Raman and electron microscopy analysis of carbon nanotubes exposed to high power laser irradiance

Abstract

High power laser radiometry requires efficient and damage-resistant detectors. The current study explores the evolving nature of carbon nanotube coatings for such detectors upon their exposure to incrementally increasing laser power levels. Electron microscopy images along with the D-band to G-band intensity ratios from the Raman spectra from eight irradiance levels are used to evaluate changes before and after the exposure. Electron microscopy images of the exposed multiwalled carbon nanotubes revealed the formation of intermittent pockets of moundlike structures at high power densities exceeding 11 kW/cm2. Raman spectroscopy measurements also demonstrated higher values for the ratio of the D-band intensity to that of the G-band, suggesting the possible transformation of nanotubes into structurally different forms of carbon. Exposure to a sample of single-walled nanotubes did not demonstrate the evolution of structural changes, which could be due in part to the higher irradiance levels relative to the damage threshold, employed in the experiment.

In situ tracking of defect healing and purification of single-wall carbon nanotubes with laser radiation by time-resolved Raman spectroscopy

“…Since the two latter parameters were kept constant, the increase in Raman signal must be associated with another factor. Although laser radiation can cause bundling of tube ends in CNT forests, thus contributing to a signal increase, 26 our randomly ordered samples make this rather unlikely. The effect of laser absorption by amorphous carbon to explain the initial increase of all the SWCNT features can only be limited, due to the equally intensied G 0 mode.…”

“…On the one hand, based on the limited literature, several noteworthy studies infer a promising ability to purify and heal defects in pristine (as-produced) or pretreated (annealed or oxidised) CNT samples with the help of different lasers. On the other hand, others report the lack of any positive effect, [25][26][27][28] or selective removal of metallic or semiconducting tubes. [29][30][31] However, in the literature, CNT purication and healing with laser has been limited in scope and data volume.…”

Evaluating the thermal damage resistance of graphene/carbon nanotube hybrid composite coatings

“…But the primary limitations of these coatings are poor laser-damage threshold and low thermal conductivity 8 . Carbon nanotubes (CNTs) have proven to be a good alternative because of their properties such as high thermal conductivity, high mechanical strength and flat spectral response over a wide wavelength range 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 . However, Multi-walled carbon nanotube (MWCNT)-based coatings suffer from severe damage or burn at power densities of approx.…”

Scaling up single-wall carbon nanotube laser annealing: effect on electrical resistance and hydrogen adsorption

“…3: red spectrum at 0.528 mW). Since sample concentration did not increase nor did tube ends bundle, which are possible causes for signal increase, 40 we can posit impurity removal and recrystallization based on the following: the signal increase is not proportional for any mode; G + grows proportionately more than G À and RBM; only one RBM peak grows, while the other is sustained. This also indicates metallic tube removal at this wavelength (532 nm), 27,29,30 as previously claried.…”