Ogi H, Fujii M, Nakamura N, Yasui T, Hirao M
Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
Phys Rev Lett. 2007 May 11;98(19):195503. doi: 10.1103/PhysRevLett.98.195503. Epub 2007 May 9.
Resonances of coherent acoustic phonons were excited and detected by femtosecond light pulses for determining the normal elastic constant of ultrathin platinum films. The elastic constant increases with the decrease of the film thickness, exceeds the bulk value at the thickness near 5 nm, and significantly increases at low temperatures. It shows a correlation with the normal lattice distance. Thus, this Letter provides evidence of the stiffness enhancement in ultrathin films caused by lattice anharmonicity.
通过飞秒光脉冲激发并检测相干声子的共振，以确定超薄铂膜的法向弹性常数。弹性常数随膜厚度的减小而增加，在厚度接近5nm时超过体材料值，并且在低温下显著增加。它与法向晶格间距存在关联。因此，本信函提供了由晶格非谐性导致的超薄薄膜刚度增强的证据。
