Angle-dependent light emission from aligned multiwalled carbon nanotubes under CO₂ laser irradiation

Abstract

This paper reports the light emission from aligned multiwalled carbon nanotubes (MWNTs) under continuous wave CO(2) laser (λ = 10.6 µm) irradiation. Results indicate that the light emission is dependent on the angle θ between the laser incident direction and the nanotube axis. The relative intensity of the light emission at certain wavelengths shows a Lorentzian feature when θ varies from 0° to 90°. The Lorentzian fitting curve displays a distinct tendency between shorter (λ<600 nm) and longer wavelength (λ>700 nm). A minimum intensity was observed at θ(m) close to 67° under shorter wavelength, whereas a maximum intensity was shown at θ(m) of about 60° at longer wavelength. These results show the anisotropic property of aligned MWNTs.

Single-color pyrometry of individual incandescent multiwalled carbon nanotubes

“…[31][32][33] The multiwavelength pyrometry measurements described in Refs. (11)(12)(13)15,17,19,21,(23)(24)(25) assume that the nanotube source is a greybody, i.e. that its emissivity ε is independent of wavelength.…”

“…30 However, multiwavelength optical pyrometry is the most common thermometry technique applied to CNTs at high temperatures. This general, non-contact method allows the detector to be remote from the source and is relatively easy to implement above 1000 K. Thus it has been applied to individual CNTs, 13,23 films, 11,17,19,21,24,25 and bundles.…”

“…In addition to being small, carbon nanotubes (CNTs) are stable at high temperatures [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and thus are of interest for many applications, including field emission tips, 10,14,15 nanoscale heaters, 22 and incandescent lights. 12,25 The temperatures T that CNTs reach have been inferred from the magnitude of their field emission current, 10 their breakdown temperature, 26 , the melting of nearby gold nanoparticles, 16 T -dependent Raman spectroscopy, 20,27 scanning thermal microscopy, 28 microfabricated Pt thermometers, 29 and their current-voltage response function.…”

“…30 However, multiwavelength optical pyrometry is the most common thermometry technique applied to CNTs at high temperatures. This general, non-contact method allows the detector to be remote from the source and is relatively easy to implement above 1000 K. Thus it has been applied to individual CNTs, 13,23 films, 11,17,19,21,24,25 and bundles. 12,15 But while some variant of optical pyrometry is often preferred for measuring high temperatures, in practice the method is challenging to implement accurately because of uncertainties associated with the radiating object's emissivity.…”

“…The greybody assumption simplifies the thermometry enormously, for then neither detailed knowledge of the source geometry nor an absolute calibration of the light collection apparatus is required; only the relative intensities matter. However, spectral and polarization-dependent features have been observed in thermal spectra of both CNT films 17,19,21 and individual CNTs 13,23,34 . Thus CNTs are known to have non-trivial emissivities that will affect multiwavelength pyrometric measurements.…”