Electronic structure and thermal conductance of the MASnI3/Bi2Te3 interface: a first-principles study

To develop high-performance thermoelectric devices that can be created using printing technology, the interface of a composite material composed of MASnI3 and Bi2Te3, which individually show excellent thermoelectric performance, was studied based on first-principles calculations. The structural stability, electronic state, and interfacial thermal conductance of the interface between Bi2Te3 and MASnI3 were evaluated. Among the interface structure models, we found stable interface structures and revealed their specific electronic states. Around the Fermi energy, the interface structures with TeII and Bi terminations exhibited interface levels attributed to the overlapping electron densities for Bi2Te3 and MASnI3 at the interface. Calculation of the interfacial thermal conductance using the diffuse mismatch model suggested that construction of the interface between Bi2Te3 and MASnI3 could reduce the thermal conductivity. The obtained value was similar to the experimental value for the inorganic/organic interface.

The impact of thermostat on interfacial thermal conductance prediction from non-equilibrium molecular dynamics simulations

The knowledge of interfacial thermal conductance (ITC) is key to understand thermal transport in nanostructures. The non-equilibrium molecular dynamics (NEMD) simulation is a useful tool to calculate the ITC. In this study, we investigate the impact of thermostat on the prediction of the ITC. The Langevin thermostat is found to result in larger ITC than the Nose-Hoover thermostat. In addition, the results from NEMD simulations with the Nose-Hoover thermostat exhibit strong size effect of thermal reservoirs. Detailed spectral heat flux decomposition and modal temperature calculation reveal that the acoustic phonons in hot and cold thermal reservoirs are of smaller temperature difference than optical phonons when using the Nose-Hoover thermostat, but in the Langevin thermostat phonons are of identical temperatures. Such a non-equilibrium state of phonons in the case of the Nose-Hoover thermostat reduces the heat flux of low-to-middle-frequency phonons. We also discuss how enlarging the reservoirs or adding an epitaxial rough wall to the reservoirs affect the predicted ITC, and find these attempts could help to thermalize the phonons, but still underestimate the heat flux from low-frequency phonons.

Effects of Microscopic Properties on Macroscopic Thermal Conductivity for Convective Heat Transfer in Porous Materials

Porous materials are widely used in many heat transfer applications. Modeling porous materials at the microscopic level can accurately incorporate the detailed structure and substance parameters and thus provides valuable information for the complex heat transfer processes in such media. In this study, we use the generalized periodic boundary condition for pore-scale simulations of thermal flows in porous materials. A two-dimensional porous model consisting of circular solid domains is considered, and comprehensive simulations are performed to study the influences on macroscopic thermal conductivity from several microscopic system parameters, including the porosity, Reynolds number, and periodic unit aspect ratio and the thermal conductance at the solid–fluid interface. Our results show that, even at the same porosity and Reynolds number, the aspect ratio of the periodic unit and the interfacial thermal conductance can significantly affect the macroscopic thermal behaviors of porous materials. Qualitative analysis is also provided to relate the apparent thermal conductivity to the complex flow and temperature distributions in the microscopic porous structure. The method, findings and discussions presented in this paper could be useful for fundamental studies, material development, and engineering applications of porous thermal flow systems.

Monte Carlo analysis of frequency domain thermoreflectance data for quantitative measurement of interfacial thermal conductance at solid-liquid interfaces modified with self-assembled monolayers

A Monte Carlo method, implemented for quantifying confidence bounds on thermoreflectance (TR) measurements of interfacial thermal conductance G at solid-liquid interfaces modified with self-assembled monolayers (SAMs) is presented in this paper. Here we used 1-decanethiol (1DT) and 1H,1H,2H,2H-Perfluorodecanethiol (PFDT) SAMs to achieve two distinct work of adhesion. Using TR measurements in conjunction with Monte Carlo simulations, we determined G values to be 51 ± 7 MWm-2K-1, 58 ± 8 MWm-2K-1, and 72 ± 17 MWm-2K-1 for Au-PFDT-H2O, Au-1DT-H2O, and Au-H2O, respectively. Our results with the new confidence bounds position our experimental data on surfaces modified with SAMs comparable to literature. However, contrary to previous results shown in the literature, our data showed that a significant decrease in G can be seen for DI water on bare Au that was exposed in ambient for extended period. Our results indicate that G could be influenced by factors beyond a simple work of adhesion, an indication also seen from the work of Park et al.. To solidify this finding, further investigation is necessary to better understand G dependence on surface wettability.

Thermal Conductance of Epoxy/Alumina Interfaces

The interfacial thermal conductance (ITC) between filler and polymer matrix is considered as one of the important factors that limits the thermal conductivity of thermally conductive polymer composites. The effect of two different surface treatments (piranha solution and plasma) on ITC of epoxy/alumina was investigated using Time-domain thermoreflectance method (TDTR). The TDTR results show that compared with non-treated samples, the ITC of samples treated by piranha solution and plasma increased 2.9 times and 3.4 times, respectively. This study provides guidance for improving the thermal conductivity of thermally conductive polymer composites.

Interfacial Thermal Conductance between Alumina and Epoxy

Interfacial thermal conductance (ITC) of inorganic/epoxy interface is regarded as one of the most significant factors in determining thermal transport performance of epoxy composite. Here, ITC between alumina and epoxy was experimentally investigated by time-domain thermoreflectance (TDTR) method. The results show that the ITC is effectively increased from 9.0 MW m-2 K-1 for non-treated alumina/epoxy interfaces to 26.3 MW m-2 K-1 for plasma treated interfaces. This work sheds some light on design and application for thermally conductive composites.

Atomistic Nodal Approach: a General Molecular Dynamics Method For Computing Local Thermal Conductance at Atomistic Resolution

The Interfacial Thermal Conductance (ITC) is a fundamental property of mate- rials and has particular relevance at the nanoscale. The ITC quanti�es the thermal resistance between materials of dierent compositions or between uids in contact with materials. Furthermore, the ITC determines the rate of cooling/heating of the materi- als and the temperature drop across the interface. Here we propose a method to com- pute local ITCs and temperature drops of nanoparticle- uid interfaces. Our approach resolves the ITC at the atomic level using the atomic coordinates of the nanomaterial as nodes to compute local thermal transport properties. We obtain high-resolution descriptions of the interfacial thermal transport by combining the atomistic nodal ap- proach, computational geometry techniques and \computational farming" using Non- Equilibrium Molecular Dynamics simulations. We illustrate our method by analyzing various nanoparticles as a function of their size and geometry, targeting experimentally relevant structures like capped octagonal rods, cuboctahedrons, decahedrons, rhombic dodecahedrons, cubes, icosahedrons, truncated octahedrons, octahedrons and spheres. We show that the ITC of these very dierent geometries can be accurately described in terms of the local coordination number of the atoms in the nanoparticle surface. Nanoparticle geometries with lower surface coordination numbers feature higher ITCs, and the ITC generally increases with decreasing particle size.