Thermal transport across isotopic 28Si/mSi interfaces

In this work non-equilibrium molecular dynamics simulations are performed to investigate the transport of thermal energy across isotopic 28Si/mSi interfaces. The thermal boundary resistance at the isotopic silicon interface is deduced from the cooling behaviour of a 30 nm 28Si layer on top of a 400 nm mSi substrate after pulsed heating. The observed linear dependence of thermal boundary resistance on isotopic mass difference between 28Si layer and mSi substrate is explained within the framework of the acoustic mismatch model. For artificial heavy silicon substrate isotopes (m⩾34 u) the occurrence of pronounced thermal waves is observed. This wave-like contribution to thermal transport is due to the influence of the thermal boundary resistance. A delay between pulsed heating and heat flow across the interface is induced, because phonons can no longer easily overcome the isotopic interface. This means that Fourier's law of heat conduction is no longer valid, because application of the temperature gradient and heat flow across the interface do not happen simultaneously. Instead the propagation of heat along the sample is described by a wave-like heat equation which takes the delay between pulsed heating and heat flow into account.