Biomedical Engineering Reference
In-Depth Information
and having a frequency different (usually lower) from the frequency of the incident photons. As this
frequency is specific to the chemical bond under investigation it allows identification of the species.
FTIR is similar to Raman spectroscopy in that it also uses molecular bond vibration for chemi-
cal species identification. In particular though, in FTIR the resonant frequency of bond vibration after
exposure to infrared radiation is detected as an identifier for the species under examination. Fourier-
transform techniques are based on measurement of the radiation temporal coherence. In the FTIR
technique, this relates to the measurement of the frequencies of vibration of the molecular bonds. The
resonant frequencies are determined by the shape of the molecular potential energy surfaces, the masses
of the atoms and associated vibronic coupling. Procedurally, a split beam of infrared light is typically
sent though the sample dissolved in a liquid solvent medium and at the same time through a sample of
the solvent. Both beams are alternatively recorded in the detector. Differences between the signals are
used to measure the frequencies of bond vibrations in the sample to be analyzed. Typical applications of
FTIR include forensic chemical analysis, measurement of polymer type, degree of polymerization, poly-
mer degradation, and semiconductor type. Most commercial instruments automatically suggest the type
and quantity of species present by comparing the spectra to large databases of reference spectra.
It can be seen from a number of the case studies reported that additional information on the mech-
anism of fabrication or functionality of nanoscale features can be found by using a number of these
techniques simultaneously or consecutively. Examples of these can be seen in the work presented
above from Pap et al., Moghadam et al., and Pisarek et al.
[6,44,68]
. Often one of these techniques is
used to back up another. With so many advanced techniques for the characterization of nanostructures
available, it is important to understand these and their capabilities so that they can be selected and
used correctly. Due to the important technological advancements that can be envisaged from the con-
trol and understanding of nanostructures, the development of improved and new nanocharacterization
techniques will continue for the foreseeable future.
References
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