Piezoelectric Energy Harvesting Nanofibers - Hierarchical Nanostructures for Energy Devices - page 150

above 600 1C, the pervoskite phase starts to appear while coexisting with the
pyrochlore phase. It is only above 850 1C that the pyrochlore phase is
completely replaced by the pervoskite phase. Chen et al. conduct a similar
experiment using a PZT sol-gel, a poly vinyl pyrrolidone and alcohol mix-
ture. 64 The XRD results confirm the pure pervoskite phase of the fibers with
an annealing temperature of 650 1C.

d n 3 r 4 n g | 2

7.3.2 Fourier Transform Infrared Spectroscopy (FTIR)
Fourier transform infrared spectroscopy (FTIR) can be used to characterize
both the dipole orientation and crystallographic structure of nanofibers
based on the sensitivity of CF 2 orientation changes. For example, Mandal
et al. have used FTIR to examine the dipole orientation of electrospun P(VDF-
TrFE) nanofibers. 50 They have shown that the dipoles were aligned in the
direction of the electrical field during the electrospinning process. 50 A
comparison between the FTIR spectra of an as-spun fiber and a heat-treated
electrospun fiber (heated above the Curie temperature in order to assure the
random dipole alignments) have resulted in a difference in absorbance of
perpendicular polarized light for CF 2 sensitive wavelengths. Baji et al. have
also confirmed the presence of the crystal b-phase using FTIR in good cor-
respondence to the results obtained using XRD. 65 Similarly Wang et al. use
FTIR in order to examine the PZT fiber annealing process with which the
decomposition temperature of organic groups as well as the appearance of
the pervoskite phase can be determined. 66

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7.3.3 Piezoelectric Force Microscopy (PFM)
This method is the most direct process to measure and detect the piezo-
electricity of the material. Piezoelectric force microscopy (PFM) measure-
ments are based on the detection of a voltage induced deformation of the
piezoelectric material. The data obtained allows quantification on the degree
of the polarization as well as the polarization direction of the tested sam-
ple. 67 The PFM setup is comparable to atomic force microscopy (AFM) in
that it uses a micro tip in contact with the surface while applying a sinus-
oidal bias voltage. In the case of a piezoelectric material with a poling dir-
ection in parallel to the direction of the PFM bias voltage, this leads to a
detectable deformation of the material due to the piezoelectric response
which is considered as the 'in phase' response. For an opposite poling dir-
ection at the contact area, the observed phase should shift by 180 degrees as
the 'out of phase' response. Lateral deformations can also be sensed by the
detection of the torsional responses of this same tip. PFM is particularly well
suited for the analysis of individual nanofibers in contrast to other charac-
terization tools because it allows local piezoelectric measurements. For ex-
ample, in the work to study triglycine sulfate (TGS) nanocrystal embedded
poly(ethylene) oxide (PEO) nanofibers, several images were taken. 68 The
morphology of the nanofiber mat was first characterized by the AFM scan in