Journal publications (peer-reviewed)

2025

[28] T. J. Shimokusu, H. Thakkar, A. Abbas, B. Jumet, T.F. Yap, K. Sefiane, D. Orejon, D. J. Preston, G. Wehmeyer. Mask-enabled topography contrast on aluminum surfaces. Langmuir (in press).

Blade-cut vinyl masking can be combined with chemical etching and functionalization of aluminum to create topographic patterns, enabling complex ~mm scale patterning of wettability and emissivity contrast for enhanced phase-change heat transfer applications. For example, stripe-patterned surfaces with superhydrophobic/hydrophobic contrast can shed droplets more easily than homogeneous superhydrophobic surfaces, leading to enhanced condensation.

 

[27] I. R. Siqueira, M. Duran-Chaves, O. S. Dewey, S. M. Williams, C. J. S. Ginestra, J. D. L. Garza, Y. Song, G. Wehmeyer, M. Pasquali. Fully recyclable carbon nanotube fibers. Carbon 223, 119899 (2025)

Carbon nanotube fibers produced from different feedstock can be dissolved in acids and re-spun into recycled fibers while maintaining properties, leading to improved material circularity and sustainability.

2024

[26] L. Castelli, M. V. Kumar, G. Wehmeyer. Multi-season passive variable insulation for buildings using magnetic thermal diodes. Cell Reports Physical Science, 102283 (2024).

Magnetic thermal diodes can enable smart building envelope insulation that passively cools the building on cold summer nights and passively heats the building on warm winter days while blocking heat flows at all other times.

 

[25] S. Liao, Y. Song, S. Yu, L. W. Taylor, O. S. Dewey, M. Pasquali, J. Kono, G. Wehmeyer, D. Natelson. Understanding the Local Seebeck Coefficient of Carbon Nanotube Fibers Using the Photothermoelectric Effect. ACS Applied Electronic Materials, 6(11), 8000 (2024).

Scanning photothermoelectric measurements map Seebeck coefficient gradients in carbon nanotube fibers with microscale spatial resolution, showing that annealed fibers have lower Seebeck coefficient variance compared to acid-doped fibers.

 

[24] T. J. Shimokusu, A. Nathani, Z. Liu, T.F. Yap, D. J. Preston, G. Wehmeyer. Teflon AF–coated nanotextured aluminum surfaces for jumping droplet thermal rectification. Advanced Materials Interfaces, 2300817  (2024)

 

2023

[23] N. Marquez Peraca, Q. Zhu, J. Kono, G. Wehmeyer. Thermal analysis of thermoelectric active cooling including external thermal resistances. Applied Physics Letters, 123 243901 (2023).

Device modeling shows that high thermal conductivity materials such as carbon nanotube fibers can outperform traditional low thermal conductivity materials for thermoelectric cooling under high heat flow rates for small external thermal resistances.

[22] L. Castelli, A. Garg, Q. Zhu, P. Sashital, T.J. Shimokusu, G. Wehmeyer. A thermal regulator using passive all-magnetic actuation. Cell Reports Physical Science, 101556 (2023).

We demonstrate a centimeter-scale thermal regulator using temperature-dependent
magnetic forces to passively make/break thermal contact between surfaces. We measure room-temperature switching with >30x thermal switch ratios in vacuum.

 

[21] T.J. Shimokusu, B. Drolen, C. Wilson, J. Didion, G. Wehmeyer. Strain gauge measurements of an oscillating heat pipe from startup to stable operation. Applied Thermal Engineering, 121118 (2023)

We use strain and temperature measurements to study the operation of an oscillating heat pipe. These measurements show a distinct thermomechanical response between the startup and stable operation regimes arising from variations in slug/plug oscillations as a function of heat flow.

 

[20] Y. Song, G. Wehmeyer. Phonon ray tracing calculations of ballistic temperature and heat flux profiles in nanostructures. Materials Today Physics, 101040 (2023)

We develop Landauer-based phonon ray tracing techniques to map temperature and heat flux profiles in nanostructures. These simulations provide insight into geometry-dependent ballistic transport physics including inverted temperature gradients and phonon focusing in nanoporous materials.

 

[19] Q. Zhu, T.J. Shimokusu, G. Wehmeyer. Thermal Analysis of Oscillating Thermomagnetic Devices Beyond the Lumped Approximation.  International Journal of Heat and Mass Transfer 205, 123876 (2023)

We used analytical solutions of the heat equation to quantify the temperature profiles in a shuttle oscillating between two surfaces. These results can be used to design magnetic thermal rectifiers and thermomagnetic energy scavenging devices.

 

[18] L. Castelli, Q. Zhu, T.J. Shimokusu, G. Wehmeyer. A three-terminal magnetic thermal transistor. Nature Communications, 14, 390 (2023)

       

        2022

[17] Q. Zhu, K. Zdrojewski, L. Castelli, G. Wehmeyer. Oscillating gadolinium thermal diode using temperature-dependent magnetic forces. Advanced Functional Materials 32, 2206733 (2022)

 

 

[16] D. Lee, S.G. Kim, S. Hong, C. Madrona, Y. Oh, M. Park, N. Komatsu, L. W. Taylor, B. Chung, J. Kim, J. Y. Hwang, J. Yu, D.S. Lee, H. S. Jeong, N. H. You, N. D. Kim, D.-Y. Kim, H. S. Lee, K.-H. Lee, J. Kono, G. Wehmeyer, M. Pasquali, J. J. Vilatela, S. Ryu, B.-C. Ku. Ultrahigh strength, modulus, and conductivity of graphitic fibers by macromolecular coalescence. Science Advances 8, eabn0939 (2022).

Graphitization of carbon nanotube fibers due to high-temperature annealing dramatically increases the mechanical strength of the fibers with modest impacts on the thermal conductivity and electrical conductivity.

 

[15] T.J. Shimokusu*, Q. Zhu*, N. Rivera, G. Wehmeyer. Time-periodic thermal rectification in heterojunction thermal diodes. International Journal of Heat and Mass Transfer 182, 122035 (2022) (* indicates equal contribution)

We use macroscopic thermal modeling to study the frequency-dependent rectification for thermal diodes that use materials with temperature-dependent thermal conductivities. This work introduces a metric quantifying the ac-to-dc thermal rectification performance, and shows that the rectification metric is optimized for high heating frequencies.

        2021

[14] N. Komatsu, Y. Ichinose, O.S. Dewey, L. W. Taylor, M. Trafford, Y. Yomogida, G. Wehmeyer, M. Pasquali, K. Yanagi, J. Kono. Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor. Nature Communications 12, 4931 (2021).

Optimally-doped carbon nanotube fibers have simultaneous high thermoelectric power factor and high thermal conductivity, making CNT fibers appealing options for thermoelectric active cooling or heat switching applications.

 

[13] Y. Song, G. Wehmeyer. Maximizing and minimizing the boundary scattering mean free path in diameter-modulated coaxial cylindrical nanowires. Journal of Applied Physics 130, 045104 (2021).

Phonon ray tracing simulations show that the mean free path and thermal conductivity in modulated nanowires is dictated by the smaller nanowire diameter and can be fine-tuned by controlling the diameter ratio and pitch ratio.

 

[12] L.W. Taylor, O.S. Dewey, R.J. Headrick, N. Komatsu, N.M. Peraca, G. Wehmeyer, J. Kono, M. Pasquali. Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers. Carbon 171, 689 (2021).

The electrical conductivity, tensile strength, and modulus of wet-spun carbon nanotube fibers has continually improved while maintaining high room-temperature thermal conductivity near 400 W/m.K, making the fibers potential lightweight, high-strength metallic conductor replacements.

 

[11] S.M. Rehn, T.M. Gerrard-Anderson, L. Qiao, Q. Zhu, G. Wehmeyer, M. R. Jones. Mechanical Reshaping of Inorganic Nanostructures with Weak Nanoscale Forces, Nano Letters 21,  130-135 (2021).

Bend contours in transmission electron microscopy images show that van-der-Waals forces enable unusually localized plastic mechanical deformations for nanoplates draped on templated nanoparticles.

        2019

[10] G. Wehmeyer, Modeling ballistic phonon transport from a cylindrical electron beam heat source. Journal of Applied Physics 126, 124306 (2019).

We use phonon Boltzmann Transport Equation solutions to study beam heating in scanning transmission electron microscopy experiments. The results show that the ballistic thermal resistance dominates over the Fourier thermal resistance for high-thermal conductivity semiconductors, but that beam heating is still typically <1 K under typical imaging conditions.

 

[9]  O. Kwon, G. Wehmeyer, C. Dames. Modified ballistic–diffusive equations for obtaining phonon mean free path spectrum from ballistic thermal resistance: II. Derivation of Integral Equation Based on Ballistic Thermal Resistance . Nanoscale and Microscale Thermophysical Engineering  23, 334 (2019).

[8]  O. Kwon, G. Wehmeyer, C. Dames. Modified ballistic–diffusive equations for obtaining phonon mean free path spectrum from ballistic thermal resistance: I. Introduction and validation of the equations. Nanoscale and Microscale Thermophysical Engineering 23, 259-273 (2019).

Phonon ballistic-diffusive equations can quantify thermal conductivity size effects in planar and non-planar geometries used into phonon mean free path spectroscopy measurements.

 

[7]  H.S. Choe*, R. Prabhakar*, G.Wehmeyer*, F.I. Allen, W. Lee, L. Jin, Y. Li, P. Yang, C. Qiu, C. Dames, M. Scott, A. M. Minor, J.-H. Bahk, and J. Wu. Ion write micro-thermotics: programing thermal metamaterials at the microscale. Nano Letters  19, 3830−3837 (2019). (* indicates equal contribution)

Helium ion microscopes can be used to locally amorphize regions of a silicon wafer upon irradiation, enabling microscale pattering of heterogeneous thermal conductivity for thermal cloaking or heat routing.

     

 2018 and earlier

[6]  G. Wehmeyer, K. Bustillo, A.M. Minor, and C. Dames. Measuring temperature-dependent thermal diffuse scattering using scanning transmission electron microscopy. Applied Physics Letters 113, 253101 (2018). (Featured article)

[5]  G. Wehmeyer, A.D. Pickel, and C.Dames. Onsager reciprocity relation for ballistic phonon heat transport in anisotropic thin films of arbitrary orientation.Physical Review B 98, 014304 (2018)

[4]  G. Wehmeyer, T. Yabuki, C. Monachon, J. Wu, and C. Dames. Thermal diodes, regulators, and switches: physical mechanisms and potential applications. Applied Physics Reviews 4, 041304 (2017). (Editor’s Pick)

[3]  J. Lee* , W. Lee* , G. Wehmeyer* , S. Dhuey , D. Olynick , S. Cabrini , C. Dames , J. Urban, and P. Yang. Investigation of phonon coherence and backscattering using silicon nanomeshes. Nature Communications 8, 14054 (2017). (* indicates equal contribution)

[2]  Z. Wei, G. Wehmeyer, C. Dames, and Y. Chen. Geometric tuning of thermal conductivity in three-dimensional anisotropic phononic crystals. Nanoscale 8, 16612-16620 (2016).

[1]  S. D. Lubner, J. Choi, G. Wehmeyer, B. Waag, V. Mishra, H. Natesan, J.C. Bischof, and C. Dames. Reusable bi-directional 3ω sensor to measure thermal conductivity of 100-μm thick biological tissues. Review of Scientific Instruments 86, 014905 (2015).