Physics Commons^™

Two Dimensional Electron Gas At Oxide Interfaces, Karolina Janicka

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

Extraordinary phenomena can occur at the interface between two oxide materials. A spectacular example is a formation of a two-dimensional electron gas (2DEG) at the SrTiO₃/LaAlO₃ interface. In this dissertation the properties of the 2DEG are investigated from first principles.

The spatial extent of the 2DEG formed at the SrTiO₃/LaAlO₃ n-type interface is studied. It is shown that the confinement of the 2DEG is controlled by metal induced gap states formed in the band gap of SrTiO₃. The confinement width is then determined by the attenuation length of the metal induced gap …

First-Principles Studies On Physical And Chemical Properties Of Nanostructures, Menghao Wu

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

The physical and chemical properties of decorated graphene and graphene ribbons, single-layer III-V systems, three-dimensional carbon and BN foam, and transition-metal-molecular sandwich nanowires have been investigated by first-principle calculations and their potential applications have been predicted. First, it is shown that zigzag graphene nanoribbons (ZGNRs) can be converted into half metal when their edges are decorated by some chemical functional groups, and the half-metalicity is induced by chemical potential difference between two edges when one edge is decorated by electron-donating group like –OH and the other edge is decorated by electron-accepting group like –F, -NH₂, -N(CH₃) …

Thermodynamics Of Magnetic Multilayers, Tathagata Mukherjee

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

Our interest in thermodynamics of magnetic thin film heterostructure began by exploring the possibility to use magnetic nanostructures in the search for optimized magnetocaloric materials for potential room temperature refrigeration. In the present thesis magnetic thin film heterostructures are experimentally realized by Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD). Co/Cr and Fe/Cr superlattices were fabricated using mean-field theoretical concepts as guiding principles. The potential of artificial antiferromagnets for near room-temperature refrigeration is explored. Magnetocaloric properties are deduced from measurements of the temperature and field dependence of the magnetization of our samples. The effects of intra-plane and inter-plane exchange …

Self Assembly And Interface Chemistry Of Non-Metallated Tetraphenyl Porphyrin, Geoffrey Rojas

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

The study of the electronic properties and geometrical arrangement of 5, 10, 15, 20-tetraphenyl-21H, 23H-porphine on metal is presented. The systems were analyzed using both scanning tunneling microscopy and photoelectron spectroscopy and compared across surfaces to determine how the interface chemistry between the metal and molecule affect the self-assembly and band structure of the adsorbed species. The molecules are found to self-assemble and grow on the Ag(111) surface in a manner described by similar models to weakly bound metal/metal surface systems. The CH-pi bonds between molecules are found to largely determine the relative inter-molecular arrangement, while the more isotropic van …

Functional Two-Dimensional Electronic Gases At Interfaces Of Oxide Heterostructures, Yong Wang

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

A quasi-two dimensional electron gas (2DEG) in oxide heterostructures such as LaAlO₃/SrTiO₃ has unique properties that are promising for applications in all-oxide electronic devices. In this dissertation, we focus on understanding and predicting novel properties of the 2DEG by performing first-principles electronic calculations within the frame work of density-functional theory (DFT).

The effects of polarization in all-oxide heterostructures incorporating different ferroelectric constituents, such as KNbO₃/ATiO₃ (A = Sr, Ba, Pb), are investigated. It is found that screening charge at the interface that counteracts the depolarizing electric field in the ferroelectric material significantly changes the …

The Interplay Between Symmetry And Static Dipoles With Adsorption On Molecular Substrates, Zhengzheng Zhang

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

This thesis presents evidence of preferential adsorption and the associated dipole-dipole interactions that can occur at molecule to molecule interfaces. The results are discussed in the context of the possibility of interactions caused by strong intrinsic dipoles when adsorbed on electrostatically biased substrates. Key is the discovery of lock and key adsorption chemistry by comparing the reversible absorption of the three isomers of di-iodobenzene (1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene) on molecular films of a quinonoid zwitterion. There is unequivocal evidence that the molecular adsorption and absorption of 1, 3-diiodobenzene is strongly favored at 150 K over the other isomers of di-iodobenzene. …

The Photofragmentation Processes Of The Closo-Carborane And The Local Structure Of Transition Metal Doped Semiconducting Boron Carbide Thin Films, Jing Liu

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

I investigated the photofragmentation processes of various closo-carboranes in an effort to understand the radical-induced polymerization of the closo-carboranes (i.e., semiconducting film growth), based on their partial dehydrogenation during plasma-enhanced chemical vapor deposition. The chemistry of vacuum ultraviolet VUV assisted dehydrogenation processes of both the closo-carboranes and related closo-phosphacarboranes were compared by photoionization mass spectrometry studies. The dominant ion pairs were identified and compared with the energetics constructed by theoretical modeling for the possible dissociation pathways.

Transition metal (Mn, Fe, Co) doped boron carbides thin films produced by plasma-enhanced chemical vapor deposition of orthocarborane (closo …