Department of Energetics, University of Rome La Sapienza, Via A. Scarpa 16, 00161 Rome, Italy.
Anal Bioanal Chem. 2010 Apr;396(8):2769-83. doi: 10.1007/s00216-009-3402-8. Epub 2010 Jan 13.
The science and technology of thin films require the development of nondestructive methods for their quantitative mechanical characterization with nanometric spatial resolution. High-frequency ultrasonic techniques--especially acoustic microscopy--and atomic force microscopy (AFM) have been demonstrated to represent versatile tools for developing such methods. In particular, in the last 15 years, the combination of AFM, which can probe the surface of a sample by applying ultralow loads (from micronewtons down to piconewtons) with a micromachined tip having an apex radius of a few nanometers, and ultrasonics techniques led researchers to develop some unique tools which allow one to perform not only spot measurements of the sample elastic modulus, but also to obtain both the qualitative imaging of mechanical properties and the quantitative mapping of the elastic modulus of the sample surface with nanometric lateral resolution. In the present review, firstly a brief overview of the main ultrasound-based techniques for thin film characterization is reported. Then, some of the ultrasonic AFM techniques are described, emphasizing their capability of retrieving maps of both the tip-sample contact stiffness and the sample elastic modulus. Although these techniques are less affected by the mechanical properties of the substrates than standard indentation tests, a method for the correction of the substrate effect in ultrathin films is reported in detail. Finally, by probing the mechanical properties of a small portion of the sample volume underneath the tip, we illustrate the techniques as tools for the qualitative and quantitative characterization of variations in the adhesion between a thin film and a buried interface, as well as for detecting subsurface defects, voids, cracks, and dislocations.
薄膜的科学和技术需要开发无损方法来对其进行具有纳米空间分辨率的定量力学特性描述。高频超声技术——特别是声显微镜——和原子力显微镜（AFM）已被证明是开发此类方法的多功能工具。特别是在过去的 15 年中，AFM 与超声技术相结合，AFM 可以通过施加具有几纳米尖端半径的微加工尖端施加超低压（从微牛顿到皮牛顿）来探测样品的表面，从而使研究人员开发出一些独特的工具，这些工具不仅可以进行样品弹性模量的点测量，还可以对机械性能进行定性成像，以及对样品表面弹性模量进行纳米级横向分辨率的定量映射。在本综述中，首先简要概述了用于薄膜特性描述的主要超声技术。然后，描述了一些超声 AFM 技术，重点介绍了它们获取尖端-样品接触刚度和样品弹性模量图的能力。尽管这些技术比标准压痕测试受基底机械性能的影响较小，但详细报告了一种用于校正超薄薄膜中基底效应的方法。最后，通过探测尖端下方样品体积的一小部分的机械性能，我们说明了这些技术作为定性和定量描述薄膜和埋置界面之间粘附变化以及检测亚表面缺陷、空隙、裂缝和位错的工具。
