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Introduction to Nanotechnology

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8.2.3. Raman Spectroscopy<br />

8.2. INFRARED FREQUENCY RANGE 203<br />

The general principles of Raman spectroscopy were explained in Section 3.4.1.<br />

Raman scattering measures the frequency shift AW = Wphonon = Iw,, - wScatI<br />

between the incident uinc and scattered uscat light frequencies when Wphonon is an<br />

optical phonon mode vibration. When Wphonon is an acoustic phonon, the process<br />

is called Brillouin scattering, discussed in the next section. Figure 2.10 makes it<br />

clear that the optical mode corresponds <strong>to</strong> high-frequency lattice vibrations,<br />

and the acoustic mode conforms <strong>to</strong> lattice vibrations at much lower frequencies:<br />

w , ~

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