Phononic and photonic properties of shape-engineered silicon nanoscale pillar arrays

Abstract

We report the results of Brillouin–Mandelstam spectroscopy and Mueller matrix spectroscopic ellipsometry of the nanoscale ‘pillar with the hat’ periodic silicon structures, revealing intriguing phononic and photonic—phoxonic—properties. It has been theoretically shown that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic crystals, strongly affecting the light-matter interactions. Acoustic phonon states can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures, or as a result of artificially induced external periodicity, as in the phononic crystals. The shape of the nanoscale pillar array was engineered to ensure the interplay of both effects. The Brillouin–Mandelstam spectroscopy data indicated strong flattening of the acoustic phonon dispersion in the frequency range from 2 GHz to 20 GHz and the phonon wave vector extending to the higher-order Brillouin zones. The specifics of the phonon dispersion dependence on the pillar arrays’ orientation suggest the presence of both periodic modulation and spatial localization effects for the acoustic phonons. The ellipsometry data reveal a distinct scatter pattern of four-fold symmetry due to nanoscale periodicity of the pillar arrays. Our results confirm the dual functionality of the nanostructured shape-engineered structure and indicate a possible new direction for fine-tuning the light–matter interaction in the next generation of photonic, optoelectronic, and phononic devices.

Cryogenic characteristics of graphene composites—evolution from thermal conductors to thermal insulators

“…The intensity of the 2D peak is much lower than the G-peak indicating the presence of a mixture of single-layer and few-layer graphene in the composite samples. The Brillouin spectroscopy allows probing low-energy acoustic phonons near the Brillouin-zone (BZ) center with energies in the range of 2 GHz to 900 GHz 30 , 34 – 36 . In bulk polymers, the Brillouin spectrum is dominated by the inelastic scattering of light from bulk phonons, i.e., elastic vibrations, through the opto-elastic effect 37 .…”

Effects of Boron Doping on the Bulk and Surface Acoustic Phonons in Single-Crystal Diamond

“…The incident light was p -polarized; no specific polarization selection was used for the collection of the scattered light. The details of our BMS procedures are provided in the Methods section and prior reports for other material systems. ,, The top surfaces of the samples were the diamond’s (001) crystallographic plane with an off-cut plane angle of ∼3°. This small off-cut angle had a negligible effect on the light scattering and did not affect the interpretation of BMS data.…”

Fundamentals, progress and perspectives on high-frequency phononic crystals

“…The comparable structural length scales, i.e. submicrometer ranges, of hypersonic PnCs and PhCs in the visible spectrum allow simultaneously manipulating the elastic and electromagnetic waves [163,164] by tailoring material properties, such as the dielectric constant, mass density, elastic constants, and geometric parameters, such as periodic patterns and scatter shape. This unique structure, termed as phoxonic crystals (PxCs) [164], presents band gaps for hypersound and visible light concurrently, evoking a thrilled perspective for modulation on the light-matter interaction [165].…”