Bridging overwhelms binding for enhancing thermal boundary conductance

The redox reaction between Al and metallic oxide has its advantage compared with intermetallic reaction and Al/NiO nanomutlilayers are a promising candidate for enhancing the performance of energetic igniter. Al/NiO nanomutlilayers with different modulation periods are prepared on alumina substrate by direct current (DC) magnetron sputtering. The thicknesses of each period are 250 nm, 500 nm, 750 nm, 1000 nm, and 1500 nm, respectively, and the total thickness is 3 μm. The X-ray diffraction (XRD) and scanning electron microscope (SEM) results of the as-deposited Al/NiO nanomutlilayers show that the NiO films are amorphous and the layered structures are clearly distinguished. The X-ray photoelectron spectroscopy (XPS) demonstrates that the thickness of Al2O3increases on the side of Al monolayer after annealing at 450°C. The thermal diffusion time becomes greater significantly as the amount of thermal boundary conductance across the interfaces increases with relatively smaller modulation period. Differential scanning calorimeter (DSC) curve suggests that the energy release per unit mass is below the theoretical heat of the reaction due to the nonstoichiometric ratio between Al and NiO and the presence of impurities.

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Thermal boundary conductance between Al films and GaN nanowires investigated with molecular dynamics

Physical Chemistry Chemical Physics ◽

10.1039/c4cp00261j ◽

2014 ◽

Vol 16 (20) ◽

pp. 9403-9410 ◽

Cited By ~ 8

Author(s):

Xiao-wang Zhou ◽

Reese E. Jones ◽

Patrick E. Hopkins ◽

Thomas E. Beechem

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Thermal Transport ◽

Thermal Boundary Conductance ◽

Gan Nanowires ◽

System P ◽

Dynamics Simulations ◽

Important System

Using molecular dynamics simulations, we studied the thermal boundary conductance between GaN nanowires and Al films and showed how it may be possible to enhance interfacial thermal transport in this important system.

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Relative Contributions of Inelastic and Elastic Diffuse Phonon Scattering to Thermal Boundary Conductance Across Solid Interfaces

Journal of Heat Transfer ◽

10.1115/1.2995623 ◽

2009 ◽

Vol 131 (2) ◽

Cited By ~ 45

Author(s):

Patrick E. Hopkins ◽

Pamela M. Norris

Keyword(s):

Experimental Data ◽

Elastic Scattering ◽

Inelastic Scattering ◽

Debye Temperature ◽

Diffuse Scattering ◽

Phonon Scattering ◽

Interfacial Transport ◽

Thermal Boundary Conductance ◽

Dielectric Interfaces ◽

Scattering Events

The accuracy of predictions of phonon thermal boundary conductance using traditional models such as the diffuse mismatch model (DMM) varies depending on the types of material comprising the interface. The DMM assumes that phonons, undergoing diffuse scattering events, are elastically scattered, which drives the energy conductance across the interface. It has been shown that at relatively high temperatures (i.e., above the Debye temperature) previously ignored inelastic scattering events can contribute substantially to interfacial transport. In this case, the predictions from the DMM become highly inaccurate. In this paper, the effects of inelastic scattering on thermal boundary conductance at metal/dielectric interfaces are studied. Experimental transient thermoreflectance data showing inelastic trends are reviewed and compared to traditional models. Using the physical assumptions in the traditional models and experimental data, the relative contributions of inelastic and elastic scattering to thermal boundary conductance are inferred.

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Influence of Interfacial Mixing on Thermal Boundary Conductance Across a Chromium/Silicon Interface

Journal of Heat Transfer ◽

10.1115/1.2897344 ◽

2008 ◽

Vol 130 (6) ◽

Cited By ~ 85

Author(s):

Patrick E. Hopkins ◽

Pamela M. Norris ◽

Robert J. Stevens ◽

Thomas E. Beechem ◽

Samuel Graham

Keyword(s):

Electron Spectroscopy ◽

Finite Thickness ◽

Thermal Conductance ◽

Phase Region ◽

Two Phase ◽

Thermal Boundary Conductance ◽

Si Substrates ◽

Interfacial Mixing ◽

Silicon Interface ◽

Deposition Conditions

The thermal conductance at solid-solid interfaces is becoming increasingly important in thermal considerations dealing with devices on nanometer length scales. Specifically, interdiffusion or mixing around the interface, which is generally ignored, must be taken into account when the characteristic lengths of the devices are on the order of the thickness of this mixing region. To study the effect of this interfacial mixing on thermal conductance, a series of Cr films is grown on Si substrates subject to various deposition conditions to control the growth around the Cr∕Si boundary. The Cr∕Si interfaces are characterized with Auger electron spectroscopy. The thermal boundary conductance (hBD) is measured with the transient thermoreflectance technique. Values of hBD are found to vary with both the thickness of the mixing region and the rate of compositional change in the mixing region. The effects of the varying mixing regions in each sample on hBD are discussed, and the results are compared to the diffuse mismatch model (DMM) and the virtual crystal DMM (VCDMM), which takes into account the effects of a two-phase region of finite thickness around the interface on hBD. An excellent agreement is shown between the measured hBD and that predicted by the VCDMM for a change in thickness of the two-phase region around the interface.

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Influence of Hot Electron Scattering and Electron–Phonon Interactions on Thermal Boundary Conductance at Metal/Nonmetal Interfaces

Journal of Heat Transfer ◽

10.1115/1.4027785 ◽

2014 ◽

Vol 136 (9) ◽

Cited By ~ 13

Author(s):

Ashutosh Giri ◽

Brian M. Foley ◽

Patrick E. Hopkins

Keyword(s):

Phonon Scattering ◽

Energy Levels ◽

Golden Rule ◽

Energy Coupling ◽

Hot Electron ◽

Nonequilibrium Electron ◽

Simplified Approach ◽

Thermal Boundary Conductance ◽

Order Of Magnitude ◽

Unique Mechanism

It has recently been demonstrated that under certain conditions of electron nonequilibrium, electron to substrate energy coupling could represent a unique mechanism to enhance heat flow across interfaces. In this work, we present a coupled thermodynamic and quantum mechanical derivation of electron–phonon scattering at free electron metal/nonmetal substrate interfaces. A simplified approach to the Fermi's Golden Rule with electron energy transitions between only three energy levels is adopted to derive an electron–phonon diffuse mismatch model, that account for the electron–phonon thermal boundary conductance at metal/insulator interfaces increases with electron temperature. Our approach demonstrates that the metal-electron/nonmetal phonon conductance at interfaces can be an order of magnitude larger than purely phonon driven processes when the electrons are driven out of equilibrium with the phonons, consistent with recent experimental observations.

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