Phonon Dynamics of Exotic Materials Bi2Se3, Bi2Te3, Sb2Te3 and WSe2

Download or read book Phonon Dynamics of Exotic Materials Bi2Se3, Bi2Te3, Sb2Te3 and WSe2 written by Kolawole Akintola and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Raman and Brillouin spectroscopy have been employed to investigate the phonon dynamics of Bi2Se3, Bi2Te3, Sb2Te3 (all topological insulators) and WSe2 (a 2D semiconductor). In the frequency range studied, two peaks were observed in the Raman spectra of Bi2Se3, Bi2Te3, Sb2Te3. Polarization studies were done to study the nature of these peaks and assign them to particular vibrational modes. Due to the fact that all three materials belong to the same space group and have the same Wycko↵ positions, it stands to reason that their Raman spectra will be identical in every respect except for the position where the peaks appear. This was found only to be partially true from what we observed. The presence of Te atoms in Bi2Te3, and Sb2Te3 was observed to play a prominent role in determining mode intensity. We verified that the higher intensity of the peak observed due to the A1g(2) 1g mode compared to that due to the Eg(2) g mode in Bi2Te3, and Sb2Te3, is most probably due some resonance effect induced by the laser excitation wavelength used. Raman scattering studies of WSe2 have generated much controversy with regards mode assignment and the shifts at with spectral peaks appear while there are no reports from Brillouin scattering studies of this material. Our Raman experiment shows that the Raman active E2g(1) 2g and A1g modes in WSe2 initially thought to be degenerate are not degenerate. This was verified by collecting spectra at different polarization configurations. One of the polarization configurations showed two closely separated peaks, enabling us to identify the constituent modes from the originally near-degenerate mode in the unpolarized spectrum. The velocity of the Rayleigh surface wave was extracted from the Brillouin spectra collected at different angles of incidence ranging from 35 to 80 degrees in a Brillouin light scattering experiment. The value of the velocity compares well with those previously reported for related materials. This work reports new results on the vibrational properties of Bi2Se3, Bi2Te3, Sb2Te3 and WSe2. Our results also resolves the inconsistencies reported in previous studies on the vibrational properties of these materials.