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Description
Two-dimensional (2D) materials have nanometer-scale thickness in one dimension but macroscopic sizes in the other two dimensions and have unique physical and chemical properties that arise from this dimensionality. For example, atomically thin forms of semiconducting materials like transition metal dichalcogenides (TMDs) have attracted significant attention for electric and optical

Two-dimensional (2D) materials have nanometer-scale thickness in one dimension but macroscopic sizes in the other two dimensions and have unique physical and chemical properties that arise from this dimensionality. For example, atomically thin forms of semiconducting materials like transition metal dichalcogenides (TMDs) have attracted significant attention for electric and optical device applications due to their tunable bandgaps. Most 2D materials are derived from layered materials with weak van der Waals (vdW) bonds between layers, but more recently, non-vdW materials with stronger bonds and non-layered structures have also been formed into nanosheets. Because of their aspect ratios, surface chemistry plays a substantial role in both vdW- and non-vdW-derived 2D materials, and involves intercalation and exfoliation, surface modification and functionalization, which contribute to their use in diverse applications. In this thesis, the materials chemistry of nanosheets from both vdW and non-vdW materials has been studied. First, this work demonstrates the covalent functionalization of a new rising 2D material in the TMDs family, palladium diselenide (PdSe2), which has a layer-dependent bandgap and is much more stable in air than many other 2D materials. Aryl diazonium salts were used to functionalize monolayer PdSe2 nanosheets, and the reaction kinetics were studied as a function of reaction time and concentrations. Raman spectroscopy suggests the structure of PdSe2 is undisturbed after functionalization, which will expand its future applications in areas like electronics, sensors, and energy storage. Next, liquid-phase exfoliation (LPE), an economical, scalable, and efficient method, was used to produce nanosheets of two types of non-vdW materials: metal diborides (MB2) which are a family of ceramic materials with a layered structure, and boron carbide (B4C), a non-layered material with covalent bonding. Quasi-2D nanosheets were formed from eight different metal diborides, with sizes and thicknesses that were found to correlate with the hardness of the bulk compounds. CrB2 nanosheets incorporated into polyvinyl alcohol (PVA) thin films showed enhanced mechanical properties that exceed the specific performance of additives from other 2D materials. Boron carbide, the third hardest known material, has also been successfully exfoliated into ultrathin by LPE. Combined theory and experiment show the rich surface structures of B4C nanosheets.
ContributorsGuo, Yuqi (Author) / Wang, Qing Hua QW (Thesis advisor) / Green, Alexander AG (Committee member) / Jiao, Yang YJ (Committee member) / Arizona State University (Publisher)
Created2021
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Description
There is a high demand for customized designs of various types of cement-based materials in order to address specific purposes in the construction field. These demands stem from the need to optimize the cementitious matrix properties and reinforcement choices, especially in high reliability, durability, and performance applications that include infrastructure,

There is a high demand for customized designs of various types of cement-based materials in order to address specific purposes in the construction field. These demands stem from the need to optimize the cementitious matrix properties and reinforcement choices, especially in high reliability, durability, and performance applications that include infrastructure, energy production, commercial buildings, and may ultimately be extended to low risk/high volume applications such as residential applications. The typical tools required to guide practicing engineers should be based on optimization algorithms that require highly efficient capacity and design alternatives and optimal computational tools. The general case of flexural design of members is an important aspect of design of structural members which can be extended to a variety of applications that include various cross-sections such as rectangular, W-sections, channels, angles, and T sections. The model utilized the simplified linear constitutive response of cement-based composite in compression and tension and extends into a two-segment elastic-plastic, strain softening, hardening, tension-stiffening, and a multi-segment system. The generalized parametric model proposed uses a dimensionless system in the stress-strain materials diagram to formulate piecewise equations for an equilibrium of internal stresses and obtains strain distributions for the closed-form solution of neutral axis location. This would allow for the computation of piecewise moment-curvature response. The number of linear residual stress implemented is flexible to a user to maintain a robust response. In the present approach bilinear, trilinear, and quad-linear models are addressed and a procedure for incorporating additional segments is presented. Moreover, a closed-form solution of moment-curvature can be solved and employed in calculating load-deflection response. The model is adaptable for various types of fiber-reinforced and textile reinforced concrete (FRC, TRC, UHPC, AAC, and Reinforced Concrete). The extensions to cover continuous fiber reinforcement such as textile reinforced concrete (TRC, FRCM) strengthening and repair are addressed. The theoretical model is extended to incorporate the hybrid design (HRC) with continuous rebar with FRC to increase the ductility and ultimate moment capacity. HRC extends the performance of the fiber system to incorporate residual capacity into a serviceability-based design that reduced the reliance on the design based on the limit state. The design chart for HRC and as well as conventional RC has been generated for practicing engineering applications. Results are compared to a large array of data from experimental results conducted at the ASU structural lab facilities and other published literature.
Contributorspleesudjai, chidchanok (Author) / Mobasher, Barzin (Thesis advisor) / Neithalath, Narayanan (Committee member) / Rajan, Subramaniam (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Nanoholes on the basal plane of graphene can provide abundant mass transport channels and chemically active sites for enhancing the electrochemical performance, making this material highly promising in applications such as supercapacitors, batteries, desalination, molecule or ion detection, and biosensing. However, the current solution-based chemical etching processes to manufacture these

Nanoholes on the basal plane of graphene can provide abundant mass transport channels and chemically active sites for enhancing the electrochemical performance, making this material highly promising in applications such as supercapacitors, batteries, desalination, molecule or ion detection, and biosensing. However, the current solution-based chemical etching processes to manufacture these nanoholes commonly suffer from low process efficiency, scalability, and controllability, because conventional bulk heating cannot promote the etching reactions. Herein, a novel manufacturing method is developed to address this issue using microwave irradiation to facilitate and control the chemical etching of graphene. In this process, microwave irradiation induces selective heating of graphene in the aqueous solution due to an energy dissipation mechanism coupled with the dielectric and conduction losses. This strategy brings a remarkable reduction of processing time from hour-scale to minute-scale compared to the conventional approaches. By further incorporating microwave pretreatment, it is possible to control the population and area percentage of the in-plane nanoholes on graphene. Theoretical calculations reveal that the nanoholes emerge and grow by a repeating reduction–oxidation process occurring at the edge-sites atoms around vacancy defects on the graphene basal plane. The reduced holey graphene oxide sheets obtained via the microwave-assisted chemical etching method exhibit great potentials in supercapacitors and electrocatalysis. Excellent capacitive performance and electrocatalytic activity are observed in electrochemical measurements. The improvements against the non-holey counterpart are attributed to the enhanced kinetics involving ion diffusion and heterogeneous charge transfer.
ContributorsWang, Dini (Author) / Nian, Qiong (Thesis advisor) / Alford, Terry (Committee member) / Wang, Qing Hua (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2021
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Description
In this dissertation, far UV spectroscopy is applied to investigate the optical properties of dielectric thin films grown by atomic layer deposition. The far UV (120 – 200 nm) reflectance for several dielectric oxides and fluorides, including AlF3, Al2O3, Ga2O3, HfO2, and SiO2, was measured at variable angles and thicknesses.

In this dissertation, far UV spectroscopy is applied to investigate the optical properties of dielectric thin films grown by atomic layer deposition. The far UV (120 – 200 nm) reflectance for several dielectric oxides and fluorides, including AlF3, Al2O3, Ga2O3, HfO2, and SiO2, was measured at variable angles and thicknesses. Multiple optical calculation methods were developed for the accurate determination of the optical constants from the reflectance. The deduced optical constants were used for optical designs, such as high-reflectivity coatings, and Fabry-Perot bandpass interference filters. Three filters were designed for use at 157 nm, 212 nm, and 248 nm wavelengths, based on multilayer structures consisting of SiO2, Al2O3, HfO2, and AlF3. A thorough error analysis was made to quantify the non-idealities of the optical performance for the designed filters. Far UV spectroscopy was also applied to analyze material mixtures, such as AlF3/Al and h-BN/c-BN mixtures. Using far UV spectroscopy, different phases in the composite can be distinguished, and the volume concentration of each constituent can be determined. A middle UV reflective coating based on A2O3 and AlF3 was fabricated and characterized. The reflective coating has a smooth surface (?? < 1 nm), and a peak reflectance of 25 – 30 % at a wavelength of 196 nm. The peak reflectance deviated from the design, and an analysis of the AlF3 layer prepared by plasma-enhanced atomic layer deposition (PEALD) indicated the presence of Al-rich clusters, which were associated with the UV absorption. Complementary techniques, such as spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, were used to verify the results from far UV spectroscopy. In conclusion, this Dissertation demonstrated the use of in-situ far UV spectroscopy to investigate the optical properties of thin films at short wavelengths. This work extends the application of far UV spectroscopy to ultrawide bandgap semiconductors and insulators. This work supports a path forward for far UV optical filters and devices. Various errors have been discussed with solutions proposed for future research of methods and materials for UV optics.
ContributorsHuang, Zhiyu (Author) / Nemanich, Robert (Thesis advisor) / Ponce, Fernando (Committee member) / Menéndez, Jose (Committee member) / Holman, Zachary (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) technology that has emerged as the predominant technology for metal 3D printing. An alloy of particular interest to the aerospace industry is the nickel-based superalloy, Inconel 718 (IN718), which is widely used for its superior performance in elevated temperature conditions,

Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) technology that has emerged as the predominant technology for metal 3D printing. An alloy of particular interest to the aerospace industry is the nickel-based superalloy, Inconel 718 (IN718), which is widely used for its superior performance in elevated temperature conditions, particularly for gas-turbine engine blades and heat exchangers. With LPBF providing new ways of exploiting complex part geometry, the high-temperature properties of the AM version of the alloy must be understood. Of additional interest is how these properties change as a function of geometry and post-processing. This research focuses on the behavior of LPBF IN718 as a function of hot isostatic pressing (HIP) and specimen thickness at elevated temperatures. These results and behavior were compared to the behavior of IN718 sheet metal for properties such as True Ultimate Tensile Strength (UTS), Yield Strength, Young’s Modulus, percent elongation, and necking. The results showed dependence of strength on both thickness and HIP condition, and also exhibited a steep drop in UTS and yield strength at 1600 °F, linearly declining modulus, and excess dynamic strain ageing (DSA) behavior at certain temperatures.
ContributorsTemes, Samuel (Author) / Bhate, Dhruv (Thesis advisor) / Azeredo, Bruno (Committee member) / Das, Partha (Committee member) / Arizona State University (Publisher)
Created2021
Description
Layer-wise extrusion of soft-solid like cement pastes and mortars is commonly used in 3D printing of concrete. Rheological and mechanical characterization of the printable binder for on-demand flow and subsequent structuration is a critical challenge. This research is an effort to understand the mechanics of cementitious binders as soft solids

Layer-wise extrusion of soft-solid like cement pastes and mortars is commonly used in 3D printing of concrete. Rheological and mechanical characterization of the printable binder for on-demand flow and subsequent structuration is a critical challenge. This research is an effort to understand the mechanics of cementitious binders as soft solids in the fresh state, towards establishing material-process relationships to enhance print quality. This study introduces 3D printable binders developed based on rotational and capillary rheology test parameters, and establish the direct influence of packing coefficients, geometric ratio, slip velocities, and critical print velocities on the extrudate quality. The ratio of packing fraction to the square of average particle diameter (0.01-0.02), and equivalent microstructural index (5-20) were suitable for printing, and were directly related to the cohesion and extrusional yield stress of the material. In fact, steady state pressure for printing (30-40 kPa) is proportional to the extrusional yield stress, and increases with the geometric ratio (0-60) and print velocity (5-50 mm/s). Higher print velocities results in higher wall shear stresses and was exponentially related to the slip layer thickness (estimated between 1-5μ), while the addition of superplasticizers improve the slip layer thickness and the extrudate flow. However, the steady state pressure and printer capacity limits the maximum print velocity while the deadzone length limits the minimum velocity allowable (critical velocity regime) for printing. The evolution of buildability with time for the fresh state mortars was characterized with digital image correlation using compressive strain and strain rate in printed layers. The fresh state characteristics (interlayer and interfilamentous) and process parameters (layer height and fiber dimensions) influence the hardened mechanical properties. A lower layer height generally improves the mechanical properties and slight addition of fiber (up to 0.3% by volume) results in a 15-30% increase in the mechanical properties. 3D scanning and point-cloud analysis was also used to assess the geometric tolerance of a print based on mean error distances, print accuracy index, and layer-wise percent overlap. The research output will contribute to a synergistic material-process design and development of test methods for printability in the context of 3D printing of concrete.
ContributorsAmbadi Omanakuttan Nair, Sooraj Kumar (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam (Committee member) / Mobasher, Barzin (Committee member) / Hoover, Christian (Committee member) / Chawla, Nikhilesh (Committee member) / Arizona State University (Publisher)
Created2021
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Description
High-pressure science has been advancing rapidly in the past several decades due to its potential to access bond engineering and lattice reconstruction. Thanks to the development of pressure devices and advanced in-situ probing technics, it is possible to probe structural phase transitions as well as materials’ optical, electrical, and magnetic

High-pressure science has been advancing rapidly in the past several decades due to its potential to access bond engineering and lattice reconstruction. Thanks to the development of pressure devices and advanced in-situ probing technics, it is possible to probe structural phase transitions as well as materials’ optical, electrical, and magnetic properties under extreme pressure, which will in turn help explain new emerging materials’ phases and phenomena. As one of the most popular high-pressure devices, the diamond anvil cell has been used to control the crystal structure and interatomic spacing of materials by applying high pressure while accessing their material properties in-situ. In this dissertation, advanced spectroscopy techniques combined with diamond anvil cells are used to help determine how emergent quantum materials behave under high pressure. A comprehensive summary is offered on the synthesis, characterization, and high-pressure studies of various low-dimensional material systems, such as 2D Ruddlesden-Popper hybrid lead bromide perovskites (CH3(CH2)3NH3)2(CH3NH3)nPbnBr3n+1, (n = 1 and n = 2); guanidinium based lead iodides (2D Gua2PbI4 and 1D GuaPbI3), in which researchers discovered extraordinary luminescent properties and extremely high quantum conversion efficiency; 2D Janus MoSSe and WSSe monolayers, in which the mirror symmetry is broken and an electrical field is built in due to different electronegativity of the top and bottom atom layers; and 2D tellurene, which possess a large potential application in optoelectronic devices and sensors. In combination with the density function theory simulations of such collaborators as Dr. Can Ataca (organic–inorganic halide perovskite), Dr. Arunima K. Singh (tellurene), and Dr. Houlong Zhuang (Janus), this study offers comprehensive and detailed insights into the fundamental physics and mechanics of how crystal structure and band structure evolve at high pressure, discovering new phases, understanding the phase transition mechanism, and determining optoelectronic device applications.
ContributorsLi, Han (Author) / Tongay, Sefaattin ST (Thesis advisor) / Botana, Antia Sanchez (Committee member) / Singh, Arunima K. (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Crystalline silicon covers more than 85% of the global photovoltaics industry and has sustained a nearly 30% year-over-year growth rate. Continued cost and capital expenditure (CAPEX) reductions are needed to sustain this growth. Using thin silicon wafers well below the current industry standard of 160 µm can reduce manufacturing cost,

Crystalline silicon covers more than 85% of the global photovoltaics industry and has sustained a nearly 30% year-over-year growth rate. Continued cost and capital expenditure (CAPEX) reductions are needed to sustain this growth. Using thin silicon wafers well below the current industry standard of 160 µm can reduce manufacturing cost, CAPEX, and levelized cost of electricity. Additionally, thinner wafers enable more flexible and lighter module designs, making them more compelling in market segments like building-integrated photovoltaics, portable power, aerospace, and automotive industries. Advanced architectures and superior surface passivation schemes are needed to enable the use of very thin silicon wafers. Silicon heterojunction (SHJ) and SHJ with interdigitated back contact solar cells have demonstrated open-circuit voltages surpassing 720 mV and the potential to surpass 25% conversion efficiency. These factors have led to an increasing interest in exploring SHJ solar cells on thin wafers. In this work, the passivation capability of the thin intrinsic hydrogenated amorphous silicon layer is improved by controlling the deposition temperature and the silane-to-hydrogen dilution ratio. An effective way to parametrize surface recombination is by using surface saturation current density and a very low surface saturation density is achieved on textured wafers for wafer thicknesses ranging between 40 and 180 µm which is an order of magnitude lesser compared to the prevalent industry standards. Implied open-circuit voltages over 760 mV were accomplished on SHJ structures deposited on n-type silicon wafers with thicknesses below 50 µm. An analytical model is also described for a better understanding of the variation of the recombination fractions for varying substrate thicknesses. The potential of using very thin wafers is also established by manufacturing SHJ solar cells, using industrially pertinent processing steps, on 40 µm thin standalone wafers while achieving maximum efficiency of 20.7%. It is also demonstrated that 40 µm thin SHJ solar cells can be manufactured using these processes on large areas. An analysis of the percentage contribution of current, voltage, and resistive losses are also characterized for the SHJ devices fabricated in this work for varying substrate thicknesses.
ContributorsBalaji, Pradeep (Author) / Bowden, Stuart (Thesis advisor) / Alford, Terry (Thesis advisor) / Goryll, Michael (Committee member) / Augusto, Andre (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Oxygen transfer reactions are central to many catalytic processes, including those underlying automotive exhaust emissions control and clean energy conversion. The catalysts used in these applications typically consist of metal nanoparticles dispersed on reducible oxides (e.g., Pt/CeO2), since reducible oxides can transfer their lattice oxygen to reactive adsorbates at the

Oxygen transfer reactions are central to many catalytic processes, including those underlying automotive exhaust emissions control and clean energy conversion. The catalysts used in these applications typically consist of metal nanoparticles dispersed on reducible oxides (e.g., Pt/CeO2), since reducible oxides can transfer their lattice oxygen to reactive adsorbates at the metal-support interface. There are many outstanding questions regarding the atomic and nanoscale spatial variation of the Pt/CeO2 interface, Pt metal particle, and adjacent CeO2 oxide surface during catalysis. To this end, a range of techniques centered around aberration-corrected environmental transmission electron microscopy (ETEM) were developed and employed to visualize and characterize the atomic-scale structural behavior of CeO2-supported Pt catalysts under reaction conditions (in situ) and/or during catalysis (operando). A model of the operando ETEM reactor was developed to simulate the gas and temperature profiles during conditions of catalysis. Most importantly, the model provides a tool for relating the reactant conversion measured with spectroscopy to the reaction rate of the catalyst that is imaged on the TEM grid. As a result, this work has produced a truly operando TEM methodology, since the structure observed during an experiment can be directly linked to quantitative chemical kinetics of the same catalyst. This operando ETEM approach was leveraged to investigate structure-activity relationships for CO oxidation over Pt/CeO2 catalysts. Correlating atomic-level imaging with catalytic turnover frequency reveals a direct relationship between activity and dynamic structural behavior that (a) destabilizes the supported Pt particle, (b) marks an enhanced rate of oxygen vacancy creation and annihilation, and (c) leads to increased strain and reduction in the surface of the CeO2 support. To further investigate the structural meta-stability (i.e., fluxionality) of 1 – 2 nm CeO2-supported Pt nanoparticles, time-resolved in situ AC-ETEM was employed to visualize the catalyst’s dynamical behavior with high spatiotemporal resolution. Observations are made under conditions relevant to the CO oxidation and water-gas shift (WGS) reactions. Finally, deep learning-based convolutional neural networks were leveraged to develop novel denoising techniques for ultra-low signal-to-noise images of catalytic nanoparticles.
ContributorsVincent, Joshua Lawrence (Author) / Crozier, Peter A (Thesis advisor) / Liu, Jingyue (Committee member) / Muhich, Christopher L (Committee member) / Nannenga, Brent L (Committee member) / Singh, Arunima K (Committee member) / Arizona State University (Publisher)
Created2021
Description
Current Li-ion battery technologies are limited by the low capacities of theelectrode materials and require developments to meet stringent performance demands for future energy storage devices. Electrode materials that alloy with Li, such as Si, are one of the most promising alternatives for Li-ion battery anodes due to their high capacities. Tetrel (Si,

Current Li-ion battery technologies are limited by the low capacities of theelectrode materials and require developments to meet stringent performance demands for future energy storage devices. Electrode materials that alloy with Li, such as Si, are one of the most promising alternatives for Li-ion battery anodes due to their high capacities. Tetrel (Si, Ge, Sn) clathrates are a class of host-guest crystalline structures in which Tetrel elements form a cage framework and encapsulate metal guest atoms. These structures can form with defects such as framework/guest atom substitutions and vacancies which result in a wide design space for tuning materials properties. The goal of this work is to establish structure property relationships within the context of Li-ion battery anode applications. The type I Ba 8 Al y Ge 46-y clathrates are investigated for their electrochemical reactions with Li and show high capacities indicative of alloying reactions. DFT calculations show that Li insertion into the framework vacancies is favorable, but the migration barriers are too high for room temperature diffusion. Then, guest free type I clathrates are investigated for their Li and Na migration barriers. The results show that Li migration in the clathrate frameworks have low energy barriers (0.1- 0.4 eV) which suggest the possibility for room temperature diffusion. Then, the guest free, type II Si clathrate (Na 1 Si 136 ) is synthesized and reversible Li insertion into the type II Si clathrate structure is demonstrated. Based on the reasonable capacity (230 mAh/g), low reaction voltage (0.30 V) and low volume expansion (0.21 %), the Si clathrate could be a promising insertion anode for Li-ion batteries. Next, synchrotron X-ray measurements and pair distribution function (PDF) analysis are used to investigate the lithiation pathways of Ba 8 Ge 43 , Ba 8 Al 16 Ge 30 , Ba 8 Ga 15 Sn 31 and Na 0.3 Si 136 . The results show that the Ba-clathrates undergo amorphous phase transformations which is distinct from their elemental analogues (Ge, Sn) which feature crystalline lithiation pathways. Based on the high capacities and solid-solution reaction mechanism, guest-filled clathrates could be promising precursors to form alloying anodes with novel electrochemical properties. Finally, several high temperature (300-550 °C) electrochemical synthesis methods for Na-Si and Na-Ge clathrates are demonstrated in a cell using a Na β’’-alumina solid electrolyte.
ContributorsDopilka, Andrew (Author) / Chan, Candace K (Thesis advisor) / Zhuang, Houlong (Committee member) / Peng, Xihong (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2021