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.

Localized surface plasmon resonance of metallic nanostructures receives noticeable attention in photonics, electronics, catalysis, and so on. Core-shell nanostructures are particularly attractive due to the versatile tunability of plasmonic properties along with the independent control of core size, shell thickness, and corresponding chemical composition, but they commonly suffer from difficult synthetic procedures. We present a reliable and controllable route to a highly ordered uniform Au@Ag core-shell nanoparticle array via block copolymer lithography and subsequent seeded-shell growth. Size-tunable monodisperse Au nanodot arrays are generated by block copolymer self-assembly and are used as seed layers to grow Ag shells with variable thickness. The resultant Au@Ag core-shell nanoparticle arrays exhibit widely tunable broadband enhancement of plasmonic resonance, greatly surpassing single-element nanoparticle or homogeneous alloy nanoparticle arrays. Surface-enhanced Raman scattering of the core-shell nanoparticle arrays showed an enhancement factor greater than 270 from Au nanoparticle arrays.

Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces.

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