|Ph.D Student||Drezner Haika|
|Subject||Nanoscale Modulus Mapping: Implementation on Material|
Interfaces and Biogenic Materials
|Department||Department of Mechanical Engineering||Supervisor||Professor Doron Shilo|
|Full Thesis text|
Nanoscale modulus mapping is a newly developed technique that has not yet been accepted as a common characterization method. Prior to this work, modulus mapping has mainly been used as an imaging tool to provide qualitative data. The general goal of this thesis is to develop and demonstrate the capabilities of nanoscale modulus mapping as a quantitative method. For this purpose, new analysis methods were developed and tested based on comparing measured modulus profiles with finite element simulations.
The modulus mapping capabilities and new analyses have been implemented on mechanical problems of materials related to two important fields of research: the study of material interfaces and the characterization of biogenic composite materials. The obtained results provide unique and valuable data, which can hardly be acquired by other characterization techniques.
The capability of modulus mapping in investigating material interfaces has been demonstrated by characterizing ferroelectric twin walls in PbTiO3 single crystals. Comparing the measured maps and finite element simulations revealed an abnormal effect of softening in the vicinity of twin walls, an effect caused by the accumulation of point defects.
Interfaces in biogenic materials were studied by characterizing mineral/organic interfaces in the nacre of mollusk shells. The modulus mapping results revealed gradual changes in elastic modulus across the mineral/organic interface over a spatial range up to 2-3 times wider than the thickness of the organic layer. We explained this phenomenon as a result of the heterogeneous distribution of organic macromolecules within mineral tablets. This finding indicates that the commonly accepted concept of nacre ultra-structure as a simple assembly of ceramic tablets separated by organic layers with sharp interfaces does not adequately describe the mechanical properties of nacre. Instead, nacre should be considered a compositionally and functionally graded material.
In addition, we characterized spicules of Monorhaphis chuni marine sponges, a biogenic material that has been studied less thoroughly from a mechanical perspective. The sponge filament exhibited the same reduced modulus value by modulus mapping with two different tip radii (R = 100 nm and R = 1000 nm) and by nanoindentation. This observation demonstrates the validity of the modulus mapping technique as an accurate quantitative characterization tool. The obtained reduced modulus of 30 GPa is much higher than expected for soft silicatein proteins.
We believe that the findings and methodologies presented in this work can turn nano-scale modulus mapping to common and valuable method of quantitative materials characterization.