About

David G. Cahill is a professor associated with the Department of Materials Science and Engineering at the University of Illinois. His research focuses on materials science and engineering, with a particular emphasis on thermal transport, heat conduction, and related phenomena. He is involved in various research activities, including working with visiting scientists, post-doctoral research associates, graduate students, and undergraduate students, contributing to the advancement of knowledge in his field. His contact information is provided through the College of Engineering at the University of Illinois, located in Urbana, Illinois.

Research topics

• Materials science
• Composite material
• Physics
• Chemistry
• Condensed matter physics
• Optics
• Organic chemistry
• Chemical engineering
• Nanotechnology
• Nuclear physics
• Thermodynamics
• Optoelectronics

Selected publications

• Revealing Phonon Bridge Effect for Amorphous vs Crystalline Metal–Silicide Layers at Si/Ti Interfaces by a Machine Learning Potential

  ACS Applied Electronic Materials · 2026-03-11

  articleOpen access

  Metal–semiconductor interfaces play a central role in micro- and nanoelectronic devices, as heat dissipation or temperature drop across these interfaces can significantly affect device performance. Prediction of accurate thermal boundary resistance (TBR) across these interfaces, considering realistic structures and their correlation with underlying thermal transport, remains challenging. In this work, we develop a unified Neuroevolution Potential (NEP) for the Si–Ti system that accurately reproduces energies, forces, and phonon properties of bulk Si, Ti, and TiSi2 and extends naturally to interfacial environments to analyze interfacial transport. An important development over current machine-learned interatomic potentials is the capability to model complex structures at metal–semiconductor interfaces, as the NEP enables large-scale nonequilibrium molecular dynamics simulations of epitaxial Si/Ti interfaces to elucidate the effect of amorphous or crystalline silicide interfacial layers. Simulated TBRs show excellent agreement with our time-domain thermoreflectance (TDTR) measurements, validating the robustness of our predictions. Spectral analyses reveal that the amorphous TiSi2 interfacial layer helps in efficient interfacial transport when the thickness is less than 1.5 nm compared to the crystalline TiSi2 layer, due to the high spectral conductance in the 3–6 THz frequency range and also due to the opening of channels for anharmonic transport, but this trend reverses when the interfacial layer thickness increases beyond 1.5 nm. Comparison of TBRs at the Si/TiSi2 interface for different crystalline phases of TiSi2 establishes that the C54 phase has reduced TBR compared to the C49 phase, which is correlated with the difference in their phonon density of states (PDOS) overlap with Si. These results provide atomistic insight into the role of crystalline versus amorphous silicides in interfacial heat transport and demonstrate a transferable machine-learned potential for studying heat dissipation in advanced semiconductor devices.

  PublisherDOI

• Strong temperature dependence of thermal conductivity in high-purity cubic boron arsenide

  Physical review. B./Physical review. B · 2025-06-05 · 4 citations

  preprintOpen access

  Materials with high thermal conductivity $(\mathrm{\ensuremath{\Lambda}})$ are needed to conduct heat away from hot spots in high-power electronics and optoelectronic devices. Cubic boron arsenide (c-BAs) has a high thermal conductivity due to its special phonon dispersion relation. Previous experimental studies of c-BAs report a room-temperature thermal conductivity between 1000 and $1300\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. We synthesized high-purity isotopically enriched c-BAs single crystals with room-temperature thermal conductivity of $\ensuremath{\approx}1500\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. Using time-domain thermoreflectance, we measured thermal conductivity and found a $1/{T}^{2}$ temperature dependence between 300 and 600 K--slightly stronger than predictions from state-of-the-art theoretical models. Brillouin and Raman scattering revealed minimal changes in phonon frequencies over the same temperature range, suggesting that the observed $1/{T}^{2}$ dependence is not caused by temperature-dependent changes in phonon dispersion. To probe defect densities in the BAs crystals we studied, we conducted transient reflectivity microscopy (TRM) measurements of absorption at sub-band-gap photon energies. We observe a correlation between TRM signal intensity and thermal conductivity. Notably, samples with thermal conductivity near $1500\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ still exhibited nonzero TRM signals, suggesting the presence of defects despite the high thermal conductivity.

  PublisherOA PDFDOI

• Probing thermodynamics of Li-ion solvation through reversible heat

  Cell Reports Physical Science · 2025-10-23

  articleOpen accessSenior author

  <h2>Summary</h2> The reversible heat generated during lithium electrochemical reactions—known as the Peltier heat—offers a direct probe of Li-ion solvation thermodynamics in electrolytes. Using temperature difference metrology (TDM) in a coin cell geometry, we systematically explore how lithium-ion solvation varies with the solvent, the choice of anion, and the salt concentration. We find that ether-based solvents produce larger entropy changes upon Li-ion solvation than carbonate-based solvents. As the salt concentration in the electrolyte increases, fewer solvent molecules coordinate with Li ions, reducing the entropy changes. In binary mixture electrolytes, Li ions exhibit preferential interactions with one component of the solvent over the other, causing deviations from a linear dependence on solvent composition. We also extract salt diffusion coefficients and heat of transport from transient features in the reversible heat. Our approach provides fundamental insights into electrolyte solvation thermodynamic, structure, and transport properties that will aid the design of electrolytes and electrode/electrolyte interfaces with improved performance.

  PublisherOA PDFDOI

• Intrinsic and Extrinsic Thermal Conductivities of Gallium Nitride and Silicon Carbide

  ˜The œMaterials Research Society series · 2025-01-01

  book-chapter
  PublisherDOI

• Reduction of the Thermal Conductivity of Polyurethanes by Fluorination: Impact of Crystallinity, Atomic Density, and Sound Velocity

  Angewandte Chemie International Edition · 2025-04-25 · 5 citations

  articleOpen accessCorresponding

  Abstract The intrinsic thermal conductivity () of polymers ranges between 0.13 W m −1 K −1 in amorphous polyvinyl chloride to 60 W m −1 K −1 in ultrahigh molecular weight polyethylene. Increasing the amorphous content of polymers to further lower is insufficient as this approach reaches a practical limit at approximately 0.15 W m −1 K −1 . Inspired by the low and low speed of sound of fluorinated liquids, we explored whether this behavior in liquids can be extended to polymers. We synthesized seven partially fluorinated (9%–17% atomic fraction F) and ten conventional polyurethanes. Fluorinated polyurethanes exhibit a reduction in up to 50% compared to their nonfluorinated counterparts. Microstructural analysis revealed that the fluorinated polyurethanes exhibited reduced crystallinity and increased molecular spacing. Furthermore, we observed a decreased speed of sound in fluorinated polymers by forced Brillouin scattering via a new analysis method that captures weak signals from highly scattering semicrystalline polymers. The lowest thermal conductivity, 0.13 W m −1 K −1 at room temperature, was observed in polyurethane synthesized from 2,2,3,3,4,4,5,5‐octafluoro‐1,6‐hexanediol (16F) and isophorone diisocyanate (IPDI). Our study provides deeper insights into the relationship between , microstructure, and chemical structure, paving the way to rational design of polymers with thermal conductivity below the lowest limit of conventional amorphous polymers.

  PublisherOA PDFDOI

• Optical spin–orbit torque in Pd/Co bilayers

  Journal of Magnetism and Magnetic Materials · 2025-07-21 · 1 citations

  article
  PublisherDOI

• Heat flow in solvent–free, dense amorphous and semi–crystalline cellulose derivatives

  ChemRxiv · 2025-09-29

  article

  Polymers are essential in our everyday life due to their versatility and tunable properties, but common synthetic polymers pose significant environmental challenges. This has led to growing interest in natural, biodegradable alternatives such as cellulose. For cellulose to serve as a viable alternative, it must match or ideally exceed materials properties of synthetic polymers. Thermal conductivity, κ, is one such critical property that often determines the suitability of polymers for a wide range of applications. In this study, we employ large–scale molecular dynamics simulations to investigate heat transport in dense, solvent–free cellulose and cellulose acetate systems. Our focus is on the amorphous phases of both materials, as well as the semi–crystalline phase of pure cellulose. By analyzing the vibrational density of states, g(ν), we report quantum–corrected estimates of the heat capacity, c, and consequently κ, enabling reasonable comparison with experimental data. Our results show that κ ≃ 0.14 − 0.26 Wm−1 K−1 across different cellulose samples investigated in this study– values comparable to those of standard synthetic polymers– highlighting cellulose as a viable alternative. This study demonstrates that cellulose offers a natural, sustainable alternative to common synthetic polymers, while also providing insight into the thermal behavior of cellulose– based materials.

  PublisherDOI

• Design of molecular structure for low and high thermal conductivity in soft materials

  Journal of materials research/Pratt's guide to venture capital sources · 2025-10-17 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract We review our recent work on the thermal conductivity of polymers that examines changes in conductivity that are produced by systematic variations in molecular structure, density, and crystallinity. Our interests are in exploring both the lower and upper limits of the isotropic thermal conductivity in polymers that are relatively simple to synthesize and process. Our recent work emphasizes (i) low and high thermal conductivity in epoxies synthesized from diepoxides and diamines; (ii) amorphous and semicrystalline polyesters; and (iii) the lower limit to thermal conductivity that we can achieve in polyurethane chemistry, i.e., reactions of polyols and isocyanates. For each system, we strive to fully characterize the thermal conductivity, heat capacity, density, coefficient of thermal expansion, longitudinal modulus, vibrational spectra by vibrational spectroscopy, and microstructure via X-ray scattering. Our data for epoxies, polyesters, and polyurethanes provide a baseline for the design of polymeric materials with reduced and enhanced thermal conductivity. Graphical abstract

  PublisherOA PDFDOI

• Phenyl Side Groups Enhance Phonon Transport in Rubrene Crystals

  Journal of the American Chemical Society · 2025-11-06 · 1 citations

  article

  temperature dependence of thermal conductivities along all three axes suggests crystalline behavior in rubrene as might be expected despite its complex molecular structure. These findings uncover a previously underappreciated role of side group dynamics in phonon transport in molecular crystals and provide new insights into developing thermal management strategies for organic electronic devices.

  PublisherDOI

• Photo‐Switching Thermal and Lithium‐Ion Conductivity in Azobenzene Polymers

  Advanced Functional Materials · 2025-10-07 · 1 citations

  articleOpen accessSenior author

  Abstract Developing materials with dynamic control over multiple transport properties is crucial for developing responsive energy management. Utilizing in situ time‐domain thermoreflectance (TDTR), synchrotron X‐ray scattering, and electrical impedance spectroscopy (EIS), a light‐responsive azobenzene polymer (pPPHM) is demonstrated, featuring simultaneously photo‐switchable thermal and ionic transport properties. Through UV and visible light illumination, pPPHM undergoes a reversible phase transition from a crystalline solid trans state to an amorphous liquid cis state driven by the conformational change of azobenzene moieties. The ordered crystalline structure in the trans state creates pathways for efficient thermal transport while restricting ion mobility, whereas the disordered amorphous state in the cis configuration disrupts thermal conductivity pathways but enables facile ion diffusion. This structural reorganization causes thermal conductivity to switch between solid trans (0.45 W·m −1 ·K −1 ) and liquid cis (0.15 W·m −1 ·K −1 ) states, while ionic conductivity shows 100 fold enhancement compared to liquid trans (≈10 −7 cm 2 ·s −1 ) and liquid cis (≈10 −5 cm 2 ·s −1 ) states. This dual transport offers functional energy materials that can adapt to changing conditions. For example, smart batteries that prevent overheating and regulate ion flow, thermal interfaces that switch between insulating and conducting modes on demand, and solid electrolytes that activate only when needed. These materials will replace multiple separate components with a single responsive system.

  PublisherDOI

Recent grants

• MRSEC: Illinois Materials Research Center

  NSF · $16.1M · 2017–2024

• Collaborative Research: Nanoscale Heat Transfer and Phase Transformation Surrounding Intensely Heated Nanoparticles

  NSF · $214k · 2010–2014

• Evolution of Stress and Mass Transport During keV Ion Bombardment

  NSF · $380k · 2004–2007

Frequent coauthors

• Darrell G. Schlom

  Leibniz Institute for Crystal Growth

  76 shared

• Simon R. Phillpot

  University of Florida

  69 shared

• Ella Pek

  67 shared

• Kiyoung Lee

  National Central University

  64 shared

• Natalie M. Dawley

  64 shared

• Aleksandr Chernatynskiy

  Missouri University of Science and Technology

  64 shared

• Che-Hui Lee

  Missouri University of Science and Technology

  64 shared

• Xue Xiong

  Hebei Normal University

  64 shared

Awards & honors

• Paul G. Klemens Award, International Conference on Phonon Sc…
• Elected member, American Academy of Arts and Sciences, Engin…
• Tau Beta Pi Daniel C. Drucker Eminent Faculty Award, College…
• Fellow, American Association for the Advancement of Science,…
• Innovation in Materials Characterization Award, Materials Re…