Acoustic phonons in nanostructures

点击翻译按钮获取中文摘要

Vibrations of small metal spheres embedded in a glass block can be observed using reflected laser light. The wavelength of a steady laser beam is shifted up or down according to the frequency of the vibration in Raman scattering. The vibrations can be more directly observed using brief pulses of laser light shorter than one billionth of a second. Theoretical work is needed to calculate the frequencies of these vibrations, taking into consideration the elastic response of the metal as well as the shape and surroundings of the metal sphere. Molecular dynamics simulations, in which the positions and velocities of many (up to 100000) point masses are calculated with time on a computer, are used. The Fourier transform of the motion is used to find the frequencies of individual modes. Materials with direction dependent (anisotropic) speed of sound can be simulated in this way. Nanoclusters with non-spherical shape can also be handled. Finally, the effect of a surrounding material, such as a glass block, can be studied. The results of these investigations will give new insight into the mechanical properties of very small objects. This knowledge has potential future application when very small mechanical devices are designed.