Date of Award

2020-01-01

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Advisor(s)

Ramana Chintalapalle

Abstract

An approach is presented to design refractory-metal (RM) incorporated Ga2O3-based materials with controlled structural, mechanical, and optical properties. A model system based on molybdenum (Mo) doped Ga2O3 (GMO) has been considered to elucidate the combined effect of RM-doping and processing parameters on the properties and oxygen sensor performance of GWO nanomaterials. The molybdenum (Mo) content in Ga2O3 was varied from 0 to 11 at% in the sputter-deposited Ga-Mo-O films. Molybdenum was found to significantly affect the structure and optical properties. While low Mo content (≤4 at%) results in the formation of single-phase (β-Ga2O3), higher Mo content results in amorphization. Chemically induced bandgap variability (Eg~1 eV) coupled with structure modification indicates the electronic structure changes in Ga-Mo-O. The linear relationship between chemical composition and optical properties suggests that tailoring the optical quality and performance of Ga-Mo-O films is possible by tuning the Mo content.

The present approach of Mo-doping also allows designing Ga2O3-based nanomaterials with tunable mechanical properties. In GMO, where Mo content (x) was varied up to ~11 at%, Mo-incorporation induced effects were reflected in mechanical characterization, where the hardness of the Ga-Mo-O nanocrystalline films increases for Mo ≤10 at%, at which point hardness decreases due to Mo-induced structural transformation. However, the elastic modulus of G-Mo-O decreases continuously with Mo incorporation. The Ga-Mo-O exhibits maximum H (~36 GPa) for 10 at% Mo, where Mo incorporation induces enhancement in hardness as well as in the plasticity index parameter. Based on the results, a structure-composition-mechanical property correlation in Ga-Mo-O films is established. Finally, performance evaluation made using laboratory based measurements indicate enhanced sensor performance of GMO. Incorporating Mo into Ga2O3 reduces response time of the oxygen sensor by several orders of magnitude.

Language

en

Provenance

Received from ProQuest

File Size

131 pages

File Format

application/pdf

Rights Holder

Anil Krishna Battu

Available for download on Saturday, December 19, 2020

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