This thesis is a continuous effort contributed to the field of developing a new type of functional porous materials - Nanocarbon Foam (NCF) by crosslinking multi-walled carbon nanotubes (MWNTs) into networks in three-dimensional (3D). Synthetic routes and characterizations of NCF, and their applications as strain-gauge sensors and electrode materials in lithium-air (Li-air) battery are described. In this research, the first accomplishment is proposing a robust methodology for creating superealstic 3D macroscopic NCF with controlled cellular structure. The key contributions contain: (1) understanding the premise of the design that gives the NCF with desired structure and porosity; (2) designing fabrication protocol for NCFs with controlled densities and macroscopic structure; (3) fabricating varied NCF with tunable porosity and structures, which in turn will endow the NCF with different characteristics. This experimental methodology for systematic and quantitative investigation of the processing-structure relationships provides a means for the fabrication optimization of NCF with desired structures. Though the mechanical, electronic, and thermal properties of CNTs have been extensively studied, for NCF that is a mixture of pristine and functionalized CNTs, it will not only have the collective behavior of the individual tubes, but will also have properties generated from the interactions between the tubes and engineered components. To understand the structure-properties relationship of NCF, the second accomplishment is studying the properties of obtained NCFs. Density, specific surface area, porosity, compressive behavior, mechanical robustness, electrical and electromechanical properties of NCF have been characterized in details. For comparison, properties originated from cellular structures built of other materials, such as polymeric foam, fiber aerogels, etc., are compared with that of NCF. Moreover, some engineering applications of NCF have been discussed. With the unique features of NCFs, my proposed future work will focus on understanding porous structure formation and resulted unique properties by the means of scientific modelling. In addition, NCF will be explored as the skeleton for fabricating hybrid systems. / A Thesis submitted to the Materials Science and Engineering Program in partial fulfillment of the Master of Science. / Fall Semester 2015. / November 5, 2015. / Includes bibliographical references. / Eric Hellstrom, Professor Co-Directing Thesis; Mei Zhang, Professor Co-Directing Thesis; Richard Liang, Committee Member; Zhibin Yu, Committee Member.

Enhancing the beam energy of particle accelerators like the Large Hadron Collider (LHC), at CERN, can increase our probability of finding new fundamental particles of matter beyond those predicted by the standard model. Such discoveries could improve our understanding of the birth of universe, the universe itself, and/or many other mysteries of matter—that have been unresolved for decades—such as dark matter and dark energy. This is obviously a very exciting field of research, and therefore a worldwide collaboration (of universities, laboratories, and the industry) is attempting to increase the beam energy in the LHC. One of the most challenging requirements for an energy increase is the production of a magnetic field homogeneous enough and strong enough to bend the high energy particle beam to keep it inside the accelerating ring. In the current LHC design, these beam bending magnets are made of Nb-Ti superconductors, reaching peak fields of ~8 T. However, in order to move to higher fields, future magnets will have to use different and more advanced superconducting materials. Among the most viable superconductor wire technologies for future particle accelerator magnets is Nb₃Sn, a technology that has been used in high field magnets for many decades. However, Nb₃Sn magnet fabrication has an important challenge: the fact the wire fabrication and the coil assembly itself must be done using ductile metallic components (Nb, Sn, and Cu) before the superconducting compound (Nb₃Sn) is activated inside the wires through a heat treatment. The studies presented in this thesis work have found that the heat treatment schedule used on the most advanced Nb₃Sn wire technology (the Restacked Rod Process wires, RRP®) can still undergo significant improvements. These improvements have already led to an increase of the figure of merit of these wires (critical current density) by 28%. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / April 11, 2017. / image anaylsis, LHC, magnets, Nb3Sn, RRP, superconductivity / Includes bibliographical references. / David Larbalestier, Professor Directing Dissertation; Vincent Salters, University Representative; William Oates, Committee Member; Michael Shatruk, Committee Member; Irinel Chiorescu, Committee Member; Chiara Tarantini, Committee Member; Peter Lee, Committee Member.

My research has been focusing on the development and processing of metal halide perovskites, an emerging class of semiconductor materials, for various types of light emitting diodes (LEDs). In this dissertation, introduction to metal halide perovskites will be presented in the chapter 1, followed by three chapters detailing the work on the use of metal halide perovskites as hole transport layer for organic LEDs (chapter 2), as light emitting layer for electrically driven LEDs (chapter 3), and down conversion LEDs (chapter 4). A new type of hole transport layer based on metal halide perovskite, CH3NH3PbCl3 has been demonstrated for highly efficient OLEDs. Two types of hole transport layer have been fabricated, including PIP-CH3NH3PbCl3 composite thin films and neat CH3NH3PbCl3 thin films. Solution processed multilayer green phosphorescent OLEDs based on this new PIP- CH3NH3PbCl3 nanograss HTLshowed superior performance over devices using conventional PEDOT: PSS HTL with lower turn-on and operating voltages, as well as higher brightness. The improved device performance is primarily attributed to the high conductivity of CH3NH3PbCl3 and large interpenetrating interfaces between the hole transporting perovskite nanopillars and the emitting layer. In order to further enhance efficiencies of OLEDs based on CH3NH3PbCl3 as HTL, the solvent passivation approach has been adapted for the formation of smooth neat CH3NH3PbCl3 perovskite thin films with great surface coverage. Solution-processed multilayer green phosphorescent OLEDs based on this new perovskite HTL showed superior performance over the device using conventional PEDOT:PSS HTL, with lower turn-on and operating voltages, as well as higher brightness, EQE, power efficiency and luminous efficiency. The improved device performance is primarily attributed to the wide band gap of CH3NH3PbCl3, suitable energy levels, and efficient the hole injection and transport from ITO to CH3NH3PbCl3 and light emitting layer. This work demonstrates a new pathway toward highly efficient solution processed multilayer OLEDs, and further establishes organic-inorganic halide perovskites as a new class of semiconductors with highly desirable characteristics for thin film optoelectronic devices. Perovskite LEDs have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green emitting perovskite LEDs in recent years, but not blue or red ones. Highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly (ethylene oxide) (PEO) composite thin films as the light-emitting layer have been successfully demonstrated. By controlling the molar ratios of organic salt (benzyl ammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd/m2 and an EQE of 6.23%. Both the maxima brightness and external quantum efficiencies of our devices are among the highest reported to date for red perovskite LEDs. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs. This work clearly shows the effectiveness of processing and device engineering to realize high performance perovskite optoelectronic devices. Recently, our lab developed a new class of luminescent materials, zero-dimensional perovskites. These novel luminescent materials show very high photoluminescence quantum efficiencies (PLQEs) with a very broad emission. For these new 0D perovskites, their excellent optical properties enable us to fabricate down conversion white LEDs. By combing these new 0D perovskites with commercialized blue phosphor, I have successfully fabricated down conversion white LEDs with high color quality. For example, a new type of mixed halide 0D perovskite, (C4N2H14Br)4SnBrxI6–x (x = 3), with a PL emission peak of 582 nm, a larger FWHM of 126 nm and a high PLQEs of 85% have been used as yellow phosphors in down conversion LEDs. By overcoming the issue of deficiency in the red emission present in most yellow phosphors, this 0D tin mixed-halide perovskite enabled optically pumped WLEDs with high color rendering index (CRIs) of up to 85. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 20, 2018. / CH3NH3PbCl3, hole transport layer, light emitting diodes, OLEDs, perovskites, quasi-2D perovskites / Includes bibliographical references. / Biwu Ma, Professor Directing Dissertation; Peng Xiong, University Representative; Eric Hellstrom, Committee Member; Theo M. Siegrist, Committee Member; Chen Huang, Committee Member.

Self-assembled bilayers consisting of a monolayer of molecules, a metal linking ion and a second molecular layer were prepared and used in controlling critical energy and electron transfer events in dye-sensitized solar cells (DSSCs). DSSCs have shown promise as an alternative to traditional silicon solar cells due to their ease of fabrication and lower manufacturing costs. Despite the high efficiency to cost ratio, DSSCs face the limitations of detrimental recombination across the dye-semiconductor interface as well as narrow absorption transitions which respectively lower the open circuit voltage and short circuit current of these cells. Bilayers consisting of a bridging molecule, zirconium metal ion and N3 dye were assembled on a nanocrystalline metal oxide electrode as a means of inhibiting deleterious recombination processes in DSSCs. Bilayer formation was confirmed by ATR-IR and UV−vis spectroscopy. Interfacial electron transfer events in DSSCs were characterized by electrochemical and photophysical measurements. The results show an increased electron lifetime, diffusion length and open circuit voltage with increasing bridge length. The increased separation between the TiO2 and dye however also reduced injection rate, by extension, photocurrent and the overall efficiency of the DSSC devices. Self-assembled bilayer was also used to achieve broadband light harvesting in DSSCs by incorporating two complementary absorbing dyes. The bilayer here consisted of a monolayer of pN3 dye, zirconium metal ion and p1M dye. The UV-vis and ATR-IR absorption spectra of the bilayer were found to be the sum of the individual dyes. The bilayer devices also demonstrated about 10% higher photocurrent, voltage and power conversion efficiency over the monolayer DSSCs. This was attributed to slower recombination losses at the TiO2-dye1-dye2-electrolyte interfaces as well as higher photon-to-current conversion efficiency across the visible spectrum. A key factor towards the higher performance of the bilayer is directional energy and electron transfer from p1M to pN3 dye. Investigations into the role and properties of the metal ion when coordinated to a dye was further performed to understand how the nature of the metal ion influence the dynamics of the different processes at the dye-semiconductor interface. This can allow optimization of the bilayer architecture and enable its use for an even wider range of applications. 8 different metal ions were studied and coordination to the dye was confirmed by XPS, ATR-IR and UV-vis. Metal ion coordination had minimal influence on energetic levels of the dye with minimal shifts observed. Results suggest that electrostatic interactions between the metal ion and the iodide/triiodide species in the electrolyte as a primary determining factor in the rates of regeneration, back electron transfer and recombination processes as well as the photovoltaic parameters. A remarkable improvement of 130 mV was achieved with two of these metal ions. X-ray photoelectron spectroscopy was used to study the effect of zinc and zirconium metal ion treatment on the core binding energies of un-sensitized and sensitized TiO2 thin films. The metal treatment included treating the TiO2 film with metal ions without further treatment (TiO2 (Mn)) as well as prior to dye sensitization (TiO2 (Mn)-N3). Metal coordinated samples were also prepared (TiO2-N3-Mn). The results indicate there is no change in chemical state of the TiO2 but suggest that zinc treatment might have significant influence on the sulphur atom in the N3 dye. This interaction may also be a clue as to its perturbed diode behavior. / A Dissertation submitted to the Materials Science and Engineering Program in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 13, 2018. / bilayer, dssc, electron transfer, recombination, self-assembled / Includes bibliographical references. / Kenneth Hanson, Professor Directing Dissertation; Simon Foo, University Representative; Hanwei Gao, Committee Member; Eric Hellstrom, Committee Member; Zhibin Yu, Committee Member.

Two Dimensional Materials has been the focus of much research in the past decade. We review 145 stable two dimensional materials in both bulk and monolayer. We compare their final electronic properties and discuss the results. Specifically, we discuss notable materials that have transitions between bulk and monolayer. Additionally, we use both the bulk and monolayer data to search for structural trends that may be corralated with the electronic properties using machine learning techniques. We find that our machine was able to produce results that predict the basic electronic properties with approximately 65% accuracy. / A Thesis submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / July 17, 2018. / Monolayer, Two Dimensional Materials / Includes bibliographical references. / Jose Mendoza-Cortes, Professor Directing Thesis; Stratos Manousakis, Committee Member; Chen Huang, Committee Member.

In the last decade, biological molecules such as Deoxyribonucleic acid (DNA) and some proteins have attracted attention as material candidates for molecular electronics applications. Yet, despite numerous studies of electron transport in DNA in particular, inconsistencies in experimental results persist. As a result, both the degree and mechanism of charge transport in these biological molecules remain disputed. To understand if different binding configurations of DNA on metal electrodes through unexpected moieties could be responsible for experimental inconsistencies in the literature, we investigate whether small molecules ubiquitous in both nucleic acids and amino acids, such as purines and imidazole, bind to gold electrodes and produce conductance signature. In this study, we use the Scanning Probe Microscope-based Break Junctions approach method to study single molecule conductance and binding geometry of the purine bases of DNA, particularly adenine and guanine. In addition, the Conductive Atomic Force Microscope-based Break Junction (CAFMBJ) platform has been created to simultaneously measure both electrical and mechanical properties of these single molecule junctions. Our measurements indicate that purines bind in the junction and display several robust conductance signatures on gold. We find that both purine and adenine bind through the imidazole, which is identified, for the first time, as a new linker group for single molecule conductance measurements.

REBCO (REBa2Cu3O7-δ, RE=rare earth elements) coated conductor (CC) is one of the best candidates for building high-field magnets and it has been improved greatly in recent years. CC overcome the grain boundary problem by using either a rolling assisted biaxially textured substrate (RABiTS) or ion beam assisted deposition (IBAD) of a template for the REBCO. Artificial pinning centers were also introduced to increase critical current density. Despite all these improvements, one significant residual problem is lengthwise critical current (Ic) variations of the CCs. Characterizations of CCs can not only identify the variations, but also provide insight that can help improve the manufacturing process. This study focuses on cross-sectional and vortex pinning variations in CCs. With the reel-to-reel Ic and magnetization measurement system (YateStar), a systematic study has been carried out for CCs made in the last 5-6 years as this technology has rapidly developed. We found that cross-section variations exist for almost all conductors because of width variations. But this contribution to the total Ic variation is small. Vortex pinning variations are found to be the main reason for Ic variations, especially for conductors from different production runs. Even for conductors from the same run, pinning variations are often present. Microscopy studies show that the density and length of BaZrO3 (BZO) nanorods vary between different conductors even though they have nominally the same specifications. Pinning variations in one single tape are mostly attributed to the size variations of BZO nanorods and the configurations of RE2O3 precipitates. Deconstruction of magnet coils and cables were carried out to understand the reasons for in-service degradation. The prototype coil for the 32 T project was safely quenched more than 100 times but it degraded in 3 spontaneous quenches (conducted in an accelerated fatigue testing campaign at ramp rates much larger than service specification). Its pancake coil deconstruction showed three extremely localized burned regions, whose temperature went to over 800oC based on the appearance of a Cu-Ag eutectic above the damaged REBCO layer. Transverse propagation of the damage was almost as effective as longitudinal propagation. Transmission electron microscope images show that thicker BaZrO3 (BZO) nanorods exist near the centers of damaged zones, compared to longer and thinner BZO nanorods from normal, good regions. Because of the lack of detailed Ic(x) characterizations of the length prior to use, the cause the cause of the coil degradation is not clear. It is possible that local degradation of the vortex pinning initiated the final quenches but another possibility is indicated by deconstruction of a no-insulation coil, which reached 45.5 T in a background field of 31 T. In this case no burn marks were observed but some tapes were heavily deformed on one edge, and some joints delaminated after quenches. Transport measurements show that the deformations correlate to Ic degradations, especially for the outer turns of pancakes. Microstructural studies reveal that the deformed (and cracked) edges are always the one that were slit during manufacturing. It appears that small, pre-existing micro-cracks on slit edges propagate after high-field tests. Study of individual strands of conductor on round core (CORC®) cables demonstrated their steady improvements in the last few years. Overall cable current density, Je, has been greatly improved by replacement of 50 m by 30 m thick substrate in CCs and improved winding procedures cause no damage to the tapes. However, some degradation may appear after cables are bent and tested in high-field (20 T). It is found that inner layers are more vulnerable than outer layers. Winding angles and gaps strongly influence where degradations start. To understand the failure mechanisms and establish the limiting winding conditions for CORC® cables/wires, tapes were wound on different formers at different angles: 23o, 30o, 45o and 60o. For a 2 mm former diameter, the highest winding angle gives the least degradation while the other three are comparable. A major defect type introduced during winding is propagation of pre-existing edge (slitting) cracks, but some delamination under winding stress can also be seen. For the former with 2.54 mm in diameter, no propagations of pre-existing cracks or delaminations were observed after winding. Our studies of CCs made and tested in different ways has shown that further improvement of CC and of CORC® cables/wires can be made and also that some inherent features of the manufacture of CCs exert a strong influence on their service performance. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / November 17, 2017. / Includes bibliographical references. / David Larbalestier, Professor Co-Directing Dissertation; Jan Jaroszynski, Professor Co-Directing Dissertation; Timothy Cross, University Representative; Eric Hellstrom, Committee Member; Christianne Beekman, Committee Member; Theo Siegrist, Committee Member; Dmytro Abraimov, Committee Member.

A bio-inspired, modular terpolymer adhesive has been synthesized containing three different functionalities: a photocrosslinking segment, wet adhesion segment, and a water soluble segment. Wet adhesion is brought on by an amino acid from mussel byssal plaques called 3,4-dihydroxyphenyl–L-alanine, which has been known to generate strong bonding under wet conditions. The photocrosslinking segment consists of an anthracene based monomer used for mechanical fortification of polymer chains. The water soluble segment consists of poly(acrylic acid), which has been known to increase water solubility of polymers and increase adhesion strength of adhesives. The terpolymer was designed to easily applicable using biologically friendly solvents including water and ethanol. Structural design was confirmed by NMR and UV-Vis spectroscopy. Reversible cycloaddition reactions were executed using a handheld UV lamp along with a photoreactor. Molecular weight increases were seen from 4.120 x 10⁴ Da to 7.429 x 10⁴ Da. Lap shear strength testing showed effects of UV exposure through increases in adhesion energy above 450%. Multiple application variables were tested to determine optimal conditions, such as solvent, concentration, and substrate. Currently, optimal conditions show a 1:1 weight ratio of polymer:solvent in water for all surfaces. / A Thesis submitted to the Materials Science and Engineering Program in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / November 5, 2015. / Adhesives, Anthracene, Biomimetic, DOPA, Photo-crosslinking, Terpolymer / Includes bibliographical references. / Hoyong Chung, Professor Directing Thesis; Justin Kennemur, Committee Member; William Oates, Committee Member.

Osteoarthritis (OA) is a debilitating condition of articular cartilage that leads to pain and severe limitations in mobility. The generation of functional tissue-engineered cartilage in vitro that can be used for cartilage repair is a growing and promising OA treatment strategy. However, there exists a fundamental challenge in generating engineered cartilage which possesses native levels of cartilaginous extracellular matrix constituents (glycosaminoglycans [GAG] and type-II collagen) and mechanical properties, leaving engineered tissues inferior to their native counterparts and inherently more vulnerable to degeneration upon implantation in the mechanical environment of the synovial joint. In particular, while engineered cartilage tissues generally synthesize GAG at a rapid rate, the content of collagen is far more limited, compromising the tensile stiffness and long-term stability of engineered cartilage. A promising strategy has recently been developed to promote collagen enhancements in engineered cartilage. Here, GAG-degrading enzymes (e.g. chondroitinase, hyaluronidase) are administered to the tissues, which digest and suppress the accumulation of abundantly synthesized GAG matrix molecules, providing more room in the tissue for collagen deposition. While the short term exposure of high doses of these enzymes has exhibited measured success in enhancing tissue collagen levels, it is further associated with considerable limitations such as limited tissue penetration and significant loss of cell viability. A major goal of this research project is to optimize the delivery of GAG-depleting enzymes to achieve sufficient levels of GAG depletion without loss of cell viability. However, these enzymes exhibit highly complex transport kinetics into engineered tissues, influenced by ECM binding interactions and activity kinetics. As such, the methodology to optimize the concentration and temporal exposure of these enzymes remains quite complex. In the first study of the thesis, the effect of different doses of hyaluronidase supplement in tissue engineering is investigated. In the following chapter, an optimized fluorescent conjugation to hyaluronidase to maintain functionality is studied, then the transport distributions of the hyaluronidase in live tissue constructs are observed. The results demonstrate that fluorophore labeled hyaluronidase with a degree of labeling of 1 still remain 90% functionality. And the GAG content and cell viability in constructs are vary after being treated with hyaluronidase of different concentration. These results pave the path for future development of the application of hyaluronidase in cartilage tissue engineering.

Osteoarthritis (OA) is a painful, debilitating condition that results from the mechanical degeneration of articular cartilage. Cartilage tissue engineering is a promising OA therapy, whereby chondrogenic cells are encapsulation in a hydrogel scaffold and cultivated in vitro in an attempt to create a suitable replacement tissue. Transforming growth factor-beta (TGF-b) is a highly anabolic hormone that has served as one of the most prominent cartilage growth mediators, promoting the development of engineered tissues with native levels of mechanical properties and biochemical contents. In cartilage tissue engineering, TGF-b is conventionally administered supplemented in culture medium with the expectation that it will readily diffuse into tissue constructs. However, recent evidence has brought to light severe limitations with this approach when attempting to generate engineered cartilage of sufficient size to repair clinical OA defects (10-25mm), as mediasupplemented TGF-b exhibits vast transport limitations in constructs, giving rise to undesirable, highly heterogeneous cartilage formation. Consequently, a long-term goal of our research group is to develop novel TGF-b chemical delivery strategies that achieve improved uniformity of its activity in the tissue. Critically, the development of these strategies require a fundamental understanding of the optimal delivery profile (exposure concentration and duration) of TGF-b activity to achieve optimal cartilage tissue growth. Interestingly, while low doses of TGF-b are typically associated with insufficient growth and matrix deposition, supraphysiologic doses are associated with the induction of pathological tissue features, such as fibrosis, chondrocyte hypertrophy and the clustering of chondrocytes in a phenotype that does not resemble healthy articular chondrocytes. Here we perform this characterization by examining the effect of near physiologic doses (0.1- 1ng/mL) and supraphysiologic doses (3-100ng/mL) of TGF-b on constructs growth. Further, we exposed tissue constructs to varying temporal delivery profiles. Results demonstrate that, interestingly, physiologic TGF-b doses (0.1-1 ng/mL) induce the formation of engineered cartilage with native mechanical properties (350-780 kPa) but with improved tissue quality, as marked by more isolated chondrocytes that resemble the phenotype of native cartilage. These results pave the path for the future development of large sized engineered cartilage tissues, whereby, physiologic levels can be delivered uniformly throughout the tissue via biomaterial delivery strategies. / 2020-07-02T00:00:00Z