Coherent acoustic phonon dynamics in single-crystalline bismuth nanofilms transferred to a glass substrate were investigated with ultrafast pump–probe spectroscopy. Coherent phonon signals were substantially enhanced by more than four times when compared with as-grown films on Si (111) substrates. Furthermore, more than 10% reduction of the acoustic phonon velocity was observed when the film thickness decreases to 22 nm, which is attributed to the modified phonon dispersion in extremely thin films from quantum confinement effects.

中文翻译：

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转移单晶铋纳米膜中相干声子的量子限制

用超快泵浦-探针光谱研究了转移到玻璃基板上的单晶铋纳米膜中的相干声学声子动力学。与 Si (111) 衬底上的生长膜相比，相干声子信号显着增强了四倍以上。此外，当薄膜厚度减小到 22 nm 时，观察到声学声子速度降低了 10% 以上，这归因于量子限制效应在极薄的薄膜中改进了声子色散。