Matching Items (75)
Description
Recently a new materials platform consisting of semiconductors grown on GaSb and InAs substrates with lattice constants close to 6.1 A was proposed by our group for various electronic and optoelectronic applications. This materials platform consists of both II-VI (MgZnCdHg)(SeTe) and III-V (InGaAl)(AsSb) compound semiconductors, which have direct bandgaps spanning the entire energy spectrum from far-IR (~0 eV) up to UV (~3.4 eV). The broad range of bandgaps and material properties make it very attractive for a wide range of applications in optoelectronics, such as solar cells, laser diodes, light emitting diodes, and photodetectors. Moreover, this novel materials system potentially offers unlimited degrees of freedom for integration of electronic and optoelectronic devices onto a single substrate while keeping the best possible materials quality with very low densities of misfit dislocations. This capability is not achievable with any other known lattice-matched semiconductors on any available substrate. In the 6.1-A materials system, the semiconductors ZnTe and GaSb are almost perfectly lattice-matched with a lattice mismatch of only 0.13%. Correspondingly, it is expected that high quality ZnTe/GaSb and GaSb/ZnTe heterostructures can be achieved with very few dislocations generated during growth. To fulfill the task, their MBE growth and material properties are carefully investigated. High quality ZnTe layers grown on various III-V substrates and GaSb grown on ZnTe are successfully achieved using MBE. It is also noticed that ZnTe and GaSb have a type-I band-edge alignment with large band offsets (delta_Ec=0.934 eV, delta_Ev=0.6 eV), which provides strong confinement for both electrons and holes. Furthermore, a large difference in refractive index is found between ZnTe and GaSb (2.7 and 3.9, respectively, at 0.7 eV), leading to excellent optical confinement of the guided optical modes in planar semiconductor lasers or distributed Bragg reflectors (DBR) for vertical-cavity surface-emitting lasers. Therefore, GaSb/ZnTe double-heterostructure and ZnTe/GaSb DBR structure are suitable for use in light emitting devices. In this thesis work, experimental demonstration of these structures with excellent structural and optical properties is reported. During the exploration on the properties of various ZnTe heterostructures, it is found that residual tensile strains exist in the thick ZnTe epilayers when they are grown on GaAs, InP, InAs and GaSb substrates. The presence of tensile strains is due to the difference in thermal expansion coefficients between the epilayers and the substrates. The defect densities in these ZnTe layers become lower as the ZnTe layer thickness increases. Growth of high quality GaSb on ZnTe can be achieved using a temperature ramp during growth. The influence of temperature ramps with different ramping rates in the optical properties of GaSb layer is studied, and the samples grown with a temperature ramp from 360 to 470 C at a rate of 33 C/min show the narrowest bound exciton emission peak with a full width at half maximum of 15 meV. ZnTe/GaSb DBR structures show excellent reflectivity properties in the mid-infrared range. A peak reflectance of 99% with a wide stopband of 480 nm centered at 2.5 um is measured from a ZnTe/GaSb DBR sample of only 7 quarter-wavelength pairs.
ContributorsFan, Jin (Author) / Zhang, Yong-Hang (Thesis advisor) / Smith, David (Committee member) / Yu, Hongbin (Committee member) / Menéndez, Jose (Committee member) / Johnson, Shane (Committee member) / Arizona State University (Publisher)
Created2012
Description
As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode.
ContributorsCavendish, Rio (Author) / Crozier, Peter (Thesis advisor) / Adams, James (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
In this dissertation, in-situ X-ray and ultraviolet photoemission spectroscopy have been employed to study the interface chemistry and electronic structure of potential high-k gate stack materials. In these gate stack materials, HfO2 and La2O3 are selected as high-k dielectrics, VO2 and ZnO serve as potential channel layer materials. The gate stack structures have been prepared using a reactive electron beam system and a plasma enhanced atomic layer deposition system. Three interrelated issues represent the central themes of the research: 1) the interface band alignment, 2) candidate high-k materials, and 3) band bending, internal electric fields, and charge transfer. 1) The most highlighted issue is the band alignment of specific high-k structures. Band alignment relationships were deduced by analysis of XPS and UPS spectra for three different structures: a) HfO2/VO2/SiO2/Si, b) HfO2-La2O3/ZnO/SiO2/Si, and c) HfO2/VO2/ HfO2/SiO2/Si. The valence band offset of HfO2/VO2, ZnO/SiO2 and HfO2/SiO2 are determined to be 3.4 ± 0.1, 1.5 ± 0.1, and 0.7 ± 0.1 eV. The valence band offset between HfO2-La2O3 and ZnO was almost negligible. Two band alignment models, the electron affinity model and the charge neutrality level model, are discussed. The results show the charge neutrality model is preferred to describe these structures. 2) High-k candidate materials were studied through comparison of pure Hf oxide, pure La oxide, and alloyed Hf-La oxide films. An issue with the application of pure HfO2 is crystallization which may increase the leakage current in gate stack structures. An issue with the application of pure La2O3 is the presence of carbon contamination in the film. Our study shows that the alloyed Hf-La oxide films exhibit an amorphous structure along with reduced carbon contamination. 3) Band bending and internal electric fields in the gate stack structure were observed by XPS and UPS and indicate the charge transfer during the growth and process. The oxygen plasma may induce excess oxygen species with negative charges, which could be removed by He plasma treatment. The final HfO2 capping layer deposition may reduce the internal potential inside the structures. The band structure was approaching to a flat band condition.
ContributorsZhu, Chiyu (Author) / Nemanich, Robert (Thesis advisor) / Chamberlin, Ralph (Committee member) / Chen, Tingyong (Committee member) / Ponce, Fernando (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
When examining the medical doctrines of previous empires, they reveal the influence of religion, societal attitudes, and the historical context that influenced the scholars that penned them. The advancements during the Islamic Golden age can be seen in the field of medicine, which had the Greco-Roman medical corpus as their foundation and the source of the theory of the four humors and anatomical beliefs. This paper will analyze the effect of cultural, societal, and historical influences on the medical doctrines of Muslim medieval physicians in the Golden Age and the works of the Roman physician Galen, and demonstrate how these effects result in similarities and differences in medical practice and the understanding of disease and anatomy. Due to translation efforts that were supported by religious views on the accumulation of knowledge and the efforts of the Abbasid empire, resultant acceptance of the theory of the four humors and anatomical doctrines is observed in the treatment and perception of disease, which would consist of this paper's focus on surgery, diet therapy and associations with nature. However, with further analysis of the extent of this acceptance and the findings in the Islamic medical doctrines, the differences in experimental methods, religious interpretations, and cultural attitudes shows a deviation from the Galenic tradition, with the second set of the paper's focus being human dissection, cause of disease, and experimentation. The purpose of this research is to demonstrate the impact of religion, societal attitudes, culture and the accepted paradigm on the practice of medicine and the study of anatomy, and what would cause a challenge against the legacy of Galen.
ContributorsAlzuhairi, Fatemah Saad (Author) / Vélez-Ibáñez, Carlos (Thesis director) / Smith, Brian (Committee member) / Historical, Philosophical & Religious Studies (Contributor) / Historical, Philosophical & Religious Studies, Sch (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Honey bee (Apis mellifera) colonies have experienced substantial losses due to colony collapse disorder (CCD) since the first officially reported cases in 2006. Many factors have been implicated in CCD, including pests, pathogens, malnutrition, and pesticide use, but no correlation has been found between a single factor and the occurrence of CCD. Fungicides have received less research attention compared to insecticides, despite the fact that fungicide application coincides with bloom and the presence of bees. Pristine fungicide is widely used in agriculture and is commonly found as a residue in hives. Several studies have concluded that Pristine can be used without harming bees, but reports of brood loss following Pristine application continue to surface across the country. The primary objectives of this study were to determine whether Pristine causes an aversive gustatory response in bees and whether consumption of an acute dose affects responsiveness to sucrose. An awareness of how foragers interact with contaminated food is useful to understand the likelihood that Pristine is ingested and how that may affect bees' ability to evaluate floral resources. Our results indicated that Pristine has no significant effect on gustatory response or sucrose responsiveness. There was no significant difference between bee responses to Pristine contaminated sucrose and sucrose alone, and no significant effect of Pristine on sucrose responsiveness. These results indicate that honey bees do not have a gustatory aversion to Pristine. A lack of aversion means that honey bees will continue collecting contaminated resources and dispersing them throughout the colony where it can affect brood and clean food stores.
ContributorsMcHugh, Cora Elizabeth (Co-author) / Jernigan, Christopher (Co-author, Committee member) / Burden, Christina (Co-author) / DeGrandi-Hoffman, Gloria (Co-author) / Smith, Brian (Thesis director) / Fewell, Jennifer (Committee member) / Barrett, The Honors College (Contributor) / School of Geographical Sciences and Urban Planning (Contributor) / School of Life Sciences (Contributor) / School of Art (Contributor)
Created2015-05
Description
This study illustrates the abilities of the honeybee, Apis mellifera, to learn and differentiate between patterns solely off their spatial frequencies. Patterns were chosen based off of calculations derived from the measurements of the physical construction of the apposition compound eye, which led to predictions of what the bees could theoretically see. The hypothesis was then that bees would have a visual threshold where patterns with spatial frequencies that fall below this line should be easily distinguishable, and patterns above the threshold would have scores that mimic if the bees made choices randomly. There were 9 patterns tested, all with different spatial frequencies and in the colors of black, white, and gray. The bees were tested on their learning and pattern differentiation abilities with 10 pattern comparisons, with the lower frequency of the two being associated with an unscented sucrose solution reward. The results were surprising in that the previous studies pointing towards this visual threshold were inaccurate because of some of the patterns being learning in an intermediate ability. These intermediate scores suggest that the calculations predicting what the bees could see clearly were slightly wrong because it was more likely that the bees saw those images in more of a blur, which resulted in their intermediate score. Honeybees have served as a useful model organisms over the decades with studying learning involving visual information. This study lacked in its total numbers of trials and bees tested, which could have led to incomplete results, and this showing of an intermediate score and ability. Future studies should continue in order to advance this understanding of a perceptually and cognitively advance processing animal.
ContributorsBalsino, Brandon Bartholomew (Author) / Harrison, Jon (Thesis director) / Smith, Brian (Committee member) / Duell, Meghan (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2015-12
Description
Selenium, a group 16 metalloid on the periodic table, is a necessary mineral for many organisms. Trace amounts of selenium are essential for normal development, antioxidant protein function, enzyme function, and hormone regulation (Burden et al., 2016). However, when selenium is found in toxic amounts in organisms, it has been found to substitute for sulfur in proteins, which can be toxic to these animals, and cause oxidative stress (Quinn et al., 2007). Using the previous research done with acute exposure to organic and inorganic selenium compounds, we hypothesized that the inorganic sodium selenate would significantly decrease learning and memory recall for both chronic and acute exposure. We also hypothesized that the consumption of organic methylseleno-L-cysteine by honey bees would decrease learning and memory recall for both the chronic and acute exposure. We further hypothesized that protein carbonyl content would be increased due to oxidative damage caused by selenium in both the sodium selenate and the methylseleno-L-cysteine treatment groups, but that the inorganic selenium compound would increase the carbonyl content more than the methylseleno-L-cysteine. To run the experiments, three tents outside had two colonies in each tent. One tent contained the sodium selenate group, another had the sucrose control, and one contained the methylseleno-L-cysteine group. The treatment groups were fed selenium in their sucrose feeders. The first part of the experiment was training the bees by using proboscis extension response (PER) to teach them to extend their proboscis to the rewarded odor and not to the unrewarded odor. This was done by pairing the rewarded odor with a sucrose reward and not pairing it with the unrewarded odor. Then their short-term and long-term memory recall was tested. The second part of the experiment was checking for oxidative damage by measuring the protein carbonyl content in the bees. Three boxes were set up with the same three treatment groups as used in the tents. The treatment group bees were exposed to selenium in the sucrose feeders and in the pollen patties. After one week, the living bees were removed and frozen. They were then homogenized to extract protein. The first assay run was the protein content assay to establish a standard protein concentration for samples. Then a protein carbonyl assay was run, to determine the protein carbonyl content. Overall, the experiment found that exposure to selenium negatively impacted honey bees learning and memory recall significantly. Chronic exposure to the inorganic selenate reduced the bees' long-term memory abilities to differentiate between odors. With methylseleno-L-cysteine, it had no significant effect for the chronic exposure, but for the acute exposure, it had a significant impairment on their abilities to distinguish between the rewarded and unrewarded odors during conditioning. Our results showed that from our experiment there appeared to be no significant effect of selenium exposure on the increase of carbonylation content in the different treatment groups. This is most likely due to the fact the carbonyl content was not detectable because the protein concentration was low in the samples (approximately 3.5 mg/mL).
ContributorsWinski, Alexandra (Co-author) / Winski, Brandon (Co-author) / Smith, Brian (Thesis director) / Harrison, Jon (Committee member) / Burden, Christina (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Water affinity and condensation on Si-based surfaces is investigated to address the problem of fogging on silicone intraocular lenses (IOL) during cataract surgery, using Si(100), silica (SiO2) and polydimethylsiloxane (PDMS) silicone (SiOC2H6)n. Condensation is described by two step nucleation and growth where roughness controls heterogeneous nucleation of droplets followed by Ostwald ripening. Wetting on hydrophilic surfaces consists of continuous aqueous films while hydrophobic surfaces exhibit fogging with discrete droplets. Si-based surfaces with wavelength above 200 nm exhibit fogging during condensation. Below 200 nm, surfaces are found to wet during condensation. Water affinity of Si-based surfaces is quantified via the surface free energy (SFE) using Sessile drop contact angle analysis, the Young-Dupré equation, and Van Oss theory. Topography is analyzed using tapping mode atomic force microscopy (TMAFM). Polymer adsorption and ion beam modification of materials (IBMM) can modify surface topography, composition, and SFE, and alter water affinity of the Si-based surfaces we studied. Wet adsorption of hydroxypropyl methylcellulose (HPMC) C32H60O19 with areal densities ranging from 1018 atom/cm2 to 1019 atom/cm2 characterized via Rutherford backscattering spectrometry (RBS), allows for the substrate to adopt the topography of the HPMC film and its hydrophilic properties. The HPMC surface composition maintains a bulk stoichiometric ratio as confirmed by 4.265 MeV 12C(α, α)12C and 3.045 MeV 16O(α, α)16O, and 2.8 MeV He++ elastic recoil detection (ERD) of hydrogen. Both PIXE and RBS methods give comparable areal density results of polymer films on Si(100), silica, and PDMS silicone substrates. The SFE and topography of PDMS silicone polymers used for IOLs can also be modified by IBMM. IBMM of HPMC cellulose occurs during IBA as well. Damage curves and ERD are shown to characterize surface desorption accurately during IBMM so that ion beam damage can be accounted for during analysis of polymer areal density and composition. IBMM of Si(100)-SiO2 ordered interfaces also induces changes of SFE, as ions disorder surface atoms. The SFE converges for all surfaces, hydrophobic and hydrophilic, as ions alter electrochemical properties of the surface via atomic and electronic displacements.
ContributorsXing, Qian (Author) / Herbots, Nicole (Thesis advisor) / Culbertson, Robert (Thesis advisor) / Chamberlin, Ralph (Committee member) / Treacy, Michael (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2011
Description
Fruit flies show a strong attraction to fruit odors. Most fruit odors, including strawberry scent, are complex multimolecular mixtures comprised of many chemically distinct constituents. How animals are able to process these mixtures and derive behaviorally relevant information is largely unknown. A new procedure was created to test odor preference for Heisenberg canton-s strain of Drosophila melanogaster. 30 flies were cold anesthetized at 4.2°C for 30 minutes and then placed in a testing arena. After acclimating for 45 minutes, the flies were exposed to two sources of air, one with ripe strawberry odor and one with only humidified air. Images were captured every minute for an hour and a preference index was calculated for every 10th image. The Drosophila had a positive average preference for the strawberry odor. Five out of six trials showed a general increase in odor preference over the course of the trial. While there was a generally positive trend for average preference over time, there was not a significant increase in average odor preference from time 1 to time 60. The data indicates that Drosophila show a preference for strawberry odor over humidified air, and we propose to extend this test to investigate how Drosophila process and react to complex odors and their chemical constituents.
ContributorsSteinmetz, Kyle J (Author) / Smith, Brian (Thesis director) / Jernigan, Chris (Committee member) / School of Life Sciences (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Recent data suggests that olfactory input is important for antennal lobe development in honey bees. Chronic association of a single odor to food resources during crucial stages of development results in delayed antennal lobe development for mature foraging bees. The antennal lobes of these bees instead closely resemble an immature network observed in young, newly emerged bees. Using an odor stimuli variance assay, learning and memory tests can be used to explore how well honey bees discriminate single odors within complex odor mixtures. Here we are validating two different odor mixtures, a Brassica rapa floral blend and a second replicate mixture composed of common molecularly dissimilar odors. Odors in each mixture are either held constant or varied in concentration over 16 conditioning trials. Subsequent memory tests are performed two hours later to observe the ability of bees to distinguish and recognize specific odor components in each mixture. So far in our assay we find high rates of generalization for both odor mixtures. In general, more bees responded to all odors in the replicate treatment group over the Brassica treatment group. Additionally, bees in the Brassica treatment group did not respond to the target odor. More data is being collected to validate this assay. In future studies, I propose to apply this behavioral assay to bees with an altered olfactory developmental in order to see the functional impacts of this chronic odor association treatment.
ContributorsHalby, Rachael (Author) / Smith, Brian (Thesis director) / Jernigan, Christopher (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05