Son Dong Hee, Wittenberg Joshua S, Banin Uri, Alivisatos A Paul
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2006 Oct 12;110(40):19884-90. doi: 10.1021/jp062028o.
The photo-induced enhancement of second harmonic generation and the effect of nanocrystal shape and pump intensity on confined acoustic phonons in semiconductor nanocrystals have been investigated with time-resolved scattering and absorption measurements. The second harmonic signal showed a sublinear increase of the second-order susceptibility with respect to the pump pulse energy, indicating a reduction of the effective one-electron second-order nonlinearity with increasing electron-hole density in the nanocrystals. The coherent acoustic phonons in spherical and rod-shaped semiconductor nanocrystals were detected in a time-resolved absorption measurement. Both nanocrystal morphologies exhibited oscillatory modulation of the absorption cross section, the frequency of which corresponded to their coherent radial breathing modes. The amplitude of the oscillation also increased with the level of photoexcitation, suggesting an increase in the amplitude of the lattice displacement as well.
通过时间分辨散射和吸收测量，研究了光致二次谐波产生的增强以及半导体纳米晶体中纳米晶体形状和泵浦强度对受限声子的影响。二次谐波信号显示二阶极化率相对于泵浦脉冲能量呈亚线性增加，表明随着纳米晶体中电子 - 空穴密度的增加，有效单电子二阶非线性降低。在时间分辨吸收测量中检测到球形和棒状半导体纳米晶体中的相干声子。两种纳米晶体形态均表现出吸收截面的振荡调制，其频率对应于它们的相干径向呼吸模式。振荡幅度也随着光激发水平的增加而增加，这也表明晶格位移幅度的增加。
