Brick D, Hofstetter M, Stritt P, Rinder J, Gusev V, Dekorsy T, Hettich M
Department of Physics, University of Konstanz, 78464 Konstanz, Germany.
Laboratoire d'Acoustique de l'Université du Mans (LAUM), UMR 6613, Institut d'Acoustique - Graduate School (IA-GS), CNRS, Le Mans Université, Av. O. Messiaen, 72085 Le Mans, France.
Ultrasonics. 2022 Feb;119:106630. doi: 10.1016/j.ultras.2021.106630. Epub 2021 Oct 21.
The possibility to measure the glass transition temperature in poly(methyl methacrylate) (PMMA) films by picosecond ultrasonics with thicknesses ranging from 458 nm to 32 nm is demonstrated. A shift of the longitudinal acoustic eigenmodes towards lower frequencies with temperature is observed accompanied by a change in the temperature-frequency slopes at the glass transition temperature. The contributions to the frequency shift from changes in film thickness and sound velocity are discussed and the latter is extracted below the glass transition temperature. Finally, the advantages and disadvantages of the current approach in a comparison to other methods based on acoustic measurements in the GHz regime are reviewed.
本文证明了利用皮秒超声技术测量厚度范围为458纳米至32纳米的聚甲基丙烯酸甲酯（PMMA）薄膜玻璃化转变温度的可能性。观察到纵向声学本征模随温度向低频方向移动，同时在玻璃化转变温度处温度-频率斜率发生变化。讨论了薄膜厚度和声速变化对频率偏移的贡献，并在玻璃化转变温度以下提取了声速变化的贡献。最后，回顾了与基于GHz频段声学测量的其他方法相比，当前方法的优缺点。
