Theory and simulation of surface effects on intrinsic dissipation

intrinsic dissipation, Akhiezer, MD, surface, phonon

De, Subhadeep ; Aluru ; Narayana R.

关键词: intrinsic dissipation, Akhiezer, MD, surface, phonon;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/90672/DE-THESIS-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The goal of this research is to study the role of surface on intrinsic dissipation in silicon (Si) nanostructures. We look at two different cases namely (i) Si(100) surface with (2x1) reconstruction and (ii) Hydrogen (H) terminated Si surface. We utilize molecular dynamics (MD) simulations and show that the two surfaces play opposing role on intrinsic dissipation. While surface defects always aid in the entropy generation process, the scattering of phonons from rough surfaces can suppress Akhiezer damping. For the case of (2x1) reconstructed silicon surface, the former dominates and the inverse quality factor (Q^-1) is found to increase with the decrease in size. However, different scaling trends are observed in the case of a 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 Ω such thatΩτph < 1, where τph is the phonon relaxation time, Q^-1 is found to decrease with the decrease in size. The opposite scaling is observed for Ωτph. A simplified model, based on two phonon groups (with positive and negative Grüneisen 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 factor with frequency for these cases.