Topic: Crystallinity effects on nanoscale vibrational properties of metal nanocrystals: An atomistic modeling study
Speaker: Prof. Minyao Wu from Guangzhou high energy computer science and Technology Co., Ltd., China
Time: 9:00 a.m., Sep. 29, 2016
Venue: Conference Room on the 2nd Floor, Building 8, Wushan Campus
Abstract:
Over recent years, laser-induced ultrafast structural dynamics in nanocrystals have been a subject of considerable study using time-resolved optical pump-probe techniques. The remarkable dynamics phenomena due to transient responses of electrons and phonons in nanostructures have been attractive to researchers. Recently, the structural stability, elastic, and thermal properties were studied via the observation of vibration features of their confined phonon modes. Particular phonon modes with (totally symmetric) radial in-phase vibration and low frequencies, the so-called photoinduced modes, can be excited abruptly by ultrafast laser heating due to much shorter heating time as compared with their oscillation period. The photoinduced modes in nanocrystals can be calculated using a continuum method based on an isotropic elastic model. Even though the calculated frequencies from the continuum model have a good agreement with experimental results, their displacement patterns of atoms are incorrect after considering the crystal structure of metal nanocrystals. In this report, we adopt a theoretical method based on a realistic atomistic model and group theory to study the crystallinity-dependent vibrational properties of photoinduced modes in silver nanoprisms. Group theory is applied not only can reduce dramatically the computational effort required for matrix diagonalization but also can classify the phonon modes in nanocrystals according to their symmetry properties.