Pulsed laser vaporization (PLV) production of single-wall carbon nanotubes (SWNTs) on traditional Co/Ni catalyst was explored with respect to variations in the production temperature. The Rh/Pd results were also reproduced for comparison. The nanotube-type populations were measured via photoluminescence (PL), UV-Vis-NIR (ultraviolet-visible-near-infrared) absorption, and Raman spectroscopy. A small reduction in the average nanotube diameter at lowered production temperature has long been known to occur; however, temperature effect on nanotube population (and not just for diameters) has never been explored.
The main result from the current work is that PLV setup run at 900 °C with Co/Ni catalyst produces SWNTs with exceptionally narrow-diameter distribution (1.025 ±0.025 nm). Only six metallic and ten semiconductor nanotubes were identified in all the spectral data. Moreover, the sample was substantially enriched in semiconducting nanotubes. This stands in contrast to the sample produced on Rh/Pd catalyst, where 19 semiconducting and ten metallic nanotubes in the 1.0 ±1.15 nm diameter range were identified, with noticeable enrichment in semiconducting types. Interestingly, dominant nanotube types in the current sample have chiral angles close to armchair. For the sake of comparison, 33 semiconducting nanotubes were identified in HiPco (high pressure CO conversion) samples.
Single-wall carbon nanotubes were produced in the PLV setup at Johnson Space Center under the following conditions:
- Co/Ni catalyst (1 atomic % each), 900 °C temperature, argon buffer gas, 500 torr pressure, 100 sccm flow rate, green/IR laser combination with 50 ns pulse delay, 1.6 J/cm2 energy density, 60 Hz repetition rate (sample Armchair Quantum Wire (AQW) 19 in this work).
- Rh/Pd catalyst (1 atomic % each), 1,200 °C temperature, argon buffer gas, 750 torr pressure, 100 sccm flow rate, green/IR laser combination with 50-ns pulse delay, 1.6 J/cm2 energy density, 10-Hz repetition rate (sample AQW 27 in this work)
The samples were collected from the PLV setup, dispersed in H2O/1% SDBS (surfactant), and centrifuged at 74,000g for 2 hours. Supernatant was used for photoluminescence and absorption spectroscopy measurements. Raman spectra were acquired with 514, 633, and 785 nm excitations on dry nanotubes.
Comparison of the spectral samples showed that sample AQW 19 has rather narrow-diameter distribution compared to AQW 27. The dominant semiconducting nanotube type present is (8,7) that has chiral angle close to armchair. Chiral metallic nanotubes present are (9,6), (11,5) and (12,3). Armchair nanotubes present are (7,7), (8,8), and (9,9); however, their signatures are weaker than that of chiral metallic. There is some preference towards armchair structure in a sense that the dominant semiconducting nanotube is (8,7) with 27.8° chiral angle and there are not types with <7chiral angles, but the rest of the nanotubes are distributed quite evenly in the 7-30° range of chiral angles.