Shape-Dependent Light Scattering Properties of Subwavelength Silicon Nanoblocks

Abstract

We explore the shape-dependent light scattering properties of silicon (Si) nanoblocks and their physical origin. These high-refractive-index nanostructures are easily fabricated using planar fabrication technologies and support strong, leaky-mode resonances that enable light manipulation beyond the optical diffraction limit.-Dark-field microscopy and a numerical modal analysis show that the nanoblocks can be viewed as truncated Si waveguides, and the waveguide dispersion strongly controls the resonant properties. This explains why the lowest-order transverse magnetic (TM01 mode resonance can be widely tuned over the entire visible wavelength range depending on the nanoblock length, whereas the wavelength-scale TM11 mode resonance does not change greatly. For sufficiently short lengths, the TM01 and TM11 modes can be made to spectrally overlap, and a substantial scattering efficiency, which is defined as the ratio of the scattering cross-section to the physical cross section of the nanoblock, Of,similar to 9.95, approaching the theoretical lOwest-order single-channel scattering limit, is achievable. Control over the subwavelength-scaleleaky-mode resonance allows Si nanoblOcks to generate vivid structural color, manipulate forward and backward scattering, and as excellent photonic artificial atoms for metasurfaces.