Spectra of radiation emitted by single-walled and multi-walled carbon nanotubes during multiple microwave irradiation and cooling cycles

TL;DR

This study investigates the radiation emitted by single-walled and multi-walled carbon nanotubes under microwave irradiation, revealing increased emission over cycles, with multi-walled nanotubes emitting more radiation, likely due to structural differences.

Contribution

It provides experimental evidence that multi-walled nanotubes emit more radiation than single-walled ones during microwave exposure, highlighting the role of nanotube structure and end opening in emission intensity.

Findings

Radiation intensity increased over multiple irradiation cycles.

Multi-walled nanotubes emitted more radiation than single-walled.

Bundling of nanotubes affects emission due to screening effects.

Abstract

Carbon nanotubes have been observed to emit ultraviolet, visible, and infrared radiation when exposed to microwave fields. We have performed experiments in which both single-walled (~1 nm diameters) and multi-walled carbon nanotubes (>50 nm diameters) were exposed to 2.45 GHz microwaves during several irradiation and cooling cycles at a pressure of ~10-6 torr. A comparison of the spectra of the radiation emitted by the nanotubes indicates that the intensity of radiation with wavelengths ranging from 700 to 1000 nm increased substantially during the course of five irradiation and cooling cycles. The data suggests that the mechanism responsible for the emissions is field emission-induced luminescence and that the intensity of the radiation emitted increased due to the opening of nanotube ends. Furthermore, the intensity of the radiation emitted by the multi-walled carbon nanotubes was much greater than the radiation emitted by the single-walled nanotubes. Scanning electron microscopy images indicate that most of the single-walled nanotubes were bundled together, while the multi-walled nanotubes were not. This bundling may have resulted in a lower field enhancement factor and/or screening effects which might help to explain the difference in the intensities of the radiation emitted by the samples.