An investigation of the Si-Ge thermal boundary resistance in use of MD and wave packet methods
Date Issued
2011
Date
2011
Author(s)
Ang, Ai-Tee
Abstract
This thesis employs the non-equilibrium molecular dynamics (NEMD) to investigate the thermal transport phenomena across both perfect and imperfect interfaces formed by two dielectric thin films (Si and Ge) at 500K. The conditions of imperfect interfaces, the interface thickness and compositions, were manipulated and their effects on the thermal boundary resistance (TBR) were explored. Changing the Ge atomic composition creates different levels of mass disorders. The Stillinger-Weber (SW) potentials were used to describe the interaction between and among atoms of Si and Ge. The adiabatic boundary condition was applied in the main heat transfer direction at both ends of the simulation domain. The simulation results show that the TBRs of thick and thin interfaces possess remarkably different variation trends. The thick interface reveals a single bump in its variation curve having the maximum occurring at a Ge atomic fraction of 0.5. This implies that the mass difference scattering effect overtakes other scattering effects. The thin interface nonetheless has two additional dips on both sides of the peak, both smaller than the TBR of the perfect interface.
For a further understanding, the wave-packet experiment was employed to measure the acoustic transmissivities at 0K as well as 500K. Two alloy interfaces were inserted in the simulation domain and the periodic boundary conditions were employed in all three directions. The so measured longitudinal acoustic transmissivities at 0K decrease first and increase later with an increasing Ge atomic fraction for both thick and thin interfaces and for all wave numbers, implying the dominance of the mass difference scattering effect. The TA transmissitivity has a similar trend except that the dip is smaller in the thin interface case. The 500K experiments show reduced transmissivities compared to those measured at 0K but the variation trend remains unchanged.
The measured transmissivities support the TBR results of the alloy interface of thickness 10UC. Nonetheless, they are contradictive to the TBRs associated with the interfaces of thickness 2UC. This discrepancy may be caused by the limitations of the wave packet experiment which (1) treats the phonon mode in isolation and (2) has the incident wave always normal to the interface. Additionally, the adiabatic boundary condition and the insufficiently long simulation domain in the NEMD simulations may contribute to the discrepancy as well.
Subjects
Thermal boundary resistance
Wave packet
Molecular dynamics
Mass difference scattering
alloy interface
Type
thesis
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