Effects of chemical bonding on heat transport across interfaces

Abstract

Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump-probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold-SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.

Anisotropic failure of Fourier theory in time-domain thermoreflectance experiments

“…Here, R j is the probability that a phonon with polarization j impinging on the interface from the sample side reflects and is believed to be determined by interfacial bonding strength, interface disorder and morphology and the vibrational properties of both the sample and metal transducer 16,30 . Using equation (4) (4) The dependence of G A on f for Si 0.99 Ge 0.01 and Si 0.2 Ge 0.8 is consistent with a reduced effective thermal conductivity of the sample, K z ¼ |J z /r z T|, near the interface due to an interfacial nonequilibrium thermal resistance, G NE À 1 .…”

“…TDTR and FDTR experiments require samples to be coated with a thin metal film to serve as an optical transducer, introducing a metal/sample interface to the heat transfer problem. The interface causes a thermal resistance due to the reflection/transmission of phonons, that is, interfacialphonon scattering 16 . This thermal resistance is typically described with a radiative boundary condition on the heat diffusion equation, known as the interfacial thermal conductance 17 .…”

Metal Matrix–Metal Nanoparticle Composites with Tunable Melting Temperature and High Thermal Conductivity for Phase-Change Thermal Storage

“…It should also be noted that due to the finite thermal interface conductance between the Ag and Bi, the Bi nanoparticles contribute a negligible amount to the overall nanocomposite thermal conductivity. Based on experimental data for similar interfaces, 67,68 we estimate that the thermal interface conductance between the Bi nanoparticles and the Ag matrix is 34 MW/m 2 -K (this value is lower than typical metal-metal interface conductances 69 due to the presence of organic ligands at the Bi-Ag interface). For reference purposes, an interface conductance can be converted into an equivalent film thickness by dividing the film's thermal conductivity by its thickness.…”

A review on the role of interface in mechanical, thermal, and electrical properties of polymer composites

“…Therefore, the interfacial zones predominantly affect the thermal conductivity of the composite [245,246]. As a result, anything that can affect the interfacial regions (e.g., geometry of particles [247][248][249][250][251][252][253], aggregation [254][255][256], interfacial pressure [257], roughness [258][259][260], and the strength of interactions at the interfaces [261][262][263][264][265]) in the composites would influence their thermal conductivity. In this section, we will review the parameters affecting the interfacial interactions and their subsequent impact on the thermal conductivity of the composites.…”

“…This phenomenon was explained by increasing the transmission coefficient of the phonons [263,278]. Modification of the end groups of the polymer chains [261] and surface modification of the fillers (either with [237,[280][281][282][283][284] or applying specific coatings [285][286][287]) are common methods for improving the adhesion at the interfaces with subsequent thermal conductivity enhancement. However, it should be considered that the functionalization of the filler may create defects and decrease the intrinsic thermal conductivity of them [288].…”