Nanomechanical Characterization of Functional Materials Using Scanning Probe Microscopy Methods

Abstract

The study of mechanical properties of materials (stiffness, toughness, and so on) using scanning probe microscopy (SPM) methods has received increased interest over the past few years. Atomic force microscopy (AFM) is an SPM method to image different properties of a wide range of materials down to the atomic scale. This thesis focuses on an in-depth description of various AFM-based methods to characterize the mechanical properties of biomaterials and ferroic materials on the nanometer scale. The high-order structures that form natural hierarchical shapes are claimed to be the main factor to enhance the extraordinary mechanical properties of biological structures. In this thesis, we are using three different types of AFM-based techniques (consisting of contact resonance force microscopy, force-distance map, and nanoindentation) and related fitting methods to analyse the mechanical properties of two different biomaterials, including (1) Paua abalone shell and (2) Tonkin bamboo. By combining those methods, we affirm the quantitativeness of our mechanical measurements. The obtained results reveal the detailed mechanical properties of the hierarchical structure of biomaterials and provide a strategy for accurately testing the nanoscale mechanical properties of advanced composite materials. To investigate the pressure-induced mechanical changes on the ferroelectric lead titanate, PbTiO3, single crystal, we used AFM methods to characterize the ferroelectric 90- and 180-degree in-plane and out-of-plane domain walls and observe that, despite their separation mechanically identical domains, the walls appear different in mechanical responses compared to the domains. Moreover, for the first time, we study the crackling noise concept at the length scale of a few nanometres of the ferroelectric PbTiO3 domain wall. It represents that the ultimate functional feature can be potentially exploited for new concepts in information storage and processing, sensing, and actuating. In general, these results indicate that SPM methods can provide comprehensive information and a deep insight into unique properties in a wide range of materials and their applicability in nanoscale regimes, and guide new developments on promising nanoscale devices.