Physics Commons^™

Angle-Resolved Observation Of X-Ray Second Harmonic Generation In Diamond, Björn Senfftleben

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

This thesis reports angularly-resolved observation of X-ray second harmonic generation (XSHG) in diamond at several phase-matching geometries. The XSHG signal was produced by ultra-short, highly intense X-ray pulses with a photon energy of 9.831 keV generated by a free-electron laser. In some geometries for high pulse energies more than 10 second harmonic photons per pulse were generated.

Different phase-matched geometries were used for XSHG to investigate the angular dependence of the efficiency of the process. Furthermore, for each phase-matching condition, the quadratic dependence for second harmonic generation at each geometry was verified and the crystal rocking curves were measured. The …

Design And Construction Of A High-Current Femtosecond Gas-Phase Electron Diffraction Setup, Omid Zandi

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

We designed and constructed a state-of-the-art high current ultrafast gas electron diffraction experimental setup, which resolved two main challenges that constraint temporal resolution in previous setups. These aforementioned bottlenecks were: the space charge effect due to the Coulomb expansion, and the velocity mismatch between the sub-relativistic electrons (probe) and the exciting laser pulse (pump). In our setup, the problem of space charge effect was ameliorated by compressing 90 keV photo-emitted electron pulses using a radio-frequency electric field. The compression allowed us to increase the beam current by almost two orders of magnitude higher than previously reported. We developed a laser-activated …

A Measurement Of The Wγ Cross Section At √S = 8 Tev In Pp Collisions With The Cms Detector, Ekaterina Avdeeva

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

A measurement of cross section of the Wγ → lνγ production in proton-proton collisions using 19.6 fb − 1 of LHC data collected by CMS detector at the center- √ of-mass collision energy of s = 8 TeV is reported. The W bosons are identified in their electron and muon decay modes. The process of Wγ production in the Standard Model (SM) involves a pure gauge boson coupling, a WWγ vertex, which allows one to test the electroweak sector of the SM in a unique way not achievable by studies of other processes. In addition to the total cross section, …

From Quantum To Classical Interactions Between A Free Electron And A Surface, Peter Beierle

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Quantum theory is often cited as being one of the most empirically validated theories in terms of its predictive power and precision. These attributes have led to numerous scientific discoveries and technological advancements. However, the precise relationship between quantum and classical physics remains obscure. The prevailing description is known as decoherence theory, where classical physics emerges from a more general quantum theory through environmental interaction. Sometimes referred to as the decoherence program, it does not solve the quantum measurement problem. We believe experiments performed between the microscopic and macroscopic world may help finish the program. The following considers a free …

Surfaces And Interfaces Of Magnetoelectric Oxide Systems, Shi Cao

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Magnetoelectric materials Cr2O3, hexagonal LuFeO3 and YbFeO3 are studied in this thesis. The surface of chromia (Cr2O3) has a surface electronic structure distinct from the bulk. Our work shows that placing a Cr2O3 single crystal into a single domain state will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. From the Cr 2p3=2 X-ray magnetic circular dichroism signal, there is clear evidence of interface polarization with overlayers of both Pd and Pt on chromia. Cobalt thin films on Cr2O3(0001) show larger magnetic contrast in magnetic force microscopy indicating enhancement of perpendicular …

Novel Half-Metallic And Spin-Gapless Heusler Compounds, Yunlong Jin

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

This thesis is devoted to experimental studies of Heusler compounds CoFeCrAl, CoFeCrX (X = Si, Ge) and Mn₂PtSn. These Heusler alloys present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be spin gapless semiconductors and have half-metallic properties with 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron- transport properties of the fabricated alloys were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L2₁ Heusler order. All considered types of chemical disorder destroy the spin-gapless …

Fabrication And Study Of The Structure And Magnetism Of Rare-Earth Free Nanoclusters, Bhaskar Das

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

No abstract provided.

The Organic Ferroelectric Vinylidene Fluoride Oligomer: Vacuum Deposition, Properties, And Interfaces, Keith Foreman

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Organic ferroelectric materials combine the versatility and customizability afforded by organic synthesis with the functionality of ferroelectric materials. The model ferroelectric polymer, poly(vinylidene fluoride) (PVDF), is used in a wide variety of applications and is still the subject of fundamental research nearly 80 years after it was first polymerized. Unfortunately, PVDF suffers from thermal decomposition during thin film evaporation in vacuum. Since PVDF thin films cannot be deposited in the ferroelectric phase in vacuum conditions, its use in new, 21^st century technologies may be limited since the interface between the organic and adjacent metallic thin films is less than …