Bjorn Vermeersch

Superdiffusive heat conduction in semiconductor alloys. I. Theoretical foundations

Semiconductor alloys exhibit a strong dependence of effective thermal conductivity on measurement frequency. So far this quasi-ballistic behaviour has only been interpreted phenomenologically, providing limited insight into the underlying thermal transport dynamics. Here, we show that quasi-ballistic heat conduction in semiconductor alloys is governed by Levy superdiffusion. By solving the Boltzmann transport equation (BTE) with ab initio phonon dispersions and scattering rates, we reveal a transport regime with fractal space dimension

Superdiffusive heat conduction in semiconductor alloys. II. Truncated Lévy formalism for experimental analysis

1 3)

Cross-plane heat conduction in thin films with ab-initio phonon dispersions and scattering rates

and cumulative conductivity spectra

Direct observation of nanoscale Peltier and Joule effects at metal-insulator domain walls in vanadium dioxide nanobeams.

kappa_{Sigma}(tau;Lambda)sim (tau;Lambda)^{gamma}

Thermoreflectance imaging of sub 100 ns pulsed cooling in high-speed thermoelectric microcoolers

resolved for relaxation times or mean free paths through simple relations

almaBTE : A solver of the space–time dependent Boltzmann transport equation for phonons in structured materials

alpha = 3-beta = 1 + 3/n = 2 - gamma

Fractal Lévy Heat Transport in Nanoparticle Embedded Semiconductor Alloys

. The quasi-ballistic transport inside alloys is no longer governed by Brownian motion, but instead dominated by Levy dynamics. This has important implications for the interpretation of thermoreflectance (TR) measurements with modified Fourier theory. Experimental

Compact stochastic models for multidimensional quasiballistic thermal transport

alpha

Thermal imaging for reliability characterization of copper vias

values for InGaAs and SiGe, determined through TR analysis with a novel Levy heat formalism, match ab initio BTE predictions within a few percent. Our findings lead to a deeper and more accurate quantitative understanding of the physics of nanoscale heat flow experiments.

Quasi-ballistic thermal transport in Al0.1Ga0.9N thin film semiconductors

evy dynamics with fractal dimension α< 2. Here, we present a framework that enables full three-dimensional experimental analysis by retaining all essential physics of the quasiballistic BTE dynamics phenomenologically. A stochastic process with just two fitting parameters describes the transition from pure L´ evy superdiffusion as short length and time scales to regular Fourier diffusion. The model provides accurate fits to time domain thermoreflectance raw experimental data over the full modulation frequency range without requiring any “effective” thermal parameters and without any ap rioriknowledge of microscopic phonon scattering mechanisms. Identified α values for InGaAs and SiGe match ab initio BTE predictions within a few percent. Our results provide experimental evidence of fractal L´ evy heat conduction in semiconductor alloys. The formalism additionally indicates that the transient temperature inside the material differs significantly from Fourier theory and can lead to improved thermal characterization of nanoscale devices and material interfaces.