By Cameron Chai
Scientists from King's College London together with AMOLF and ICFO have successfully mapped the interaction of light with complex photonic materials by breaking the light resolution limit at the nanoscale. This was done by employing a new technique that integrates optical detection and electronic excitation.
Better understanding of light-matter interaction paves the way to develop more efficient displays and solar cells, as well as optimized bio-sensors for use in healthcare applications. Working with 30 nm spatial resolution, the researchers were able to explore the finer details of the photonic crystals at a resolution over 10 folds tinier when compared to the light’s diffraction limit, providing more insights into the interaction of light with matter to form, for instance, the visible iridescence phenomena seen in nature on butterfly wings.
The collaborative work has been reported in the Nature Materials journal. This advancement enables researchers to study optical hypotheses to a new degree of accuracy, comprehensively characterize innovative optical materials and assess new optical devices, explained Dr Riccardo Sapienza, one of the researchers from King's College London.
The researchers fabricated an artificial two-dimensional photonic crystal by creating a hexagonal pattern of holes using etching on an ultrathin silicon nitride membrane. Photonic crystals are nanostructures, wherein two materials having different refractive indices are aligned in a standard pattern, thus demonstrating novel optical properties.
The research techniques are based on cathodoluminescence, a geological technique, wherein visible light is emitted by a luminescent material when it was hit by an electron beam released by an electron gun. This technique was modified by Professor Albert Polman’s team in AMOLF to explore nanophotonics materials.
Dr Sapienza explained that a burst of light was generated when every time an electron, released by the electron gun, reached the sample surface as if a fluorescent molecule had been placed at the impact location. The electron beam scanning was able to allow the researchers to visualize the nanostructure’s optical response, revealing finer details at an unprecedented level.
ICFO’s Niek van Hulst stated that the scanning e-beam offers a local broad-band dipolar light source, which instantly maps all localized fields within a photonic crystal cavity.