Understanding contact mechanics and adhesion processes in thin films and micro-structured materials is fundamental in phonon and heat transport phenomena and is ubiquitous for the miniaturization of mechanical and thermal devices as well as the design/functionalization of structured surfaces and membranes. Acoustic-based methods are of great interest in this context since they provide a nondestructive mean to probe interface quality and adhesion, at various scales. In particular, Laser Ultrasonics (LU) techniques allow the generation of broadband acoustic pulses with a frequency content extending up to a few THz due to the thermoelastic expansion induced by the absorption of short laser pulses. In this review, we will explore the specificities of the LU generation/detection schemes and the unusual wide frequency range that make these opto-acoustic techniques a unique tool to study adhesion processes from micro- to nanoscales, and in a variety of systems, ranging from continuous films and coatings to nano-objects. Because the size of the contact area with respect to the acoustic wavelength dictates the acoustic dispersion, we will describe separately continuous structures, in which the contact is large, before discussing micro- and nanostructured media, where the contact is localized.

中文翻译：

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微纳尺度界面力学的激光超声评价进展


了解薄膜和微结构材料中的接触力学和粘附过程是声子和热传输现象的基础，对于机械和热器件的小型化以及结构化表面和膜的设计/功能化来说无处不在。在这种情况下，基于声学的方法非常有趣，因为它们提供了一种无损方法来探测各种尺度的界面质量和粘附力。特别是，由于吸收短激光脉冲引起的热弹性膨胀，激光超声波 （LU） 技术允许产生频率成分扩展到几太赫兹的宽带声脉冲。在这篇综述中，我们将探讨 LU 生成/检测方案的特性和不寻常的宽频率范围，这些使这些光声技术成为研究从微米级到纳米级以及从连续薄膜和涂层到纳米物体的各种系统中的粘附过程的独特工具。由于接触区域相对于声波长的大小决定了声色散，因此在讨论接触局域化的微纳米结构介质之前，我们将分别描述接触较大的连续结构。