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In this work, the impact of roughness and amorphization on the effective thermal conductivity of silicon nanofilms and nanowires is studied with atomistic simulations. The discrepancy between simulations and experimental measurements shows that it is necessary to consider realistic roughness and amorphization to reach an agreement. We show that subnanometric roughness and specific correlation length can reduce thermal transport by a factor of two in both nanofilms and nanowires; in addition, this reduction is even more pronounced than the one related to the existence of native oxides or amorphous phases on nanostructure edges. Furthermore, an interfacial thermal resistance parallel to the heat flux is observed. This thermal resistance is increasing upon the increase of the amorphous shell thickness, reaching a maximum value for thickness of 6 nm. Our findings could improve the strategy to elaborate nanomaterials with enhanced thermoelectric efficiency by tuning thermal conductivity through the engineering of surfaces. [ABSTRACT FROM AUTHOR]

Germanium manganese compounds exhibit a variety of stable and metastable phases with different stoichiometries. These materials entail interesting electronic, magnetic, and thermal properties both in their bulk form and as heterostructures. Here, we develop and validate a transferable machine learning potential, based on the high-dimensional neural network formalism, to enable the study of Mn x Ge y materials over a wide range of compositions. We show that a neural network potential fitted on a minimal training set reproduces successfully the structural and vibrational properties and the thermal conductivity of systems with different local chemical environments, and it can be used to predict phononic effects in nanoscale heterostructures. [ABSTRACT FROM AUTHOR]

In this work, we investigated the tensile and compression forces effect on the thermal conductivity of silicon. We used the equilibrium molecular dynamics approach for the evaluation of thermal conductivity considering different interatomic potentials. More specifically, we tested Stillinger-Weber, Tersoff, Environment-Dependent Interatomic Potential, and Modified Embedded Atom Method potentials for the description of silicon atom motion under different strain and temperature conditions. It was shown that the Tersoff potential gives a correct trend of the thermal conductivity with the hydrostatic strain, while other potentials fail, especially when the compression strain is applied. Additionally, we extracted phonon density of states and dispersion curves from molecular dynamics simulations. These data were used for direct calculations of the thermal conductivity considering the kinetic theory approach. Comparison of molecular dynamics and kinetic theory simulations results as a function of strain and temperature allowed us to investigate the different factors affecting the thermal conductivity of the strained silicon. [ABSTRACT FROM AUTHOR]

We study heat transport in semiconductor nanostructures by solving the Boltzmann transport equation by means of the discrete ordinate method. Relaxation time and phase and group velocity spectral dependencies are taken into account. The Holland model of phonon relaxation time is revisited and recalculated from dispersion relations (taken in literature) in order to match bulk silicon and germanium values. This improved model is then used to predict silicon nanowire and nanofilm thermal properties in both ballistic and mesoscopic regimes. [ABSTRACT FROM AUTHOR]