TAILIEUCHUNG - Báo cáo hóa học: " Theory of Raman Scattering by Phonons in Germanium Nanostructures"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Theory of Raman Scattering by Phonons in Germanium Nanostructures | Nanoscale Res Lett 2008 3 55-59 DOI S11671-007-9114-0 NANO EXPRESS Theory of Raman Scattering by Phonons in Germanium Nanostructures Pedro Alfaro-Calderon Miguel Cruz-Irisson Chumin Wang-Chen Received 24 September 2007 Accepted 5 December 2007 Published online 21 December 2007 to the authors 2007 Abstract Within the linear response theory a local bondpolarization model based on the displacement-displacement Green s function and the Born potential including central and non-central interatomic forces is used to investigate the Raman response and the phonon band structure of Ge nanostructures. In particular a supercell model is employed in which along the 001 direction empty-column pores and nanowires are constructed preserving the crystalline Ge atomic structure. An advantage of this model is the interconnection between Ge nanocrystals in porous Ge and then all the phonon states are delocalized. The results of both porous Ge and nanowires show a shift of the highest-energy Raman peak toward lower frequencies with respect to the Raman response of bulk crystalline Ge. This fact could be related to the confinement of phonons and is in good agreement with the experimental data. Finally a detailed discussion of the dynamical matrix is given in the appendix section. Keywords Raman scattering Phonons Germanium nanostructures P. Alfaro-Calderon M. Cruz-Irisson El Instituto Politecnico Nacional ESIME-Culhuacan Av. Santa Ana 1000 Mexico 04430 DF Mexico e-mail irisson@ C. Wang-Chen Instituto de Investigaciones en Materiales Universidad Nacional Autonoma de Mexico Apartado Postal 70-360 Mexico 04510 DF Mexico Introduction In comparison with silicon Si and III-V compounds germanium Ge has a larger dielectric constant and then is particularly suitable for photonic crystal applications. Also one can incorporate Ge islands into Si-based solar cells for more efficient light absorption. In general the presence of many arrays of quantum dots with lower bandgap .