Acoustic cavities in 2D heterostructures

Abstract

Two-dimensional (2D) materials offer unique opportunities in engineering the ultrafast spatiotemporal response of composite nanomechanical structures. In this work, we report on high frequency, high quality factor (Q) 2D acoustic cavities operating in the 50–600 GHz frequency (f) range with f × Q up to 1 × 1014. Monolayer steps and material interfaces expand cavity functionality, as demonstrated by building adjacent cavities that are isolated or strongly-coupled, as well as a frequency comb generator in MoS2/h-BN systems. Energy dissipation measurements in 2D cavities are compared with attenuation derived from phonon-phonon scattering rates calculated using a fully microscopic ab initio approach. Phonon lifetime calculations extended to low frequencies (<1 THz) and combined with sound propagation analysis in ultrathin plates provide a framework for designing acoustic cavities that approach their fundamental performance limit. These results provide a pathway for developing platforms employing phonon-based signal processing and for exploring the quantum nature of phonons.

3D Hypersound Microscopy of van der Waals Heterostructures

“…Thin layered materials and VdW heterostructures remain insufficiently explored. In refs − , several picoacoustical approaches were first applied to thin flakes and VdW heterostructures. In particular, the bubbles were identified using the acoustical resonance technique .…”

Coupling of MoS$_2$ Excitons with Lattice Phonons and Cavity Vibrational Phonons in Hybrid Nanobeam Cavities

“…Meanwhile, the T N dependence is consistent with the Bose occupation of cavity vibrational phonons 1 + n cP ≈ n cP ∝ T , and N would be determined by the number of cavity vibrational phonons mediating the resonant Raman scattering process. Finally, additional supporting evidence for the exciton-phononphonon coupling is observed from the T -dependent Raman linewidth, where the phonon-phonon coupling (anharmonicity) between cavity and lattice phonons introduces a T -broadening [10,24]. Figure 3(b) presents the Raman linewidth of one 2LA peak extracted from multi-Lorentz fitting (details in Supplement).…”

“…A 1g and 2LA, are tuned to be near the exciton emission energies, the exci- ton couples to both the cavity vibrational phonons and the MoS 2 lattice phonons simultaneously. In this case, anharmonic effects arise from the coupling between the cavity and lattice phonons, as evidenced by the temperature broadening of Raman linewidth [10,24]. The selective X 0 -cavity phonon-lattice phonon coupling results in the enhancement of X 0 -induced Raman scatterings while X − -induced scatterings are found to be suppressed, a conclusion based on their detuning-dependent Raman intensities [25,26] and the ratio of X − /X 0 emission intensities [26].…”

“…Monolayers of transition metal dichalcogenides (TMDs) are of particular interest in this context since they: (i) can be attached via van der Waals bonding to a wide range of different substrates, (ii) combine strong-light matter interactions mediated by excitonic processes at room temperature, (iii) have large photoelastic coupling strengths and (iv) feature atomically-thin layers with electronical and optical properties that are intrinsically sensitive to both hydrostatic, biaxial, uniaxial and flexural strain [6][7][8]. Mechanical cavities formed from freely suspended TMD monolayers have been previously prepared to study their vibrational and torsional phonon modes [7][8][9][10]. However, in such studies the TMD monolayer is not usually fully encapsulated within hexagonal boron nitride (hBN), an approach known to enhance the optical linewidth and stability of the excitonic transitions.…”

Ultra-sensitive gas sensor based fano resonance modes in periodic and fibonacci quasi-periodic Pt/PtS2 structures

“…Meanwhile, the FC(7, 1) quasi-periodic structure has a large number of layers than others. In our work, we used Pt/PtS 2 layers with nano thickness as the mismatching in the acoustic impedance between 2D materials layers grew as the thicknesses of their construction layers were reduced, which in turn led to forming a wide range band gaps 55 , 56 . As a result, when the Pt/PtS 2 structures layers thickness decreased, it allows appearing of wide phononic band gab at a very high frequency 57 .…”