Acoustics and atomic force microscopy for the mechanical characterization of thin films |
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Authors: | Daniele Passeri Andrea Bettucci Marco Rossi |
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Institution: | (1) Department of Energetics, University of Rome “La Sapienza”, Via A. Scarpa 16, 00161 Rome, Italy;(2) Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Via A. Scarpa 16, 00161 Rome, Italy |
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Abstract: | 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. |
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