Page 304 - Book Hosokawa Nanoparticle Technology Handbook

5.3 SURFACE STRUCTURE FUNDAMENTALS
been applied to various studies of the phase char- from some single-crystal samples with different
acterization near a crack, deformation of a fiber, orientations. The orientation of a crystal can be
self-diffusion coefficient of oxygen, and stresses determined by polarization Raman spectra.
of a local area in semiconductors. Mapping of 9. The development of time-resolved Raman tech-
micro-Raman data enables the visualization of niques enabled measurements of Raman spectra
the spatial distribution of stresses and existing of a phenomenon occurring within picoseconds.
phases. Average structure in any area can easily 10. Raman excitations with different wavelengths
be obtained by changing the probe size from 1 m enable the reduction of the influence of fluo-
to 1 cm with different lens and/or optical systems. rescence and thermal radiation, and the reso-
5. Applying the stresses to a material changes the nance Raman studies.
spring constant, thus, we can characterize the 11. High carrier density in a semiconductor induces
stresses from the Raman peak position. The an LO-phonon–plasmon-coupled mode. Carrier
peak width of a phonon Raman band is gov- concentrations can be studied from the plasma
erned by the lifetime of phonons. The Raman frequency. If the surface recombination velocity
peak is broadened by the stresses without direc- is relatively low and the carriers induced by the
tions and compositional distributions. incident laser remain, the velocity can be stud-
6. It is possible to conduct in situ observations at ied from the remaining carrier quantity.
high temperatures, at high pressures and in
The advance of Raman scattering techniques is a
aqueous solutions. By installing an attachment
rapid progress. The range of the application will
such as furnace, high-pressure cell and aqueous extend more and more because of the progress of
solution cell around the sample, we can observe lasers, detectors, and measurement methods.
in situ and non-destructively the phase transition
and kinetics of chemical reactions. In a conven-
References
tional Raman technique with visible-light exci-
tations, the Raman measurements from the [1] T. Katoda: Characterization of Semiconductors by
materials at high temperatures above 1,000 C Laser Raman Spectroscopy, University of Tokyo Press,
are difficult due to strong thermal radiation Japan (1988).
from the specimen, but through the Raman exci- [2] T. Kitagawa, A.T. Tu: Introduction to Raman
Spectroscopy, Kagaku-Dojin Publishing Co., Kyoto,
tations by light with short wavelength such as
Japan (1988).
ultraviolet light, the influence of the thermal
[3] H. Hamaguchi, A. Hirakawa: Raman Spectroscopy,
radiation can be reduced considerably [6, 7].
Japan Scientific Societies Press, Japan (1988).
There is an example of Raman measurements [4] M. Yashima, M. Kakihana and M. Yoshimura: J. Tech.
from the material at about 2,000 K, by ca. 364 Assoc. Refractories Jpn., 46, 150–156 (1994).
nm excitations. An alternative effective tech- [5] M. Yashima, K. Ohtake, M. Kakihana, H. Arashi and
nique for measuring the Raman spectra from the M. Yoshimura, J. Phys. Chem. Solids, 57, 17–24 (1996).
materials at high temperatures is the time- [6] M. Yashima, M. Kakihana, R. Shimidzu, H. Fujimori and
resolved Raman method. Raman intensity and M. Yoshimura, Appl. Spectrosc., 51, 1224–1228 (1997).
scattering efficiency are strongly dependent on [7] H. Fujimori, M. Yashima, M. Kakihana, and M.
sample temperature. Sample temperature can be Yoshimura, J. Am. Ceram. Soc., 84, 663–65 (2001).
estimated from the intensity ratio between the
Stokes and anti-Stokes signals. 5.3 Surface structure
7. The Raman scattering technique is effective for
investigating the phase transition. In particular,
5.3.1 AFM
the mechanism of phase transition can be stud-
ied by measuring the soft mode. AFM (atomic force microscopy) is one of SPM
(scanning probe microscope) for imaging of surface
8. Raman spectra from a polycrystalline material
profile. A typical horizontal distance resolution is
consist of components, which depend on the crys-
about 0.2 nm. AFM can provide higher resolution
tal orientation and polarization. Each component than normal SEM (scanning electron microscope). It
can be obtained by the polarization Raman spectra is comparable in resolution to TEM.

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