Date of Completion

7-26-2013

Embargo Period

7-26-2013

Keywords

Nano-heterostructure, First principles, Bandgap engineering

Major Advisor

Ramamurthy (Rampi) Ramprasad

Associate Advisor

Harold D. Brody

Associate Advisor

Xiang-Yang (Ben) Liu

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Reducing the size of components to the nanoscale (e.g., in nano-heterostructures) gives rise to new possibilities. Nano-heterostructures are material systems involving at least two different materials with at least one of them having dimensions less than 100 nm. Such architectures have demonstrated great potential for diverse functionalities within a single nanostructure, which is nonexistent in the individual component materials. Nevertheless, it has been difficult to utilize their full potential due to a lack of understanding of the complex correlation between structure and properties. In this bifocal thesis, state-of-the-art first principles computations are employed to perform systematic studies of (1) the electronic properties of semiconductor/semiconductor nano-heterostructures, and (2) the mechanical properties of metal/ceramic nano-heterostructures. In the first half, I explore the possibility of tuning the bandgap of semiconductors through strain in semiconductors. The study is further extended to show that large modulation of the bandgap can be achieved even by modest epitaxial strains, and that a range of bandgap values can be achieved. In the second half, taking a Al/TiN nano-heterostructure as a model metal/ceramic system I attempt to explain its high strength and compressibility, in which the role of interfaces is explored first. High compressibility of such nano-heterostructures is due to the plastic deformation of thin layers of TiN (a ceramic), which otherwise does not deform. To explain the plastic deformation of TiN, I develop a first principles based method to study the core structure of dislocations. The core structure is used to estimate the stress required to plastically deform TiN, which is then used to explain its deformation behavior.

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