Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Dr. Peng Xiong, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 19, 2005). Document formatted into pages; contains xvii, 119 pages. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 304-307). Also available on the Internet.

Zinc, cobalt and iron phenylthio substituted phthalocyanines have been synthesized and characterized. Cyclic and square wave voltammetry in dimethylformamide containing tetrabutylammonium perchlorate revealed five and six redox processes respectively for the cobalt and iron phenylthio substituted phthalocyanines. These complexes are easier to reduce compared to the corresponding unsubstituted MPc and to butylthio substituted derivatives. Spectroelectrochemistry (in dimethylformamide containing tetrabutylammonium perchlorate) was employed to assign the cyclic voltammetry peaks, and gave spectra characteristic of Fe(I)Pc for reduction of iron phenylthio substituted phthalocyanine and Co(I)Pc for the reduction of cobalt phenylthio substituted phthalocyanine. The spectrum of the former is particularly of importance since such species have not received much attention in literature. Cobalt and iron phenylthio substituted phthalocyanines have been deposited on Au electrode surfaces through the self assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of L-cysteine. Amine substituted cobalt phthalocyanine (CoTAPc) was deposited on gold surfaces by using an interconnecting SAM of mercaptopropionic acid or dithiobis(N-succinimidyl propionate) through the creation of an amide. Reductive and oxidative desorption of the SAMs limit the useful potential window. The SAM-CoTAPc layers show electrocatalytic activities towards oxygen reduction through the Co(I) central metal ion. Both SAMs were highly stable and hence will be interesting tools for further research in surface modification and sensor development.

Femetinide is a synthetic retinoid with chemotherapeutic activity against various malignancies. After oral administration to animals, femetinide was found to be incompletely absorbed and excreted primarily in feces. The purpose of this study was to investigate the mechanism(s) responsible for the transport of femetinide across Caco-2 cell monolayers with an aim to determine the possible reasons for poor oral absorption of fenretinide. Fenretinide was found to be highly lipophilic (log P = 7.4) and practically insoluble in water. The water solubility of fenretinide was enhanced by formulating it as a Povidone K 25 solid dispersion. The Transepithelial Electrical Resistance (TEER) and antipyrine permeability (transcellular marker) were not affected after treatment with 0.5% PVP K 25 on the apical side. The apparent permeability coefficient (Papp) of fenreti nide was extremely low [(8.8 ± 0.5) x 10-8 cm/sec] even in the presence of 4% bovine serum albumin (BSA) in the receiver. The apical to basolateral (AP-BL) transport appeared linearly related to the fenretinide concentration ( 125-640 μM), thereby indicating that femetinide penneates the Caco-2 monolayer by passive diffusion within the concentration range. Transport studies at different donor (apical) pH conditions (6.0 or 7.4) revealed that no pH-dependent transporters were involved in the apical to basolateral transport of fenretinide across the Caco-2 monolayer. Efflux transporters like P-glycoprotein (P-gp) and the paracellular pathway did not play a significant role on the permeability of fenretinide. The partitioning of highly lipophilic molecules like fenretinicle from the cell membrane into the receiver depends on the composition of the receiving medium. The permeability of fenretinide increased with an increase in the bovine serum albumin (BSA) concentration (0 to 4 %) in the receiver. The addition of RBP to the receiving medium containing 4 % BSA increased the permeability of femetinicle clue to a greater binding affinity of fenretinicle for RBP. Significant amount (13-15% of the initial amount) of drug was found to accumulate in the cell membrane. The permeation of femetinide in Caco-2 monolayers is limited due to extensive accumulation in the cell membrane and poor partitioning from the cell membrane into the receiver medium.

Master of Science

No description available.

A monolayer film of methyl stearate was compressed until catastrophic film collapse took place. Surface pressure relaxation was then followed as a function of time. Investigation involving the effects of film compression beyond the collapse pressure revealed an important process involved in the surface pressure relaxation mechanism. When the monolayer is compressed beyond the collapse pressure and then held at a constant area, the surface pressure relaxation, in a plot of surface pressure vs time, was delayed during the initial stage of the process. A similar delay in the surface pressure relaxation was also observed for a monolayer film of methyl stearate when it was compressed and held at 40 mN/m, below the collapse pressure, for some time before allowing it to relax under a constant area condition. A relaxation mechanism has been proposed to explain the delay phenomenon observed during the surface pressure relaxation at constant area: At collapse, the monolayer film buckles and folds over to form bilayer molecular channels (ridges and ribbons). The ridges and ribbons act as a reservoir for monolayer material to make up for lost molecules at the air/water interface due to the growth of a bulk (crystalline) phase under a constant area condition. The results from temperature dependence studies as well as from the area-relaxation experiments strongly support the proposed relaxation mechanism. The Langmuir-Blodgett films of methyl stearate, deposited before and after the catastrophic film collapse, revealed interesting structural features of the collapsed film. The experimental results from the pressure-time, area-time, and pressure-area isotherms strongly suggest that the methyl stearate monolayer film undergoes an organized film collapse. This work helps to better understand the relaxation mechanism in monolayer films at the air/water interface. / Master of Science

Thesis (Ph. D.)--University of Oregon, 1999. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 303-350). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9955917.

Atomically thin two-dimensional materials, such as graphene and semiconductor transition metal dichalcogenides (TMDCs), exhibit remarkable and desirable optical and electronic properties. This dissertation focuses on the excitonic properties of monolayer TMDCs taken first in isolation and then in contact with another material. We begin with a study of the exciton binding energy in two monolayer TMDCs, WS₂ and MoS₂. We observe excited states of the exciton by two different optical spectroscopy techniques: reflectance contrast and photoluminescence excitation (PLE) spectroscopy. We fit a hydrogenic model to the energies associated with the excited states and infer a binding energy, which is an order of magnitude higher than the bulk material. In the second half of this work, we study two types of two-dimensional vertical heterostructures. First, we investigate heterostructures composed of monolayer WS₂ partially capped with graphene one to four layers thick. Using reflectance contrast to measure the spectral broadening of the excitonic features, we measure the decrease in the coherence lifetime of the exciton in WS₂ due to charge and energy transfer when in contact with graphene. We then compare our results with the exciton lifetime in MoS₂/WS₂ and MoSe₂/WSe₂ heterostructures. In TMDC/TMDC heterostructures, the decrease in exciton lifetime is twice that in WS₂/graphene heterostructures and due predominantly to charge transfer between the layers. Finally, we probe the band alignment in MoS₂/WS₂ heterostructures using scanning tunneling microscopy (STM) and spectroscopy (STS).We confirm the monolayer band gaps and the predicted type II band alignment in the heterostructure. Drawing from all the research presented, we arrive at a favorable conclusion about the viability of TMDC based devices.

Two-Dimensional (2D) materials such as graphene, Transition Metal Dichalcogenides (TMDs) and Metal Monochalcogenides (MMs) are the next generation of smart devices because of their outstanding novel properties. Monolayer (one molecule thick.) of famous TMDs such as MoS2, MoSe2, WS2 and WSe2 exhibit phenomenal physical properties including but not limited to low-energy direct bandgap and large piezoelectric responses. These have made them potential candidates for cutting-edge electronic and mechanical devices such as novel transistors and PN-junctions, on-chip energy storage and piezoelectric devices which could be applied in smart sensors and actuators technologies. Additionally, reversible structural phase transition in these materials from semiconducting phase (1H) to metallic phase (1T') as a function of strain, provide compelling physics which facilitates new era of sophisticated flexoelectric devices, novel switches and a giant leap in new regime of transistors. One iconic characteristics of monolayer 2D materials is their incredible stretchability which allows them to be subjected to several percent strains before yielding. In this thesis I provide facile techniques based on polymer encapsulation to apply several percent (6.5%) controllable, non-destructive and reproducible strains. This is the highest reproducible strain reported so far. Then I show our experimental techniques and object detection algorithm to verify the amount of strain. These followed up by device fabrication techniques as well as in-depth polarized and unpolarized Raman spectroscopy. Then, I show interesting physics of monolayer and bilayer TMDs under strain and how their photoluminescence behaviors change under tensile and compressive strains. Monolayers of TMDs and MMs exhibit 1-10 larger piezoelectric coefficients comparing to bulk piezo materials. These surprising characteristics together with being able to apply large range strains, opens a new avenue of piezoelectricity with enormous magnitudes higher than those commercially available. Further on 2D materials, I show our transport experiments on doped and pristine graphene micro devices and unveil the discoveries of magneto conductance behaviors. To complete, we present our computerized techniques and experimental platforms to make these 2D materials.