Study On Phonon Transport And Manipulation At The Interface By Microstructural Engineering

Interfacial thermal transport is a critical issue for micro/nano electronics,energy conversion and energy storage.Currently,researchers have been mainly focusing on exploring the mechanisms of interfacial thermal transport and modulating the interfacial thermal properties,as these works play important roles in improving the thermal management of microelectronic devices and increasing the energy conversion efficiency of thermoelectric devices.In this thesis,we have realized the phonon manipulation in three material systems,including tin selenide（Sn Se）bulk crystals,aluminum（Al）/erbium arsenide（Er As）/gallium arsenide（Ga As）heterojunctions and metal/antimony telluride（Sb₂Te₃）multilayers,by constructing a variety of interfacial microstructures based on the idea of microstructural engineering.We have studied the interfacial thermal properties in these material systems by time-domain thermoreflectance（TDTR）and explored the mechanisms of interfacial thermal transport behind.The key results are summarized as follows:1.Phonon manipulation has been realized by constructing atomic-level interfaces according to the differences in the intrinsic phonon characteristics of the two materials,Sn Se and Sn Se₂.The room temperature a-axis thermal conductivity of Sn Se was reduced from 0.77 W/m/K to 0.45 W/m/K by introducing the Sn Se₂intercalations using Bridgeman method.The Raman spectroscopy results showed that the optical phonon characteristics of Sn Se and Sn Se₂ are very different from each other.Therefore,the introduction of interfacial microstructures can lead to an optical phonon mismatch at the interface,which enhances the phonon scattering and reduces the thermal conductivity of the system significantly.2.Clear transitions of phonon transport mechanisms have been realized by constructing interfaces with tunable morphologies and thicknesses.A series of Al/Er As/Ga As heterojunction samples were prepared by molecular beam epitaxy.Different interfacial microstructures were constructed by adjusting the Er As thickness.As the Er As thickness increases,the phonon behavior at the interface changed from scattered transport to ballistic transport and then to diffusive transport.Quantitative analysis further confirmed the transition from ballistic to diffusive transport and extrapolated the critical interface thickness to be 7 nm.3.The modulation of interfacial thermal transport has also been realized by changing the material type,the interface density and the temperature in the metal/semiconductor multilayer system.A series of（Pt,Au,Ag）/Sb₂Te₃ multilayer samples with different periodic length were prepared by magnetron sputtering.The phonon scattering was enhanced by increasing the interface density,resulting in a lower total out of plane thermal conductivity of the system.In addition to phonon-phonon coupling,electron-phonon coupling is introduced at the interfaces of the metal/semiconductor multilayer system.The electron-phonon coupling coefficient of the metal is the key factor affecting the thermal transport contributed by electron-phonon coupling.As the electron-phonon coupling coefficient of Pt is much larger than that of Au and Ag,the total thermal conductivity of Pt/Sb₂Te₃ is much higher than Au/Sb₂Te₃ and Ag/Sb₂Te₃.Phonon manipulation by interfacial microstructures in the three above-mentioned material systems has some common characteristics.The interfacial microstructures can introduce new phonon transport mechanisms,which may result in either a cooperative or competitive relationship to the original phonon transport mechanisms in the material system.The dominance,transition or synergy of different interfacial thermal transport mechanisms can be controlled by changing the characteristic parameters of the interfacial microstructures,to further affect the interfacial thermal properties of the system.This thesis provides a new perspective for understanding the interfacial thermal transport and new ideas for interfacial thermal transport modulation.The results improve and contribute to the deeper understanding of the interfacial thermal transport theories.In addition,the study can be helpful to promote the practical applications of thermal interfacial materials and thermoelectric materials in micro/nano-scale devices.