High-Speed Modulation of Polarized Thermal Radiation from an On-Chip Aligned Carbon Nanotube Film

Abstract

Spectroscopic analysis with polarized light has been widely used to investigate molecular structure and material behavior. A broadband polarized light source that can be switched on and off at a high speed is indispensable for reading faint signals, but such a source has not been developed. Here, using aligned carbon nanotube (CNT) films, we have developed broadband thermal emitters of polarized infrared radiation with switching speeds of ≲20 MHz. We found that the switching speed depends on whether the electrical current is parallel or perpendicular to the CNT alignment direction with a significantly higher speed achieved in the parallel case. Together with detailed theoretical simulations, our experimental results demonstrate that the contact thermal conductance to the substrate and the conductance to the electrodes are important factors that determine the switching speed. These emitters can lead to advanced spectroscopic analysis techniques with polarized radiation.

Efficient Emission of Highly Polarized Thermal Radiation from a Suspended Aligned Carbon Nanotube Film

“…The suspended devices present relaxation time values of about a few microseconds (5.7 μs parallel, 9.7 μs perpendicular), while the on-substrate devices have a relaxation time value of about hundreds of nanoseconds (0.11 μs parallel, 0.17 μs perpendicular). As explained in our previous work (ref 25), the parallel configurations show a faster response speed rather than the perpendicular ones in both suspended and onsubstrate structures because of the larger thermal conductivity along the channel direction that leads to faster thermal transport. However, the response speeds of the suspended structures are 1 order of magnitude larger than the respective on-substrate ones.…”

“…Radiation sources based on nanocarbon materials, such as graphene and carbon nanotubes (CNTs), have emerged as a promising solution for achieving micro/nano-scale emitters of broadband polarized radiation, particularly thermal radiation. − Previous research has explored the thermal emission characteristics of CNTs in various configurations, including bundled ropes, − vertically aligned arrays, and individual wires. − Notably, Matano et al , have reported polarized thermal radiation emitted from a film of highly aligned CNTs on a SiO 2 /Si substrate. However, the achieved polarization degree remained unsatisfactory for practical applications, although CNTs have the potential to emit highly polarized radiation. − In the previous study, the degree of light polarization (DLP), defined as D L P = I ∥ − I ⊥ I ∥ + I ⊥ (where I ∥ and I ⊥ are the intensities of light polarized in the parallel and perpendicular direction, respectively), was limited to ∼0.6, and the thermal performance of the devices was poor due to the presence of the underlying oxide layer.…”

“…6−15 Previous research has explored the thermal emission characteristics of CNTs in various configurations, including bundled ropes, 16−18 vertically aligned arrays, 19 and individual wires. 20−23 Notably, Matano et al 24,25 have reported polarized thermal radiation emitted from a film of highly aligned CNTs on a SiO 2 /Si substrate. However, the achieved polarization degree remained unsatisfactory for practical applications, although CNTs have the potential to emit highly polarized radiation.…”