Biomedical Engineering Reference
In-Depth Information
FIGURE 9.2
Raman spectra collected from three calcined TiO
2
samples and processed at RT, 400°C, 700°C, and
1000°C. Each individual spectrum is an average of 15
randomly collected spectra per sample.
9.3.2
Raman Microscopy
Raman microspectroscopy is a non-destructive vibrational/structural characterization method that can
be utilized to identify naturally occurring crystalline forms. Here, Raman spectroscopic characteriza-
tion technique was applied to analyze crystalline distribution based on thermal-induced properties of
TiO
2
nanoparticles. An inVia confocal Raman microspectroscopy system (Renishaw, UK) equipped
with a 785 nm laser, 1,200 line/mm grating and a 20
objective (Leica) was used and spectral and
image data were acquired at 100% laser power, 3 s integration times under WiRE 3.0 software with
streamline mapping capability.
Figure 9.2
shows Raman spectra of four TiO
2
nanoparticle samples at different temperatures: room
temperature (RT) and calcine temperatures of 400°C, 700°C, and 1000°C. In the case of the calcined
samples through 700°C a series of peaks are visible, which correspond to both TiO
2
crystalline anatase
(A) and rutile (R). From analysis of these Raman spectra, there are three distinctive Raman modes:
A1g, B1g, and Eg. They were mode Eg for rutile at circa 236 cm
1
, B1g for anatase and rutile at 395
and 445 cm
1
, B1g/A1g for anatase and rutile at 515 and 609 cm
1
, and Eg for rutile at 637 cm
1
.
However, in the case of the 1000°C sample, there are only modes associated with rutile observed at
peaks 236, 445, and 609 cm
1
. It is well established that the crystalline transition of amorphous TiO
2
powders can be viewed as a two-step process: (1) amorphous to anatase and (2) anatase to rutile.
TiO
2
Raman spectra have been studied extensively, but Raman mapping investigations of
the anatase/rutile ratio distribution of nanocrystalline TiO
2
is limited.
Figure 9.3
shows the
bright field image (A) of RT TiO
2
sample along with selected Raman map area (B), where each
2.6
2.6 mm
2
within the boxed area is an individual Raman spectrum over a 410 wave num-
ber range beginning at 324 and ending at 734 cm
1
. Direct classical least squares (DCLS)