Semester

Summer

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Nianqiang Wu

Committee Co-Chair

Terence Musho

Committee Member

Lawrence Hornak

Committee Member

Ever Barbero

Committee Member

Dongling Ma

Abstract

Semiconductor devices are the basis of modern technology. Semiconductor-based photoconversion devices that convert light into electrical signals have shown potential for light energy harvesting and conversion, environmental remediation, and sensors for detection of light, chemicals, and biological substances. Despite this potential for use in many applications, semiconductor photoconversion devices need further improvement in the photoconversion performance. This photoconversion improvement may be manifested as increased photoconversion efficiencies for light harvesting devices for power generation such as photovoltaics and photoelectrochemical (PEC) cells or improved photoconversion modulation to increase the sensitivity of semiconductor photoconversion-based sensors. In addition, alternative semiconductor materials to semiconductors that utilize toxic heavy metals such as cadmium and lead must be found for use in certain semiconductor photoconversion devices.

In this dissertation, three separate projects related to improving the performance of semiconductor photoconversion devices are presented. In the first project presented, a rutile titanium dioxide (TiO2) nanorod array photoanrode is coated with an ultra-thin porphyrin-based metal-organic framework (MOF) layer to improve the overall photoconversion of the photoelectrode for solar water splitting. The porphyrin-based MOF coated TiO2 nanorod array showed a 2.7x increase in photocurrent versus bare TiO2 nanorod arrays. The porphyrin-based MOF layer suppressed surface states on the rutile TiO2 nanorod array and increased charge separation and extraction from the rutile TiO2 due to the built-in electric field formed by a depleted p-n junction between the porphyrin-based MOF layer and the rutile TiO2 nanorods.

In the second project presented, different plasmonic (hot electron injection and plasmon-induced resonant energy transfer (PIRET)) and non-plasmonic photoconversion enhancement mechanisms were tested for modulating photocurrent in PEC-based sensors using Bi3FeMo2O12 (BFMO) thin film semiconductor photoelectrodes and Hg2+ as a proof-of-concept analyte for detection. The possible plasmonic and non-plasmonic photoconversion enhancement mechanisms were controlled by choice of conjugated plasmonic nanoprobe between Au and Au@SiO2 core-shell nanoparticles with the BFMO. The conjugated Au NPs enhanced the BFMO thin film’s PEC performance through a combination of plasmonic hot electron injection, PIRET, Fermi-level equilibration, and a non-plasmonic internal reflection within the BFMO caused by the conjugated Au NPs. The conjugated Au@SiO2 NPs enhanced the BFMO thin film’s PEC performance via PIRET and the non-plasmonic internal reflection within the BFMO caused by the Au@SiO2 NPs. A PEC sensor using the Au NPs as nanoprobes showed sensitivity and selectivity towards Hg2+ showing this PEC sensor design’s potential.

In the third project presented, based on the comparison study of plasmonic and non-plasmonic photoconversion enhancement mechanisms with BFMO thin-film photoanodes, a PEC-based immunosensor utilizing PIRET from Au NP-based nanoprobes conjugated to BFMO thin- film photoanodes to modulate photoconversion of the BFMO is synthesized and studied using human immunoglobulin G (IGG) as a proof-of-concept analyte. The plasmonic Au NPs are conjugated in the presence of human IGG via antibody-antigen reactions. The resulting PIRET-based PEC immunosensor shows some sensitivity towards IGG detection. However, the sensitivity of the PIRET-based PEC immunosensor is limited due to the large separation distance (~10 nm) between the plasmonic Au NPs the BFMO thin films from the antibody-antigen sandwich used for Au NP conjugation. As such, further work must focus on improving PIRET between the Au NP based nanoprobes and the BFMO thin film photoanodes.

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