Kim Ju Young, Kim Hyowook, Kim Bong Hoon, Chang Taeyong, Lim Joonwon, Jin Hyeong Min, Mun Jeong Ho, Choi Young Joo, Chung Kyungjae, Shin Jonghwa, Fan Shanhui, Kim Sang Ouk
Department of Materials Science and Engineering, National Creative Research Initiative Center for Multi-Dimensional Directed Nanoscale Assembly, KAIST, Daejeon 34141, Republic of Korea.
Department of Materials Science and Engineering, KAIST, Daejeon 34141, Republic of Korea.
Nat Commun. 2016 Sep 29;7:12911. doi: 10.1038/ncomms12911.
The refractive index of natural transparent materials is limited to 2-3 throughout the visible wavelength range. Wider controllability of the refractive index is desired for novel optical applications such as nanoimaging and integrated photonics. We report that metamaterials consisting of period and symmetry-tunable self-assembled nanopatterns can provide a controllable refractive index medium for a broad wavelength range, including the visible region. Our approach exploits the independent control of permeability and permittivity with nanoscale objects smaller than the skin depth. The precise manipulation of the interobject distance in block copolymer nanopatterns via pattern shrinkage increased the effective refractive index up to 5.10. The effective refractive index remains above 3.0 over more than 1,000 nm wavelength bandwidth. Spatially graded and anisotropic refractive indices are also obtained with the design of transitional and rotational symmetry modification.
在整个可见波长范围内，天然透明材料的折射率限制在2至3。对于诸如纳米成像和集成光子学等新型光学应用而言，需要更宽的折射率可控性。我们报道，由周期和对称性可调的自组装纳米图案组成的超材料可为包括可见光区域在内的宽波长范围提供可控折射率介质。我们的方法利用比趋肤深度小的纳米级物体对磁导率和介电常数进行独立控制。通过图案收缩对嵌段共聚物纳米图案中的物体间距离进行精确操纵，可将有效折射率提高到5.10。在超过1000纳米的波长带宽上，有效折射率保持在3.0以上。通过设计过渡和旋转对称性修饰，还可获得空间渐变和各向异性的折射率。
