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Title: Silkworm silk - CNT composite fibers: fabrication, characterization and application in cell stimulation for tissue regeneration
Creator: Zheng, Shuyao
Date: 2019
Description: Silk fibroin, a structural protein of the Bombyx mori cocoons, is widely studied for biomedical applications because of its strong mechanical...
Show moreSilk fibroin, a structural protein of the Bombyx mori cocoons, is widely studied for biomedical applications because of its strong mechanical property, biocompatibility, low degradation rate and ease of processing. In this study, we incorporated functionalized CNT in silkworm silk proteins to generate biocomposite fibers by electrospinning. The electro-spun (E-spun) fibers were unidirectionally aligned with a diameter at the sub-micrometer scale, mimicking the locally oriented ECM proteins in native tissues. The addition of a minute amount of CNT not only reinforced the stability and the mechanical strength of the flexible scaffolds, but also rendered the fibers electrical conductivity to not only facilitate the E-spun fiber formation but also grant the fibers an additional functionality that can be utilized for cell stimulation. It is known that endogenous electric field is present in the human body at various locations and plays critical physiological roles through its effect on cell proliferation, migration and activation mediated by its interference with growth factor secretion and intracellular signaling pathways. Electrical stimulation (ES) has been widely investigated as a potential method to regulate cell functions for the treatment of a number of diseases. It has been reported that in dermal fibroblasts, ES induces the secretion of FGF-1 and FGF-2 which promotes cell proliferation, contraction, migration, and activation/differentiation into myofibroblasts for increased collagen synthesis in favor of tissue repair. In this work, the modulation effect of the aligned E-spun SWS-CNT fibers was examined by their application in inducing polarization and activation of fibroblasts with cellular deficit, like those from pelvic organ prolapse (POP) patients. These cells are characterized by low productivity of collagen with abnormally high COLI/COLIII ratio, leading to a loose and fragile collagen network, decreased integration among the tissue constituents and reduced tissue strength. Electrical stimulation boosted the collagen productivity by 20 folds in cells on silk-CNT than on pure silk due to silk-CNT’s high electrical conductivity. The developed approach can be potentially utilized to remedy the dysfunctional fibroblasts for therapeutic treatment of diseases and health conditions associated with collagen disorder.
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Title: Control Surface Synthesis of Propane Dehydrogenation Catalysts
Creator: Zhao, Yiqing
Date: 2019
Description: Alkane dehydrogenation is one of the primary chemical reactions to convert light alkanes into light olefins. The conversion of small alkanes...
Show moreAlkane dehydrogenation is one of the primary chemical reactions to convert light alkanes into light olefins. The conversion of small alkanes to alkenes by dehydrogenation reactions is important for polymer and chemical industrial process because it makes direct producing the possible alkenes. Controlled synthesis of single-site catalysts are still challenges. This makes tuning of the catalysts structure and active sites difficult. We developed method of Zirconium modified SiO2 to support single-site catalysts. My research is focusing on the synthesis new single-site heterogeneous catalysts for high selectivity alkane dehydrogenation reaction and the general principles to design better preformed catalysts (e.g., more active, more selective, more stable) for dehydrogenation reaction, especially on propane dehydrogenation. The study described in this thesis was conducted to understand how zirconium ions can modify the electronic properties and catalytic performance.In this study, with the Zr promoted cobalt catalysts show high propane conversion and propene selectivity compared to the previous reported Co/SiO2 catalyst by our group previous work. The Co/Zr/SiO2 material exhibited good catalytic activity, stability and high propylene selectivity which can reach up to 97% for catalytic propane dehydrogenation at 550 ℃. The catalyst was characterized by TEM, STEM, EPR, DRIFTS, UV-vis, XANES and EXAFS for synthesized material, under reaction conditions and post reaction samples. We hypothesized the reason behind is due to the π donation of Zr will lead to ease of heterolytic cleavage of the propane by have a lower metal-oxygen bond dissociation energy in the rate-determining step which is consistent with the previous calculations found that weaker catalyst-oxygen bonds led to facile heterolytic cleavage. A varieties of single-site Ga catalysts supported on Zr modified SiO2 were synthesized by different methods. The Ga/Zr/SiO2 catalysts prepared by the difference method also exhibit higher or similar activity and selectivity. Those catalysts have more isolated active sites show that rational catalyst design method, such as surface organometallic chemistry synthesize, can be applied in heterogeneous systems using homogeneous catalyst design method. But the origin of those effects is unclear, some discussion of possible origins of observation of catalysts behavior are discussed in Chapter 4. And we will do more characterization to find the origins behind.
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Title: Nanopore Detection of Heavy Metal Ions
Creator: MohammadiRoozbahani, Golbarg
Date: 2019
Description: Nanopore sensing is an emerging analytical technique for measuring single molecules. Under an applied potential bias, analyte molecules are...
Show moreNanopore sensing is an emerging analytical technique for measuring single molecules. Under an applied potential bias, analyte molecules are transported through the nanopore and cause ionic current modulations. Accordingly, the fingerprint of the analyte is reflected in the signature of the current blockage events. Due to its advantages such as lable-free and multi-analyte detection, nanopore sensing technology has been utilized as an attractive versatile tool to study a variety of topics, including biosensing of different species, such as DNA, RNA, proteins, peptides, anions, and metal ions.Metal ions play a crucial role in human health and environmental safety. Although metal ions are essential for numerous biological processes, the presence of the wrong metal, or even the essential metals in the wrong concentration or location, can lead to undesirable results and serious health concerns, including antibiotic resistance, metabolic disorders, mental retardation, and even cancer. Therefore, it is still of prime importance to develop highly sensitive and selective sensors for metal ions.In this dissertation, various nanopore sensing strategies to detect metal ions will first be discussed. These include: a) construction of metal ion binding sites in the nanopore inner surface; b) utilization of a biomolecule as a ligand probe; and c) employing enzymatic reactions. Then, three projects will be summarized. Among them, two projects are involved with detection of non-essential metal ions: uranyl and thorium ions, while the other is targeted at essential element, zinc ion. To be more specific, uranyl and thorium ions are detected by taking advantage of peptide molecules as ligand probes. In this case, the event signatures of peptide molecules in the nanopore are significantly different in the absence and presence of metal ions, which might be attributed to the conformational change of the biomolecules induced by the metal ion-biomolecule interaction. On the other hand, zinc ion is detected based on enzymatic reaction: without Zn2+, ADAM17 (a zinc dependent protease) is inactive and cannot cleave peptide substrate molecules; in contrast, with Zn2+ ion in the solution, the enzyme was activated, and its cleavage of the peptide substrate produced new types of blockage events with smaller residence time and amplitude values than those the peptide substrate.
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Title: HETEROGENEOUS CATALYST FOR ALKANE DEHYDYGENATION AND IMPLEMENTING TO SOLID OXIDE FUEL CELL
Creator: Xu, Yunjie
Date: 2019
Description: In the past decade, shale gas has become the most import source of natural gas in the United States. Large amounts of light alkanes in shale...
Show moreIn the past decade, shale gas has become the most import source of natural gas in the United States. Large amounts of light alkanes in shale gas, such as methane, ethane, and propane are available as an industrial source of chemicals through the catalyzed, on-purpose light alkane dehydrogenation to olefins. Therefore, it is obvious there is a benefit to developing catalysts to directly convert shale gas to olefins. However, alkane dehydrogenation and non-oxidative methane coupling are thermodynamically unfavorable reactions at low temperatures. The energy requirements make these reactions less attractive for shale gas utilization. In principle, consuming the hydrogen product with a fuel cell can drive the thermodynamically unfavorable reaction by reducing the hydrogen partial pressure in the anode and by heat generating by the fuel cell, while also generating electricity in the process. Moreover, catalyst integration with fuel cell can facilitate the transfer of charge in anode which is rate determine step in the fuel cell. This thesis will focus on catalyst development for alkane dehydrogenation and exploring a way to integrate these catalysts with fuel cells.Chapters 2, 3 and 4 focus on designing, characterizing, and studying catalysts for non-oxidative coupling of methane (NOCM) and propane dehydrogenation (PDH). PtM (M is a transition metal) alloys were found to efficiently decrease the desorption energy of olefin products and avoid deeper C-H bond activation compared to metallic Pt. Based on the previous study of single cobalt on silica, a novel synthesis of PtCo3 was developed to further increase the activity of the PDH reaction. The Pt bimetallic catalyst made by novel synthesis route was proven to be one of several types of alloy. It was observed that extremely high conversion of PDH and high selectivity of target olefin were catalyzed by PtCo3/SiO2. Ga, as another promotor to replace Co, was also investigated. As expected, PtGa3 alloy was formed by a similar synthesis, and it showed extraordinary stability and activity for propane dehydrogenation. A Mo-Pt dual-metal catalyst was found to catalyze methane coupling even though Pt-Mo bimetallic alloys do not form. We hypothesize that Pt catalyzed C-H bond cleavage of CH4 to form methyl radical, and a MoOC species, formed by MoO3 reacting with CH4, could effectively facilitate methyl radical coupling to form larger alkanes and alkenes. Pt-Mo dual-metal catalyst had higher catalytic activity for methane coupling than a physical mixture of Pt and Mo and genuine PtMo alloy. Chapter 5 details our efforts to transplant PtM catalysts from silica support to target fuel cell material--(La,Sr)(Cr,Fe)O3 as a support. Different catalyst structures were observed, and, in this case, second transition metals become a barrier to prevent Pt aggregation. When using propane as fuel for fuel cell, we observed electrochemical redox reactions occurred via electrochemical analysis. However, the resistance of cell is comparatively high and limited overall system performance. Chapter 6 details a study of the impact of the electrode oxide phase on overall cell performance. In this case, we conducted a fundamental study of degradation of cathode material, (La,Sr)(Co,Fe)O3. We found that raw material and cells can degrade even under room temperature. Thus, the storage of raw powder and fabricated cells is critical for performance studies. This also indicates that our high cell resistance in previous electrochemical measurements could come from the insulating compound formation during storage. Some directions for future research on catalyst integration and electrochemical testing are outlined.
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Title: Novel Chelating Agents for Positron Emission Tomography Imaging and Theranostic Applications
Creator: Zhang, Shuyuan
Date: 2022
Description: Positron emission tomography (PET) is a molecular imaging technology that can be used to detect various diseases including cancer. Zirconium...
Show morePositron emission tomography (PET) is a molecular imaging technology that can be used to detect various diseases including cancer. Zirconium-89 (t1/2 = 78.4 h) is one of the positron-emitting radionuclides that has been widely explored for PET imaging because its half-life matches the long biological half-life of antibody. Research efforts have been devoted to the development of chelation chemistry for 89Zr, a bone-seeking radionuclide. Deferoxamine (DFO) is the most frequently used chelator for 89Zr in both clinical and preclinical trials. DFO can rapidly sequester 89Zr to form 89Zr-DFO complex. However, DFO is not an ideal ligand for 89Zr because 89Zr-labeled DFO-antibody conjugate showed high bone uptake in mice. We wanted to develop novel small molecule donors and novel chelators for 89Zr. We discovered N-methyl-N-(pyridin-2-yl)hydroxylamine (Py-HA) and 2,6-bis(N-methylhydroxylamino)pyridine (Py-BHA) as small molecule donors for 89Zr. Based on the new small molecule donors (Py-HA and Py-BHA), we have designed and synthesized a series of novel macrocyclic chelators containing TACN (1,4,7-triazacyclononane), CYCLEN (1,4,7,10-tetraazacyclododecane), and a diaza-crown ether backbone for 89Zr-based PET imaging applications. Moreover, bifunctional chelators (BFCs) structured on TACN and diaza-18-crown-6 were synthesized for conjugation to antibody. Theranostics contains a diagnostic agent and a therapeutic drug that can be used for simultaneous therapy and imaging of diseases. Radiotheranostics includes radiometal complexes for both therapy and imaging. 177Lu is a promising radiotheranostic metal because it can emit gamma radiation for single photon emission computed tomography (SPECT) imaging and emit β radiation for radiotherapy. A radioisotope pair with complementary emission such as 64Cu/67Cu and 86Y/90Y, can be used for PET imaging and radiotherapy. In this study, we synthesized nonfunctional TACN and diaza crown ether-backboned chelators containing different donor groups for 177Lu, 64Cu/67Cu, and 86Y/90Y. Finally, two bifunctional chelators were synthesized for coupling with hydroxamic acid-based small molecule as a potential histone deacetylase (HDAC) inhibitor to generate a small molecule ligand-chelator conjugate (SMLC) for theranostic applications.
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Title: Investigation of Novel Solid Polymer Electrolytes and Lithium Salts for Rechargeable Lithium Batteries
Creator: Zhao, Wendy
Date: 2021
Description: Lithium-ion batteries (LIBs) are extensively used in many consumer electronic products. LIBs have great potential for application in electric...
Show moreLithium-ion batteries (LIBs) are extensively used in many consumer electronic products. LIBs have great potential for application in electric vehicles by virtue of their high power density and charge cycles. Research and development in this area has been focused on all around the globe. The major challenges include high cost, safety issues of the solvent based electrolytes, and low conductivities at ambient temperature of the solid polymer electrolytes (SPEs).This dissertation describes four novel electrolyte systems and a series of low lattice energy lithium salts synthesized and characterized for applications in LIBs. First, a new SPE has been derived from oligomeric poly(ethylene oxide) (PEO)-grafted crosslinked polystyrene (XPS) microspheres containing 1-2 lithium sulfonate moieties. This SPE possesses amorphous character with a glass transition temperature (Tg) around 135 ºC, displayed a good electrochemical stability with excellent ionic conductivity in excess of 10^-4 S/cm at 25ºC, and no significant thermal decomposition until 420 ºC. Second, a hybrid composite polymer electrolyte (CPE) was constructed with a gel matrix formed through hydrogen bonding by incorporating nanoparticles of fumed silica into the nanoscale network of PEO-XPS. Fumed silica with large surface modification group like polysiloxane formed an ideal gel structure offering significant high mechanical strength above 10^4 Pa, and a good ionic conductivity at 25°C. Third, a nonvolatile x-linked gel membrane electrolyte was synthesized with amino methacrylate, to introduce hemi-labile ligands as ionic liquid, into the polymer network. This new material exhibited improved salt solubility and ionic conductivity, due to the fast ligand exchange that facilitates the lithium ion structural transport, and also displayed an excellent electrochemical stability(4.8 V vs, Li/Li+). Fourth, a self-healing and thermal reversible polymer electrolyte designed based on Diels-Alder conjugation between multi-maleimides (2M-3M) and multi-furans (2F-4F) was synthesized. The reversible x-linking was realized through Diels-Alder (DA) and Retro-DA reactions by applying heating (>130°C)/cooling (<90°C) cycles. Last, new lithium salts with star and branch structures containing 1-4 of imide or methide moieties were synthesized and evaluated in PEO electrolyte system. These salts demonstrated good ambient temperature ionic conductivity at low concentrations, and the electrochemical stabilities were equal to or better than the most commonly used lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Synthesis and characterization, including electrochemical properties, thermal and electrochemical stabilities, mechanical behaviors and surface morphologies of these new materials are described and discussed.
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Title: Organo-Functionalized Polyoxometalates
Creator: Alsaleh, Musaed Riyadh A
Date: 2023
Description: Polyoxometalates (POM) or transition metal oxide clusters are a sub-class of metal oxide-based materials of contemporary interest. POMs are...
Show morePolyoxometalates (POM) or transition metal oxide clusters are a sub-class of metal oxide-based materials of contemporary interest. POMs are molecular systems which contain highly symmetrical structures and are characteristics of group 5 and 6 metals, especially V, Mo, and W. Typical POM clusters have nuclearities ranging from 6 to 18 metal centers and are purely inorganic in their compositions. POMs can act as multielectron redox systems, while retaining their robust oxometallic framework structure. POMs have been receiving increasing attention, in part due to their potential as redox active materials for applications in various areas and their suitability as attractive molecular building units for making new functional materials of desirable properties and functions.In recent years, there has been a growing interest in the functionalization of polyoxometalates with organic moieties to synthesize organo-functionalized POMs. During the course of the work described in this thesis, we explored the synthesis of organo-functionalized polyoxometalates with special interest in polyoxovanadates incorporating heterometal center(s) in addition to vanadium in the structure. The focus of the work was on low nuclearity POMs. The thesis describes the synthesis and full characterization of a new organo-functionalized polyoxovanadate cluster - [(n-C4H9)4N]2[V6O13{(OCH2)3C (CH2CH3)}2]. The cluster compound has been characterized by a series of analytical techniques- FT-IR, Thermo Gravimetric Analysis, Bond Valence Sum calculations and complete single X-ray diffraction structure analysis. The hexavanadate cluster features {V6O19} oxometallate core composed of six edge sharing {VO6} octahedra defined by five bridging oxygen atoms and a terminal {V=Ot} oxo group. The {V6O19} oxometallic core of the cluster adopts the Lindqvist structure incorporating two 1,1,1-tris(hydroxymethyl)propane organic ligands. Six of the oxygens in the {V6O19} core come from the three alkoxy groups from two organic ligands. To the best of our knowledge, this organo-functionalized POM cluster has not been reported in the literature previously.
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Title: Critical Understanding of Multi-Mode Luminescence Properties of Eu3+ Doped LaAlO3
Creator: Alolayan, Abdulelah Abdulaziz H
Date: 2023
Description: Fluorescent anti-counterfeit materials with multi-luminescent modes under different external excitation sources are always advantageous over...
Show moreFluorescent anti-counterfeit materials with multi-luminescent modes under different external excitation sources are always advantageous over the conventional anti-counterfeit techniques. In the present thesis, our aim is to develop efficient Eu3+ doped LaAlO3 phosphor materials with different modes of luminescence properties such as down conversion-luminescence (DCL), persistent-luminescence (PersL), and optically stimulated luminescence (OSL), Thermo-luminescence (TL), radioluminescence (RL) Although, there are many reports on persistent-luminescence and optically stimulated luminescence based on Eu3+ doped matrices but the red persistent luminescence of Eu3+ ion on those matrices is not very long and the OSL intensities are also low. Herein, we report a long red persistent luminescence which lasted for 17 hrs. and the OSL intensity is very high. Furthermore, we have observed that the OSL property can be achieved even after 35 days of UV excitation and indicating its potential application for optical storage phosphor. From carrying out TSL studies we have found that three different types of traps namely Trap 1, Trap 2 and Trap 3 with trap depth 0.63 eV, 0.82 eV, 1.02 eV respectively are responsible for the persistent and OSL properties. It has been concluded that Trap 1 is mostly responsible for the persistent luminescence in short term while Trap 2 and Trap 3 are responsible for intermediate and long persistent luminescence. Further, Trap 2 and Trap 3 were also found to be present even after 35 days and responsible for the OSL properties. Anti-counterfeiting PersL composite has been developed in which AC real-life application is demonstrated.
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Title: AN EXPLORATION INTO THE EFFECTS OF CHROMATIN STRUCTURAL PROTEINS ON THE DYNAMICS AND ENERGETIC LANDSCAPE OF NUCLEOSOME ARCHITECTURES
Creator: Woods, Dustin C
Date: 2022
Description: Comprised of eight core histones wrapped around at least 147 base pairs of DNA, nucleosomes are the fundamental unit the chromatin fiber from...
Show moreComprised of eight core histones wrapped around at least 147 base pairs of DNA, nucleosomes are the fundamental unit the chromatin fiber from which long arrays are built to compact genetic information into the cell nucleus. Structural proteins, such as linker histones (LH) and centromere proteins (CENP), interact with the DNA to dictate the exact architecture of the fiber which can directly influence the regulation of epigentic processes. However, the mechanisms by which structural proteins affect these processes are poorly understood. In this thesis, I will explore the various way in which LHs and CENP-N affect nucleosome and, by extension, chromatin fiber dynamics. First, I present a series of simulations of nucleosomes bound to LHs, otherwise known as chromatosomes, with the globular domain of two LH variants, generic H1 (genGH1) and H1.0 (GH1.0), to determine how their differences influence chromatosome structures, energetics and dynamics. These simulations highlight the thermodynamic basis for different LH binding motifs, and details their physical and chemical effects on chromatosomes. Second, I examine how well the findings above translate from mono-nucleosomes to poly-nucleosome arrays. I present a series of molecular dynamics simulations of octa-nucleosome arrays, based on a cryo-EMstructure of the 30-nm chromatin fiber, with and without the globular domains of the H1 LH to determine how they influence fiber structures and dynamics. These simulations highlight the effects of LH binding on the internal dynamics and global structure of poly- nucleosome arrays, while providing physical insight into a mechanism of chromatin compaction. Third, I took a brief departure from LHs to study the effects that the centromere protein N (CENP-N) has on the poly-nucleosome systems. I present a series of molecular dynamics simulations of CENP-N and di-nucleosome complexes based on cryo- EM and crystal structures provided by Keda Zhou and Karolin Luger. Simulations were conducted with nucleosomes in complex with one, two, and no CENP-Ns. This work, in collaboration with the Karolin Luger Group (University of Colorado – Boulder) and the Aaron Straight Group (Stanford University), represents the first atomistic simulations of this novel complex, providing the foundation for a plethora of future research opportunities exploring centromeric chromatin the effect that its structure and dynamics have on epigenetics. Lastly, I return to the chromatosome to study how DNA sequence affects the free energy surface and detailed mechanism of LH transitions between binding modes. I used umbrella sampling simulations to produce PMFs of chromatosomes wrapped in three different DNA sequences: Widom 601, poly-AT, and poly-CG. This work, my final in the series, represents a culmination of my studies furthering the understanding of biophysical phenomena surrounding LHs and how they can be extrapolated towards epigentic mechanisms. I was able to report on the first PMFs illustrating a previously unknown transition and describe the transition mechanism as it depends on DNA sequence.
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Title: Synthesis and Photophysical Characterization of Novel Aromatic Triplet Dyes for Photodynamic Therapy Applications
Creator: Morgan, Jayla A
Date: 2022
Description: Photodynamic therapy is a biomedical approach to treating specific types of cancerous tumor cells and harmful bacteria. The core principle of...
Show morePhotodynamic therapy is a biomedical approach to treating specific types of cancerous tumor cells and harmful bacteria. The core principle of photodynamic therapy involves the usage of a photosensitizer, which is an agent with the capability of transforming molecular, triplet state oxygen, into a reactive oxygen species upon a reaction with near-infrared (NIR) light. The reactive oxygen species has been demonstrated to cause apoptosis among harmful cells without damaging cancer free cells. The effectiveness of photodynamic is highly dependent upon the identity of the photosensitizer; a powerful and efficient photosensitizer should be non-toxic, exhibit high light absorption capabilities, and should produce large amounts of the reactive oxygen species. A novel chromophore bis-iodo-dipyrrolonaphthyridine-dione was demonstrated to have all vital characteristics of an ideal photosensitizer, however produced low amounts of the reactive oxygen species of interest due to the chemical instability of a carbon-halogen bond present in the molecule. Various subsequent halogenations (bis-bromo and bis-chloro) completed in order to remedy this instability revealed specific regioselectivity in regards to the dipyrrolonaphthyridinedione parent that are exhibited upon substituents effects by the substrate, electronic effects exhibited by the reagents of interest, and overall photophysical characterization of the molecules.
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Title: SYNTHESIS AND APPLICATION OF ORGANOMETALLIC PRECURSORS FOR TUNGSTEN AND MOLYBDENUM SULFIDE
Creator: Liu, Bo
Date: 2021
Description: Transition metal chalcogenides (TMCs) have unique properties. They are promising materials for the next generation electrical devices due to...
Show moreTransition metal chalcogenides (TMCs) have unique properties. They are promising materials for the next generation electrical devices due to their suitable band gap, outstanding electron mobility, and controllable atomic thickness. In the last few decades, atomic layer deposition (ALD) has been one of the hottest research frontiers for the fabrication of TMCs films. Signification progress has been made on the varieties of material grown by ALD and the improvement of ALD equipment. However, the fast-evolving microelectronic industry set higher requirements for the ALD application. In the potential electronic fabrication process, low-temperature preparation and non-corrosive procedure are critical for the advanced device architecture. Thus the novel precursor development and the investigation of reaction mechanism are necessary. In addition, as the comprehensive research of film deposition, the prevailing crystallographic defects on the as-prepared films are another appealing thing for us to think about and try to eliminate for better film quality. Therefore, this dissertation will describe the precursor ligand design and its effect on the morphology, the development of W/Mo precursors for tungsten/molybdenum disulfide, and the defect passivation of tungsten diselenide films.In chapter 2, a series of heteroleptic tungsten precursors of tetrathiotungstates (WS42-) were prepared through the facile ligand transfer method. Ligand variation has a significant effect on the crystallinity of the resulting tetrathiotungstate products. Crystalline tetrathiotungstates with preferred orientation were prepared from the reaction of synthesized precursors with H2S at room temperature. Results indicated the morphologies and crystallinities of the tetrathiotungstates can be well controlled by their ligand behaviors which give us a better understanding of the growth mechanism. Chapters 3 and 4 focus on the development of W and Mo precursors for W/Mo disulfide and their performance in wet chemistry reactions and ALD. WS2 can be synthesized at the ambient temperature in solution by the non-redox reaction. WS2 film growth can be achieved at the exciting low temperature of 125°C by ALD. Based on the performance of the tungsten precursor, a new molybdenum dimer precursor with improved reactivity was synthesized, and MoSx can be prepared at the ambient temperature in seconds. X-ray absorption spectroscopy (XAS) was also utilized to investigate the interaction between the organometallic precursor and the SiO2 surface. Chapter 5 will focus on the defect passivation of WSe2 films for the improvement of their electrical performance. Precursors were synthesized, and the wet chemistry method was designed for oxidation removal and vacancy healing. Raman spectroscopy was used as the express characterization method to reveal the treatment results. A promising healing reagent was screened out, and the repaired films were fabricated to field-effect transistors (FETs) for electrical measurements. The final results showed the electrical performance of the WSe2 films was improved after the convenient chemical treatment.
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Title: ORGANOFUNCTIONALIZED OXOMETALATES: SYNTHESIS, STRUCTURE, AND PROPERTIES OF A NEW CLASS OF MIXED-METAL TETRAMETALATE CLUSTERS
Creator: Shuaib, Damola Taye
Date: 2022
Description: Oxometalates (OMs) are metal-oxide clusters with addenda mental atom mainly V, Mo, and W and bridged by oxide anions. Prototypical examples...
Show moreOxometalates (OMs) are metal-oxide clusters with addenda mental atom mainly V, Mo, and W and bridged by oxide anions. Prototypical examples like polyoxometalates (POMs) are completely inorganic. While clusters with nuclearities ranging from 6 to 18 are common for purely inorganic examples, those with less than nuclearity 6 are rare. Therefore, functionalization by covalent interaction with organic moiety via self-assembly has been utilized as a viable route for making compact clusters with nuclearity of 4 and below. These compounds constitute the organo-functionalized examples of the purely inorganic structure ([XMaOb]n-) POM. Reports of organo-functionalized tetrametalates (TMs), ([MxOyLz])n- (where M = metal, x = 4 and L represents an organic ligand) are sparse. Mixed metal species are especially interesting as potential redox active materials as they contain energetically distinct potential redox centers. OMs have ability to accept electrons in a chemically reversible manner through the terminal oxo-ligand (M=Ot) leading to dπ–pπ electron transfer. Considering the rich structural and electronic properties of these complexes, four neutral mixed-metal (M-V) tetrametalate clusters, [(CoIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2}2] (1), [(ZnIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2}2] (2), [CoII2(VIVOF)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (3), and [ZnII2(VIVOF)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (4) containing unprecedented oxometallocyclic {M2V2X2N4O8}(M = Co, Zn; X = F, Cl) frameworks decorated with diethanolamine ligand in bidentate and tridentate manners. The type of halo-ligand has direct influence on the geometry of the metal M and UV-Vis reflectance spectra revealed changes in electronic structure consistent with charge transfer processes expected. Computational and magnetic properties studies revealed that the ground state multiplicity of 1 is confirmed as an open-shell singlet with a prediction of an isotropic exchange coupling of -6.6 cm-1 but less clear for 2. The vanadium centers are best described as a V(IV) center and the cobalt centers are high-spin Co(II) centers. Less orbital destabilization was observed due to weaker interaction of Cl- ligand on Co than what was observed for O2- ligand on V centers. In 2, there are four weakly coupled spin centers, where the isotropic exchange couplings are defined as J1, J2’, and J2’’. These couplings are approximated as J1 = 1.5/+11.7 cm-1, J2’ = -22.1/-14.8 cm-1, and J2’’ = +4.2/+4.8 cm-1. Although J2’’ is predicted to be weakly ferromagnetic in nature, whereas the fit suggested a weak antiferromagnetic interaction for each of the V(IV)-Co(II) couplings. The low-temperature magnetic susceptibility suggests a Type III spin frustration present in the system. However, competing magnetic interactions are known to be operative in tetranuclear system which is even observed to be more prominent in the mixed-metal tetranuclear system considering the edge-sharing consequence on magnetic behavior. A new route to metal complex synthesis via in situ ligand transformation from diethanolamine to bicine by disproportionation and oxidation reactions yielded three isostructural mononuclear clusters Bis[N,N-bis(2-hydroxyethyl)glycinato]-Cobalt(II) 5, Bis[N,N-bis(2-hydroxyethyl)glycinato]-Nickel(II) 6, and Bis[N,N-bis(2-hydroxyethyl)glycinato]-Copper(II) 7. The observed transformation is predicted to proceed through nucleophilic substitution (SN2) as expected for substituted ammines. These metal complexes are characterized by various analytical techniques such as, FT-IR and UV-Vis spectroscopies, single crystal and powdered X-ray diffraction analyses, Energy-Dispersed X-ray spectroscopy, magnetic properties measurements, thermal gravimetric analysis, bond valence sum calculations etc. Based on their features and detailed structure-property-application analyses, the clusters showed great potentials for catalysis, materials for digital tools, chemical sensing, molecular magnets and precursors as molecular building blocks for extended open frameworks.
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Title: ELECTROSPUN SILKWORM SILK FIBROIN - INDOCYANINE GREEN BIOCOMPOSITE FIBERS: FABRICATION, CHARACTERIZATION AND APPLICATION TOWARDS HEMORRHAGE CONTROL
Creator: Siddiqua, Ayesha
Date: 2022
Description: Silk fibroin (SF), a structural protein found in the Bombyx mori cocoons has gained attention in several biomedical applications as tissue...
Show moreSilk fibroin (SF), a structural protein found in the Bombyx mori cocoons has gained attention in several biomedical applications as tissue engineering scaffolds and wound dressings owing to its properties such as biocompatibility, water vapor permeability and biodegradability. Indocyanine Green (ICG) is an FDA approved tricarbocyanine dye used in medical diagnostics due to its unique photothermal and fluorescent properties. Electrospinning is a highly efficient, easy, and inexpensive technique used to generate nanometer to micrometer thick fibers. In this study, SF and ICG were co-spun to generate flexible microfibers with high surface area to volume ratios. Pure silk, SF-ICG (0.1%) and SF-ICG (0.4%) were chosen for the purpose of this study. Since, as-spun fibers are unstable in aqueous solutions, post treatment methods were explored to enhance the durability of the fibers and to minimize ICG leaching. It was found that ethanol vapor treatment (EVT) not only induced β-sheet formation in SF but also improved the SF-ICG interaction thereby reducing ICG leaching from the composite fibers. Ethanol vapor treated SF-ICG fibers showed less ICG leaching than liquid ethanol treated (LET) SF-ICG fibers indicating the efficacy of the EVT. The increase in SF solution viscosity with ICG concentration suggested a strong silk-ICG interaction which was further confirmed by DSC. The 1h water uptake and the three-day mass loss experiments indicated that the fibers are stable and highly absorbent material. Heat evolution was evaluated by measuring the temperature change in water of a fixed volume after irradiation with a 500 mW, 808 nm diode laser. The heat evolved by the flat fiber scaffolds was higher than the 3D fiber balls, indicating improved light penetration in the former. Pure silk produced negligible heat and it was used as a control. With 14.9 W/cm2 irradiation, the post-treated SF-ICG (0.4%) 3D fibrous ball of 2-3 mg dry weight, solidified a drop of bovine blood in 40 s. In contrast, a single layer fiber matrix required 3 min. to achieve the same clotting effect. Fibers folded into flat scaffolds were able to solidify a blood drop in 25 s. Pure silk fibers in all the cases showed negligible change after irradiation. The results suggest that a larger contact area of fibers is desirable for faster blood clotting, and EVT prompted better ICG retention in SF fibers. Based on the above results, SF-ICG (0.4%) fibers were utilized in a device developed to mimic blood flowing at a rate of 0.5 mL/h through a damaged blood vessel. It was found that irradiation of SF-ICG locally placed at the “damage” region effectively stopped “bleeding” whereas irradiated pure silk was unable to control the blood flow, which demonstrated the success of our SF-ICG fibers towards hemorrhage control.
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Title: Stimulation-Responsive Materials for the Treatment of Disordered Tissues
Creator: Clutter II, Elwin Dean
Date: 2022
Description: Microenvironments offer physical and chemical cues to cells that affect their behavior. These cues can be bioactive chemicals such as drugs...
Show moreMicroenvironments offer physical and chemical cues to cells that affect their behavior. These cues can be bioactive chemicals such as drugs and cytokines, matrix cues like stiffness and composition, and electrical signals as seen in membrane potentials and epithelial wound healing. Controlling these cues can drive cell behavior toward apoptosis, proliferation, or changes in protein expression. In this thesis research, three components were used to model changes in cell behavior: the near infrared dye indocyanine green (ICG), silk fibroin (SF) from Bombyx mori silkworm cocoons, and carbon nanotubes (CNT). The mechanism of ICG photobleaching was studied for the efficacy to kill neuroblastoma cancer cells. ICG was twice as effective at killing neuroblastoma than fibroblast cells. Albumin stabilized monomeric ICG to enhance photobleaching by improving light interaction, and photodegradation of ICG into α,β-unsaturated aldehydes led to significant reduction of proliferation in neuroblastoma cells by targeting cell signaling components such as protein transcription factors. SF-ICG composite materials were developed into films and electrospun fibers. These composite materials were examined as light-activated wound coverings to control bleeding in hemorrhage, using ICG’s photothermal effect. ICG added an absorbance peak to SF at 805 nm. Irradiation decreased this peak, produced a new absorbance peak at 352 nm, and an increased fluorescence peak around 490 nm, showing photochemical changes that may be useful in sensor design. Increased heat production from irradiation of SF-ICG occurred in the films with 0.2% w/w ICG in SF during 1 min irradiation, whereas SF-ICG fibers required improvement of processing by ethanol vapor treatment (EVT) to reduce loss of ICG during preparation. EVT improved ICG retention in SF fibers during sterilization with 70% ethanol solution thus improving heat generation in the SF-ICG fibers. Heat evolved from SF-ICG 0.2% film solidified bovine blood within 42 s, with visible changes after the first 6 s. SF electrospun fibers were investigated to optimize silk preparation to reduce diameters and increase alignment to mimic local native cell environments with and without CNT to add conductivity for enhancement of electrical stimulation. CNT reduced SF fiber diameters below 1% and effected alignment differently as the concentration increased. Longer degumming times decreased SF fiber diameters and alignment of the same concentration. The optimized conditions were 1 h degumming time with 1.5 ml/h flow rate at a concentration of 100 mg/ml spinning solution with 0.25% CNT to form fibers with 1.36 (± 0.09) µm diameter and 0.31 (± 0.01) a.u. alignment. Additionally, SF fibers were used as a long-term cell growth scaffold to compare with decellularized native tissue. Decellularized tissue decreased fibroblast mRNA expression of collagen type 1, lysyl oxidase-like 1 and matrix metalloproteinase 9, while all other genes expression was the same as cells on plastic. The SF fiber scaffold reduced fibroblast expression of collagen type 3 compared to growth on plastic, and both collagen types 1 and 3 increased over growth time on SF. Immunofluorescence staining showed both collagens newly deposited on the SF scaffold and improved over time. In conclusion, proteins stabilized ICG monomers to improve light interaction, efficacy of photobleaching, and heat evolution to induce apoptosis in neuroblastoma and agglutination of blood in SF composites. Irradiation of ICG enhanced changes in optical properties and may have sensor applications. The decrease of genes may be due to each scaffold having lower stiffness compared to plastic. ICG and SF are both materials with applications as biological scaffolds in pelvic organ prolapse and treatment of neuroblastoma and hemorrhage.
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Title: Synthesis and Photophysical Characterization of Novel Organic Triplet Donor–Acceptor Dyads for Light-Harvesting/Modulation Application
Creator: Yun, Young Ju
Date: 2022
Description: Donor–acceptor chromophoric systems (D–A) are important scaffolds for several light-harvesting/initiated processes and devices, including...
Show moreDonor–acceptor chromophoric systems (D–A) are important scaffolds for several light-harvesting/initiated processes and devices, including light-emitting diodes, photo-catalytic/redox systems, and photovoltaic cells. It has been hypothesized that for efficient photophysical processes (viz. energy/charge-transfer or excited-state interactions); it is ideal to tether the donor and acceptor chromophores into molecular dyads. To this end, I devised and synthesized several dyads by tethering an organic triplet energy donor and various polyaromatic chromophores (e.g., perylene derivatives and anthracene derivatives) onto a conjugated-/non-conjugated-linker (phenylene- and triptycene- linker, respectively). During the 4-5 years of my Ph.D., I synthesized a total of five (5) dyads: o–, p–3, and dyads 3–5. These systems were fully characterized using different spectroscopy tools/techniques. The spectroscopy investigations of the dyads have allowed me to decipher two important energy transfer pathways: through-bond and through-space with the phenylene linker and only through-space energy with the triptycene linker. Furthermore, the investigations led to the discovery that geometrical features such as face-to-face (co-facial) or slip-stacked interactions between the donor and acceptors chromophores might dictate the dynamic/kinetic of light-induced energy transfer in the dyads. Findings from my graduate research project paved the way for developing molecular engineering studies for light-harvesting/modulation applications.Subsequently, I was able to employ the dyads of my interest to achieve intramolecular and intermolecular triplet energy transfer (TEnT) triplet-triplet annihilation-based photon upconversion (TTA-PUC).
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Title: Unraveling the Factors Affecting Virus Adhesion to Food Contact Materials and Virus-Virus Interaction – A Nanoscopic Study
Creator: Guo, Ao
Date: 2020
Description: Food safety is a worldwide issue nowadays since pathogens cause diseases, even death. Human enteric viruses are a major cause of non-bacterial...
Show moreFood safety is a worldwide issue nowadays since pathogens cause diseases, even death. Human enteric viruses are a major cause of non-bacterial foodborne gastroenteritis. In the United States, they are the most life-threatening pathogenic agents for the foodborne illnesses. The fecal-oral route is responsible for the attachment and transmission of such foodborne pathogens, which lead to contamination of food-contact materials (FCMs) during food preparation, enhancing the risk of transmission. The interaction between viruses and contact surface is the source of virus adhesion.Due to lack of knowledge on virus adhesion to various FCMs, this thesis aims to reveal the key factors that mediate the virus-FCM and virus-virus interactions in order to effectively prevent virus infection or spread. The objectives are (1) to identify the physical and chemical features of a material surface that affect virus adhesion to determine an optimal FCM, (2) to reduce virus adhesion via nanofabrication of a material’s surface; (3) to investigate the effect of thermal inactivation (heat treatment) on virus-virus interaction toward the establishment of a non-culture-based infectivity assay for laboratory assessment of the effectiveness of disinfection methods. In this study, virus adhesion on various FCMs, including glass, polyvinyl chloride (PVC), polyethylene (PE) and graphite which have been widely used in food storages, food packages and utensil handling during food preparations, was investigated. Male-specific coliphage (MS2) was used as a virus surrogate of the highly infectious human enteric virus with similar physiochemical properties. Atomic force microscopy (AFM) was predominantly used in quantitative analyses of the strength of MS2 adhesion to various food-contact surfaces. Dynamic light scattering (DLS) was applied in MS2 dimensional analysis in aqueous suspension. Moreover, surface modification, such as nanofabrication, was employed to create controllable surface textures to reduce virus adhesion on FCM. Thermal inactivation was employed as a disinfection method. A comparative study was carried out to differentiate the active and inactivated MS2 in the virus-FCM and the virus-virus interactions. The results of this examination indicate that a material’s surface property, such as topography, hydrophobicity and surface charge, contributed to virus adhesion in aqueous phase at neutral pH (=7.4). Each surface feature played a distinctive role; however, the combined effect as well as the chemical signature of a virion’s surface determined the virus-FCM interaction. A delicate control of a surface’s chemical affinity and physical feature is expected to effectively reduce/interfere virus adhesion. It was also discovered that thermally inactivated MS2 particles became larger, softer, and more hydrophobic. These properties can be utilized in developing a non-culture-based assay to assess the effectiveness of disinfection methods for human enteric viruses, which can hardly be cultured in laboratory.
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Title: Design and Synthesis of New Sulfur Cathodes Containing Polysulfide Adsorbing Materials
Creator: Suzanowicz, Artur M
Date: 2023
Description: Lithium-sulfur battery (LSB) technology has tremendous prospects to substitute lithium-ion battery (LIB) technology due to its high...
Show moreLithium-sulfur battery (LSB) technology has tremendous prospects to substitute lithium-ion battery (LIB) technology due to its high theoretical specific capacity and energy density. However, escaping polysulfide intermediates (produced during the redox reaction process) from the cathode structure is the primary reason for rapid capacity fading. Suppressing the polysulfide shuttle (PSS) is a viable solution for this technology to move closer to commercialization and supersede the established LIB technology. In this dissertation, I have analyzed the challenges faced by LSBs and selected methods and materials to address these problems. I have concluded that in order to further pioneer LSBs, it is necessary to address these essential features of the sulfur cathode: superior electrical conductivity to ensure faster redox reaction kinetics and high discharge capacity, high pore volume of the cathode host to maximize sulfur loading/utilization, and polar polysulfide-resistive materials to anchor and suppress the migration of lithium polysulfides.Furthermore, a versatile, low-cost, and practical scalable synthesis method is essential for translating bench-level development to large-scale production. This dissertation covers designing and synthesizing new scalable cathode structures for lithium-sulfur batteries that are inexpensive and highly functional. The rationally chosen cathode components accommodate sulfur, suppress the migration of polysulfide intermediates via chemical interactions, enhance redox kinetics, and provide electrical conductivity to sulfur, rendering excellent electrochemical performance in terms of high initial specific capacity and good long-term cycling performance. TiO2, Ni12P5, and g-C3N4 as polysulfide adsorbing materials (PAMs) have been fully studied in this thesis along with three distinct types of host structures for lithium-sulfur batteries: Polymer, Carbon Cloth, and Reduced Graphene Oxide. I have created adaptable bulk synthesis techniques that are inexpensive, easily scalable, and suitable for bench-level research as well as large-scale manufacturing. The exceptional performance and scalability of these materials make my cathodes attractive options for the commercialization of lithium-sulfur batteries.
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Title: Utilizing Image Processing in Evaluation of Fibroblast Stimulation for Collagen Remodeling
Creator: Yoon, Shin Hae
Date: 2023
Description: This research delves into the realm of image processing as a pivotal component in the evaluation of fibroblast stimulation for collagen...
Show moreThis research delves into the realm of image processing as a pivotal component in the evaluation of fibroblast stimulation for collagen remodeling. The study focuses on unraveling the intricate synergy between electrospun silk fibroin-carbon nanotube (SF-CNT) fibers and electrical stimulation, working in harmony to enhance tissue regeneration. Building upon our previous work, we successfully engineered SF-CNT fibers through the electrospinning process, yielding highly aligned structures reminiscent of natural extracellular matrix proteins. These fibers were fortified with water stability through post-treatment with ethanol vapor, while subtle additions of carbon nanotubes (CNTs) significantly improved fiber alignment, strength, and conductivity without compromising biocompatibility. This innovative platform served as a cell culture matrix for fibroblasts harvested from pelvic organ prolapse (POP) patients, facilitating electrical stimulation that triggered a substantial increase in collagen production. In this study, we harnessed the power of various image-processing software tools, including ImageJ and Python, to analyze immunostained images of fibroblasts obtained from POP patients. Under carefully tailored electrical stimulation conditions, the stimulated cells exhibited an astonishing up to 11.97-fold increase in alpha-smooth muscle actin (α-SMA) expression, unequivocally signifying the successful activation of myofibroblasts. Additionally, in an animal model employing LOX-knockout mice to mimic collagen disorders associated with POP, the application of optimized electrical stimulation conditions for patient 003 led to a remarkable surge in collagen production and structural enhancement, underlining the potential of electrical stimulation in expediting tissue remodeling. Intriguingly, fibroblasts from patient 005 and patient 006 exhibited a distinct response, shedding light on the influence of POP severity on cellular behavior. This study firmly reinforces the imperative of personalized therapeutic approaches, emphasizing the need to customize treatment strategies to align with individual patient characteristics through innovative biological image analysis techniques.
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Title: Nanopore sensing for environmental and biomarker analysis
Creator: Arora, Pearl
Date: 2024
Description: Nanopore stochastic sensing is a powerful analytical tool for detecting target molecules through a nanoscale pore. The analyte and electrolyte...
Show moreNanopore stochastic sensing is a powerful analytical tool for detecting target molecules through a nanoscale pore. The analyte and electrolyte ions are subjected to a voltage bias which drives them to translocate through the nanopore, resulting in disruptions in the ionic current. These disruptions are translated to blockage events which can serve as a signature of the analyte. Owing to its unique features of single-molecule and label-free sensing, nanopore technique has been exploited in a wide array of applications such as detection of metal ions, proteins, DNA, microRNA, toxic agents etc. In this dissertation, projects showcasing nanopore’s sensing capability of different biomarkers and in the detection of a wide range of target molecules based on non-covalent interactions are presented. Particularly in the first two projects, nanopore detection of ferric ions relevant to environmental regulation as well as a biomarker for human health and a miRNA-based biomarker for oral cancer and oral related diseases are summarized. Ferric ions, which are benign if present in balanced quantities but can be toxic otherwise, are detected by using an engineered multifunctional nanopore and a chelating organophosphonic acid ligand. The chelate complex formed after ferric ions bind to ligand gives significantly different event signatures than the free ligand in the solution enabling ferric ion detection. Even in the presence of interfering ions, the ferric ions could be recognized easily because of the conformational changes brought in the nanopore lumen by the interaction of the interfering metal ions with the His-tags of the nanopore which in turn resulted in variations in the characteristics of blocking events. In the second project, miR31, an oral cancer biomarker, is selectively detected with the help of an engineered nanopore, and a DNA based probe. Several probes with variations in length, composition and position of the overhangs or probes with no overhangs were compared and studied as the probes play a crucial role in capturing the target of interest with high specificity. Our strategically designed probe emerged as the most effective in capturing the target even in presence of large background from human saliva samples and enhanced the sensitivity of the system. In the first two projects, nanopores are utilized for selective and specific detection of certain target molecules. However, in order to analyze diverse range of analytes, numerous sensing systems have to be constructed which can be a time-consuming and challenging task. To circumvent this limitation, in the third project, diverse recognition sites based on various non-covalent interactions are incorporated into the α-hemolysin protein pore to achieve detection of not just a single analyte but broad category of molecules such as cations, anions, aromatic and hydrophobic compounds.
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Title: ATOMIC LAYER DEPOSITION STUDIES OF GOLD AND TUNGSTEN DISULFIDE
Creator: Liu, Pengfei
Date: 2020
Description: In the last few decades, atomic layer deposition (ALD), as a vapor deposition technique and a powerful thin film fabrication method, has...
Show moreIn the last few decades, atomic layer deposition (ALD), as a vapor deposition technique and a powerful thin film fabrication method, has received more and more attention in many fields. A variety of materials can be made by ALD; however, the progress of ALD application is still necessary. Meanwhile, in the process of film fabrication by ALD, the interfacial chemistry is interesting and well worth studying. This dissertation mainly described the process of exploring two materials, gold and tungsten disulfide, fabrication and related content.For the portion of applying ALD in gold thin film deposition, a relatively comprehensive process was explored, studied, analyzed and discussed. Start with the synthesis of the gold precursor, Me2Au(S2CNEt2), the synthetic reaction was explored. By modified the conditions, such as solvent system, twice the yield as previously reported in the literature were achieved. Next, the application of in situ microbalance and infrared spectroscopic technique illuminate the organometallic chemistry during the gold thermal ALD process with Me2Au(S2CNEt2) and ozone. In situ quartz crystal microbalance (QCM) studies give an explanation for the nucleation delay and island growth of gold on a freshly prepared aluminum oxide surface. In situ infrared spectroscopy provides insight to study the surface chemistry during the process, which supports an oxidized gold surface mechanism. The epitaxy of gold thin film was explored by X-ray diffraction. The thermal ALD gold on various substrates reveals out-of-plane orientation, however, in-plane orientation was only existed in the gold film on mica. For the portion of applying ALD in tungsten disulfide fabrication, the early work started with studying the effect of interfaces upon crystallinity. The sulfuration of indium thin film with different interface was explored. Then the idea of “interfaces” was brought into the process of tungsten compounds fabrication. Due to this “indirect” method which made tungsten disulfide by sulfurizing ALD made tungsten compounds (eg. tungsten oxide and tungsten nitride) could not reduce the reaction temperature of tungsten disulfide synthesis to less than 400 °C. Sequently, the “direct” way of tungsten disulfide fabrication which directly utilized tungsten precursor and H2S in ALD system was tested and explored. With the tungsten precursors developed by our group, finally, tungsten disulfide could be fabricated at the temperature as low as 125 °C.
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