6 μm, over which cracks

develops in the PCs. The value differs with the calculated critical crack-free film thickness of ∼19.7 μm with randomly-packed colloidal spheres.15 The deviation may arise from the higher

tensile stress generated in a highly ordered system and the weakness of the closest packed crystal structure.29 The specific requirement for large area crack-free PCs determined herein

provides great guidance for the fabrication of crack-free PCs and has great implications for PC practical applications. It should be mentioned that water has an important role in the

fabrication process of the large area crack-free single-crystal PCs, due to the hydrophilic property of the latex spheres. Water adsorbed in the PNIPAm hydrogel makes the composite PCs more

robust, which decreases the tensile stress during the assembly process through reducing latex shrinkage. The slower water evaporation form the PNIPAm hydrogel ensures the timely release of

the generated tensile stress through substrate deformation, avoiding its accumulation to cause cracks. The elastic property of the infiltrated polymer among the latex spheres strengthens

their interaction as to form large area single-crystalline PCs without cracks. However, after complete drying in the programmable constant temperature/humidity machine, the materials

scratched off from the Al foils were characterized by differential scanning calorimetry and thermogravimetric analysis. No characteristic peaks of ice melting at ∼0 °C, related to water

sorption,36 or thermal degradation at ∼110 °C, related to water loss in the thermogravimetric analysis curve,37 were observed (Supplementary Figure S10), indicating the water content in the

obtained composite PC was negligible. This negligible water content favors the practical applications of PCs at elevated temperatures. After treating the PCs at temperature from 120 °C to

180 °C, no obvious degradation of optical property was found when the film was treated at 120, 140 and 160 °C for 1 h. In contrast, crack formation and reflectance intensity drop were

observed after the film was treated at 180 °C. The crack-free PCs can be applied at an operating temperature as high as 160 °C (Supplementary Figure S11a, b), favoring their practical

applications. MECHANISM FOR CRACK ELIMINATION The crack-avoiding mechanism is clarified in Figure 6, taking the critical crack-free PC thickness assembled on Al foils with a critical

thickness of 100 μm whose _R__p0.2_ is ∼102.2 MPa, for instance. The crack-free PCs could be achieved when substrates with _Rp__0.2_⩽102.2 MPa were used and the weight ratio of

monomer/colloid was over the critical value of 1:1 (Supplementary Figure S12). In contrast, cracked PCs were found due to an insufficient infiltration of elastic polymer or the use of a

rigid substrate (Supplementary Figure S12). Proper infiltration of elastic polymer can counteract the volume shrinkage of the colloidal spheres and strengthens their interactions. The

elastic polymer could store part of the tensile stress by its elasticity, whose stretching is observed through the cracks in a cracked PC with a thickness of 7.7 μm (Supplementary Figure

S13). The stored energy in the elastic polymer was transferred to the flexible substrate and finally released by substrate deformation, which is proved by the calculated critical tensile

stress to nucleate a crack, agreeing well with the _R__p0.2_ of the flexible substrate. This critical value of _R__p0.2_ (102.2 MPa) is close to the theoretical critical tensile stress

(_σ__c_) (110.6 MPa) for the nucleation of a crack, as is calculated by the Griffith’s energy balance concept (Supplementary Figures S9).15 The deformation of substrates with _R__p0.2_⩽102 

MPa contributes to the timely release of the residual tensile stress, avoiding stress accumulation and subsequent cracking in PCs (Figure 6b). In contrast, the residual stress cannot be

effectively released by the deformation of the substrate with _R__p0.2_>102 MPa, leading to a cracked PC. (Figure 6a). In conclusion, we demonstrate a facile, reliable and general

approach for the fabrication of crack-free single-crystalline PCs with centimeter scale by the synergistic effects of substrate deformation and monomer infiltration/polymerization. The

critical thickness of crack-free PCs is ∼5.6 μm, below which crack-free PCs can be fabricated on a proper substrate. This facile approach to large-area single-crystalline PCs will be of

great significance for PCs’ applications in high-quality optics devices. Furthermore, this simple strategy for crack-free PCs may provide important insight for crack-free coatings in other

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ACKNOWLEDGEMENTS This work is supported by the National Nature Science Foundation (Grant No’s. 50973117, 50903089, 51173190, 91127029, 21074139, 20904061 and 20721061), and the 973 Program

(2007CB936403 and 2009CB930404, 2011CB932303 and 2011CB808400). We thank the beneficial discussion from Professor Jian Yu and Professor Zhaoxia Guo at Tsinghua University and the kind help

on Small-angle X-rays test from Dr Yuzhu Wang and Dr Ping Zhou at Shanghai Institute of Applied Physics. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Beijing National Laboratory for

Molecular Sciences (BNLMS), Laboratory of New Materials, Key Laboratory of Organic Solids, Laboratory of Advanced Polymer Materials, Institute of Chemistry, Chinese Academy of Sciences,

Beijing, PR China Jinming Zhou, Jingxia Wang, Yu Huang, Guoming Liu, Libin Wang, Shuoran Chen, Dujin Wang, Yanlin Song & Lei Jiang * Graduate University of Chinese Academy of Sciences,

Beijing, PR China Yu Huang, Libin Wang & Shuoran Chen * Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China

Xiuhong Li Authors * Jinming Zhou View author publications You can also search for this author inPubMed Google Scholar * Jingxia Wang View author publications You can also search for this

author inPubMed Google Scholar * Yu Huang View author publications You can also search for this author inPubMed Google Scholar * Guoming Liu View author publications You can also search for

this author inPubMed Google Scholar * Libin Wang View author publications You can also search for this author inPubMed Google Scholar * Shuoran Chen View author publications You can also

search for this author inPubMed Google Scholar * Xiuhong Li View author publications You can also search for this author inPubMed Google Scholar * Dujin Wang View author publications You can

also search for this author inPubMed Google Scholar * Yanlin Song View author publications You can also search for this author inPubMed Google Scholar * Lei Jiang View author publications

You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHORS Correspondence to Jingxia Wang or Yanlin Song. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare

no conflict of interest. ADDITIONAL INFORMATION Supplementary Information accompanies the paper on the NPG Asia Materials website SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION (DOC

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http://creativecommons.org/licenses/by-nc-nd/3.0/ Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Zhou, J., Wang, J., Huang, Y. _et al._ Large-area crack-free single-crystal

photonic crystals via combined effects of polymerization-assisted assembly and flexible substrate. _NPG Asia Mater_ 4, e21 (2012). https://doi.org/10.1038/am.2012.38 Download citation *

Received: 06 March 2012 * Revised: 24 May 2012 * Accepted: 12 June 2012 * Published: 03 August 2012 * Issue Date: August 2012 * DOI: https://doi.org/10.1038/am.2012.38 SHARE THIS ARTICLE

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by the Springer Nature SharedIt content-sharing initiative KEYWORDS * crack-free * large area * photonic crystals * self-assembly * single crystal