Phonon confinement effects in ultrathin epitaxial bismuth films on silicon studied by time-resolved electron diffraction
Phonon confinement effects in ultrathin epitaxial bismuth films on silicon studied by time-resolved electron diffraction
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DOI：
10.1103/physrevb.80.024307
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发表时间：
2009-07
影响因子：
3.7
通讯作者：
B. Krenzer;A. Hanisch-Blicharski;P. Schneider;T. Payer;S. Möllenbeck;Omair Osmani;M. Kammler;R. Meyer;M. H. Hoegen
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文献类型：
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作者：
B. Krenzer;A. Hanisch-Blicharski;P. Schneider;T. Payer;S. Möllenbeck;Omair Osmani;M. Kammler;R. Meyer;M. H. Hoegen
利用时间分辨电子衍射研究了飞秒激光激发下外延生长在硅单晶上的超薄铋薄膜的瞬态温度演化。薄膜温度的指数衰减可以用声子在界面处的反射来解释，这导致层状系统交叉面的热传导大大降低。发现热边界电导低至$1273\text{}\text{W}/(\text{K}\text{{\text{cm}}^{2})$。模型计算，包括声子约束效应，解释了观察到的薄膜温度衰减常数与薄膜厚度之间的线性关系。即使对于2.5 nm薄膜，声子通过界面的传输概率也是由体性质决定的。我们的模拟表明，当铋膜厚度大于1nm时，声子约束效应可以忽略不计。
The transient temperature evolution of ultrathin bismuth films, epitaxially grown on a silicon single crystal, upon femtosecond laser excitation is studied by time-resolved electron diffraction. The exponential decay of the film temperature is explained by phonon reflection at the interface, which results in a strongly reduced thermal conduction in the cross plane of the layered system. The thermal boundary conductance is found to be as low as $1273\text{ }\text{W}/(\text{K}\text{ }{\text{cm}}^{2})$. Model calculations, including phonon confinement effects, explain the linear relationship between the observed film-temperature decay constant and the film thickness. Even for 2.5 nm thin films the phonon transmission probability across the interface is given by bulk properties. Our simulations show that phonon confinement effects are negligible for bismuth-film thicknesses larger than 1 nm.