3.1. Thermo fisher scientific DXR smart Raman spectrometer

The primary instrument used to record the majority of the Raman spectra was a DXR SmartRaman spectrometer (that uses 780, 532, and 455 nm laser sources). The first wavelength (780 nm) was used for the bulk of the recorded spectra and utilized a high brightness laser of the single mode diode (as does the 532 nm light source), while the 455 nm source is a diodepumped solid state laser. This instrument employs the 180-degree backscattering geometry, full range grating and triplet spectrograph, coupled with automated entrance slit selections in order to provide the Stokes-shifted Raman bands.

#### 3.2. Renishaw inVia Raman spectrometer

The Renishaw inVia Raman spectrometer uses a 532-nm laser source and was used to obtain the Stokes spectra of the graphene and functionalized Nanoplatelets samples. It consists of a microscope to shine light on the sample and collecting the scattered light, filtering all the light except for the tiny fraction that has been Raman scattered, together with a diffraction grating for splitting the Raman scattered light into component wavelengths, and a CCD camera for final detection of the Raman spectrum.

#### 3.3. Ventacon heated cell

symmetry across planes containing the tube axis [3]. An additional benefit of the latter viewpoint is its more direct path to the discovery of there being only three overall structural categories of

Chiral SWNTs are formed such that the orientation of the carbon hexagons on the tube surface do not allow the sides of the tube across a vertical mirror plane to be superimposed on one another. The remaining two subcategories achiral SWNTs, armchair and zig-zag SWNTs however, do allow for such reflection symmetry based on the arrangement of the Carbon hexagons along the cylinder walls. The names armchair and zig-zag refer to the circular cross-sections of each of these achiral SWNT types shown by the bold lines in Figure 1. We conclude this section dealing with the structural properties of primarily SWNTs with the actual construction of a

Relying on the example of Figure 1 which demonstrates the formation of a (3, 3) armchair nanotube, the planar unit cell is formed by rolling the gray shaded region along the chiral vector such that points C and D coincide respectively with points D and B. After performing the previous conceptual rolling operation the pertinent quantity that defines the SWNT unit

Figure 1. As its name suggests this vector is the shortest vector that is perpendicular to the chiral vector, and represents the axial component of the SWNT unit cell that is repeated in this same direction. This formalism of SWNT construction that begins from the planar graphene lattice provides the readily obvious interpretation for the magnitude of the chiral vector, namely its magnitude equaling the nanotube circumference given by the expression,

<sup>m</sup><sup>2</sup> <sup>þ</sup> <sup>n</sup><sup>2</sup> <sup>þ</sup> nm <sup>p</sup> where a <sup>≈</sup> 2.46 Å is the graphene hexagonal lattice constant equal to ffiffiffi

times the nearest neighbor C-C distance of 1.42 Å. The remaining structural parameter in Figure 1, the angle q, is the chiral angle, conventionally chosen to be the angle between the

corresponding to zig-zag SWNTs and the upper bound corresponding to armchair SWNTs.

construction of the chiral vector usually with the convention of n ≥ m. For zig-zag SWNTs

In Raman spectroscopy, a laser diode emits photons, which interacts with the sample, most of the light bouncing off unchanged with the same frequency as the source (Rayleigh scattering). However, a small amount of light experiences an energy shift (Raman scattering) and is filtered to allow only the Raman scattered light to be collected by the detector. The sample vibrates uniquely to its structure and each vibration mode uniquely alters the emitted photons wavelength and that change is graphed as intensity per wavelength. An unknown sample's Raman

m = 0, and in the case of armchair SWNTs both chiral indices are identical [3].

! and a<sup>2</sup>

respectively.

!

! lattice vector. This angle ranges from 0� ≤ q ≤ 30� with the lower bound

! and a<sup>2</sup>

!, which have the follow-

3 p

as shown in the right hand portion of

! lattice vectors used in the

SWNT, starting just the two SWNT graphene lattice vectors, a<sup>1</sup>

, and <sup>a</sup> ffiffi 3 p <sup>2</sup> ; � <sup>a</sup> 2 h i

3 p <sup>2</sup> ; <sup>a</sup> 2 h i

cell in the resultant nanotube is the translational vector T

The integers, n and m simply refer to the number of a<sup>1</sup>

spectrum can be compared to the known Raman spectral graph.

SWNT as shown in Figure 1.

158 Raman Spectroscopy

ing Cartesian components <sup>a</sup> ffiffi

C !

<sup>h</sup> <sup>¼</sup> <sup>a</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

chiral vector and the a<sup>1</sup>

3. Experimental

The Raman spectral data in this study of the two different SWNT samples were obtained under thermal loading from room temperature to 200C in steps of 10C. Both powdered samples were heated externally via a Ventacon™ model H4–200 heat cell that is diagrammed in Figure 2. The first SWNT sample was produced by Unidym™ Carbon Nanotubes. The Hipco technique was used in the production of this sample, which involves the nucleation of SWNTs on Fe(CO)5 catalyst material using high pressure CO, followed by various quality control methods (Misra et al., 2013) [6]. According to manufacturer specifications, the diameters and lengths of the nanotubes in this sample ranged between 0.8 to 1.2 nm, and 100 to 1000 nm, respectively. The sample data also claimed a purity level of only 8% residual Fe catalyst by weight present.

Information about the method of production or purity levels of the second SWNT sample was not available. In the data sets for both samples each point in the ωRBM vs. temperature plots is the mean value from two separate Raman collections. The standard error of each data point obtained from both Raman spectra collected at each temperature is also displayed for both samples. The spectra recorded at each pre-set temperature were obtained with a temperature variation of 0.1C.

#### 3.4. Aluminum disk cell for graphene gas exposure Raman spectroscopy

Figure 3 is a diagram of the components of the sample cell and how it is placed underneath the Renishaw Raman spectrometer. The cell contains apertures that connect to the center of the cell, where the sample is placed and sealed through means of a glass disk and an O-ring. In addition, the cell has an aperture to place a thermocouple to read the temperature of the cell and another one where we place a voltage-induced heating cylinder. The gas flow comes from the gas cylinder into the rotameter and then through a series of tubing to the cell. These tubes

Figure 2. Top: Ventacon H4-200 heat cell. Middle: Cross sectional layout of oven. Bottom: Cylindrical powdered/solid sample holder.

The measurement sequence for the gas exposure of graphene samples is as follows:

voltage is adjusted in order to control the temperature increase.

to verify the effects of the gas exposure on the graphene sample.

and maximum values for a total of 2-hour exposure.

3.5. JEOL JSM-7600F scanning electron microscope

to near ambient value.

gate structures.

1. The sample is placed in the cell, nitrogen gas flows into the sample chamber and heated up to the 130–150C temperature range. Raman spectroscopy data are taken as the cell heats up. Typically, 60 scans are taken, with a 20-second exposure for graphene. The

Figure 4. Left: Setup showing the tubing layout for the gas exposure Raman spectroscopy experiments; center: Filling the bubbler with liquid nitrogen to break up dangerous gas components; right: Bubbler after experiments had concluded [7].

Raman Spectroscopy of Graphitic Nanomaterials http://dx.doi.org/10.5772/intechopen.72769 161

2. Voltage is reduced and the Raman spectral data recorded, as the temperature drops back

3. Nitrogen flow stops and the toxic gas for that experiment flows into the sample chamber. We take sets of 120 exposures with laser exposure and delays that result in a 30-minute exposure. This is repeated for different gas flows, with the rotameter reading 50, 100, 150

4. We repeat Steps 1 and 2 to see if the Raman features return back to normal; this allows us

Images of functionalized graphene nanoplatelets were taken with the JEOL JSM-7600F scanning electron microscope [8]. The secondary electron detector on the SEM uses an EMI current of 138.20 nA. Beam current has a range of 1 pA to 200 nA. The JEOL JSM-7600F SEM contains a large variety of detectors that can be used on specimen samples up to 200 mm in diameter. Various magnifications were selected when appropriate to accurately display the sample structure; SEM magnifications range between 25 and 1000000. The modular software program Gwyddion was used to generate 3-dimensional visualization of the nanoplatelet aggre-

Figure 3. Aluminum disk cell used for gathering Raman spectral data during gas exposure of graphene samples; top view (left) | under Raman microscope (right) [7].

connect to holes within the sealed sample chamber and flow out through the other output tube and into the bubbler. The bubbler is submerged in liquid nitrogen in order to separate the more dangerous components of the gases used and flow the rest through an inlet fan connected do an exhaust. At the end of the experiment, the bubbler is placed in a fume hood and left until the following day. Figure 4 shows multiple components of this setup that were used for the gas exposure experiments.

Figure 4. Left: Setup showing the tubing layout for the gas exposure Raman spectroscopy experiments; center: Filling the bubbler with liquid nitrogen to break up dangerous gas components; right: Bubbler after experiments had concluded [7].

The measurement sequence for the gas exposure of graphene samples is as follows:


#### 3.5. JEOL JSM-7600F scanning electron microscope

connect to holes within the sealed sample chamber and flow out through the other output tube and into the bubbler. The bubbler is submerged in liquid nitrogen in order to separate the more dangerous components of the gases used and flow the rest through an inlet fan connected do an exhaust. At the end of the experiment, the bubbler is placed in a fume hood and left until the following day. Figure 4 shows multiple components of this setup that were used for the gas

Figure 3. Aluminum disk cell used for gathering Raman spectral data during gas exposure of graphene samples; top

Figure 2. Top: Ventacon H4-200 heat cell. Middle: Cross sectional layout of oven. Bottom: Cylindrical powdered/solid

exposure experiments.

sample holder.

160 Raman Spectroscopy

view (left) | under Raman microscope (right) [7].

Images of functionalized graphene nanoplatelets were taken with the JEOL JSM-7600F scanning electron microscope [8]. The secondary electron detector on the SEM uses an EMI current of 138.20 nA. Beam current has a range of 1 pA to 200 nA. The JEOL JSM-7600F SEM contains a large variety of detectors that can be used on specimen samples up to 200 mm in diameter. Various magnifications were selected when appropriate to accurately display the sample structure; SEM magnifications range between 25 and 1000000. The modular software program Gwyddion was used to generate 3-dimensional visualization of the nanoplatelet aggregate structures.
