Multidisciplinary research in Raman spectroscopy, phase imaging and their applications in heat transfer

Abstract

Recent advances in micro-to-nanoscale heat transfer have led to tremendous research interests in the high spatial resolution thermal characterization techniques. Although great improvement has been made in temperature probe, heat flux measurement and thermophysical properties characterization especially for solid-state materials and structures, precision thermal characterization is still challenging due to the presence of multiphysics coupling, the limitation of resolution and the restriction of materials that can be studied. The goal of this thesis is to explore more possible opportunities for advanced thermal measurement techniques. Specifically, this thesis mainly focuses on the development of Raman spectroscopy and phase imaging and demonstrates their applications to micro-to-nanoscale heat transfer. Due to the superior spatial resolution and the non-contact nature, micro-Raman spectroscopy has been widely applied for local temperature measurement. However, the presence of multiphysics coupling to the optical phonon modes and the necessity to have Raman signature for the test materials limit the application of micro-Raman thermometry to simple solid-state devices. In this thesis, we present several advancements which extend the capability of Raman spectroscopy to multiphysics coupling systems, Raman-inactive materials and nanoscale thermometry. Specifically, we simultaneously measured the temperature, stress and electric field in GaN HEMTs and the linear thermal expansion coefficient of MoS2 monolayer flake using the multiple peaks fit method. We presented a method to interface micro-Raman system with a phase change heat transfer test setup and used this integrated setup to study the thin film evaporation on structured surfaces. To measure the temperature of Raman-inactive materials, we used nanoparticles as the Raman agent. We measured the temperature distribution of the optically transparent and thermally insulated silica aerogel. Additionally, this thesis also proposed a concept of nanoscale Raman thermometry using plasmon enhanced gold-silicon nanoparticles. The electric field concentration properties and in situ measurement capability were proven using simulation and experiments. Attributed to the high sensitivity to geometrical structures and refractive index of materials, phase imaging techniques were useful for weakly scattering systems. Although the property of imaging transparent materials has been well-demonstrated, the application of nanoscale detection using phase imaging is lacking. In this thesis, we developed robust phase imaging method based on transport of intensity equation and depth scanning technique and proved the ultrahigh sensitivity of phase in nanoscale inspection. This developed technology was validated through a number of simulations and experiments, including detecting the deep subwavelength defects on 9 nm semiconductor wafers. The thesis finally shows the opportunity of using phase imaging to study micro-to-nanoscale phase change heat transfer. The dynamic interactions and growth of condensing droplets were investigated using the phase imaging enhanced environmental scanning electron microscopy.