Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


Asel Dissertation Final.pdf (4.84 MB)

ETD Abstract Container

Abstract Header

Nanoscale Characterization of Defects in Complex Oxides and Germanane

Asel, Thaddeus J
http://rave.ohiolink.edu/etdc/view?acc_num=osu1523982077791833

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Physics.
Understanding the nature of atomic scale defects inside electronic materials can lead to new ways of eliminating them and thereby refining electronics for high performance. Such defect engineering can create pathways of tuning electronic and magnetic properties for next-generation devices. An interesting class of materials are the complex oxides due to their numerous properties, such as a tunable dielectric constant, ferroelectricity, ferromagnetism, superconductivity, and high dielectric constants, they are studied for use in a variety of device applications. Similarly, two-dimensional (2D) materials have been of interest due to their dimensional limitations which allows them to exhibit new physical phenomena. It has been shown that these two classes of materials can work together as the ferroelectric properties of complex oxides can enhance the conduction in 2D materials. Depth-resolved Cathodoluminescence Spectroscopy (DRCLS) is a technique that is ideal for studying the origins of defects in these materials as well as offering a way to analyze the manipulation of defects to build next-generation devices. Ba0.5Sr0.5TiO3 films were grown on MgO (001) via molecular beam epitaxy (MBE) for microwave studies and annealed in air at various temperatures. DRCLS was used to measure relative defect concentrations of the films. It was determined that films annealed in air at 950 ºC contained significantly fewer oxygen vacancies. SrTiO3 (STO) grown via MBE was studied via DRCLS to measure the effects of the electric field on the defects. DRCLS revealed that when the sample was under 3.1 MV/cm the sample showed significant changes in the position of the oxygen vacancy that indicated a change in the position of the oxygen vacancy in the sample. DRCLS confirmed a lack of oxygen vacancies at a STO interface when compared to oxygen vacancies in the STO substrate on which the structure was grown. These experiments illustrate the ability to manipulate and reduce defects, and how it affects materials in device applications. We used DRCLS and surface photovoltage spectroscopy (SPS) to identify multiple mid-gap defect states in germanane, a 2D material with a direct band gap. By using a combination of chemical processing and comparison with DFT density of states calculations we were able to identify the origin of the defect states. DRCLS/SPS optical transitions yielded energy level positions 0.81 and 1.35 eV below the conduction band and 0.96 eV above the valence band within the 1.60 eV band gap that matched with DFT levels for Ge vacancies coordinated with H atoms. Varying the extent of de-intercalation we identified the nature of an additional state at EV+1.05 eV due to Ca between the GeCH3 layers. We used a photoluminescence spectroscopy (PLS) to observe how air and other gases affect band-to-band recombination in germanane. PLS exhibits a commonly observed 1.9 eV luminescence in air, which is quenched in vacuum and replaced by the 1.6 eV band gap emission. Gas-dependent studies reveal that H2O intercalation is the cause of the 1.9 eV emission. These experiments illustrate the role of intrinsic and extrinsic defects on the electronic structure, which affects a material in a heterostructure.
Leonard Brillson (Advisor)
Fengyuan Yang (Committee Member)
Ilya Gruzberg (Committee Member)
Perry Robert (Committee Member)
156 p.
Condensed Matter Physics; Physics
Depth-Resolved Cathodoluminescence Spectroscopy, defects, complex oxides, germanane, 2D materials, Surface photovoltage Spectroscopy

Recommended Citations

Citations

  • Asel, T. J. (2018). Nanoscale Characterization of Defects in Complex Oxides and Germanane [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523982077791833

    APA Style (7th edition)

  • Asel, Thaddeus. Nanoscale Characterization of Defects in Complex Oxides and Germanane . 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1523982077791833.

    MLA Style (8th edition)

  • Asel, Thaddeus. "Nanoscale Characterization of Defects in Complex Oxides and Germanane ." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523982077791833

    Chicago Manual of Style (17th edition)

osu1523982077791833
558
© 2018, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.