Mixed role of surface on intrinsic losses in silicon nanostructures

Abstract

We utilize molecular dynamics simulations and show opposing roles of surface on dissipation in nanostructures. While the surface defects always aid in the entropy generation process, the scattering of phonons from rough surfaces can suppress Akhiezer damping. For the case of a silicon (2 Â 1) reconstructed surface, the former dominates and Q À1 (Q is the quality factor) is found to increase with the decrease in size. However, different scaling trends are observed in the case of a hydrogen (H) terminated silicon surface with no defects and dimers. Particularly, in the case of a H-terminated silicon, if the resonator is operated with a frequency X such that Xs ph < 1, where s ph is the phonon relaxation time and Q À1 is found to decrease with the decrease in size. The opposite scaling is observed for Xs ph > 1. A simplified model, based on two phonon groups (with positive and negative Gr€ uneisen parameters), is considered to explain the observed trend. We show that the equilibration time between the two mode groups decreases with the decrease in size for the H-terminated structure. We also study the scaling of Q À1 factor with frequency for these cases.

Thermodynamic stability and contributions to the Gibbs free energy of nanocrystalline Ni3Fe

“…If the phonon is scattered at the interface by effects of disorder or anharmonicity, its lifetime may be only tens of vibrational periods or less. The spectral shape of a damped harmonic oscillator function has an asymmetrical broadening about the central frequency that can often account for the broadened phonon DOS of nanostructured materials [2,3,21,[31][32][33][34][35]40,41,65].…”

Energy Dissipation in Fluid Coupled Nanoresonators: The Effect of Phonon-Fluid Coupling

“…When (Ω ≪ ω i ), the ratio E i /ω i is an adiabatic invariant . Using this, the rate of change of phonon energies can be related to a time-varying strain field as . Here, ϵ­( t ) can be regarded as ϵ 0 sin­(Ω t ) where ϵ 0 is the strain amplitude.…”

“…The energy dissipation associated with this whole process is termed as Akhiezer dissipation. The approximate analytical form for Akhiezer dissipation for a system of N phonons is given by …”

Nonlinear intrinsic dissipation in single layer MoS2 resonators

“…To simplify the system of phonon modes, we employ the phonon grouping technique 39 and derive an expression for dissipation. The mean Grüneisen parameter of the ensemble of phonons is dened as g ¼…”