  Hyperbolic metamaterials (HMMs) offer unconventional properties in the field
of optics, enabling opportunities for confinement and propagation of light at
the nanoscale. In-plane orientation of the optical axis, in the direction
coinciding with the anisotropy of the HMMs, is desirable for a variety of novel
applications in nanophotonics and imaging. Here, a method for creating
localized HMMs with in-plane optical axis, based on block copolymer (BCP) blend
instability, is introduced. The dewetting of BCP thin film over topographically
defined substrates generates droplets composed of highly ordered lamellar
nanostructures in hierarchical configuration. The hierarchical nanostructures
represent a valuable platform for the subsequent pattern transfer into a Au/air
HMM, exhibiting hyperbolic behavior in a broad wavelength range in the visible
spectrum. A computed Purcell factor as high as 32 at 580 nm supports the strong
reduction in the fluorescence lifetime of defects in nanodiamonds placed on top
of the HMM.
