Abstract
The efficiency in modern technologies and green energy solutions has boiled down to a thermal engineering problem on the nanoscale. Due to the magnitudes of the thermal mean free paths approaching or overpassing typical length scales in nanomaterials (i.e., materials with length scales less than one micrometer), the thermal transport across interfaces can dictate the overall thermal resistance in nanosystems. However, the fundamental mechanisms driving these electron and phonon interactions at nanoscale interfaces are difficult to predict and control since the thermal boundary conductance across interfaces is intimately related to the characteristics of the interface (structure, bonding, geometry, etc.) in addition to the fundamental atomistic properties of the materials comprising the interface itself. In this paper, I review the recent experimental progress in understanding the interplay between interfacial properties on the atomic scale and thermal transport across solid interfaces. I focus this discussion specifically on the role of interfacial nanoscale “imperfections,” such as surface roughness, compositional disorder, atomic dislocations, or interfacial bonding. Each type of interfacial imperfection leads to different scattering mechanisms that can be used to control the thermal boundary conductance. This offers a unique avenue for controlling scattering and thermal transport in nanotechnology.
Highlights
As the world’s population and power demands increase, our technological solutions continue to rely on power-hungry applications. e shear population increase in the world along with skyrocketing electricity, power, and transportation needs in emerging markets has led to necessary minimum levels of energy for sustainable growth and livelihood of human kind. e trends in energy use are marked by our society’s continued advancement of technology, communication, transportation, and quality of life
It is important to note that due to the laser pulse accumulation in the sample from a Ti : Sapphire oscillator, the temperature rise on the sample surface consists of two parts: (1) a real component that represents the temperature rise due to the excitation of a single pulse and subsequent thermal diffusion from the surface of the metal into the underlying material and across the material interfaces; this real response is directly related to the time domain response of the surface temperature following the optical pump pulse; and (2) an imaginary component that represents the temperature rise from the pulse accumulation; this imaginary response is predominantly controlled by the change in surface temperature subjected to the periodic heat source at frequency ff
I o en use an Si substrate as a calibration of time domain thermore ectance (TDTR) to ensure our experimental measurement can accurately reproduce the thermal conductivity of single crystalline silicon at room temperature [86, 87]
Summary
As the world’s population and power demands increase, our technological solutions continue to rely on power-hungry applications. e shear population increase in the world along with skyrocketing electricity, power, and transportation needs in emerging markets has led to necessary minimum levels of energy for sustainable growth and livelihood of human kind. e trends in energy use are marked by our society’s continued advancement of technology, communication, transportation, and quality of life. Erefore, an understanding of the effects of interfacial imperfections and other “non-idealities” (such as roughness, disorder, and bonding) on thermal transport across complex nanoscale interfaces is warranted to fully develop the potential to control electron and phonon thermal processes in nanosystems. To this end, in this paper I will review recent advancements in the underlying physics of thermal boundary conductance at solid interfaces, focusing speci cally on the role of interfacial nanoscale “imperfections,” such as surface roughness, compositional disorder, atomic dislocations, or interfacial bonding. The remainder of the sections will focus on examining the effects of various interfacial imperfections on either the electron- or phonon-dominated thermal boundary conductance across interfaces. ese sections will focus on the effects of interfacial interspecies mixing on electron and phonon thermal boundary conductance (Sections 5 and 6, resp.) and roughness, dislocations, and bonding effects on phonon thermal boundary conductance (Sections 7, 8, and 9, resp.)
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