English

• Graphene based materials have attracted more attentions due to their structural flexibility, large surface area, and excellent optical electronical [1, 2], thermal [3], and mechanical [4] performances. These properties endorse the graphene-based composite promising applications in optoelectronic material [5], photocatalysts [6], transparent conductors [7], chemical and biosensors [8], supercapacitors [9] and wave guide [10]. An efficient and highyield production methods for graphene is the chemical reduction of graphite oxide (RGO) [11], in which the basal plane carbon atoms were decorated with epoxide and hydroxyl groups, and the edge atoms were attached to carbonyl and carboxyl groups [12]. The unique structures promote complete exfoliation of single graphene oxide (GO) layers in aqueous media, which makes it a suitable candidate to be hybridized into a composite for a wide range of applications.

  Photonic crystals (PhC) was first reported by Yablonovitch [13], PhC could be used as chemical and biosensors as well as optical filters, reflectors, modulators, metasurfaces, surface enhanced Raman scattering photonic devices and solar cells [14]. However, the poor flexibility, strength, area coverage, complicated fabrication process and high cost prevent its application and development. Most recently, two-dimensional PhC structure has been reported [15]. Compared to the traditional 3D PhC structure, the fabrication of 2D PhC is much simpler and more efficient, meanwhile 2D PhC is easier to be composited compared with other materials [16]. Moreover, 2D PhC composites with both attractive electrical and optical property have been rarely reported. 1D PhCs based on graphene monolayers and GO layers to enhance the bandwidth, signal intensity and capacity have also been researched. The optical absorption of graphene layers on the top of 1D PhC could be enhanced greatly over a broad spectral range, and also be tuned by either the incident angle or the distance between the graphene and the 1D PhC [17]. 1D PhC based on TiO₂/GO thin film prepared by spin-coating, which is a convenient and low-cost method have a specific response to DMSO and alkali solution, would be promising as color sensors in biochemical fields [18]. The simulation and optical characterization revealed the ability of graphene-based absorber to achieve an enhancement factor of about 19(15) for TE (TM) polarization, and the absorber was made of polymethyl-methacrylate (PMMA) stripes of PhC deposited on a tantalum pentaoxide (Ta₂O₅) slab which is supported by a silicon dioxide (SiO₂) substrate. This technique will enable the realization of devices that are less sensitive to the incident light polarization, and be efficient and innovative optical absorbers or photodetectors [19]. The graphene and its monolayer derivatives have been suggested to be an excellent platform, and the composition of RGO monolayeron 2Dcolloidal arrayhas beenexpectedtoimprove the flexibility, strength, large area fabrication and electronical performances of the 2D PhC.

  Zhang et al. used an air/waterinterface self-assemblymethod to fabricate 2D polystyrene (PS) colloidal array [20]. Xue et al. modified the above method and prepared an 2D colloidal crystal heterostructure based on different colloidal monolayer [21]. Herein, we introduced a layer-by-layer heterostructure fabricated from2D CCA and RGO, inwhich 2D CCAwere prepared byair/water interface self-assembly method, and the RGO layer was fabricated by GO suspension and reduction. The process can be repeated to obtain the desiredlayers of composite.The theoretical studyshows that the graphene-photonic crystal can increase the absorption of THz [22] and graphene in the infrared, facilitating enhanced performance of modulators, filters, sensors, and photodetectors [23]. The layer-by-layer heterostructure composite showed promising potential for the applications as sensors and optoelectronic devices. The preparation process is as follows.

  GO was made using a modified Hummers' method. The monodispersed PS colloidal particles were synthesized according to a reported method [24]. The monodispersed PMMA colloidal particles were synthesized by a seeded polymerization method, and the seed particles with a diameter of 262nmwere prepared by an emulsifier-free emulsion polymerization method [25]. Larger colloidal particles were desired to obtain high quality 2D colloidal crystals.

  The morphologies of PS and PMMA particles were investigated by SEM. As shown in Figs. 1a and b, the obtained PS and PMMA particles were monodispersed. The morphologies of the GO prepared by the improved Hummers' method (Fig. 1c) showed that GO has a good integrity, and GO film forms wrinkle due to its soft and thin texture.

  Figure 1

  

  Figure 1.  SEM images: (a) PS particles; (b) PMMA particles; (c) GO.

  DownLoad: Full-Size Img PowerPoint

  Then the RGO monolayer was prepared with the GO above. GO (50mg) was dispersed in ethanol (10mL) under ultrasonication for 120min, giving a suspension of exfoliated GO. GO sheet was obtained through dipping GO suspension onto a glass substrate, and then dried under vacuum at room temperature. The GO sheet on glass substrate was reduced by hydrazine hydrate at 60 ℃ for 24h.

  Next, 2D colloidal monolayer was prepared by gas-liquid interface self-assembly method. An aqueous alcohol-containing colloidal particle suspension could be rapidly assembled into a hexagonal closely-packed 2D CCA at the air/water interface [16]. Zhang et al. reported the self-assembly of PS nanoparticles on a water surface using PS suspension in a water/1-propanol solvent [19]. Xue et al. prepared 2D PMMA CCA employing 3:1 ratio of PMMA particle suspension (0.15g/mL) to propanol [21]. When the colloidal suspension in propanol was laid on the water surface, colloidal particles quickly spread from the sampling spot to the out edge of the water surface due to the Marangoni effect, inwhich the surface tension gradient on the water surface pushes the colloidal suspension away from the sampling spot. As the colloids spread outwards, they self-assembled rapidly into a hexagonal closepacked 2D monolayer array. The 2D arraycould be transferred onto a glass slide as shown in Fig. 3b. A perfect continuous 2D colloidal monolayer array could be fabricated within 2min. In this study, PS particles of 540nm and PMMA particles of 460nmwere selectedto form the high ordering of corresponding hexagonal 2D monolayer arrays, which were confirmed by their SEM images (Figs. 2a and b).

  Figure 2

  

  Figure 2.  SEM images: (a) Sample A: 2D CCA of PS particles with diameters of 540nm; (b) Sample C: 2D CCA of PMMA particles with diameters of 460nm.

  DownLoad: Full-Size Img PowerPoint

  Figure 3

  

  Figure 3.  The preparation process of PhC-RGO composite: (a) PS 2D CCA onto water; (b) and (c) transferring PS 2D CCA onto glass slide; (d) dipping Go suspension onto PS 2D CCA; (e) RGO sheet onto PS 2D CCA after reduction reaction; (f) and (g) transferring PMMA 2D CCA onto RGO sheet+ PS 2D CCA heterostructure.

  DownLoad: Full-Size Img PowerPoint

  With the 2D colloidal monolayer and RGO monolayer, the layerby-layer heterostructure composite was prepared. The compositions of the PhC-RGO composites were listed in Table 1. The fabrication process of sample A and C was schematically demonstrated in Figs. 3a–c, that of sample E was shown in Fig. 3e, and that of sample F was shown in Fig. 3g, sample E was obtained by repeating the fabrication process of sample G twice.

  Table 1

  

  Table 1.  The heterostructure composite fabricated layer by layer.

  DownLoad: CSV

  Sample D with a 2D monolayer array was prepared by selfassembly of PS colloidal particles (540nm), and was transferred onto a RGO sheet as described above (Fig. 4). The RGO sheet provided a relative flat surface for PS colloidal particles, the top layer of 2D CCA with PS colloidal particles exhibited a highly ordered hexagonal closely-packed structure. In contrast, the double-layer structure of Sample E was fabricated by depositing RGO sheet onto the 2D CCA of 540nm PS colloidal (Figs. 4c and d). From the top-view of SEM image, PS CCA could be observed. Sample F was prepared by depositing an array of 460nm PMMA particles on sample E (Fig. 4e), when another layer of PMMA particle (460nm) was assembled and covered with a RGO sheet, sample G (Fig. 4f) was obtained. The particle size and deposition sequence have no effect on the integrity of the layer-by-layer heterostructure composite, and the monolayer of 2D CCA was uniform and exhibited a close-packed arrangement. The crosssectional SEM images of samples D, E, F and G clearly showed the two monolayers of RGO sheet and 2D colloidal arrays were composited tightly with a clear interface, indicating its high structural integrity. The monolayer of RGO sheet of samples E, F and G have been obtained by in situ deoxidation reaction of GO by hydrazine hydrate, in which the PS CCA remained integrity. The fabrication method of the above layer by layer heterosturctures was simple, quick and low-cost, meanwhile the process can be repeated to obtain desired layers.

  Figure 4

  

  Figure 4.  SEM images: (a) top-view of sample D; (b) cross-section of sample D; (c) topview of sample E; (d) cross-section of sample E; (e) cross-section of sample F; (f) cross-section of sample G.

  DownLoad: Full-Size Img PowerPoint

  For the optical properties of the heterostructure composite, the diameterof Debye diffracted ring has been used to characterize the microstructure of 2D CCA [21]. The strong forward light diffraction of the 2D CCA results in a perfect Debye diffraction ring on a screen under the illumination of a normal monochromatic incidence [21]. The Debye diffraction of the 2D CCA follows Eq. (1):

  where α is the forward diffraction angle of the Debye diffraction, λ is the incident wavelength, and d is the adjacent particle spacing.

  The forward diffraction angle, α, can be obtained from Eq. (2).

  Where h is the distance between the 2D array and the screen, and D is the diameter of the Debye diffraction ring.

  Therefore, the 2D array particle spacing could be determined simply by measuring the diameter D of Debye ring. The Debye diffraction rings of sample A, C and F were shown in Fig. 5. The parameters of Eq. (1) from the diameter of Debye diffraction rings were listed in Table 2. It can be observed that the diameter of Debye ring decreased with the increasing of particle size in the 2D CCA. The corresponding particle spacing of sample A and C, calculated from Eq. (1), were 577 and 493 nm respectively. The difference between the calculated and measured particle spacing might be explained that the particles were not closely packed, which was confirmed in SEM images (Fig. 2).

  Table 2

  

  Table 2.  The parameters of the diameters of Debye diffraction rings.

  DownLoad: CSV

  Figure 5

  

  Figure 5.  The Photographs of Debye diffraction ring: (a) sample A, (b) sample C and (c) sample F.

  DownLoad: Full-Size Img PowerPoint

  The layer-by-layer heterostructure composites, sample D, E and F also exhibit Debye diffraction rings under a monochromatic light illumination. The sample D and E obtained similar diameters of Debye diffraction rings with sample A, which indicated the layered RGO sheet does not influence the diameters of Debye diffraction rings, but reduce the diffraction intensity. Sample F, the triple-layer was formed by 2D CCA of 540 nm PS colloidal, RGO sheet, 2D CCA of 460 nm PMMA colloidal, showed two Debye diffraction rings on the screen, which were similar from the 540 nm and 460 nm 2D monolayer arrays respectively (Fig. 5c). Therefore, it can be concluded that the optical properties of the layer-by-layer heterostructure composite is the superimposition of the optical properties of the individual 2D CCA.

  The reflection spectrum of the layer-by-layer heterostructure composite was also measured. A violet-blue laser pointer (405 nm) was used to illuminate the surface of heterostructures at normal incidence. The diffraction spectra of the heterostructure composites were recorded at 45° using a fiber optic UV–vis spectrometer (Avaspec-2048TEC, Avantes) with an Ava light-DH-S-BAL light source and a FC-UV600-2-SR fiber optic reflection probe, and the samples were placed on an aluminum mirror. The reflection spectrum of the layer-by-layer heterostructure composite were shown in Fig. 6. Sample A, D and E exhibited two peaks in near ultraviolet region (200–400 nm) and visible region (400–800 nm) respectively. 2D CCA show strong forward diffraction that can be easily monitored by using a mirror to back reflect the forward diffracted light [20, 26], and we used a front surface mirror to reflect the forward diffraction. The intense back diffracted light could easily be observed by illuminating the 2D array with a flashlight. The peak of reflection curve of the sample A located in near ultraviolet region originated from the secondary diffraction, and the peak of reflection curve in visible region (400–800 nm) obeyed the Bragg reflection. Sample D was a 2D CCA layered onto a RGO sheet, and the intense of reflection would increase in ultraviolet region (200–400 nm), but decreased in visible region (400–800 nm) compared with that of sample A. The position and shape of the reflection curve of sample E (a RGO sheet layered onto 2D CCA) were similar to that of sample A, but the intense decreased. This heterostructurehas a good regulatory of the UV and visible light. The optical property of the heterostructure composite is more prominent than that of traditional materials. The flexibility, low cost and large area fabrication were also the prominent properties of the heterostructure. This phenomenon could promote the layer-by-layer heterostructure composite to be a suitable candidate in the field of sensing and other fields.

  Figure 6

  

  Figure 6.  The reflection spectrum of sample A, sample D and sample E.

  DownLoad: Full-Size Img PowerPoint

  The electrical resistance of the layer-by-layer heterostructure composite was measured to characterize the electrical properties. The electrical conductivities of the samples were measured by using a four-probe conductivity tester (SZT-2A instrument, China) at room temperature. The electrical resistance of the samples were listed in Table 3. Graphite oxide and pure graphene have resistance of 88.5Ω and 0.69Ω reported [27]. Previous work showed that graphite oxide was almost insulating [28], but the possible incomplete oxidation of the graphite may result in the high conductivity of the prepared graphite oxide, and the resistance of sample B confirmed this assumption. The electrical conductivity depends on the thickness of RGO sheet, meanwhile in order to obtain RGO sheet with different thickness, the concentration of GO suspension was adjusted accordingly. Sample A, D and F were insulative, meanwhile Sample C, E and G were electrical conductive. The large surface area and high ratio of the RGO prepared via chemical reduction played an important role in the improvements of electrical conductivity of the layer-by-layer heterostructure composite based on RGO and 2D.Compared with the single CCA, the heterostructure composite has more excellent electronical performances.

  Table 3

  

  Table 3.  The resistance of the layer-by-layer heterostructure composite.

  DownLoad: CSV

  In summary, the main jobs we have done are as follows: with the air/water interface deposition method, 2D CCAs were prepared from PS colloidal particles (540 nm) and PMMA (460 nm) colloidal suspension. Then the double-layer, triple-layers and four-layers heterostructure composites were fabricated. The 2D CCA were highly ordered on RGO sheet, and the monolayer of RGO and 2D CCA were composited tightly. The Debye diffraction ring of the layer-by-layer heterostructure composite was the superimposition of the Debye diffraction ring of the individual monolayer of 2D CCA. The two peaks of reflection curve of the layer-by-layer heterostructure composites located in near ultraviolet region and visible region respectively, and the RGO sheet have no influence on the peak position and shape of reflection curve of the PhC. Meanwhile, the RGO sheets overcame the shortcoming of the electrical properties of PhC and improved the electrical conductivity of the layer-by-layer heterostructure composite. Therefore, these layer-by-layer heterostructure composites might have great potential applications in sensors, optoelectronic devices, separation science and smart filters/flowmeters.

  Acknowledgments

  This research was supported by the National Natural Science Foundation of China (Nos. 21375009 and U1530141) and the Fundamental Research Foundation of Beijing Institute of Technology (No. 20151042004).

• 1. [1]

     C. Casiraghi, A. Hartschuh, E. Lidorikis, et al., Nano Lett. 7(2007) 2711-2717. doi: 10.1021/nl071168m

  2. [2]

     (a) A. K. Geim, K. S. Novoselov, Nature Mater. 6(2007) 183-191;
     (b) X. F. Lin, Z. Y. Zhang, Z. K. Yuan, Chin. Chem. Lett. 27(2016) 1259-1270;
     (c) W. Wei, F. F. Jia, K. F. Wang, P. Qu, Chin. Chem. Lett. 28(2017) 324-328.

  3. [3]

     S. Subrina, J. Nanoelectron. Optoelectron. 8(2013) 317-336. doi: 10.1166/jno.2013.1482

  4. [4]

     Z.L. Cheng, X.X. Qin, Chin. Chem. Lett. 25(2014) 1305-1307. doi: 10.1016/j.cclet.2014.03.010

  5. [5]

     F. Bonaccorso, Z. Sun, T. Hasan, A.C. Ferrari, Nature. Photon. 4(2010) 611-622. doi: 10.1038/nphoton.2010.186

  6. [6]

     Q. Li, B.D. Guo, J.G. Yu, et al., J. Am. Chem. Soc. 133(2011) 10878-10884. doi: 10.1021/ja2025454

  7. [7]

     G. Xu, J. Liu, Q. Wang, et al., Adv. Mater. 24(2012) OP71-OP76. doi: 10.1002/adma.201104012

  8. [8]

     L. Saghatforoush, M. Hasanzadeh, N. Shadjou, Chin. Chem. Lett. 25(2014) 655-658. doi: 10.1016/j.cclet.2014.01.014

  9. [9]

     D.W. Wang, F. Li, J.P. Zhao, et al., ACS Nano 3(2009) 1745-1752. doi: 10.1021/nn900297m

  10. [10]

      V.M. Shalaev, Nature. Photon. 1(2007) 41-48. doi: 10.1038/nphoton.2006.49

  11. [11]

      D.A. Dikin, S. Stankovich, E.J. Zimney, et al., Nature 448(2007) 457-460. doi: 10.1038/nature06016

  12. [12]

      H.C. Schniepp, J.L. Li, M.J. McAllister, et al., J. Phys. Chem. B 110(2006) 8535-8539.

  13. [13]

      E. Yablonovitch, Phys. Rev. Lett. 58(1987) 2059-2062. doi: 10.1103/PhysRevLett.58.2059

  14. [14]

      Z.Y. Cai, Y.J. Liu, E.S.P. Leong, J.H. Teng, X.M. Lu, J. Mater. Chem. 22(2012) 24668-24675. doi: 10.1039/c2jm34896a

  15. [15]

      J.W. Fleischer, M. Segev, N.K. Efremidis, D.N. Christodoulides, Nature 422(2003) 147-150. doi: 10.1038/nature01452

  16. [16]

      Z. Cai, J.T. Zhang, F. Xue, et al., Anal. Chem. 86(2014) 4840-4847. doi: 10.1021/ac404134t

  17. [17]

      J.T. Liu, N.H. Liu, J. Li, X.J. Li, J.H. Huang, Appl. Phys. Lett. 101(2012) 052104. doi: 10.1063/1.4740261

  18. [18]

      L. Wang, Z.B. Xu, P. Wang, et al., J. Chem. Eng. Data. 58(2013) 737-740. doi: 10.1021/je301237t

  19. [19]

      Y.Q. Guo, A. Bhattacharya, E.R. Bernstein, J. Chem. Phys. 128(2008) 11.

  20. [20]

      (a) J. T. Zhang, L. Wang, D. N. Lamont, S. S. Velankar, S. A. Asher, Angew. Chem. Int. Ed. 51(2012) 6117-6120;
      (b) J. T. Zhang, L. Wang, J. Luo, et al., J. Am. Chem. Soc. 133(2011) 9152-9155.

  21. [21]

      F. Xue, S.A. Asher, Z.H. Meng, et al., Rsc Adv. 5(2015) 18939-18944. doi: 10.1039/C4RA16006A

  22. [22]

      L.Y. Xie, W.B. Xiao, G.Q. Huang, A.R. Hu, J.T. Liu, Acta Phys. Chim. Sin. 63(2014) 402-406. http://www.ntu.edu.sg/home/hzhang

  23. [23]

      T.Y. Gu, A. Andrei, F.H. Yu, et al., ACS Photon 11(2015) 1552-1558.

  24. [24]

      C.E. Reese, S.A. Asher, J. Colloid Interface Sci. 248(2002) 41-46. doi: 10.1006/jcis.2001.8193

  25. [25]

      F. Xue, Z.H. Meng, Y.F. Wang, et al., Anal. Methods 6(2014) 831-837. doi: 10.1039/C3AY42059K

  26. [26]

      A. Tikhonov, N. Kornienko, J.T. Zhang, L.L. Wang, S.A. Asher, J. Nanophoton. 6(2012) 063509. doi: 10.1117/1.JNP.6.063509

  27. [27]

      S. Bose, T. Kuila, M.E. Uddin, et al., Polymer 51(2010) 5921-5928. doi: 10.1016/j.polymer.2010.10.014

  28. [28]

      L.X. Wang, X.L. Tuo, C.H. Yi, et al., J. Mol. Graphics Modell. 28(2009) 81-87. doi: 10.1016/j.jmgm.2009.04.007

• 

  Figure 1  SEM images: (a) PS particles; (b) PMMA particles; (c) GO.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  SEM images: (a) Sample A: 2D CCA of PS particles with diameters of 540nm; (b) Sample C: 2D CCA of PMMA particles with diameters of 460nm.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  The preparation process of PhC-RGO composite: (a) PS 2D CCA onto water; (b) and (c) transferring PS 2D CCA onto glass slide; (d) dipping Go suspension onto PS 2D CCA; (e) RGO sheet onto PS 2D CCA after reduction reaction; (f) and (g) transferring PMMA 2D CCA onto RGO sheet+ PS 2D CCA heterostructure.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  SEM images: (a) top-view of sample D; (b) cross-section of sample D; (c) topview of sample E; (d) cross-section of sample E; (e) cross-section of sample F; (f) cross-section of sample G.

  下载: 全尺寸图片 幻灯片
  

  Figure 5  The Photographs of Debye diffraction ring: (a) sample A, (b) sample C and (c) sample F.

  下载: 全尺寸图片 幻灯片
  

  Figure 6  The reflection spectrum of sample A, sample D and sample E.

  下载: 全尺寸图片 幻灯片

  Table 1.  The heterostructure composite fabricated layer by layer.

  下载: 导出CSV

  Table 2.  The parameters of the diameters of Debye diffraction rings.

  下载: 导出CSV

  Table 3.  The resistance of the layer-by-layer heterostructure composite.

  下载: 导出CSV
•