A team of researchers from KAIST have succeeded in measuring and controlling the near-field thermal radiation between metallo-dielectric (MD) multilayer structures.
The thermal radiation control technology that was developed can be applied to next-generation semiconductor packaging, thermophotovoltaic cells and thermal management systems and has the potential to be applied to a sustainable energy source for IoT sensors.
In the nanoscale gaps, thermal radiation between objects increases greatly the closer the distance. The amount of heat transfer in this scale was found to be from 1,000 to 10,000 times greater than the blackbody radiation heat transfer, which was once considered the theoretical maximum for the rate of thermal radiation.
This phenomenon is called near-field thermal radiation and with developments in nanotechnology, research into near-field thermal radiation between various materials has started to be carried out.
Surface polariton coupling generated from nanostructures has been of particular interest because it enhances the amount of near-field thermal radiation between two objects, and allows the spectral control of near-field thermal radiation. This has motivated much theoretical research on the application of near-field thermal radiation using nanostructures, such as thin films, multilayer nanostructures, and nanowires. However, most of the studies have focused on measuring near-field thermal radiation between isotropic materials.
The team from KAIST, led by Professor Bong Jae Lee and Professor Seung Seob Lee from the Department of Mechanical Engineering, succeeded in measuring near-field thermal radiation according to the vacuum distance between MD multilayer nanostructures by using a custom MEMS (Micro-Electro-Mechanical Systems)-device-integrated platform with three-axis nanopositioner.
MD multilayer nanostructures refer to structures in which metal and dielectric layers with regular thickness alternate. The MD single-layer pair is referred to as a unit cell, and the ratio of the thickness occupied by the metal layer in the unit cell is called the fill factor.
By measuring the near-field thermal radiation with a varying number of unit cells and the fill factor of the multilayer nanostructures, the team were able to demonstrate that the surface plasmon polariton coupling enhances near-field thermal radiation greatly, and allows spectral control over the heat transfer.
Commenting Professor B. J. Lee said, “The isotropic materials that have so far been studied experimentally had limited spectral control over the near-field thermal radiation. Our near-field thermal radiation control technology using multilayer nanostructures is expected to become the first step toward developing various near-field thermal radiation applications.”