Probing Phonons in Nonpolar Semiconducting Nanowires with Raman Spectroscopy

Figure 2

(a) Conventional cubic unit cell for the diamond crystal structure (F4₁/d32/m). Each atom is tetrahedrally bonded to four nearest neighbors. The lattice parameter of the conventional unit cell containing four atoms, 𝑎=0.5431 Ǻ (Si) and 𝑎=0.5658 Ǻ (Ge), (b) Brillouin zone for the face-centered space lattice showing the positions of several high-symmetry axes and points [18, 19]. (c) Phonon dispersion curves of Ge [20] (left) and Si [20] (right) along high-symmetry directions. The dots are neutron scattering data [19, 21, 22], and the solid lines are calculations using up to the sixth nearest neighbor interactions in a Born-von Kármán force constant model [20]. The primitive cell contains two atoms; therefore, three optical branches (2TO and 1LO) and three acoustic branches (2TO and 1LO) are observed. These branches are degenerate at the Γ point.

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