chapter 8 nanomaterials: Synthesis and characterization
286
interactions with the inner shells. These ionization losses are characteristic of the atom involved, and thus the signal (called edge)
is directly related to an unique atomic type. In addition, the area
under the edge provides quantitative information about the particular element. The EELS technique is capable of atomic resolution
chemical analysis and allows chemical bonding information to be
acquired.
Two other spectroscopy techniques of interest for characterizing
nanomaterials are infrared (IF) and Raman spectroscopy. These
techniques are also called vibrational spectroscopies because they
involve the vibration of groups of atoms. In IF spectroscopy, the
material is first subjected to an incident infrared light. Depending on the type of atoms and type of bonds between atoms, the
frequency at which atoms vibrate is unique for each arrangement.
When the infrared light interacts with the material, groups of atoms
tend to adsorb infrared radiation in a specific frequency and therefore wavelength. The remaining light, which was not absorbed by
any of the harmonic oscillators (groups of atoms), is transmitted
through the sample to a detector. Here the transmitted light is analyzed and the frequencies absorbed by the material are determined.
The resulting plot of absorbed energy versus frequency is called the
IR spectrum. Therefore, differences in the chemical and atomic structure of materials give rise to specific vibrational characteristics and
yield unique IR spectra for each material.
From the frequencies of the absorptions, it is possible to determine
the presence of various functional groups in a chemical structure;
the magnitude of absorption due to a particular element allows us
to deduce its concentration in the mixture. In general, IR spectroscopy can be used to identify materials in the solid, liquid, or gaseous
state. In the case of nanomaterials, IF spectroscopy has been used
to determine the extent of absorption of foreign species in nanoparticles of different sizes as well as the structure of nanorods,
nanowires, and carbon nanotubes (see Figure 8.56). Modern IF
spectrometers irradiate the specimens with a wide range of frequencies, after which the signal is converted mathematically (Fourier
transform) into the classical spectrum, where typically the spectral
absorption of a sample is being scanned. This technique is called
Fourier transform infrared (FTIR) spectroscopy (see Figure 8.57).
The Raman spectroscopy technique is similar in concept to the IF
method and is complementary. However, it uses a laser source and
scattered light (see Figure 8.58). The scattered light consists of two
types: Rayleigh scattering, which has the same frequency as the
Figure 8.56
Infrared spectrum of carbon nanotubes
synthesized by chemical vapor deposition. (Appl.
Phys. Lett., 2004, 85(19), 4463–4465.)
Absorbance (a.u.)
Wave number (cm -1 )
1200
1400
1600
1800
2800
3000
2928
2856
1725
1584
1200
2962
Figure 8.57
Schematic setup of an FTIR spectrometer.
To detector
From IR source
Fixed mirror
Moving mirror
Beamsplitter
Sample
Figure 8.58
Schematic diagram of the layout for Raman
spectroscopy.
Filter
Diffraction
grafting
Scattered
light
Raman scattered
light
Laser
286
interactions with the inner shells. These ionization losses are characteristic of the atom involved, and thus the signal (called edge)
is directly related to an unique atomic type. In addition, the area
under the edge provides quantitative information about the particular element. The EELS technique is capable of atomic resolution
chemical analysis and allows chemical bonding information to be
acquired.
Two other spectroscopy techniques of interest for characterizing
nanomaterials are infrared (IF) and Raman spectroscopy. These
techniques are also called vibrational spectroscopies because they
involve the vibration of groups of atoms. In IF spectroscopy, the
material is first subjected to an incident infrared light. Depending on the type of atoms and type of bonds between atoms, the
frequency at which atoms vibrate is unique for each arrangement.
When the infrared light interacts with the material, groups of atoms
tend to adsorb infrared radiation in a specific frequency and therefore wavelength. The remaining light, which was not absorbed by
any of the harmonic oscillators (groups of atoms), is transmitted
through the sample to a detector. Here the transmitted light is analyzed and the frequencies absorbed by the material are determined.
The resulting plot of absorbed energy versus frequency is called the
IR spectrum. Therefore, differences in the chemical and atomic structure of materials give rise to specific vibrational characteristics and
yield unique IR spectra for each material.
From the frequencies of the absorptions, it is possible to determine
the presence of various functional groups in a chemical structure;
the magnitude of absorption due to a particular element allows us
to deduce its concentration in the mixture. In general, IR spectroscopy can be used to identify materials in the solid, liquid, or gaseous
state. In the case of nanomaterials, IF spectroscopy has been used
to determine the extent of absorption of foreign species in nanoparticles of different sizes as well as the structure of nanorods,
nanowires, and carbon nanotubes (see Figure 8.56). Modern IF
spectrometers irradiate the specimens with a wide range of frequencies, after which the signal is converted mathematically (Fourier
transform) into the classical spectrum, where typically the spectral
absorption of a sample is being scanned. This technique is called
Fourier transform infrared (FTIR) spectroscopy (see Figure 8.57).
The Raman spectroscopy technique is similar in concept to the IF
method and is complementary. However, it uses a laser source and
scattered light (see Figure 8.58). The scattered light consists of two
types: Rayleigh scattering, which has the same frequency as the
Figure 8.56
Infrared spectrum of carbon nanotubes
synthesized by chemical vapor deposition. (Appl.
Phys. Lett., 2004, 85(19), 4463–4465.)
Absorbance (a.u.)
Wave number (cm -1 )
1200
1400
1600
1800
2800
3000
2928
2856
1725
1584
1200
2962
Figure 8.57
Schematic setup of an FTIR spectrometer.
To detector
From IR source
Fixed mirror
Moving mirror
Beamsplitter
Sample
Figure 8.58
Schematic diagram of the layout for Raman
spectroscopy.
Filter
Diffraction
grafting
Scattered
light
Raman scattered
light
Laser