[CCoE Notice] PHD Dissertation Defense - Gharbi

[Khator, Suresh]

Nanoscale electromechanical behavior
Abstract
Mohamed Gharbi
Friday, November 18th 2011, 10.am-12.pm, Large Conference Room (202), Engineering Building I
Committee members: Dr. Pradeep Sharma, Dr. Ken W. White, Dr. Li Sun, Dr. Liping Liu, Dr. Gemunu Gunaratne

In this dissertation, we try to address some of the questions which arise while understanding the electromechanical behavior at the nanoscale. First, metals exhibit a size-dependent hardening when subject to indentation. Mechanisms for this phenomenon have been intensely researched in recent times. Our experiments on BaTiO3 indeed suggest an elastic electromechanical size-effect. We argue, through theoretical calculations and differential experiments on another non-ferroelectric piezoelectric (Quartz), that the phenomenon of flexoelectricity is most likely responsible for our observations. Second, using a combination of a theoretical framework and atomistic calculations, we highlight the concept of surface piezoelectricity that can be used to interpret the piezoelectricity of nanostructures. We discuss the renormalization of apparent piezoelectric behavior at small scales. In a rather interesting interplay of symmetry and surface effects, we show that nanostructures of certain non-piezoelectric materials may also exhibit piezoelectric behavior. Finally, the capacitance measured from a single coaxial nanowire capacitor Cu-Cu2O-C device corresponds to ~294µF/cm2, which considerably exceeds previously reported values for metal-insulator-metal micro-capacitors and is nearly fifty times larger than what is predicted by classical electrostatics. Our quantum mechanical calculations indicate that this unusually high capacitance value is attributed to negative quantum capacitance of the dielectric-metal interface. Also, we argue through first principle calculations on Graphene- Boron Nitrate- Graphene capacitors that quantum capacitance plays a key role on decreasing the total effective capacitance.
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