Fabrication of 3D Photonic Crystals toward Arbitrary Manipulation of Photons in Three Dimensions

Deep reactive ion etching of cylindrical nanopores in silicon for photonic crystals

Periodic arrays of deep nanopores etched in silicon by deep reactive ion etching are desirable structures for photonic crystals and other nanostructures for silicon nanophotonics. Previous studies focused on realizing as deep as possible nanopores with as high as possible aspect ratios. The resulting nanopores suffered from structural imperfections of the nanopores, such as mask undercut, uneven and large scallops, depth dependent pore radii and tapering. Therefore, our present focus is to realize nanopores that have as cylindrical as possible shapes, in order to obtain a better comparison of nanophotonic observations with theory and simulations. To this end in our 2-step Bosch process we have improved the mask undercut, the uneven scallops, pore widening and positive tapering by optimizing a plethora of parameters such as the etch step time, capacitively coupled plasma (ion energy) and pressure. To add further degrees of control, we implemented a 3-step DREM (deposit, remove, etch, multistep) process. Optimization of the etching process results in cylindrical nanopores with a diameter in the range between 280 and 500 nm and a depth around 7μm, corresponding to high depth-to-diameter aspect ratios between 14 and 25, that are very well suited for the realization of silicon nanophotonic structures.

Broadband circular dichroism in chiral plasmonic woodpiles

The circular dichroism (CD) of a material is the difference in optical absorption under left- and right-circularly polarized illumination. It is crucial for a number of applications, from molecular sensing to the design of circularly polarized thermal light sources. The CD in natural materials is typically weak, leading to the exploitation of artificial chiral materials. Layered chiral woodpile structures are well known to boost chiro-optical effects when realized as a photonic crystal or an optical metamaterial. We here demonstrate that light scattering at a chiral plasmonic woodpile, which is structured on the order of the wavelength of the light, can be well understood by considering the fundamental evanescent Floquet states within the structure. In particular, we report a broadband circular polarization bandgap in the complex band structure of various plasmonic woodpiles that spans the optical transparency window of the atmosphere between 3 and 4 μ m and leads to an average CD of up to 90% within this spectral range. Our findings could pave the way for an ultra-broadband circularly polarized thermal source.

Supraballs as spherical solid 3D superlattices of hydrophobic nanocrystals dispersed in water: nanoarchitectonics and properties

Herein, we use a water-dispersive 3D suprastructure of ferrite (Fe₃O₄) nanocrystals called supraballs. They are solid spherical assemblies of hydrophobic nanocrystals with a rather low Young's modulus compared to similar 3D superlattices deposited on a substrate. Using atomic force microscopy methods, their nanomechanical properties are measured, which show small flexibility and deformation. This suprastructure behaves as a nanoheater and remains self-assembled after internalization in cancer cells. Furthermore, when subjected to light, the percentage of dead cells compared to the nanocrystals used as building blocks and dispersed in the solution increases.