Semiconductor nanowires (NWs) are anticipated to play a crucial role in future electronic and optoelectronic devices. Their practical applications remain hindered by an urging need for feasible strategies to tailor their optical and electronic properties. Strategies based on strain and alloying are limited by issues such as defects, interface broadening and alloy scattering. In this thesis, a novel method to engineer the optoelectronic properties based on strain-free periodic structural modulations in chemically homogeneous Nanowire Twinning Superlattices (NTSLs) is experimentally demonstrated. NTSLs are an emerging new class of nanoscale material, composed of periodically arranged rotation twin-planes along the length of NWs. The main objective of this thesis is to establish the relationship between the electronic energy band gap (Eg) and the twin-plane spacing (d) in NTSLs, quantified using a periodicity parameter, based on ZnSe. ZnSe was chosen because of its excellent luminescence properties, and potential in fabrication of optoelectronic devices in the near-UV and blue region of the spectrum. A prerequisite to establishing this correspondence is a prior knowledge of the photoluminescence (PL) response and the nature of fundamental optical transitions in defect-free single crystal ZnSe NWs with zinc-blende (ZB) and wurtzite (WZ) crystal structures. There has been no systematic work done yet on understanding these fundamental optical processes, particularly on single NWs and in relation to their crystalline microstructure. Therefore, the secondary objective of this thesis is to study the influence of native point defects on the optical response of single ZnSe NWs in direct relation to their crystalline microstructure. The PL response from single ZB and WZ NWs was determined unambiguously, and excitonic emission linewidths close to 1 meV were observed, which are the narrowest reported linewidths thus far on ZnSe NWs. Based on this and extensive optical and structural characterization on individual NTSLs, a linear variation in Eg is shown through a monotonic shift in PL peak position from ZnSe NTSLs as a function of d, with Eg's that lie between those of ZB and WZ crystal structures. This linear variation in Eg was also validated by ab Initio electronic structure calculations. This establishes NTSLs as new nanoscale polytypes advantageous for applications requiring tunable band gaps.

Written in different time periods but set in the time of imperial expansion, E. M. Forster’s Howards End (1910) and Chinua Achebe’s Things Fall Apart (1958) offer a critical exploration of British imperialism and its aftermath. What similarities and what differences do these novels have in portraying imperialism? More specifically, do they portray modern imperialism in radically different and mutually exclusive ways since one is set in the center of the British Empire and the other in a peripheral colony? The essay draws on Frederic Jameson’s argument about modernism, and Howards End in particular, that the center representatively excludes the periphery in its literary works. By comparing the two novels, the essay explores these issues and asks whether the British Empire is structurally incomplete in its representation in early twentieth century canonical modernist novels? Moreover, does this theory of exclusivity extend to include modern canonical African novels written a few decades later? By analyzing Howards End and Things Fall Apart, the essay examines the hypothesis that the center and the periphery are indeed mutually exclusive in their literary productions. The conclusions reached require some significant modifications to Jameson’s theory. It was found that Howards End does indeed structurally exclude the periphery. However, the same cannot be said for Things Fall Apart, which structurally incorporates the center. Thus, Jameson’s theory does not extend beyond early twentieth century modernist novels. Moreover, Forster’s novel, although it does suffer from Jameson’s criticism, shows critical awareness of this disabling disconnection from the periphery.

Into the Valley: Voices I Heard Along the Way contains a preface and a collection of five short stories. The preface discusses the use of voice as a technique to develop characters and create authenticity through elements such as sentence structure, diction, dialogue, and regional, cultural, and/or gender-specific affectations to make the words on the page become audible language in the mind of the reader. Each story is written with a unique voice that presents characters who struggle to come to terms with the truth and its various shades of reality.

No description available.

Random Access Memory (RRAM) has emerged as a leading candidate for nonvolatile memory storage. RRAM devices typically consist of a metal/insulator/metal (MIM) structure and exhibit switching of the device resistivity state (low-to-high, highto- low) by application of electrical bias. It is now widely accepted that shunting and rupturing of local conductive paths (filaments) directly determines the resistance state. The size and composition of these filaments are very much an open question, but are usually attributed to high local concentrations of oxygen vacancies. Although there has been a huge body of research conducted in this field, the fundamental nature of the conductive path and basic switching/failure mechanisms are still under debate. This is largely due to a lack of structural analysis of existing filament size and composition in actual devices. Since the non-volatile nature and device reliability issues (i.e. retention and endurance) are directly related to the irreversible structural transformations in the device, microstructural characterization is essential for eventual commercialization of RRAM. In this study, I investigated oxygen vacancy defect dynamics under electric filed essential for resistive switching and aim to identify size, location, and chemical nature of the conductive filaments in RRAM devices by using a variety of devices and materials characterization methods: in situ transmission electron microscopy (TEM), highresolution TEM (HRTEM), scanning TEM (STEM)-electron energy loss spectroscopy (EELS), electron holography, rapid thermal annealing (RTA), transient thermometry, and electro-thermal simulation. I adopt an in situ electrical biasing TEM technique to study microstructural changes occurring during resistive switching using a model TiO2-based RRAM device, and confirmed the device is switchable inside of the TEM column. I observed extension and contraction of {011} and {121}-type Wadsley defects, crystallographic shear faults, associated with resistive switching. More specifically, emission and adsorption of oxygen vacancies under different polarity of electrical biases at the fault bounding dislocations were identified. The motion of Wadsley defects was used to track oxygen vacancy migration under electric field. Also, the microstructural changes that occur when the device experiences low electric field (~104 V/cm) was reported, akin to read disturb. Crossbar type RRAM device stacks consisting of TiN/a-HfAlOx/Hf/TiN were investigated to estimate filament size, filament temperature, and its chemical footprint using HRTEM, transient thermometry and numerical simulation. In each of the switched devices, a single crystallite ~ 8-16 nm in size embedded in an amorphous HfAlOx matrix was found. The HfAlOx crystallization temperature (Tc) of 850 K was determined by combining RTA and HRTEM imaging. In parallel, the filament size has been determined by transient thermometry. The temperature profile extracted from these measurements suggested that the peak filament temperature was > 1500 K at the center, with the hot zone (T > Tc = 850 K) extending to a radius of 7 nm around the filament. These results were consistent with the HRTEM observations of the crystallite size. The potential filament location (crystallite) in the switching devices was analyzed by STEM-EELS and identification of the filament chemical nature identification has been attempted.

Oleaginous yeasts are able to produce a high percentage of their weight as lipids, which can be used as the starting material for biodiesel production, producing a fuel with many of the same properties as petroleum-based diesel. The objective of this research was to compare three oleaginous yeast species, Rhodosporidium babjevae, Rhodosporidium diobovatum, and Yarrowia lipolytica to determine which species would be the best candidate for larger-scale production. Following the comparison work, it was determined that R. diobovatum was the best candidate for scale-up. Subsequent experiments used batch cultures in bioreactors at a volume of 3.5 L, followed by a 25x fold increase to 90 L production. The results of this scale-up showed that the high levels of production and growth continued in a reactor system. As such, R. diobovatum could be a possible organism to use in the production of lipids from waste glycerol for biodiesel production. / October 2015

The purpose of this investigation is to determine the change in characterization that takes place in the works of Emilia Pardo Bazán. Source material include the writings of such critics of Spanish literature as Richard Chandler, Kessel Schwartz, Emiliano Díez-Echarri, José M. Roca Franquesa, Federico C. Saínz de Robles, and José A. Balseiro. Emilia Pardo Bazán wrote a total of twenty novels. From this collection ten were selected which best exemplify the change in characterization in her writings.

A low molecular weight po1y-S-a1anine (350 row) was prepared by thermal po1ycondensation of S-a1anine ethyl ester. In thermal analysis, six transitions occurred in the initial polymer in approximate order of increasing temperature: glass transition temperature (Tg), crysta1- crystal transition, cold crystallization, melt crystallization, crystalline disorientation, and melting. Isothermal annealing of this polymer at 200 0 followed by quenching provided structures which exhibited multiple melting peaks in thermal analysis. In this work reasons are proposed for the dual endotherm. By prolonged annealing only, before analysis, part of the recrystallization exotherm can be observed in the differential scanning calorimetry (DSC) scan. DSC thermo grams obtained at varying heating rates on samples showing po1y-S-a1anine endotherms supported the assignment of superheating as the cause of the shift to higher peak temperatures with increasing heating rate. To further support the structural assignment, the infrared absorption showed typical polyamide bands, and the nuclear magnetic resonance spectrum gave two methylene peaks of equal intensity.

Several methods for analysing materials and proteins use highly concentrated beams of X-rays, e.g. SAXS and X-ray crystallography. To evaluate the outgoing beam, it is of high importance to know the light distribution of the incoming beam. Previously, a method for this has been to focus the X-ray beam onto a pinhole in front of a photodiode, a so called pinhole measurement. Although this method gives information about the radial distribution of the beam, it is very time-consuming. In this report a faster alternative has been developed and evaluated. In this new method an image is taken with an X-ray camera in the focus of the beam. Algorithms are then used to replicate a pinhole measurement by applying virtual pinholes. Different pixels in an image act differently, referred to as spatial noise. This must be compensated for before information about the beam may be extracted. To do this, the camera noise was characterized and a calibration procedure developed for its minimization. It was shown that the spatial noise was greatly reduced, making the temporal shot noise the new largest noise source. Although the noise was successfully reduced, the calibration procedure failed to accurately remove all signal not originating from registered photons. Measurements done with low photon intensities, large exposure times or at high temperatures are therefore less accurate. The measured camera signal was transformed into incident photon intensity using a responsivity proportionality constant. This constant was estimated by comparing the results from real and virtual pinhole measurements for several photon intensities and pinholes. The results gave a responsivity proportionality constant of 0,03 DN/X-ph. Further measurements were done concerning the temperature dependence of the camera responsivity and to investigate possible bleaching. The results indicated that the responsivity was held constant under changing temperatures and that the camera remained unbleached during the 114h long measurement. Finally, real and virtual pinhole measurements were done for a series of pinholes and compared using the responsivity proportionality constant. A maximum relative deviation of 6% was measured between the two, indicating that virtual pinhole measurements give accurate results. The largest deviations of the measurement seem to occur when using small or large pinholes. These errors, however, have a high potential of being further minimized, resulting in higher accuracy.

Vibrational and thermal behavior of several important systems were studied. The first study was a measurement of the infrared vibrational spectra of glucose and two important glucose dimers (cellobiose and maltose) as a function of temperature. The purpose of his study was to measure shifts in vibrational band positions to gain insight into carbohydrate reactivity. The second study was on hydrothermally treated coffee waste biomass. Here, collaborators at University of Campinas (UNICAMP, Brazil) treated coffee waste biomass in a flow-through subcritical water hydrolysis reactor. The purpose of the M.S. study on coffee waste was to understand the chemical changes that occurred to the residual solids during hydrolysis treatment. Vibrational spectroscopy and thermal analysis techniques were used. The third and final study was to understand the chemical composition of the solid product resulting from co-solvent enhanced lignin fractionation (CELF) of several biomass feeds. Collaborators at University of California Riverside (UCR) recently developed the CELF process. The purpose of the M.S. study on the CELF solid product was to understand its composition to help guide the CELF reactor design and determine applications for the CELF solids. Taken together, the 3 studies are integrated into a cohesive whole that demonstrates the use of spectroscopic and thermal techniques for characterizing biomass and understanding its composition at the molecular level.