arXiv subjects

Joseph P. Feser

Publications and source records attributed to Joseph P. Feser.

3 recordsLinked to original sources

arXiv2022

Phonon scattering and vibrational localization in 2D embedded nanoparticle composites

In this work, a Landauer approach enabled by the Frequency Domain Perfectly Matched Layer Method (FDPML) is used to study phonon transport in a series of large 2D domains with randomly embedded nanoparticles over a wide range of nanoparticle loadings and wavelengths. The effect of nanoparticle packing density on the mean free path and localization length is characterized. We observe that in the Mie scattering regime, the independent scattering approximation is valid up to volume fractions exceeding 10% and often higher depending on scattering parameter, indicating the mean free path can usually be calculated much less expensively using the number density and the scattering cross-section of a single scatterer. We also study localization lengths and their dependence on particle loading. In the case of heavy particles in a lighter matrix, we have been able to observe localization only at volume fractions >30% using the Landauer approach and only for high frequency modes, exceeding the vibration frequencies of the embedded nanoparticles. Using modal analysis we show that localization in nanoparticle laden materials is primarily due to energetic confinement rather than Anderson localization. Subsequently, we show that by using light particles in a heavy matrix the fraction of confined modes can be substantially increased.

cond-mat.mes-hall↗

arXiv2017

Thermal Transport Across Metal Silicide-Silicon Interfaces: First-Principles Calculations and Green's Function Transport Simulations

In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi$_2$-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used `mixing rules' to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi$_2$-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with predictions that include all transport processes: elastic and inelastic phonon scattering, electron-phonon coupling in the metal, and electron-phonon coupling across the interface.

cond-mat.mes-hall↗

arXiv2015

A framework for solving atomistic phonon-structure scattering problems in the frequency domain using Perfectly Matched Layer boundaries

We present a numerical approach to the solution of elastic phonon scattering problems based on a frequency domain decomposition of the atomistic equations of motion and the use of perfectly matched layer or PML boundaries. Unlike MD wavepacket analysis, the current approach has the ability to simulate scattering from individual phonon modes, including wavevectors in highly dispersive regimes. Like the Atomistic Green's Function method, the technique reduces scattering problems to a system of linear algebraic equations via a sparse, banded matrix. However, the use of PML boundaries enables rapid absorption of scattered wave energies at the boundaries, and provides a simple and inexpensive interpretation of the scattered phonon energy flux calculated from the energy dissipation rate in the PML. The accuracy of the method is demonstrated on connected monoatomic chains, for which an analytic solution is known. The parameters defining the PML are found to affect the performance and guidelines for selecting optimal parameters are given. The method is used to study the energy transmission coefficient for connected diatomic chains over all available wavevectors for both optical and longitudinal phonons; it is found that when there is discontinuity between sublattices, even connected chains of equivalent acoustic impedence have near-zero transmission coefficient for short wavelengths. The phonon scattering cross section of an embedded nanocylinder is calculated for a wide range of frequencies to demonstrate the extension of the method to high dimensions. The calculations match continuum theory for long wavelength phonons and large cylinder radii, but otherwise show complex physics including Mie oscillations which terminate when incident phonon frequencies exceeds the maximum available frequency in the embedded nanocylinder, and scattering efficiencies larger than two near the Brillouin zone edge.

cond-mat.mes-hall↗