line shape parameters were used to explore the physical properties, particularly, the
metallic or semiconducting nature of the CNTs in different CNT bundles. A detailed
Raman line shape analysis of the G-band has been performed using two functions,
Breit-Wigner-Fano (BWF) and Lorentzian band shapes. The parameters obtained
from these band deconvolutions were then used to calculate the Young’s Modulus
of the different CNTs.
4.2 Experimental
The MWCNT material with tube diameters ranging from 20 to 50 nm thickness
consisted of macroscale hollow carbon cylinders up to centimeters in diameter and
several centimeters long. For its synthesis, a continuous spray pyrolysis method was
used with ferrocene-derived iron particles acting as catalyst [19]. The well-aligned
nanotubes grew in radial directions on the walls of removable silica tube templates
leading to the formation of freestanding and continuous hollow cylindrical carbon
tubes. In this reaction, ferrocene breaks and gives nanoclusters of free iron particles,
which catalyze the growth of CNTs. Due to the high tube alignment, this material
has been suggested for nanopore filters; thus, in our previous publications [37, 38]
the term of “carbon nanotube filter” was used for this material. Furthermore, pure
graphite was also investigated.
For comparison, SWCNT materials were purchased from Aldrich (Milwaukee,
WI, U.S.A.; see also Ref. [37]). One of the charges was produced from CarboLex,
Inc. of Lexington (Kentucky, U.S.A.). The batch quantity (product# 519308) was of
AP-grade, consisting of bundles of single-walled CNTs with 10–200 individual
nanotubes per bundle with an average diameter of 1.2 to 1.5 nm and a bundle
length of approximately 20 µm and an individual tube length of 2–5 µm. The
purity of the AP-grade product ranged from 50 to 70% by volume. Major impurities
were carbon nanospheres and carbon-encapsulated catalyst nanoparticles. A second
single-walled CNT material (product # 636797), specified as SWCNT (Aldrich),
had diameters of 1–2 nm as measured by high-resolution transmission electron
microscopy (HRTEM) with the following purity statement: amorphous carbon: *3%, other nanotubes: *40%, single-walled CNT > 50% with an average
diameter of 1.1 nm and a length of 0.5–100 µm.
The dispersive Raman measurements on the CNT materials were carried out at
two of the three excitation wavelengths, 532, 785, and 1064 nm, using two different
Raman instruments, a XY-Dilor Raman spectrometer (HORIBA Jobin Yvon
GmbH) and a HoloSpec Raman Spectrometer from Kaiser Optical Systems,
respectively. For 532 nm wavelength excitation, the spectra were recorded using a
slit width of 100 µm with an integration time of 1000 s and 25 spectral frame
accumulations. An integration time of 25 s with 10 spectral frame accumulations
was used to record the Raman spectra at 785 nm wavelength with a laser power of
14 mW. The FT-NIR-Raman spectrometer model PE-2000 (PerkinElmer,
Überlingen, Germany) included a 2 W diode-pumped Nd:YAG laser (IE Optomech
126
A. K. Ojha and H. M. Heise
metallic or semiconducting nature of the CNTs in different CNT bundles. A detailed
Raman line shape analysis of the G-band has been performed using two functions,
Breit-Wigner-Fano (BWF) and Lorentzian band shapes. The parameters obtained
from these band deconvolutions were then used to calculate the Young’s Modulus
of the different CNTs.
4.2 Experimental
The MWCNT material with tube diameters ranging from 20 to 50 nm thickness
consisted of macroscale hollow carbon cylinders up to centimeters in diameter and
several centimeters long. For its synthesis, a continuous spray pyrolysis method was
used with ferrocene-derived iron particles acting as catalyst [19]. The well-aligned
nanotubes grew in radial directions on the walls of removable silica tube templates
leading to the formation of freestanding and continuous hollow cylindrical carbon
tubes. In this reaction, ferrocene breaks and gives nanoclusters of free iron particles,
which catalyze the growth of CNTs. Due to the high tube alignment, this material
has been suggested for nanopore filters; thus, in our previous publications [37, 38]
the term of “carbon nanotube filter” was used for this material. Furthermore, pure
graphite was also investigated.
For comparison, SWCNT materials were purchased from Aldrich (Milwaukee,
WI, U.S.A.; see also Ref. [37]). One of the charges was produced from CarboLex,
Inc. of Lexington (Kentucky, U.S.A.). The batch quantity (product# 519308) was of
AP-grade, consisting of bundles of single-walled CNTs with 10–200 individual
nanotubes per bundle with an average diameter of 1.2 to 1.5 nm and a bundle
length of approximately 20 µm and an individual tube length of 2–5 µm. The
purity of the AP-grade product ranged from 50 to 70% by volume. Major impurities
were carbon nanospheres and carbon-encapsulated catalyst nanoparticles. A second
single-walled CNT material (product # 636797), specified as SWCNT (Aldrich),
had diameters of 1–2 nm as measured by high-resolution transmission electron
microscopy (HRTEM) with the following purity statement: amorphous carbon: *3%, other nanotubes: *40%, single-walled CNT > 50% with an average
diameter of 1.1 nm and a length of 0.5–100 µm.
The dispersive Raman measurements on the CNT materials were carried out at
two of the three excitation wavelengths, 532, 785, and 1064 nm, using two different
Raman instruments, a XY-Dilor Raman spectrometer (HORIBA Jobin Yvon
GmbH) and a HoloSpec Raman Spectrometer from Kaiser Optical Systems,
respectively. For 532 nm wavelength excitation, the spectra were recorded using a
slit width of 100 µm with an integration time of 1000 s and 25 spectral frame
accumulations. An integration time of 25 s with 10 spectral frame accumulations
was used to record the Raman spectra at 785 nm wavelength with a laser power of
14 mW. The FT-NIR-Raman spectrometer model PE-2000 (PerkinElmer,
Überlingen, Germany) included a 2 W diode-pumped Nd:YAG laser (IE Optomech
126
A. K. Ojha and H. M. Heise