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Full-Text Articles in Engineering
Microscopic Dynamics And Transport Of Hydrogen In Proton Conducting Oxides, Erik J. Spahr
Microscopic Dynamics And Transport Of Hydrogen In Proton Conducting Oxides, Erik J. Spahr
Dissertations, Theses, and Masters Projects
The microscopic motion of hydrogen in solid oxides plays an important role in defect migration and reaction processes. Understanding the vibrational dynamics associated with both hydrogen-oxygen (O-H) bonds and the surrounding ionic environment allows one to better characterize these fundamental interactions. This thesis presents a comprehensive investigation into the vibrational decay dynamics of O-H and O-D stretch modes in crystalline oxides using time-resolved infrared pump-probe spectroscopy.;Measurements of the vibrational lifetimes of hydrogen related local modes in potassium tantalate (KTaO3) and titanium dioxide (TiO2 ) show that the localized O-H vibration is very closely tied to proton transport. In KTaO3 we …
Thin Film And Chemical Ordering Effects On The Magnetic Anisotropy In Binary Alloys, Jonathan Ronald Skuza
Thin Film And Chemical Ordering Effects On The Magnetic Anisotropy In Binary Alloys, Jonathan Ronald Skuza
Dissertations, Theses, and Masters Projects
This dissertation presents various investigations into the structure-property correlations in highly anisotropic FePt and FePd thin films and nanostructures. These binary alloy thin films may exhibit long-range chemical ordering (e.g. L10), which induces a strong uniaxial magnetic anisotropy whose orientation is dependent on the ordering direction in the thin film. The chemical ordering, and hence the magnetic anisotropy, in these thin films can be controlled and tailored through sputter deposition and ion implantation conditions followed by subsequent processing. Two novel fabrication methods, x-ray rapid thermal annealing (XRTA) and heavy ion implantation, successfully demonstrate the ability to obtain highly anisotropic nanometer-sized …
Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen
Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen
Dissertations, Theses, and Masters Projects
Recent progress and a coordinated national research program have brought considerable effort to bear on the synthesis and application of carbon nanostructures for field emission. at the College of William and Mary, we have developed field emission arrays of vertically oriented graphene (carbon nanosheets, CNS) that have demonstrated promising cathode performance, delivering emission current densities up to 2 mA/mm2 and cathode lifetime > 800 hours. The work function ( & phis;) of CNS and other carbonaceous cathode materials has been reported to be &phis;∼4.5-5.1 eV. The application of low work function thin films can achieve several orders of magnitude enhancement of …
First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis
First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis
Dissertations, Theses, and Masters Projects
Nuclear magnetic resonance (NMR) spectroscopy is one of the most important experimental probes of local atomistic structure, chemical ordering, and dynamics. Recently, NMR has increasingly been used to study complex ferroelectric perovskite alloys, where spectra can be difficult to interpret. First-principles calculations of NMR spectra can greatly assist in this task. In this work, oxygen, titanium, and niobium NMR chemical shielding tensors, s&d4; , were calculated with first-principles methods for ferroelectric transition metal prototypical ABO3 perovskites [SrTiO3, BaTiO 3, PbTiO3 and PbZrO3] and A(B,B')O3 perovskite alloys Pb(Zr1/2Ti1/2)O3 (PZT) and Pb(Mg1/3Nb2/3)O3 (PMN). The principal findings are 1) a large anisotropy between …