Physics of Phonon Transport
Phonons, which are the quantized lattice vibrations in the crystal structure, are responsible for transferring thermal energy. The velocity and scatterings of phonons generally affect the thermal conductivity of materials, which is a fundamental property for heat transfer. We are interested in understanding phonon transport and engineering the thermal conductivity of various materials.
Thermal Transport at the Nanoscale
Thermal transport in nanoscale structures has not been fully understood yet. There remain unknown parts even in the thermal conductivity of silicon, which is a primary material in the semiconductor industry. We have been trying to uncover the contributions of phonons with different mean-free paths (MFP) to the thermal conductivity of silicon, enabling us to estimate the reduction of thermal conductivity in silicon-based nanoelectronics.
Thermal Transport in Nanomaterials
The limit of miniaturization in modern electronics necessitates the substitute of silicon. Two-dimensional materials are promising candidates because of their geometrical characteristics. Notably, recent studies revealed the excellent thermal and mechanical properties of graphene. Although numerous theoretical calculations predicted the unique thermal properties of two-dimensional materials, the thermal transport in two-dimensional materials has not been elucidated yet, e.g., hydrodynamic phonon transport. We have been conducting experimental and theoretical research to explore thermal transport in two-dimensional materials.
※ Related project:
- Study on Heat Vortex and Second Sound in Phonon Hydrodynamic Transport of Graphene
- Development of ultra-broadband sub-THz absorbing/shielding/heat-dissipating all-in-one MXeneX materials and process technology
Measurement & Analysis Technique
We have experimental and theoretical capabilities to quantify the thermal properties of micro and nanoscale structures, which are crucial for understanding their thermal engineering potential and applications in electronics and energy devices.
MEMS-based Electrothermal Measurement Techniques
The 3w method is a widely used technique for measuring the thermal conductivity of thin films and bulk materials. It relies on the principle of Joule heating and the temperature dependence of the electrical resistance. Also, we are employing ultrahigh-precision measurement techniques for determining the thermal conductivities of nanostructured materials. For example, suspended micro-bridge method is used to measure the thermal conductivity of 2D thin films and nanowire/fiber. It involves fabricating micro-bridge (typically with a serpentine shape) and measuring the temperature rise across the bridge.
Optical Pump-Probe Measurement Techniques
Time/Frequency domain thermoreflectance are highly time-resolved pump-probe techniques that utilize ultrafast lasers (~200 fs) to generate and detect heat on the sample surface. Modulated pump laser (0.2–20 MHz) is used to heat a material, and another probe laser measures the resulting temperature rise.
Theoretical Calculations
We employ both analytical and numerical calculation methods to characterize the behavior of phonon transport. When examining phonons as the dominant carriers of heat conduction, the utilization of the Boltzmann transport equation enables us to predict phonon heat transport in the sub-continuum space. Furthermore, density functional theory is applied to derive accurate phonon properties, including phonon dispersion, group velocity, and phonon-phonon scattering rates.
Thermal Management
Maintaining a proper temperature is necessary for numerous applications such as turbine blades, automobile engines, computer chips, and batteries. Failures in thermal management result in material degradation, reduced lifetime, and energy efficiency. Our research interest in thermal management ranges from small electronics to large aerodynamic vehicles.
Thermal Management in Nanoscale Electronic Devices
As electronic devices continue to shrink in size, their power densities increase, leading to higher heat dissipation challenges. Understanding micro and nanoscale heat transport (especially for heat conduction beyond the classical Fourier’s law) is essential for efficiently dissipating the generated heat. Through studying heat transfer mechanisms at micro and nanoscales, we have been developing advanced thermal management strategies to prevent overheating, improve performance and reliability, and optimize management conditions.
Reduction of Hypersonic Aerodynamic Heating
Hypersonic vehicles, traveling at velocities greater than Mach 5, experience extreme heating effects due to intense aerodynamic forces and compression of air in front of the vehicle. This leads to high temperatures that can potentially compromise the structural integrity of the vehicle and limit its operational capabilities. The microporous structure is one of the strategies to delay the turbulent transition and mitigate subsequent aerodynamic heating. We have been focusing on manufacturing the microporous structure based on MEMS technology.
※ Related project: Development of Surface Microstructure for Reduction of Hypersonic Aerodynamic Heating
MEMS/NEMS Sensor Development
Our group has developed cutting-edge thermal measurement techniques and owns MEMS/NEMS fabrication experience. Based on this knowledge, we are developing novel MEMS/NEMS sensors. The novelty of this research involves the adaption of nanomaterials and the thermal deformation of temperature-sensing microfilms.
Gas Sensors
Thermal conductivity detectors (TCDs), which detect gases based on their thermal conductivity, are gas sensors with characteristics such as fast response, low power consumption, and cost-effectiveness. Conventional TCDs made of platinum possess insufficient differentiability and sensitivity. We aim to improve the performance of gas sensors by using two-dimensional materials, which have excellent mechanical, electrical, and thermal properties.
※ Related project: GIST-MIT program (AI-Driven Soft Robot Skin for Recognition, Modeling, and Exploration)
Infrared Sensors
Infrared (IR) sensors are commonly classified into two types: photon detection and thermal detection. A thermal infrared sensor, which is included in the latter, is widely used because it does not require cooling units, resulting in miniaturization and cost reduction. However, it has drawbacks such as its slow response time and low detectivity. We aim to address these issues and develop ultra-fast microthermal infrared image sensors by incorporating 2D materials, metamaterials, and optical measurement methods.
※ Related project: Research on Ultra-fast Thermal Infrared Image Sensor based on Novel Materials and the Probe Beam Deflection Technique
Previous Research
Below are the research topics, which we previously worked on. We will continue energy-relevant projects by discovering exciting research topics.
Energy Harvesting with Energy Storage Device
Energy storage devices, such as batteries, supercapacitors, and fuel cells, possess the remarkable ability to store additional energy during heat exchange. This phenomenon arises from the profound impact of heat on the device’s entropy. Notably, energy harvesting using these storage devices surpasses the capabilities of traditional thermoelectric devices, enabling the generation of greater amounts of energy. Consequently, we implemented a thermo-electrochemical cycle with a supercapacitor to effectively harness low-grade waste heat, specifically below 100 ℃. This temperature range is challenging for conventional thermoelectric devices to harvest electricity efficiently. Our comprehensive analysis focused on evaluating the performance of this innovative approach.
- ※ Related publication:
- ㆍ Jaehoon Kim, Yeongcheol park, Joo-Hyoung Lee, Jae Hun Seol, Thermal Convective Effect on the Performance of Thermally
- Regenerative Electrochemical Cycle Against Self-Discharge, Applied Thermal Engineering, 225, 5, 120160, 2023.
- ㆍ Jaehoon Kim, Sung Hoon Kim, Jongho Lee, Jae Hun Seol, A study on Thermally Regenerative Electrochemical Cycles Using Various
- Supercapacitors, Applied Thermal Engineering, 217, 25, 119200, 2022.
- ㆍ Honggil Kim, Jaehoon Kim, Sung Hoon Kim, Jae Hun Seol, Continuous Power Production Using Flowable Electrodes Based on
- Waste-Heat Assisted Capacitive Mixing, Applied Thermal Engineering, 206, 118094, 2022
Enhancing Thermal Conductivity of Polymers
Polymers are widely used in various applications due to their remarkable physical properties. However, they possess a low thermal conductivity on the order of 0.1 W m−1 K−1, which prevents their use in fields where heat dissipation is essential. We have successfully enhanced the thermal conductivity of polymers by aligning the polymer chains and augmenting bonds between the polymer chains.
※ Related publication:
ㆍ Dohun Yoon, Hyunjung Lee, Taehoon Kim, Youngbin Song, Taeyeon Lee, Jongho Lee, Jae Hun Seol, Enhancing the Thermal
Conductivity of Amorphous Polyimide by Molecular-Scale Manipulation, European Polymer Journal, 184, 7, 111775, 2023
ㆍ Jaeyeon Kim, Suyeong Lee, Changho Kim, Yeongcheol Park, Mi-Hyun Kim, Jae Hun Seol, Electromagnetic Interface Shield of Highly
Thermal-Conducting, Light-Weight, and Flexible Electrospun, Nylon 66 Nanofiber-Silver Multi-Layer Film, Polymers, 12, 8, 1805, 2020
ㆍ Yeongcheol Park, Suyeong Lee, Sung Soo Ha, Bernard Alunda, Do Young Noh, Yong Joong Lee, Sangwon Kim, Jae Hun Seol,
Crosslinking Effect on Thermal Conductivity of Electrospun Poly(acrylic acid) Nanofibers, Polymers, 11, 5, 858, 2019
ㆍ Yeongcheol Park, Myungil You, Jihoon Shin, Sumin Ha, Dukeun Kim, Min Haeng Heo, Junghyo Nah, Yoong Ahm Kim, Jae Hun
Seol, Thermal Conductivity Enhancement in Electrospun Poly(vinyl alcohol) and Poly(vinyl alcohol)/Cellulose Nanocrystal Composite Nanofibers, Scientific Reports, 9, 3026, 2019
- ㆍ Jinju Park, Duckjong Kim, Seung-Mo Lee, Ji-ung Choi, Myungil You, Hye-Mi So, Junkyu Han, Junghyo Nah, Jae Hun Seol, Effects of
- β-sheet Crystals and a Glycine-Rich Matrix on the Thermal Conductivity of Spider Dragline Silk, International Journal of Biological
- Macromolecules, 96, 384-391, 2017
