Browsing by Author "Ajayan, Pulickel M"
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Item 2D Optoelectronics: Challenges and Opportunities(2015-12-17) Lei, Sidong; Ajayan, Pulickel M; Lou, Jun; Kono, JunichiroIndium Selenide (InSe) is one of atomically layered 2D materials attracting broad interests recently, because of its good optoelectronic properties. Based on the challenges of 2D optoelectronics, several topics will be covered in this defense, such as trap states and low absorption rate. InSe is selected as a platform to study these topics. The localized states and trap states in InSe system was characterized through low temperature photocurrent measurement to reveal the evolution of band structure and origin of the localized states in few layered InSe. It is found the surface electron orbitals contribute to the localized states. By modifying the surface electron via metallic ions, the Fermi level can be tuned significantly and the inertia surface of the pristine 2D surface can be sensitized for functionalization. Via this method, the InSe photodetector can be improved by organic photosensitive molecules. On the other hand, local gating can induce trap states in 2D materials, helping to improve the photoresponse, but slowing down the response speed. By utilizing this effect, 2D charge coupled device can be fabricated to serve as flexible image sensor which can help correct the optical aberration. The discussion is based on InSe, however, the principle is very universal that can be easily apply to other 2D system. The research can help to promote the research and device development in 2D optoelectronics.Item Additive Manufacturing of Bio-inspired Sustainable Composites(2024-08-08) Thakur, Md Shajedul Hoque; Rahman, Muhammad M; Ajayan, Pulickel MMaterial efficiency is a key element of sustainable development. This can be achieved by recycling and reducing material waste, as well as through innovative designs that optimize material usage. Nature has many examples of complex hierarchical designs yielding lightweight efficient structural materials. Additive manufacturing enables the fabrication of material-optimized structures and material recycling at the product’s end-of-life. Thus, addressing both aspects- sustainable materials and sustainable design. We transform waste wood into ink to facilitate the first-ever 3D printing of recyclable wood structures, and we also 3D print material efficient origami designs for the first time using a brittle material. Natural wood has long been essential in construction and furniture but traditionally wood shaping has relied on subtractive manufacturing, which leads to substantial wood waste, raising critical sustainability concerns. Herein we extract lignin and cellulose from waste wood to formulate a water-based ink that facilitates the 3D printing of wood. The printed structures, after heat treatment, closely mimic natural wood’s properties, including aesthetics and mechanical characteristics. This method also allows for incorporating reinforcements, such as natural fibers. Adding natural fibers substantially improves the mechanical properties of 3D-printed wood. iii We also add fire retardants into the wood composite, which takes the structures very close to fire-safety standards, offering a sustainable pathway for the future development of fire-resistant and recyclable 3D-printed wood structures. The ancient art of origami is attractive in modern engineering for its material- efficiency. While origami-inspired metamaterials research often focuses on flexible materials, this study investigates the use of brittle materials, with the aim to change their failure mode through origami and bio-inspired soft material coatings. A ceramic based origami structure was 3D printed and coated with a biocompatible hyperelastic polymer. Mechanical tests, both experimental and numerical simulations, revealed that the origami design imparts its anisotropic behavior to the ceramic. The hyperelastic coating distributes tensile load throughout and hinders crack propagation, increasing damage tolerance and preventing catastrophic failure. This research opens the pathway to utilizing origami engineering in brittle materials. Overall, the goal is to take a step toward sustainable materials and design through additive manufacturing of bio-inspired composites.Item Embargo An Approach Towards Sustainable Synthesis of MXene and High-Performance Cementitious Composites(2024-04-19) Jayanthi Harikrishnan, VJ; Ajayan, Pulickel M; Vajtai, RobertThis thesis investigates innovative methods for synthesizing MXenes and enhancing cementitious materials to meet the critical need for sustainable manufacturing and improved mechanical properties in structural materials. Central to this research is the advancement in material science across two key areas: the development of environmentally friendly synthesis methods and the adoption of efficient manufacturing strategies to create advanced cement structures. A significant emphasis is placed on pushing the boundaries of material performance, sustainability, and synthesis techniques. For example, we explore modified approaches to MXene synthesis and the development of reinforced cementitious composites through the integration of nanotechnology and cutting-edge 3D printing technologies. The initial three chapters primarily concentrate on sustainable synthesis strategies for MXenes, including the exploration of alternatives to traditional hydrofluoric acid (HF) for removing aluminum (Al) from the MAX-phase. Due to HF's high toxicity and associated health and safety risks, we investigate the use of ammonium fluoride (NH4F) as a safe alternative. Our findings, supported by various analytical techniques, confirm NH4F's effectiveness in Al removal and in the production of 2D MXene flakes. Additionally, we explore a novel non-fluoride-based chemical method using iron chloride (FeCl2) as an etchant, which plays a dual role in etching and intercalating, leading to the production of high-quality Fe intercalated MXene flakes. Through detailed analysis, we evaluate the crystallinity, chemical composition, surface morphology, and defects of the MXene flakes produced by these new techniques. This part of the thesis not only aims to mitigate the environmental impact associated with MXene production due to HF use, but also to enhance their surface chemistry adaptability, broadening their application potential. Furthermore, the thesis chapters provide fundamental and an in-depth analysis of MXenes, in addition to highlighting the efficacy of these innovative synthesis techniques in maintaining the structural integrity and desired features of MXenes. The latter chapters, specifically chapters four and five, focus on enhancing the mechanical properties of cementitious materials by leveraging the unique properties of nanoparticles and the advancements in multi-material 3D printing. This section demonstrates significant improvements in compressive strength, toughness, and thermal management by incorporating hexagonal boron nitride (h-BN) into cement matrices. Additionally, it examines the application of direct ink writing (DIW) in creating reinforced cement and polyvinyl alcohol (PVA) structures, aiming to boost their impact resistance and energy absorption capabilities. Overall, this thesis offers a comprehensive overview of the synthesis, chemistry, and technologies involved in developing advanced materials with wide-ranging applications. For instance, the synthesized MXenes could be applied in electromagnetic interference shielding, catalysis, sensors, and flexible electronics. Conversely, the nanofiller and polymer-reinforced cement structures have potential applications in environments subjected to extreme thermal and mechanical stressesItem Chemical Vapor Deposition Synthesis of Graphene-Based Materials and Chemical Modulation of Graphene Electronics(2013-09-18) Yan, Zheng; Tour, James M.; Hauge, Robert H; Ajayan, Pulickel MGraphene, a two-dimensional sp2-bonded carbon material, has attracted enormous attention due to its excellent electrical, optical and mechanical properties. Recently developed chemical vapor deposition (CVD) methods could produce large-size and uniform polycrystalline graphene films, limited to gas carbon sources, metal catalyst substrates and degraded properties induced by grain boundaries. Meanwhile, pristine monolayer graphene exhibits a standard ambipolar behavior with a zero neutrality point in field-effect transistors (FETs), limiting its future electronic applications. This thesis starts with the investigation of CVD synthesis of pristine and N-doped graphene with controlled thickness using solid carbon sources on metal catalyst substrates (chapter 1), and then discusses the direct growth of bilayer graphene on insulating substrates, including SiO2, h-BN, Si3N4 and Al2O3, without needing further transfer-process (chapter 2). Chapter 3 discusses the synthesis of high-quality graphene single crystals and hexagonal onion-ring-like graphene domains, and also explores the basic growth mechanism of graphene on Cu substrates. To extend graphene’s potential applications, both vertical and planar graphene-carbon nanotube hybrids are fabricated using CVD method and their interesting properties are investigated (chapter 4). Chapter 5 discusses how to use chemical methods to modulate graphene’s electronic behaviors.Item CVD Grown Graphene-Based Materials: Synthesis, Characterization and Applications(2015-04-22) Ma, Lulu; Ajayan, Pulickel M; Lou, Jun; Zheng, Junrong; Vajtai, RobertGraphene draws a lot of attention due to its exceptional electrical, mechanical, thermal, optical and chemical properties. However, its zero bandgap is a limitation for electronics applications and its two-dimensional (2D) nature is a limitation for large scale, volumetric and macroscopic applications. Doping graphene with heteroatoms and creating graphene hetero-structures are two approaches herewith suggested to sidestep the above limitations. The illustration of thus approaches begins with the chemical vapor deposition (CVD) growth of graphene in the form of either atomically thin films or 3D porous structures; which involves the synthesis of several structures such as nitrogen-doped graphene, graphene-carbon nanotube hybrids, in-plane graphene-boron nitride heterostructures, and graphene-molybdenum carbide hybrids. The analysis of impurities in CVD grown graphene at the atomic scale and the measurement of fracture toughness of graphene will then follow. Furthermore, the potential applications of as-synthesized materials like field emitters, supercapacitors, and catalysts for water splitting are discussed.Item Development and Characterization of Titanium Compound Nanostructures(2016-07-19) Zhou, Zhou; Ajayan, Pulickel MThe development and characterization of titanium compound nanostructures have been achieved, for potential applications in energy industry. Oil and gas, one of the traditional industry fields, observes accumulating demands on active implementations of nanotechnology, for the numerous advantages that nanomaterials can introduce to both product performances and field operations. By using chemical vapor deposition and liquid exfoliation, various titanium compound nanostructures have been synthesized through this project. Attractively, these two material fabrication methods have been recognized to be industrial friendly in terms of cost efficiency and productivity. The development of nanostructures, aiming at oil and gas field applications, presents novel solutions for existing issues, such as low durability of drilling tools, high friction in mechanical operations and ineffective heat dissipation. Titanium compound nanostructures, including titanium borides, nitrides and sulfides are therefore investigated for such applications as protective coating, lubrication and thermal management.Item Engineered Nanomaterials for Energy Harvesting and Storage Applications(2014-11-03) Gullapalli, Hemtej; Ajayan, Pulickel M; Vajtai, Robert; Biswal, Sibani L; Arava, Leela Mohana ReddyEnergy harvesting and storage are independent mechanisms, each having their own significance in the energy cycle. Energy is generally harvested from temperature variations, mechanical vibrations and other phenomena which are inherently sporadic in nature, harvested energy stands a better chance of efficient utilization if it can be stored and used later, depending on the demand. In essence a comprehensive device that can harness power from surrounding environment and provide a steady and reliable source of energy would be ideal. Towards realizing such a system, for the harvesting component, a piezoelectric nano-composite material consisting of ZnO nanostructures embedded into the matrix of ‘Paper’ has been developed. Providing a flexible backbone to a brittle material makes it a robust architecture. Energy harvesting by scavenging both mechanical and thermal fluctuations using this flexible nano-composite is discussed in this thesis. On the energy storage front, Graphene based materials developed with a focus towards realizing ultra-thin lithium ion batteries and supercapacitors are introduced. Efforts for enhancing the energy storage performance of such graphitic carbon are detailed. Increasing the rate capability by direct CVD synthesis of graphene on current collectors, enhancing its electrochemical capacity through doping and engineering 3D metallic structures to increase the areal energy density have been studied.Item Fabrication and Characterization of Advanced Epoxy-based Composites and Nanocomposites(2023-08-08) Khater, Ali Zein; Ajayan, Pulickel M; Rahman, Muhammad MWe live in the age of development. The age of new technology. Of automated manufacturing and processing. Transportation is breaking new limits, passing the boundaries of the sky towards the heavens. Soon, travel across the world in minutes will become a reality with hypersonic travel. Automated and self-driving vehicles might one day be a relied means of transportation. With these advancements in technology, a new era of materials and manufacturing are necessary. Advanced materials must be developed that can reduce weight, reduce production and manufacturing time, respond intelligently or with design and intent, and reduce waste to thrust aviation, automotives, energy, technologies, and automation of technologies into this age of automation dubbed the fourth industrial revolution (IR4.0). Herein, this thesis discusses the development and testing of epoxy composites showing how additive manufacturing (AM) can be used to better process carbon nanotubes (CNTs), how the shape memory properties of epoxy can be tuned using polyrotaxane (PR), and impact tolerance of a PR epoxy. From these efforts, it has been shown that AM facilitates the processing of CNTs thus improving the processing dynamics of CNTs in epoxy in comparison to the mold cast counterpart via void reduction and CNT dispersion, wetting, and partial alignment. Likewise, this work shows that the addition of PR to a shape memory epoxy improves the strain to failure and improves shape recovery time with increased PR loading. Lastly, the effects of PR on epoxy are investigated to show how the addition of PR affects the impact resistance under repeated low velocity impacts of incrementally increasing energies. These collective works are united by the demand for advanced materials and manufacturing developments in IR4.0 where polymers provide lightweight and mechanically robust alternatives to heavy and dense metal components. Thus, this thesis will add to the body of literature and understanding necessary to continue growing the field of materials engineering and science.Item Embargo Facile Synthesis Routes for Application-Oriented Modification of Nanomaterials(2023-04-20) Kannan, Harikishan; Ajayan, Pulickel MChemical functionalization provides the necessary tools to pick and modulate specific properties while retaining most of the essential characteristics of a material. Hexagonal boron nitride (h-BN) and diamond have been uniquely identified for excellent mechanical characteristics, an ultra-wide bandgap, and a common resistance to not easily succumb to chemical modification. To that extent, the fulcrum of this thesis hinges on chalking out novel pathways that leverage their properties while chemically modifying them through a highly facile, scalable, and economical route with specific end goals. The first half of the thesis accomplishes this through a solvothermal approach using Deep Eutectic Solvents (DES) as medium in which transition metal atoms (Fe, Cu) were controllably and covalently anchored on a defect-rich h-BN. The Fe-hBN nanocomposites were used to comprehensively study the degradation of Perfluorooctanoic Acid (PFOA). On the other hand, the Cu-hBN nanocomposites were evaluated for lubrication studies Detailed bandgap measurements showed charge modulation thus cementing this approach as a sustainable option to modify h-BN. The second half of the thesis explores a facile gas-phase fluorination approach to etch diamond crystals. In light of all the attention diamond has received for its device applications, its use in quantum optics and quantum information processing has gained an increased impetus due to its negatively charged nitrogen-vacancy (NV-) defect centers. This work has upped the ante through a systematic study of correlating the fluorination conditions with the ensuing emission characteristics to form a new stable defect ensemble - Fluorine vacancy (FV) color centers in diamond, through this facile approach. The dichotomy of breaking and forming the C-F bond in the thesis’ first and latter parts respectively, remains central to its vision of modulating nanomaterials via facile chemical functionalization routes towards specific use casesItem Hypervelocity impact studies of carbon nanotubes and fiber-reinforced polymer nanocomposites(2014-04-24) Khatiwada, Suman; Barrera, Enrique V.; Ajayan, Pulickel M; Padgett, Jamie EThis dissertation studies the hypervelocity impact characteristics of carbon nanotubes (CNTs), and investigates the use of CNTs as reinforcements in ultra-high molecular weight polyethylene (UHMWPE) fiber composites for hypervelocity impact shielding applications. The first part of this dissertation is aimed at developing an understanding of the hypervelocity impact response of CNTs – at the nanotube level. Impact experiments are designed with CNTs as projectiles to impact and crater aluminum plates. The results show that carbon nanotubes are resistant to the high-energy shock pressures and the ultra-high strain loading during hypervelocity impacts. Under our experimental conditions, single-walled carbon nanotubes survive impacts up to 4.07 km/s, but transform to graphitic ribbons and nanodiamonds at higher impact velocities. The nanodiamonds are metastable and transform to onion-like nanocarbon over time. Double-walled carbon nanotubes retain their form and structure even at impacts over 7 km/s. Higher hypervelocity impact resistance of DWCNTs could be attributed to the absorption of additional energy due to relative motion between the layers in the transverse direction of these coaxial nanotubes. The second part of this dissertation researches the effect of reinforcement of carbon nanotubes and their buckypapers on the hypervelocity impact shielding properties of UHMWPE-fiber composites arranged in a Whipple Shield configuration (a shield design used for the protection of the international space station from hypervelocity impacts by orbital debris). Composite laminates were prepared via compression molding and nanotube buckypapers via vacuum filtration. Dispersed nanotubes were introduced to the composite laminates via direct spraying onto the fabric prior to composite processing. The experimental results show that nanotubes dispersed in polymer matrix do not affect the hypervelocity impact resistance of the composite system. Nanotube buckypapers, however, improve the impact resistance of the composite, owing to the collective dampening of the shock wave amplitudes by the interconnected nanotube network in a buckypaper. The location of the buckypaper inside the composite, its thickness, and its surface modification with metals, all affect its hypervelocity impact shielding properties. Buckypaper coated with nickel and placed on the top surface of the UHMWPE-fiber composite provides the best impact resistance. Physical properties such as high bulk speed of sound in the nanotubes, and a combination of high density and high bulk speed of sound in nickel make the nickel-coated buckypaper a good hypervelocity impact shielding material. In addition, an explorative study on the use of nanograin metals for hypervelocity impact shielding was conducted.Item Investigating Low Temperature Optical Properties and Structural Phase Transformation in 2D MoWSe2 Alloys(2018-04-17) Apte, Amey Anant; Ajayan, Pulickel MTwo-dimensional materials have been increasingly investigated over the last decade for their ease of exfoliation from van der Waals’ solids and the drastic change in properties when they transition from bulk to monolayer thickness. Transition metal dichalcogenides (TMDCs) are a prominent class of such materials whose prototypical monolayers have been shown to exhibit various stacking phases, electronic and optical properties, mechanical strength, improved catalytic activity, etc. Equally interesting albeit not so exhaustively explored are alloys of such 2D TMDC materials. This work focuses on monolayer molybdenum tungsten diselenide (Mo1-xWxSe2) alloy. The general properties of single phase TMDC materials are discussed, followed by alloys and their synthesis and investigation of their properties. Finally, two experiments are discussed: the photoluminescence of 2D Mo1-xWxSe2 at low temperatures and the strain induced in-situ structural phase transformation of the alloy.Item Investigation Into The Synthesis And Characterization Of Two-dimensional Molybdenum-based Dichalcogenide Alloys and Oxides And Their Properties(2019-07-29) Apte, Amey Anant; Ajayan, Pulickel MTwo-dimensional materials have been proposed as the basis of a number of upcoming applications due to their exciting electronic, optical, mechanical, and physico-chemical properties. This was experimentally demonstrated in the case of graphene, and followed by transition metal dichalcogenides (TMDCs), atomically flat sheets whose two-dimensional forms impart great flexibility along with a range of electronic band-structures. However, unlike graphene, TMDCs boast of a variety of atomic combinations due to an assortment of transition metals and chalcogens. The first part of this thesis builds upon the previous thesis work of exploring the space of multi-component TMDC alloys by doping at both cation and anion sites via different methods of chemical vapor deposition. Various doping levels are explored and characterized to detect structural phase transformations and the rise of emergent properties. Further, the thermodynamic nature of alloy vs heterostructure formation in cation-doped TMDC system is explored for the first time. The second part of the thesis explores novel elemental and compound ultra-thin materials and their properties and their uniqueness in the ever-growing library of two dimensional materials.Item Label-free as-grown double wall carbon nanotubes bundles for Salmonella typhimurium immunoassay(Chemistry Central, 2013) Punbusayakul, Niramol; Talapatra, Saikat; Ajayan, Pulickel M; Surareungchai, WerasakBackground: A label-free immunosensor from as-grown double wall carbon nanotubes (DW) bundles was developed for detecting Salmonella typhimurium. The immunosensor was fabricated by using the as-grown DW bundles as an electrode material with an anti-Salmonella impregnated on the surface. The immunosensor was electrochemically characterized by cyclic voltammetry. The working potential (100, 200, 300 and 400 mV vs. Ag/AgCl) and the anti-Salmonella concentration (10, 25, 50, 75, and 100 μg/mL) at the electrode were subsequently optimized. Then, chronoamperometry was used with the optimum potential of 100 mV vs. Ag/AgCl) and the optimum impregnated anti-Salmonella of 10 μg/mL to detect S. typhimurium cells (0-109 CFU/mL). Results: The DW immunosensor exhibited a detection range of 102 to 107 CFU/mL for the bacteria with a limit of detection of 8.9 CFU/mL according to the IUPAC recommendation. The electrode also showed specificity to S. typhimurium but no current response to Escherichia coli. Conclusions: These findings suggest that the use of a label-free DW immunosensor is promising for detecting S. typhimurium.Item Large enhancement of thermal conductivity of aluminum-reduced graphene oxide composites prepared by a single-step method(Oxford University Press, 2023) Mitra, Arijit; Sahoo, Mihir Ranjan; Samal, Aiswarya; Pradhan, Sunil Kumar; Polai, Balaram; Sahoo, Krishna Rani; Kar, Subrat; Satpathy, Bijoy Kumar; Narayanan, Tharangattu N; Ajayan, Pulickel M; Satyam, Parlapalli V; Nayak, Saroj KMetal matrix composites have attracted extensive attention from both the research and industrial perspective. In this study, we prepared aluminum-reduced graphene oxide (Al–rGO) composites with enhanced thermal conductivity in an easy single-step process. Pristine Al shows a thermal conductivity of 175 Wm−1K−1 (standard deviation <5%), which increases to 293 Wm−1K−1 for an Al–rGO composite with 1% rGO. Analysis of theoretical models shows that a higher percentage of rGO inside the Al matrix creates a continuous network resulting in more available phase space through which heat carrier phonons travel with less scattering, and hence thermal conductivity of the composite increases. Furthermore, Al–rGO composites show an ∼5% increase in microhardness compared with pristine Al. The electrical resistivity of the composite is comparable to that of pristine Al for a narrow weight percentage of rGO, whereas a 70% enhancement in the thermal conductivity of the composite is observed for the same weight percentage range, suggesting possibilities for exploiting both high electrical and thermal conductivities for various applications.Item Li-ion Batteries at Extremes: Physical-Electrochemical Phenomena at High Temperature, Energy and Power(2018-04-11) Fonseca Rodrigues, Marco Tulio; Ajayan, Pulickel MLi-ion batteries are the present and the future of energy storage. In spite of their commercial success, these devices exist in a delicate balance, and the slightest deviation from their optimal composition and operating conditions can be highly problematic. This thesis concentrates on the very events that emerge when Li-ion batteries encounter extremes: comprehensive strategies to extend the compatibility of these devices to very high temperatures are delineated; rational and experimental tools to investigate cell behavior at high power are proposed; and unconventional challenges associated with the fabrication and operation of high-energy cells are exposed. The collective work described here addresses some of the many barriers separating Li-ion batteries from a boundless future.Item Material engineering for Li-ion capacitors and Li-ion batteries(2019-12-05) Kato, Keiko; Ajayan, Pulickel M; Tang, MingElectrochemical energy storage devices are fundamental driving force behind personal and industrial electronics. Li-ion batteries became the most prevalent rechargeable energy storage technology in market because of a high energy density. However, a power density (especially charging) of Li-ion batteries is not satisfactory for certain applications. In this regard, supercapacitors serve as a complementary role. To combine the advantages of Li-ion batteries and supercapacitors and bridge the technological gap, Li-ion capacitors (LICs) are invented. A typical Li-ion capacitor consists of a battery-type anode and supercapacitor-type cathode in Li-ion containing carbonate-based electrolytes. The major challenge of LICs arises from such disparity in charge-storage mechanism and kinetic. The present work addresses the issue by engineering electrode and electrolyte materials. 1) Two-dimensional material (vanadium disulfide anode and nitrogen-doped reduced graphene oxide cathode) are developed to combat the low power density of battery-type electrodes and the low energy density of supercapacitor-type electrodes. 2) We demonstrated that the energy and power densities achievable by LICs are largely influenced (and perhaps determined) by the anion adsorption at the positive electrodes, and by the ion transport within the electrolytes. Another challenge of the current Li-ion battery technology is an environmental and sustainability aspects because of a use of toxic and scarce transitional metals. Electroactive organic molecule-based cathodes which can reversibly store Li-ions are environmentally benign alternatives. Here, we assessed electrochemical performance of a plant-based organic molecule (lawsone) and showed that its oligomer structure stabilizes the molecules, which led to an improvement in a capacity retention over repeated cyclings. Next, we exploited the light-harvesting and Li-storing capabilities of the organic molecules to demonstrate light charging capability of the molecule. This work sheds light on the unique capability of organic cathode materials and paves the way for the future development of environmentally friendly and light rechargeable Li-ion batteries.Item Embargo Morphology controlled All-Inorganic 2D Perovskite and Transition-Metal Dichalcogenides materials synthesis, characterization and application(2023-09-01) Shuai, Xinting; Mohite, Aditya D; Ajayan, Pulickel MIn recent years, 2D hybrid Ruddlesden-Popper (RP) halide perovskites have garnered significant attention due to their tunable optical and electronic properties alongside impressive stability. Their versatile applications span fields such as light emitting diodes (LEDs), field-effect transistors (FETs), photodetectors, and solar cells. This thesis delves into the evolution of traditional metal halide perovskites and 2D RP perovskites. Notably, emerging within this landscape are the all-inorganic 2D RP Cs2PbI2Cl2 (Pb-based n=1) and Cs2SnI2Cl2 (Sn-based n=1) perovskites, recognized for robust UV-light responsiveness, thermal stability, and remarkable carrier mobility. An innovative achievement is the synthesis of Pb and Sn-based n=1 2D RP perovskite films boasting sub-millimeter single crystal grains via a one-step CVD process at atmospheric pressure. These perovskites showcase a distinctive "tiled" crystal morphology and horizontally-oriented octahedral layers. The study advances to encompass the pioneering fabrication of multilayered Cs3Pb2I3Cl4 (Pb-based n=2) and Cs3Sn2I3Cl4 (Sn-based n=2) films, characterized by X-ray diffraction (XRD) and density functional theory (DFT) calculations for refined crystallographic structures. Complementary DFT calculations and experimental optical spectroscopy discern bandgap energy shifts attributable to quantum confinement effects. Intriguingly, a bias-free photodetector is realized using Sn-based n=1 perovskite, showcasing reproducible photocurrent and a swift 84ms response time. This research underscores the feasibility of growing substantial all-inorganic multilayered 2D perovskite crystals through a singular CVD process, propelling their potential as viable candidates for future photovoltaic applications. Additionally, exploration into using chloride and bromide as halide constituents yields large-area CsPbI2Br films on FTO substrate and CsPbI2Br nanowires on SiO2/Si substrate via the CVD method. Furthermore, the scope broadens to Transition-Metal Dichalcogenides materials, another semiconductor class commonly grown through CVD. Tailoring flow rates facilitates the fabrication of expansive MoS2 and WS2 films via a salt-assisted approach. For gas sensor applications, various chip treatment methodologies including wet-transfer, maskless lithography, and O2 plasma etching are investigated.Item Novel Three-Dimensional Silicon Carbide Nano-Structures(2017-02-16) Hart, Amelia HS Church; Ajayan, Pulickel M; Vajtai, RobertSilicon carbide nanotubes have been found to have the same excellent mechanical properties in extreme thermal and oxidative environments as bulk silicon carbide, but with the resiliency similar to carbon nanotubes due to quantum size effects. The simplest, most cost efficient method to synthesize silicon carbide nanotubes is conversion from carbon nanotubes. By investigating the conversion mechanisms of carbon nanotubes (CNTs) to silicon carbide nanotubes (SiCNTs), studying their resulting properties, and applying them in different ways, two composites can be created for use in applications that require optimal mechanical properties in high heat and oxidation. The first structure involves covering continuous silicon carbide fiber with protruding silicon carbide nanotubes, dubbed “fuzzy” fiber, which is created to be woven, layered, and put inside a ceramic matrix for extremely high temperature heat engines encountered in aerospace applications which come into contact with high heat and oxidation. The second structure is a silicon carbide nanotube/nanowire sphere that can be used for its excellent compressive strength and resiliency as well as its resistance to high heat and oxidation. By converting carbon nanotubes to silicon carbide nanotubes/nanowires, structures that are more easy and cost effective to obtain, can be synthesized to maintain excellent mechanical properties in high temperature and oxidative environments.Item One- and Two-Dimensional sp2-Carbon Nanomaterials: Synthesis, Properties, and Applications(2015-03-27) Raji, Abdul-Rahman Olabode; Tour, James M.; Ajayan, Pulickel M; Marti, Angel AThe unifying objective of this thesis is to synthesize, control, modify, hybridize, interface, understand, and apply one- and two-dimensional sp2-carbon nanomaterials. The materials include graphene (2D), carbon nanotubes (1D), and graphene nanoribbons (pseudo-1D); and their hybrids with each other. Other classes of materials such as molecules, polymers, and inorganic nanoparticles are also interfaced with the carbon materials. This thesis uncovers, demonstrates, and elucidates methods to (1) synthesize graphene with different number of layers; (2) to produce a full Li-ion battery based on a hybrid of graphene and carbon nanotubes; (3) to prepare a Li-ion battery electrode made from a composite of graphene nanoribbon (GNR) stacks and iron oxide nanoparticles; (4) to prepare an oxygen reduction reaction catalyst made from a composite of GNR stacks and silver nanoparticles; (5) to fabricate a conductive composite of GNR stacks and epoxy and employ it for Joule heating and deicing of surfaces; (6) to generate sprayable, electrically conductive, and radiofrequency transparent films made using functionalized GNR stacks for de-icing application; and (7) to produce conductive GNR films that are simultaneously radiofrequency and optically transparent. The various materials developed demonstrate the versatility of sp2-carbon in terms of synthesis, properties, and applications.Item Purification, Length Characterization and Quality Assessment of Carbon Nanotubes: A Roadmap to Spinning Fibers with Superior Electrical Conductivity and Strength(2015-04-24) Tsentalovich, Dmitri Evgenevich; Pasquali, Matteo; Ajayan, Pulickel M; Verduzco, RafaelThe performance of carbon nanotube (CNT) fibers has been limited by an inability to accurately measure CNT length and by an inadequate understanding of how CNT fiber properties depend on intrinsic CNT properties. This dissertation describes a new method for evaluating carbon nanotube length distributions, advances in CNT purification, and a comprehensive analysis of how CNT fiber performance is influenced by properties of the starting CNT material. We determine length distributions for CNT samples from a combination of extensional viscosity measurements and isotropic cloud point measurements of semidilute CNT solutions in chlorosulfonic acid. The scaling of isotropic cloud point concentration with average CNT aspect ratio determined from extensional viscosity measurements closely matches theoretical predictions. Unlike length measurement techniques that rely on CNT sonication or functionalization, the extensional viscosity method is the only bulk measurement method that can probe CNT samples with average lengths greater than several microns. We apply this length measurement technique, along with purity measurements via thermal gravimetric analysis (TGA), and graphitic character measurements by Raman spectroscopy to optimize hydrogen peroxide based purification of CNTs. The optimal purification conditions minimize cutting of CNTs, while maximizing CNT purity, purification yield, and graphitic character. Despite appreciable shortening of CNTs by purification, transparent and conductive thin film properties improve after purification because of improved CNT purity and graphitic character. High CNT purity, excellent graphitic character, as well as high aspect ratio are all critical for producing high-performance, multifunctional CNT fibers by wet spinning from acid solutions. Contrary to extant work, number of CNT walls does not appear to considerably affect fiber properties. High purity levels are primarily important for efficiently mixing and processing CNTs, whereas, graphitic character and high aspect ratio both strongly influence fiber strength and electrical conductivity. Using the highest quality, available CNT material, we spin continuous, high-strength fibers with the highest electrical conductivity reported in the literature. The fiber properties reported here represent significant improvements over past acid-spun and solid-state spun CNT fibers. The advances described in this thesis will improve CNT manufacturers’ ability to assess CNT quality; enabling researchers to continually improve the strength and conductivity of CNT fibers.