https://doi.org/10.1021/acsnano.3c02417

The coupled interactions among the fundamental carriers of charge, heat, and electromagnetic fields at interfaces and boundaries give rise to energetic processes that enable a wide array of technologies. The energy transduction among these coupled carriers results in thermal dissipation at these surfaces, often quantified by the thermal boundary resistance, thus driving the functionalities of the modern nanotechnologies that are continuing to provide transformational benefits in computing, communication, health care, clean energy, power recycling, sensing, and manufacturing, to name a few. It is the purpose of this Review to summarize recent works that have been reported on ultrafast and nanoscale energy transduction and heat transfer mechanisms across interfaces when different thermal carriers couple near or across interfaces. We review coupled heat transfer mechanisms at interfaces of solids, liquids, gasses, and plasmas that drive the resulting interfacial heat transfer and temperature gradients due to energy and momentum coupling among various combinations of electrons, vibrons, photons, polaritons (plasmon polaritons and phonon polaritons), and molecules. These interfacial thermal transport processes with coupled energy carriers involve relatively recent research, and thus, several opportunities exist to further develop these nascent fields, which we comment on throughout the course of this Review.

Congrats to Shafkat bin Hoque for your recent first author paper in ACS Nano reporting on the exceptionally high in-plane thermal conductivity of AlN thin films. We used SSTR to measure the in plane thermal conductivity of thin AlN films, and demonstrated that the in plane thermal conductivities of these AlN films are record setting, exceeding the heat spreading ability of even diamond.

Hoque, Md.S.B., Koh, Y.R., Braun, J.L., Mamun, A., Liu, Z., Huynh, K., Liao, M.E., Hussain, K., Cheng, Z., Hoglund, E.R., Olson, D.H., Tomko, J.A., Aryana, K., Galib, R., Gaskins, J.T., Elahi, M.M.M., Leseman, Z.C., Howe, J.M., Luo, T., Graham, S., Goorsky, M.S., Khan, A., Hopkins, P.E., “High in-plane thermal conductivity of aluminum nitride thin films,” ACS Nano 15, 9588-9599 (2021). PDF (Supporting Information).

Abstract: High thermal conductivity materials show promise for thermal mitigation and heat removal in devices. However, shrinking the length scales of these materials often leads to significant reductions in thermal conductivities, thus invalidating their applicability to functional devices. In this work, we report on high in-plane thermal conductivities of 3.05, 3.75, and 6 μm thick aluminum nitride (AlN) films measured via steady-state thermoreflectance. At room temperature, the AlN films possess an in-plane thermal conductivity of ∼260 ± 40 W m−1 K−1, one of the highest reported to date for any thin film material of equivalent thickness. At low temperatures, the in-plane thermal conductivities of the AlN films surpass even those of diamond thin films. Phonon−phonon scattering drives the in-plane thermal transport of these AlN thin films, leading to an increase in thermal conductivity as temperature decreases. This is opposite of what is observed in traditional high thermal conductivity thin films, where boundaries and defects that arise from film growth cause a thermal conductivity reduction with decreasing temperature. This study provides insight into the interplay among boundary, defect, and phonon−phonon scattering that drives the high in-plane thermal conductivity of the AlN thin films and demonstrates that these AlN films are promising materials for heat spreaders in electronic devices.

Congratulations Kiumars Aryana for your two first author Nature Communication papers. These recent work by Kiumars, in collaboration with our colleagues at Western Digital, have revealed critical nanoscale heat transfer processes that are directly influencing the performance of phase change memory. These works report on 1) the role of thermal boundary resistance on the electron and phonon heat transfer processes of ultra thin film GST across GST’s phase transition and 2) the fundamental vibrational thermal transport mechanisms driving the thermal conductivity of SiTe (a prototypical materials used in OTSs) to “ultralow” values.

Aryana, K., Gaskins, J.T., Nag, J., Stewart, D.A., Bai, Z., Mukhopadhyay, S., Read, J.C., Olson, D.H., Hoglund, E.R., Howe, J.M., Giri, A., Grobis, M.K., Hopkins, P.E., “Interface controlled thermal properties of ultra-thin chalcogenide-based phase change memory devices,” Nature Communications 12, 774 (2021). PDF (Supporting Information, Supporting Movie 1, Supporting Movie 2).

Abstract: Phase change memory (PCM) is a rapidly growing technology that not only offers advancements in storage-class memories but also enables in-memory data processing to overcome the von Neumann bottleneck. In PCMs, data storage is driven by thermal excitation. However, there is limited research regarding PCM thermal properties at length scales close to the memory cell dimensions. Our work presents a new paradigm to manage thermal transport in memory cells by manipulating the interfacial thermal resistance between the phase change unit and the electrodes without incorporating additional insulating layers. Experimental measurements show a substantial change in interfacial thermal resistance as GST transitions from cubic to hexagonal crystal structure, resulting in a factor of 4 reduction in the effective thermal conductivity. Simulations reveal that interfacial resistance between PCMand its adjacent layer can reduce the reset current for 20 and 120 nm diameter devices by up to~40% and~50%, respectively. These thermal insights present a new opportunity to reduce power and operating currents in PCMs.

Aryana, K., Stewart, D.A., Gaskins, J.T., Nag, J., Read, J.C., Olson, D.H., Grobis, M.K., Hopkins, P.E., “Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides,” Nature Communications 12, 2817 (2021). PDF (Supporting Information).

Abstract: Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10±0.01 W m−1 K−1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge -a factor of five -towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network.

Highlights

•Yb silicate top coats spatially vary in phase and microstructure during high-temperature cycling.

•Thermal conductivity in Yb silicate top coats is inhomogenous and dynamic with cycling.

•Surface volatilization of Yb₂Si₂O₇ promotes steam volatility resistance and thermal insulation.

•Near the bond coat, Yb₂SiO₅ reacts with SiO₂ to form Yb₂Si₂O₇, reducing thermal expansion mismatch.

Abstract

Environmental barrier coating (EBC) systems are applied to the surface of silicon-based composites exposed to high temperature combustion gas flow paths in gas turbine engines. They reduce the rate of composite oxidation, its volatilization by reactions with water vapor, and the temperature of the composite as their thermal conductivity decreases. Current EBC systems consist of a silicon bond coat covered by an ytterbium disilicate (Yb₂O₃⋅2SiO₂: YbDS) permeation resistant and low silica activity barrier. When applied by atmospheric-plasma spray deposition, this outer layer contains 10–15% of a secondary ytterbium monosilicate (Yb₂O₃⋅3SiO₂: YbMS) phase. YbDS has a coefficient of thermal expansion (CTE) of 4–5×10⁻⁶ °C⁻¹, similar to those of the silicon and the silicon-based composite, but a relatively high thermal conductivity of 5–7 W m⁻¹ K⁻¹. YbMS has a higher steam volatility resistance than YbDS, and it has a much lower thermal conductivity (∼2–2.5 W m⁻¹ K⁻¹) at ambient temperature compared to YbDS, but its higher, highly anisotropic CTE (3–11×10⁻⁶ °C⁻¹) results in channel cracking which reduces environmental protection. Here, we use a combination of scanning electron beam and laser-based thermoreflectance methods to spatially map the distribution of the silicate phases and thermal conductivity at ambient temperature in a Si-ytterbium disilicate EBC system exposed to thermal cycling in water vapor. We show that during thermal cycling, diffusion of silica from the thermally grown oxide on the Si bond coat surface to nearby YbMS regions transforms this phase to YbDS, thereby reducing the risk of thermomechanical coating failure but decreasing its effective thermal resistance. We also show that as silica is volatilized at the water vapor–ytterbium silicate interface, YbDS is transformed to YbMS, restoring some of the thermal protection of the coating system lost by its reduction in thickness and the YbMS to YbDS transformation near the bond coat.

Congrats John Tomko for his recent first author paper in Nature Nanotechnology on:

“Long-lived modulation of plasmonic absorption by ballistic thermal injection“

Current citation until volume and page number are assigned: Tomko, J.A., Runnerstrom, E.L., Wang, YS. et al. Long-lived modulation of plasmonic absorption by ballistic thermal injection. Nat. Nanotechnol. (2020). https://doi.org/10.1038/s41565-020-00794-z

In this work, in a collaboration with Penn State (Maria Group), Vanderbilt (Caldwell group), U. Southern California (Prezhdo Group), we demonstrate a new heat transfer mechanism across interfaces in which energy can flow from a metal to a non-metal without the flow of charge. This occurs when the electron energy in the metal is traveling ballistically, and thus injects its heat into the non-metal. We use this new mechanism to control the infrared plasmsonic response of doped CdO, a novel mid-IR plamonic material with strong ENZ mode abosorption.

Abstract

Light–matter interactions that induce charge and energy transfer across interfaces form the foundation for photocatalysis, energy harvesting and photodetection, among other technologies. One of the most common mechanisms associated with these processes relies on carrier injection. However, the exact role of the energy transport associated with this hot-electron injection remains unclear. Plasmon-assisted photocatalytic efficiencies can improve when intermediate insulation layers are used to inhibit the charge transfer or when off-resonance excitations are employed, which suggests that additional energy transport and thermal effects could play an explicit role even if the charge transfer is inhibited8. This provides an additional interfacial mechanism for the catalytic and plasmonic enhancement at interfaces that moves beyond the traditionally assumed physical charge injection. In this work, we report on a series of ultrafast plasmonic measurements that provide a direct measure of electronic distributions, both spatially and temporally, after the optical excitation of a metal/semiconductor heterostructure. We explicitly demonstrate that in cases of strong non-equilibrium, a novel energy transduction mechanism arises at the metal/semiconductor interface. We find that hot electrons in the metal contact transfer their energy to pre-existing free electrons in the semiconductor, without an equivalent spatiotemporal transfer of charge. Further, we demonstrate that this ballistic thermal injection mechanism can be utilized as a unique means to modulate plasmonic interactions. These experimental results are well-supported by both rigorous multilayer optical modelling and first-principle ab initio calculations.

We acknowledge funding from the US Department of Defense, Multidisciplinary University Research Initiative through the Army Research Office, Grant no. W911NF-16-1-0406. J.R.N. and J.D.C. appreciate support from the Office of Naval Research, Grant no. N00014-18-1-2107.

Mallory DeCoster’s recent work on the thermal conductivity of ALD grown PbTe-PbSe nano-composite thin films was published today in Advanced Functional Materials.

DeCoster, M.E., Chen, X., Zhang, K., Rost, C.M., Hoglund, E.R., Howe, J.M., Beechem, T.E., Baumgart, H., Hopkins, P.E., “Thermal conductivity and phonon scattering processes of ALD grown PbTe-PbSe thermoelectric thin films,” Advanced Functional Materials DOI: 10.1002/adfm.201904073 (2019).

In this work, in a collaboration with Prof. Helmut Baumgart from ODU, Dr. Thomas Beechem from Sandia, and Prof. Jim Howe from UVA, we studied the thermal conductivity of a series of thickness varying, compositionally varying PbTe-PbSe nano-structured thin films grown by atomic layer deposition.  We show that the thermal conductivity of these films exhibit glass like trends, and ultimately their thermal conductivities are dictated by the crystalline quality of the films, which can change as a function of thickness due to the ALD growth mode of the PbTe (Volmer-Weber).  This work has pronounced impact on understanding the thermal conductivity of ALD-grown thin films and their applications for thin film thermoelectric and thermal barriers.

Abstract

This work studies the thermal conductivity and phonon scattering processes in a series of n‐type lead telluride‐lead selenide (PbTe–PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe–PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer–Weber mode of growth promotes grains with a preferred columnar orientation. The ALD growth of these lead‐rich PbTe, PbSe, and PbTe–PbSe thin films results in secondary oxide phases, along with an increase microstructural quality with increased film thickness. The compositional variation and resulting point and planar defects in the PbTe–PbSe nanostructures give rise to additional phonon scattering events that reduce the thermal conductivity below that of the corresponding ALD‐grown control PbTe and PbSe films. Temperature‐dependent thermal conductivity measurements show that the phonon scattering in these ALD‐grown PbTe–PbSe nanostructured materials, along with ALD‐grown PbTe and PbSe thin films, are driven by extrinsic defect scattering processes as opposed to phonon–phonon scattering processes intrinsic to the PbTe or PbSe phonon spectra. The implication of this work is that polycrystalline, nanostructured ALD composites of thermoelectric PbTe–PbSe films are effective in reducing the phonon thermal conductivity, and represent a pathway for further improvement of the figure of merit (ZT), enhancing their thermoelectric application potential.

Funding

The authors appreciate funding from the Army Research Office, Grant No. W911NF‐16‐1‐0406. This work was supported in part by the NSF I/UCRC on Multi‐functional Integrated System Technology (MIST) Center IIP‐1439644, IIP‐1439680, and IIP‐1738752. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE‐NA0003525.

The recently deemed “Dr.” Jeff Braun recently published his work on steady state thermoreflectance (SSTR), an optical pump-probe technique based on continuous wave lasers in which the steady state temperature rise of a solid is monitored as a function of laser power to measure the thermal conductivity of the material.  SSTR is capable of measuring the thermal conductivity of materials over length scales from just a few microns to hundreds of microns, filling an important void in the landscape of thermal conductivity measurement capabilities.

Braun, J.L., Olson, D.H., Gaskins, J.T., Hopkins, P.E., “A steady-state thermoreflectance method to measure thermal conductivity,” Review of Scientific Instruments 90, 024905 (2019). PDF.

We demonstrate a steady-state thermoreflectance-based optical pump-probe technique to measure the thermal conductivity of materials using a continuous wave laser heat source. The technique works in principle by inducing a steady-state temperature rise in a material via long enough exposure to heating from a pump laser. A probe beam is then used to detect the resulting change in reflectance, which is proportional to the change in temperature at the sample surface. Increasing the power of the pump beam to induce larger temperature rises, Fourier’s law is used to determine the thermal conductivity. We show that this technique is capable of measuring the thermal conductivity of a wide array of materials having thermal conductivities ranging from 1 to >2000 W m−1 K−1, in excellent agreement with literature values.

We have recently demonstrated the ability to control the thermal conductivity of a material derived from squid ring teeth protein by hydrating the material with water.  In collaboration with Prof. Melik Demirel’s group at Penn State, along with collaborations from Prof. Ben Allen at Penn State and Dr. Madhusudan Tyagi from NIST and UMN, we have develop a thermal conductivity switch with higher thermal conductivity on/off ratios than any other single material that has been observed to date.  Congrats to John Tomko who was a first author on this paper that appeared in Nature Nanotechnology (Tomko, J.A., Pena-Francesch, A., Jung, H., Tyagi, M., Allen, B.D., Demirel, M.C., Hopkins, P.E., “Tunable thermal transport and reversible thermal conductivity switching in topologically-networked bio-inspired materials,” Nature Nanotechnology 13, 959-964 (2018). PDF (Supporting Information).).

Paper information below

Title:

Congratulations to Ethan Scott who recently published his paper on “Phonon scattering effects from point and extended defects on thermal conductivity studied via ion irradiation of crystals with self-impurities,” in Physical Review Materials (Scott, E. A., Hattar, K., Rost, C.M., Gaskins, J.T., Fazli, M., Ganski, C., Li, C., Bai, T., Wang, Y., Esfarjani, K., Goorsky, M., Hopkins, P.E., “Phonon-strain scattering effects from point and extended defects on thermal conductivity studied via ion irradiation of crystals with self-impurities,” Physical Review Materials 2, 095001 (2018). PDF).

Abstract

Congrats to Ethan Scott for his recent publication that experimentally determines the thickness regime in which the thermal boundary resistance at atomic layer deposited high-k dielectric interfaces dominates the total thermal resistance of the system.  In a collaboration with Dr. Sean King from Intel, we studied this with Al2O3, HfO2 and TiO2 ALD-grown thin films on silicon.

Scott, E.A., Gaskins, J.T., King, S.W., Hopkins, P.E., “Thermal conductivity and thermal boundary resistance of atomic layer deposited high-k dielectrics aluminum oxide, hafnium oxide, and titanium oxide thin films on silicon,” APL Materials 6, 058302 (2018). PDF.

Abstract