Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 58-59). Also available on the World Wide Web.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2005. / Includes bibliographical references.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Graphene is a one-atom thick sheet of graphite which made of carbon atoms arranged in a hexagonal lattice. Carbon nanotubes and graphene nanoribbons can be viewed as single molecules in nanometer scale. Carbon nanotubes are usually labeled in terms of the chiral vectors which are also the directions that graphene sheets are rolled up. Due to their small scale and special structures, carbon nanotubes present interesting electrical, optical, mechanical, thermal, and toxic properties. Graphene nanoribbons can be viewed as strips cut from infinite graphene. Graphene nanoribbons can be either metallic or semiconducting depending on their edge structures. These are robust materials with excellent electrical conduction properties and have the potential for device applications. In this research project, we present a theoretical study of electrical properties of the carbon structures. Electronic band structures, density of states, and conductance are calculated. The theoretical models include a tight-binding model, a Green’s function methodology, and the Landauer formalism. We have investigated the effects of vacancy and weak disorder on the conductance of zigzag carbon nanoribbons. The resulting local density of states (LDOS) and conductance bands show that electron transport has interesting behavior in the presence of any disorder. In general, the presence of any disorder in the GNRs causes a decrease in conductance. In the presence of a vacancy at the edge site, a maximum decrease in conductance has been observed which is due to the presence of quasi-localized states. / Theory -- Band structure and density of states of carbon nanotubes -- Band structure and density of states of graphene nanoribbons -- Quantum conductance of zigzag graphene nanoribbons -- Quantum conductance of a zigzag graphene nanoribbon with defects. / Department of Physics and Astronomy

The results presented in this thesis demonstrate the first synthesis of several nanostructured transition metal oxides and lithium containing transition metal oxides. Their uses in lithium-ion batteries and/or as magnetic materials have been investigated. The first example of two and three dimensional mesoporous Fe₂O₃ has been prepared by using the soft templating (surfactant) method. The materials have amorphous walls and exhibit superparamagnetic behaviour. By using a hard template route, a mesoporous α-Fe₂O₃ with highly crystalline walls has been synthesized. Its unique magnetic behaviour, distinct from bulk α-Fe₂O₃, nanoparticulate α-Fe₂O₃, and mesoporous Fe₂O₃ with disordered walls, has been demonstrated. The hard template method was also used to prepare nanowire and mesoporous Co₃O₄, β-MnO₂ and MnO₃ with crystalline walls. Their electrochemical properties as electrodes in Li-ion batteries have been investigated. Mesoporous β-MnO₂ can accommodate 0.9 Li/Mn in stark contrast to bulk β-MnO₂ which cannot accommodate Li. To prepare mesoporous materials which cannot be obtained directly by the hard template method, a post-templating route has been developed. Mesoporous Fe₃O₄, γ-Fe₂O₃, and Mn3O4 with ordered mesostructures and highly crystalline walls have been obtained by post-synthesis reduction/oxidation treatments. All the materials show unique magnetic properties compared with nanoparticulate and bulk materials. Also, the first example of lithium containing mesoporous material, LT-LiCoO₂, was synthesized by first preparing mesoporous Co₃O₄, then reacting this with LiOH to form LT-LiCoO₂, with retention of the ordered nanostructure. The nanostructured LT-LiCoO₂ compounds demonstrate superior performance compared with normal or nanoparticulate LT-LiCoO₂, when used as intercalation electrodes in lithium batteries. Finally, monodispersed Mn₃O₄ nanoparticles (diameter ~ 8 nm) with a core-shell structure (a highly crystalline Mn₃O₄ core encased in a thin MnO₂ shell) have been prepared for the first time. Ordered three-dimensional arrays form by spontaneous self-assembly. Magnetic measurements demonstrated that the self-assembled three-dimensional arrays exhibit spin-glass behaviour, rather than the anticipated superparamagnetic behaviour for isolated nanoparticles. Such behaviour is interpreted as arising from strong interactions between the core (crystallized Mn₃O₄) and shell (MnO₂).

M.Sc. (Nanoscience) / Please refer to full text to view abstract

Molecular fluorophores and semiconductor quantum dots (QDs) have been used as cellular imaging agents for biomedical research, but each class has challenges associated with their use, including poor photostability or toxicity. Silicon is a semiconductor material that is inexpensive and relatively environmental benign in comparison to heavy metal-containing quantum dots. Thus, red-emitting silicon nanoparticles (Si NPs) are desirable to prepare for cellular imaging application to be used in place of more toxic QDs. However, Si NPs currently suffer poorly understood photoinstability, and furthermore, the origin of the PL remains under debate. This dissertation first describes the use of diatomaceous earth as a new precursor for the synthesis of photoluminescent Si NPs. Second, the stabilization of red PL from Si NPs in aqueous solution via micellar encapsulation is reported. Thirdly, red to blue PL conversion of decane-terminated Si NPs in alcohol dispersions is described and the origins (i.e., color centers) of the emission events were studied with a comprehensive characterization suite including FT-IR, UV-vis, photoluminescence excitation, and time-resolved photoluminescence spectroscopies in order to determine size or chemical changes underlying the PL color change. In this study, the red and blue PL was determined to result from intrinsic and surface states, respectively. Lastly, we determined that the blue emission band assigned to a surface state can be introduced by base addition in originally red-emitting silicon nanoparticles, and that red PL can be restored by subsequent acid addition. This experimentally demonstrates blue PL is surface state related and can overcome the intrinsic state related excitonic recombination pathway in red PL event. Based on all the data collected and analyzed, we present a simple energy level diagram detailing the multiple origins of Si NP PL, which are related to both size and surface chemistry.