Spectral Control of Thermal Boundary Conductance between Copper and Carbon Crystals by Self-Assembled Monolayers

Abstract

Controlling the thermal boundary conductance (TBC) between copper and carbon crystals is important since it can bottleneck the thermal conductivity when reinforcing copper with carbon-crystals fillers, namely diamond or graphite, to develop heat sinks and spreaders needed for the thermal management. In this work, by using the nonequilibrium molecular dynamics simulation, we show how the TBC of copper/diamond is smaller than that of copper/graphite by an order of magnitude due to poorer overlap of the lattice vibrational spectra. To improve the TBC at the copper/diamond interface, the covalently bonded self-assembled monolayers (SAMs) with different chain lengths are installed at the interface. The TBC is significantly improved and increases with the chain length to approach the value of the copper/graphite interface. The spectral analysis further identifies that this is because the SAMs become softer with increasing chain length due to disordering of the collective SAMs structure, enhancing the spectral transmission in low-frequency vibrational modes with copper. The obtained results are useful to improve the thermal conductivity of metal/carbon-crystal composite materials.

Scalable monolayer-functionalized nanointerface for thermal conductivity enhancement in copper/diamond composite

“…Besides, the trend is nonlinear, with the slope of TBC increasing as the SAM coverage increases. As the previous study [18] has demonstrated, the SAM can bridge the phonon vibration spectra of the two materials with distinctly different vibrational properties [42], like Cu and diamond, it is possible to attribute the TBC enhancement to the increasing number of SAM bridges.…”

“…Non-equilibrium molecular dynamics (NEMD) [25] simulations were carried out to study the TBC across Cu/SAM/diamond surfaces. The generation of Cu and diamond surfaces follows the procedure of our previous study [18] to form a 5.0×5.0×30.0 nm 3 slab for each surface. The diamond surface was fully hydroxylated initially.…”

“…Luo et al indicated that thermal transport across gold (Au)-SAM-Au [15][16] and GaAs-SAM-GaAs [17] could be promoted by bridging the mismatch of the vibrational density of states (vDOS) of the interface by SAM. Hung et al studied the thickness of the SAM layer on TBC determination at Cu/SAM/diamond interface, discovering that the thickness-dependent spectral transmission of low-frequency phonons predominate the TBC [18]. Experimental studies using the TDTR method also clarified the effect of SAM on TBC enhancement.…”

Weaker bonding can give larger thermal conductance at highly mismatched interfaces

“…At interfaces such as gold/quartz ( 13 ) and Cu/silica ( 14 ), by varying the end groups from CH 3 [van der Waals (vdWs) interface] to SH (covalently bonded interface), which increases the interfacial adhesion strength by approximately two orders of magnitude, the TBC increases from 36 to 65 MW/m 2 ·K, and from 260 to 430 MW/m 2 ·K, respectively. In addition, fewer, but still several, works have demonstrated enhancement of the TBC through the bridging effect at interfaces such as gold/polymer (25 to 165 MW/m 2 ·K) ( 15 ) and Cu/diamond (40 to 80 MW/m 2 ·K) ( 16 ). Bridging the vibrational frequency mismatch between the materials on the sides of the interface with the SAM can extend the phonon transmission spectrum to a broader range, the same as that of the expanded vibrational density of states (vDOSs) overlap, which creates extra phonon channels for an enhanced interfacial thermal transport.…”

Enhancement of Interfacial Thermal Transport between Metal and Organic Semiconductor Using Self-Assembled Monolayers with Different Terminal Groups

“…25−27 Luo et al 25 The interfacial thermal transports of water−solid interfaces functionalized with different SAMs were investigated using time-domain thermoreflectance, 26 and the experimental results exhibited that the thermal resistances at hydrophobic interfaces were two to three times larger than those of hydrophilic interfaces. The positive correlation between the chain length of SAMs and the ITC of SAM-modified copper−carbon interfaces was observed by Hung et al 27 Moreover, many research studies demonstrate that the ITC is strongly associated with the adhesion energy. 28,29 Using MD simulations, Shenogina et al found that the thermal conductance of the SAM-modified metal−water interface was proportional to the adhesion energy.…”