Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

By making electron energy-loss spectroscopy (EELS) measurements in a scanning transmission electron microscope (STEM), the optoelectronic properties of a material can be determined with nanometer spatial resolution. Since these optoelectronic properties can be related to the electronic structure of a material, STEM-EELS can also probe the local bonding environment at the interface of two materials. Such measurements could be key in developing more efficient P3HT:PCBM bulk-heterojunction organic photovoltaics (OPVs) (P3HT = poly(3-hexylthiophene), PCBM = [6,6] phenyl C61 butyric acid methyl ester), as understanding the local electronic structure at P3HT/PCBM interfaces should provide insight into charge generation/transport. However, organic materials are extremely susceptible to beam-damage when placed under a high energy electron beam, making it difficult to use STEM-EELS to collect reliable data. It was demonstrated that, via a beam damage-minimization EELS acquisition method, reliable high-resolution valence-loss STEM-EELS data could be collected for electron beam-sensitive materials. Using this method, valence-loss EELS spectra were acquired (using an FEI Titan3 60-300 Image-Corrected S/TEM) for thin films of four OPV materials – P3HT, PCBM, CuPc (copper phthalocyanine), and C60. From these valence-loss spectra, the real (e1) and imaginary (e2) parts of the complex dielectric function were extracted and compared to similar spectra obtained via a technique that should not damage these organic materials (variable-angle spectroscopic ellipsometry, VASE), thus proving that the acquisition method developed was suitable for collecting reliable valence-loss EELS spectra of P3HT, PCBM, CuPc, and C60. Valence-loss EELS spectra were then collected for P3HT, PCBM, CuPc, and C60 using a Nion UltraSTEM 100 MC `HERMES' S/TEM. With this STEM, it was possible to collect valence-loss spectra with higher energy resolutions (35 meV) than what was achievable using the FEI T (open full item for complete abstract)

Committee: David McComb (Advisor); Tyler Grassman (Committee Member); Vicky Doan-Nguyen (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2017, Electrical Engineering

Electrically conductive hair-like structures, referred to as whiskers, can bridge the gap between densely spaced electronic components. This can cause current leakage and short circuits resulting in significant losses and, in some cases, catastrophic failures in the automotive, aerospace, electronics and other industries since 1946. Detecting a metal whiskers (MWs) is often a challenging task because of their random growth nature and very small size (diameters can be less than 1 µm, lengths vary from 1µm to several millimeters). Many decades ago the industry introduced whisker mitigating Pb in the solders used to fabricate electric and electronic parts. In recent years, this changed because the European Union (EU) passed a legislation in 2006, called “Restriction of the use of Certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment”, which requires a reduction and elimination of the use of Pb in technology. Thus, the issue of undesirable and unpredictable whiskers growth has returned and there is a renewed interest in the mechanisms of formation of these structures. None of the whisker growth models proposed to date are capable of answering consistently and universally why whisker grow in the first place and why Pb addition suppresses their growth. Understanding MW nucleation and growth mechanism are of significant interest to this project, since this would potentially allow the development of new accelerated-failure testing methods of electronic components to replace existing testing methods which are generally found to be unreliable. In particular, this research is intended to study the effects of electric fields on the whisker growth, which according to the recently developed electrostatic theory[1] of whisker growth, are of crucial importance. This theory proposes that the imperfections on metal surfaces can form small patches of net positive or negative electric charge leading to the formation of the anomalous electric field (E), which go (open full item for complete abstract)

Committee: Daniel Georgiev Dr. (Committee Chair); Vijay Devabhaktuni Dr. (Committee Member); Victor Karpov Dr. (Committee Member); Devinder Kaur Dr. (Committee Member); Anthony Johnson Dr. (Committee Member) Subjects: Aerospace Materials; Chemical Engineering; Condensed Matter Physics; Electrical Engineering; Engineering; Experiments; Materials Science; Metallurgy; Nanoscience; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Theoretical Physics

Bachelor of Science (BS), Ohio University, 2014, Engineering Physics

We have used the physical vapor deposition technique, plasma sputtering, to fabricate single junction n-type amorphous Silicon and amorphous Indium Gallium Nitride on p-type polycrystalline Silicon. We proceeded to study the open circuit voltage, short circuit current, fill factor, efficiency, and activation spectrum of each sample. After, we identified the structural morphology and elemental composition of the complete sample and each individual layer in the scanning electron microscope (SEM) and transmission electron microscope (TEM). Finally, we determined the limitations of our fabrication method and discuss methods of rectifying these limitations.

Committee: Martin Kordesch (Advisor) Subjects: Electrical Engineering; Energy; Engineering; Materials Science; Physics