Mechanisms of Subsurface Imaging and Friction Reduction using Ultrasonic Atomic Force Microscopy
Date
2018-11-13
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Abstract
To gain insight on composite materials having nanoscale constituent phases, non-destructive methods with nanoscale resolution are needed to visualize the surface and subsurface inhomogeneities. Coupling ultrasonic technique with atomic force microscopy (AFM), as well as scanning thermal microscopy (SThM), brings together two non-destructive techniques in a single instrument that can elucidate the surface and subsurface structures and properties. Although many different ultrasonic-AFM (U-AFM) methods have been reported for subsurface imaging, the fundamental mechanisms responsible for subsurface imaging for both mechanical (U-AFM) and thermal (SThM) modes, and thus crucial parameters required to enhance the techniques, have not been fully addressed yet. To understand U-AFM mechanisms, a comprehensive model combining ultrasonic wave scattering and tip-sample contact stiffness was developed to better reproduce the experimentally measured phase variations over subsurface features in two model systems. Then, the effects of various parameters, such as mechanical properties, size and buried depth of subsurface features, as well as ultrasonic excitation frequency on the measured phase variation over the surface were explored. The theoretical analysis presented and associated comparisons with experimental results suggest that image contrast depends on the linear superposition of two contrast mechanisms: the perturbation of the scattered ultrasonic waves and the local variation of the contact stiffness at the tip-sample contact. SThM was then similarly analyzed, as it can provide additional information about subsurface features beyond what can be detected with U-AFM, which operates in contact mode and thus experiences experimental artefacts resulting from the convolution of the tip shape and sample topography. Through detecting the local, nanoscale thermal properties of samples, SThM can be used to find the exact location of the nano-features, allowing for one to better distinguish between small and closely located features, which is not possible with U-AFM because of the previously mentioned tip convolution limitation. However, similar to U-AFM, the precise mechanisms of heat conduction in a nanoscale contact in a composite material are not well-defined. Thus, the thermal contrast of SThM method needs to be modelled and investigated through the simulations and experiments, to gain a better insight on the contrast measured in experiments.
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Keywords
Ultrasonic, Atomic force microscopy, Subsurface imaging, Nanocomposite, Finite Element Analysis, Thermal imaging, Friction
Citation
Jiriyaeisharahi, H. (2018). Mechanisms of Subsurface Imaging and Friction Reduction using Ultrasonic Atomic Force Microscopy (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/34502