Matching Items (156)
Description
Graphene is a very strong two-dimensional material with a lot of potential applications in microelectromechanical systems (MEMS). In this research, graphene is being optimized for use in a 5 m x 5 m graphene resonator. To work properly, this graphene resonator must have a uniform strain across all manufactured devices. To reduce strain induced in graphene sheets grown for use in these resonators, evaporated platinum has been used in this investigation due to its relatively lower surface roughness compared to copper films. The final goal is to have the layer of ultrathin platinum (<=200 nm) deposited on the MEMS graphene resonator and used to grow graphene directly onto the devices to remove the manual transfer step due to its inscalability. After growth, graphene is coated with polymer and the platinum is then etched. This investigation concentrated on the transfer process of graphene onto Si/SiO2 substrate from the platinum films. It was determined that the ideal platinum etchant was aqua regia at a volumetric ratio of 6:3:1 (H2O:HCl:HNO3). This concentration was dilute enough to preserve the polymer and graphene layer, but strong enough to etch within a day. Type and thickness of polymer support layers were also investigated. PMMA at a thickness of 200 nm was ideal because it was easy to remove with acetone and strong enough to support the graphene during the etch process. A reference growth recipe was used in this investigation, but now that the transfer has been demonstrated, growth can be optimized for even thinner films.
ContributorsCayll, David Richard (Author) / Tongay, Sefaattin (Thesis director) / Lee, Hyunglae (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
The devastating 2014 Ebola virus outbreak in Western Africa demonstrated the lack of therapeutic approaches available for the virus. Although monoclonal antibodies (mAb) and other molecules have been developed that bind the virus, no therapeutic has shown the efficacy needed for FDA approval. Here, a library of 50 peptide based ligands that bind the glycoprotein of the Zaire Ebola virus (GP) were developed. Using whole virus screening of vesicular stomatitis virus pseudotyped with GP, low affinity peptides were identified for ligand construction. In depth analysis showed that two of the peptide based molecules bound the Zaire GP with <100 nM KD. One of these two ligands was blocked by a known neutralizing mAb, 2G4, and showed cross-reactivity to the Sudan GP. This work presents ligands with promise for therapeutic applications across multiple variants of the Ebola virus.
ContributorsRabinowitz, Joshua Avraam (Author) / Diehnelt, Chris (Thesis director) / Johnston, Stephen (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Both technological and scientific fields continue to revolutionize in a similar fashion; however, a major difference is that high-tech corporations have found models to continue progressions while still keeping product costs low. The main objective was to identify which, if any, components of certain technological models could be used with the vaccine and pharmaceutical markets to significantly lower their costs. Smartphones and computers were the two main items investigated while the two main items from the scientific standpoint were vaccines and pharmaceuticals. One concept had the ability to conceivably decrease the costs of vaccines and drugs and that was "market competition". If the United States were able to allow competition within the vaccine and drug companies, it would allow for the product prices to be best affected. It would only take a few small companies to generate generic versions of the drugs and decrease the prices. It would force the larger competition to most likely decrease their prices. Furthermore, the PC companies use a cumulative density function (CDF) to effectively divide their price setting in each product cycle. It was predicted that if this CDF model were applied to the vaccine and drug markets, the prices would no longer have to be extreme. The corporations would be able to set the highest price for the wealthiest consumers and then slowly begin to decrease the costs for the middle and lower class. Unfortunately, the problem within the vaccine and pharmaceutical markets was not the lack of innovation or business models. The problem lied with their liberty to choose product costs due to poor U.S. government regulations.
ContributorsCalderon, Gerardo (Author) / Johnston, Stephen (Thesis director) / Diehnelt, Chris (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for use as a solid-state electrolyte due to its high ionic conductivity. The material exists in two dierent phases, one that is cubic in structure and one that is tetragonal. One potential synthesis method that results in LLZO in the more useful, cubic phase, is electrospinning, where a mat of nanowires is spun and then calcined into LLZO. A phase containing lanthanum zirconate (LZO) and amorphous lithium occursas an intermediate during the calcination process. LZO has been shown to be a sintering aid for LLZO, allowing for lower sintering temperatures. Here it is shown the eects of internal LZO on the sintered pellets. This is done by varying the 700C calcination time to transform diering amounts of LZO and LLZO in electrospun nanowires, and then using the same sintering parameters for each sample. X-ray diraction was used to get structural and compositional analysis of both the calcined powders and sintered pellets. Pellets formed from wires calcined at 1 hour or longer contained only LLZO even if the calcined powder had only undergone the rst phase transformation. The relative density of the pellet with no initial LLZO of 61.0% was higher than that of the pellet with no LZO, which had a relative density of 57.7%. This allows for the same, or slightly higher, quality material to be synthesized with a shorter amount of processing time.
ContributorsLondon, Nathan Harry (Author) / Chan, Candace (Thesis director) / Tongay, Sefaattin (Committee member) / Department of Physics (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
The fence between the US and Mexico had been and continues to be a controversial topic in both the U.S., Mexico and around the world. This study will look at the negative externalities related to the environment, society, and economy of the current fence on the border. The central question behind the thesis is whether or not the fence has a direct impact on the ecosystem and people around it.
ContributorsHoyt, Stephanie Alexis (Author) / Schoon, Michael (Thesis director) / Breetz, Hanna (Committee member) / School of Sustainability (Contributor) / School of Politics and Global Studies (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
ABSTRACT Peptide microarrays may prove to be a powerful tool for proteomics research and clinical diagnosis applications. Fodor et al. and Maurer et al. have shown proof-of-concept methods of light- and electrochemically-directed peptide microarray fabrication on glass and semiconductor microchips respectively. In this work, peptide microarray fabrication based on the abovementioned techniques were optimized. In addition, MALDI mass spectrometry based peptide synthesis characterization on semiconductor microchips was developed and novel applications of a CombiMatrix (CBMX) platform for electrochemically controlled synthesis were explored. We have investigated performance of 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) derivatives as photo-labile protecting group. Specifically, influence of substituents on 4 and 5 positions of phenyl ring of NPPOC group on the rate of photolysis and the yield of the amine was investigated. The results indicated that substituents capable of forming a π-network with the nitro group enhanced the rate of photolysis and yield. Once such properly substituted NPPOC groups were used, the rate of photolysis/yield depended on the nature of protected amino group indicating that a different chemical step during the photo-cleavage process became the rate limiting step. We also focused on electrochemically-directed parallel synthesis of high-density peptide microarrays using the CBMX technology referred to above which uses electrochemically generated acids to perform patterned chemistry. Several issues related to peptide synthesis on the CBMX platform were studied and optimized, with emphasis placed on the reactions of electro-generated acids during the deprotection step of peptide synthesis. We have developed a MALDI mass spectrometry based method to determine the chemical composition of microarray synthesis, directly on the feature. This method utilizes non-diffusional chemical cleavage from the surface, thereby making the chemical characterization of high-density microarray features simple, accurate, and amenable to high-throughput. CBMX Corp. has developed a microarray reader which is based on electro-chemical detection of redox chemical species. Several parameters of the instrument were studied and optimized and novel redox applications of peptide microarrays on CBMX platform were also investigated using the instrument. These include (i) a search of metal binding catalytic peptides to reduce overpotential associated with water oxidation reaction and (ii) an immobilization of peptide microarrays using electro-polymerized polypyrrole.
ContributorsKumar, Pallav (Author) / Woodbury, Neal (Thesis advisor) / Allen, James (Committee member) / Johnston, Stephen (Committee member) / Arizona State University (Publisher)
Created2013
Description
In the Rare-earth-Tri-telluride family, (RTe3s) [R=La, Ce, Nd, Sm, Gd, Tb, Dy, Er, Ho, Tm] the emergence of Charge Density Waves, (CDW) has been under investigation for a long time due to broadly tunable properties by either chemical substitution or pressure application. These quasi 2D Layered materials RTe3s undergo Fermi Surface Nesting leading to CDW instability. CDWs are electronic instabilities found in low-dimensional materials with highly anisotropic electronic structures. Since the CDW is predominantly driven by Fermi-surface (FS) nesting, it is especially sensitive to pressure-induced changes in the electronic structure. The FS of RTe3s is a function of p-orbitals of Tellurium atoms, which are arranged in two adjacent planes in the crystal structure. Although the FS and electronic structure possess a nearly four-fold symmetry, RTe3s form an incommensurate CDW.This dissertation is structured as follows: Chapter 1 includes basic ideas of Quantum materials, followed by an introduction to CDW and RTe3s. In Chapter 2, there are fundamentals of crystal growth by Chemical Vapor Transport, including various precursors, transport agent, temperature gradient, and rate of the reaction. After the growth, the crystals were confirmed for lattice vibrations by Raman, for composition by Energy Dispersive Spectroscopy; crystal structure and orientation were confirmed by X-ray Diffraction; magnetic ordering was established by Vibrating sample measurement. Detailed CDW study was done on various RTe3s by Raman spectroscopy. The basic mechanism and instrumentations used in these characterizations are explained in Chapter 3. Chapter 4 includes experimental data for crystal growth and results of these characterizations for Parent RTe3s. Chapter 5 includes fundamental insights on Cationic alloying of RTe3s, along with one alloy system’s crystal growth and characterization. This work tries to explain the behavior of CDW by a Temperature-dependent Raman study of RTe3s established the CDW transition temperature accompanied by Phonon softening; Angle-resolved Raman data confirming the nearly four-fold symmetry; thickness-dependent Raman spectroscopy resulting in the conclusion that as thickness decreases CDW transition temperature increases. Also, CDW transition is analyzed as a function of alloying.
ContributorsAttarde, Yashika (Author) / Tongay, Sefaattin (Thesis advisor) / Botana, Antia (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2021
Description
ABSTRACT Over the past several decades, the dilemma of free-roaming horses in the U.S. has proven to be one of the most divisive issues in management of public lands. According to federal land management agencies, without population regulation, horses can increase at the rate of 15-20% a year on arid rangelands with inadequate numbers of natural, large predators. Horses compete for valuable forage and water resources alongside cattle and native wildlife in delicate riparian areas highly susceptible to the negative ecological effects of soil compaction and overgrazing. Most U.S. management policies, therefore, call for increased removal of free-roaming horses as they are categorized as “un-authorized livestock” or "non-native" species. Wild horse advocates, however, continue to petition for improvement in animal welfare and expansion of the horses’ territory. With heightened social conflict spurred by animal rights and ecological concerns, not to mention the often-stark differences over what really “belongs” on the landscape, the success of appropriate management strategies hinges on managing agencies’ preparedness and ability to respond in a timely and inclusive manner. A critical element of the management context is the public’s views toward the wild horse and the science used to manage them. Synthesizing the vast literature in the history and philosophy of wildlife management in the American West, and utilizing an ethnographic and case study approach, my research examines the range of stakeholder concerns and analyzes the factors that have led to the disconnect between public values of wild horses and public policy for the management of the federally protected free-roaming horses in Arizona’s Apache-Sitgreaves National Forests.
ContributorsMurphree, Julie Joan (Author) / Minteer, Ben A. (Thesis advisor) / Schoon, Michael (Thesis advisor) / Bradshaw, Karen (Committee member) / Chew, Matthew (Committee member) / Arizona State University (Publisher)
Created2022
Description
In the last few decades, extensive research efforts have been focused on scaling down silicon-based complementary metal-oxide semiconductor (CMOS) technology to enable the continuation of Moore’s law. State-of-art CMOS includes fully depleted silicon-on-insulator (FDSOI) field-effect-transistors (FETs) with ultra-thin silicon channels (6 nm), as well as other three-dimensional (3D) device architectures like Fin-FETs, nanosheet FETs, etc. Significant research efforts have characterized these technologies towards various applications, and at different conditions including a wide range of temperatures from room temperature (300 K) down to cryogenic temperatures. Theoretical efforts have studied ultrascaled devices using Landauer theory to further understand their transport properties and predict their performance in the quasi-ballistic regime.Further scaling of CMOS devices requires the introduction of new semiconducting channel materials, as now established by the research community. Here, two-dimensional (2D) semiconductors have emerged as a promising candidate to replace silicon for next-generation ultrascaled CMOS devices. These emerging 2D semiconductors also have applications beyond CMOS, for example in novel memory, neuromorphic, and spintronic devices. Graphene is a promising candidate for spintronic devices due to its outstanding spin transport properties as evidenced by numerous studies in non-local lateral spin valve (LSV) geometries. The essential components of graphene-based LSV, such as graphene FETs, metal-graphene contacts, and tunneling barriers, were individually investigated as part of this doctoral dissertation.
In this work, several contributions were made to these CMOS and beyond CMOS technologies. This includes comprehensive characterization and modeling of FDSOI nanoscale FETs from room temperature down to cryogenic temperatures. Using Landauer theory for nanoscale transistors, FDSOI devices were analyzed and modeled under quasi-ballistic operation. This was extended towards a virtual-source modeling approach that accounts for temperature-dependent quasi-ballistic transport and back-gate biasing effects. Additionally, graphene devices with ultrathin high-k gate dielectrics were investigated towards FETs, non-volatile memory, and spintronic devices. New contributions were made relating to charge trapping effects and their impact on graphene device electrostatics (Dirac voltage shifts) and transport properties (impact on mobility and conductivity). This work also studied contact resistance and tunneling effects using transfer length method (TLM) graphene FET structures and magnetic tunneling junction (MTJ) towards graphene-based LSV.
ContributorsZhou, Guantong (Author) / Sanchez Esqueda, Ivan (Thesis advisor) / Vasileska, Dragica (Committee member) / Tongay, Sefaattin (Committee member) / Thornton, Trevor (Committee member) / Arizona State University (Publisher)
Created2023
Description
Communications around sustainability have been found to be incongruent with eliciting the transformative change required to address global climate change and its' repercussions. Recent research has been exploring storytelling in sustainability, specifically with an emphasis on reflexive and emancipatory methods. These methods encourage embracing and contextualizing complexity and intend to target entire cognitive hierarchies. This study explores the possibility of using emancipatory and reflexive storytelling as a tool to change attitudes pertaining to the Valley Metro Light Rail, an example of a complex sustainability mitigation effort. I explore this in four steps: 1) Conducted a pre-survey to gauge preexisting attitudes and predispositions; 2) Provided a narrative that uses storytelling methodologies of reflexivity and emancipation through a story about the light rail; 3) Conducted a post-survey to gauge attitude shift resulting from the narrative intervention; 4) Facilitated a focus group discussion to examine impact qualitatively. These steps intended to provide an answer to the question: How does emancipatory and reflexive storytelling impact affective, cognitive and conative attitudes regarding local alternative transportation? By using tripartite attitude model, qualitative and quantitative analysis this paper determines that reflexive and emancipatory storytelling impacts attitudinal structures. The impact is marginal in the survey response, though the shift indicated a narrowing of participant responses towards one another, indicative of participants subscribing to emancipation and reflexivity of their held attitudes. From the group discussion, it was evident from qualitative responses that participants engaged in emancipating themselves from their held attitudes and reflected upon them. In doing so they engaged in collaboration to make suggestions and suggest actions to help those with experiences that differed from their own. Though this research doesn’t provide conclusive evidence, it opens the door for future research to assess these methodologies as a tool to elicit shared values, beliefs and norms, which are necessary for collective action leading to transformative change in response to global climate change.
ContributorsSwanson, Jake Ryan (Author) / Roseland, Mark (Thesis advisor) / Larson, Kelli (Committee member) / Calhoun, Craig (Committee member) / Schoon, Michael (Committee member) / Arizona State University (Publisher)
Created2023