Shape-Dependent Light Scattering Properties of Subwavelength Silicon Nanoblocks

• Published in: Nano letters Vol. 15; no. 3; pp. 1759 - 1765
• Main Authors: Ee, Ho-Seok, Kang, Ju-Hyung, Brongersma, Mark L, Seo, Min-Kyo
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11.03.2015
• Subjects: Light scattering; Magnetic resonance; Nanostructure; Resonance scattering; Scattering; Scattering cross sections; Silicon; Waveguides; resonant scattering; structural color; Silicon nanoblock; scattering cross section; leaky-mode resonance
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl504442v

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 ∼9.95, approaching the theoretical lowest-order single-channel scattering limit, is achievable. Control over the subwavelength-scale leaky-mode resonance allows Si nanoblocks to generate vivid structural color, manipulate forward and backward scattering, and act as excellent photonic artificial atoms for metasurfaces.