These signals can be assigned to the fundamental longitudinal optical phonon
mode [E.sub.1](LO) and its first overtone mode (2LO), respectively [28, 29].
Processes (0) and (0') are transitions that do not require a phonon, whereas processes (1) and ([1.sup.[dagger]]) require an optical phonon
. Similarly, (n) and ([n.sup.[dagger]]) are transitions involving n optical phonons
(n = 2,3,4,...).
Wasilewski, "Optical phonons
in [Al.sub.x][Ga.sub.1 - x]As: raman spectroscopy," Physical Review B: Condensed Matter and Materials Physics, vol.
The decrease in drift mobility with temperature at low fields is due to increased intra-valley polar optical phonon
scattering whereas the decrease in velocity at higher fields is due to increased intra and inter valley scattering.
The corresponding average optical phonon
energy is given within the present formalism (due to (21)) just by the fourth discrete oscillator; that is, [[bar.[epsilon]].sub.U] = [[bar.[epsilon]].sub.TO&LO] = [[epsilon].sub.4].
In short-period superlattice, the large gaps between acoustic and optical phonon
branches make the scattering rarely happen and thus lead to high thermal conductivity, even higher than its corresponding pure materials.
Choi, "Derivation of linewidths for optical transitions in quantum wells due to longitudinal optical phonon
scattering," Journal of Physics Condensed Matter, vol.
George, "Optical phonon
confinement in ZnO nanorods and nanotubes," Indian Journal of Pure and Applied Physics, vol.
On the other hand, vibration with frequencies corresponding to optical phonon
modes in various materials has been observed by pump-probe spectroscopy.
In our previous work, the carrier escape and capture processes between the unconfined bulk states and the confined quantum states have been calculated from the first principle by evaluating the carrier-polar optical phonon
interactions, and the details of their physical meaning have been discussed and will not be repeated here for simplicity.
They show a dominant peak of typical characteristic of the wurtzite ZnO structure at 439 [cm.sup.-1], assigned to be the optical phonon
There are nine zone-center optical phonon
modes with symmetries 4[A.sub.u] + 5[B.sub.u] + [A.sub.g] + 2[B.sub.g]; only three [A.sub.g] + 2[B.sub.g] modes are Raman active.