Browsing by Subject "Defect"
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Item Aspects of supersymmetric defects in theories of class S(2022-04-21) Hao, Qianyu; Distler, Jacques; Neitzke, Andrew; Ben-Zvi, David; Kilic, Can; Paban, SoniaClass S theories are an important type of 4d N = 2 theories drawing people’s attention. This thesis aims to talk about several interesting parts related to supersymmetric defects. We begin with an introduction containing some background for the Class S theory. An important piecewise invariant we can calculate in a class S theory is the BPS index, it can be obtained using supersymmetric interfaces. We study a specific example of Minahan-Nemeschansky E₇ theory, and calculate BPS indices using spectral network. This part is based on the joint work with Lotte Hollands and Andrew Neitzke[85]. We also introduce a special type of theories found in class S theories which are actually factorized into multiple decoupled nontrivial theories. We propose a way of constructing examples of this phenomenon using the physics of surface defects, and check that it works in one simple example. We also present explicit checks that the Coulomb branch of a putative factorized class S theory has the expected product structure, in two examples. This is based on the joint work with Behzat Ergun, Andrew Neitzke and Fei Yan[54]. At last, we introduce a connection between 4d N = 2 theories and differential equations, and enlarge the dictionary to include the 2d-4d BPS states. We study different definitions of quantum periods which are related to vevs of line defects in the example of SU(2) N [subscript f]=1 theory and provide some evidence for the equivalence between different definitions. This is based on the joint work with Alba Grassi and Andrew Neitzke[79].Item Automatic semiconductor wafer map defect signature detection using a neural network classifier(2010-12) Radhamohan, Ranjan Subbaraya; Ghosh, Joydeep; El-Hamdi, MohamedThe application of popular image processing and classification algorithms, including agglomerative clustering and neural networks, is explored for the purpose of grouping semiconductor wafer defect map patterns. Challenges such as overlapping pattern separation, wafer rotation, and false data removal are examined and solutions proposed. After grouping, wafer processing history is used to automatically determine the most likely source of the issue. Results are provided that indicate these methods hold promise for wafer analysis applications.Item Design of magneto-inductive waveguide for sensing applications(2014-05) Chen, Ye, 1986-; Neikirk, Dean P., 1957-This dissertation has been motivated by the increasing application of sensing technologies in structural health monitoring. Many wireless sensor techniques exist for structural health monitoring while a challenge faced is the finite lifetime of batteries. The objective of this dissertation is to develop passive wireless technology to provide early warning of conditions that damage the structure. In this dissertation, sensing mechanism is proposed based on time and frequency domain characteristics of magneto-inductive (MI) waves. Experimental results are also presented to demonstrate the sensing mechanism. MI waves are predominantly magnetic waves that are supported in periodic arrays of magnetically coupled resonators and propagate within a narrow frequency band around the resonant frequency. The array is to be embedded in a structure and different types of transducers can be integrated for different sensing applications. With the onset of structure defect, the transducer introduces an impedance discontinuity that generates reflected MI waves along the array, which are monitored and processed by Smoothed Wigner-Ville distribution (WVD) to extract time-of-flight for frequency components in the narrow passband. The transmission and reflection coefficients of MI waves are also investigated based on the lumped-element circuit model of the array. Based on MI waves travel time, amplitude and group velocity, the position and severity of structure defect are decided. The sensing mechanisms for different distribution of defects are proposed. The validity of the sensing mechanism is examined in experiments. The guided wave testing is implemented in one-dimensional square-shaped printed spiral resonators with Q-factor of 161 at 13.6 MHz. It demonstrates that low MI waves propagation loss is achieved with value of 0.098 dB per element at mid-band with center-to-center distance of half an inch. A pitch-catch measurement system is built to capture traveling MI signal in resonant element and extract group velocity, and a pulse-echo measurement system is designed to monitor reflected MI signal and locate structure discontinuity. In both measurement systems, MI waves are excited with wide bandwidth voltage pulse, and a digitizer is attached to sense the MI signal in a specific resonant element circuit. A baseline signal is obtained from the healthy state to use as reference and comparison with the test case using pitch-catch system. The test signal subtracted from baseline signal infers the structure damage information with time and frequency domain characteristics. It can offer an effective method to estimate the structure discontinuity location, severity and type of damage. The experimental results are consistent with the theoretical predictions. At the end, future directions for the research to integrate with other technologies are suggested.Item Engineering two-dimensional materials : discovery, defects, and environment(2021-05-21) Holbrook, Madisen A.; Shih, Chih-Kang; Shi, Li; Li, Xiaoqin; Lai, KejiThe discovery of graphene and its unprecedented properties inspired an extraordinary increase in research progress, launching an era of two-dimensional (2D) electronic materials. These stable crystalline atomic layers enable the design of ultrathin 2D devices by combining different 2D materials as the foundational components. In order to control the properties of these devices, materials with a variety of electronic properties must be available. In this dissertation, we explore three distinct paths to achieve this goal: expanding the library of 2D materials, post synthesis defect engineering, and proximity engineering of the electrostatic environment. First, we report the MBE synthesis and STM/S characterization of a new 2D insulator, honeycomb structure BeO. In addition to determining the atomic structure and density of states, we used moiré pattern analysis to demonstrate the high crystallinity of the BeO and determined the work function modulation across the moiré pattern. We illustrate that the scalable growth, weak substrate interactions, and long-range crystallinity make honeycomb BeO an attractive candidate for future technological applications. The next focus of this work was defect engineering of monolayer WS₂ by UHV annealing. A high concentration of S vacancies was generated by UHV annealing of the WS2, leading to S vacancy defect-defect coupling. Using STM/S we determined that the interaction of nearby S vacancies leads to an increase of deep in-gap states for different divacancy geometries. This indicates that vacancy engineering can be a useful tool to controllably manipulate 2D material electronic properties. Finally, we demonstrate the creation of a nanoscale planar p-n junction within a single monolayer of MoSe₂ by modulating the electronic properties of the underlying substrate. By intercalating Se at the interface of the hBN/Ru substrate, the hBN becomes decoupled from the Ru, changing its conductivity and work function. We find that this change in the electronic landscape tunes the band gap of the overlying MoSe₂, by screening and shifting the MoSe₂ work function. Thus, this dissertation shines a light on the vast opportunities 2D materials provide for exploration of novel approaches to materials engineering, and demonstrates a tool set for manipulating the electronic properties of these fascinating materials.Item Growth and defect engineering of two-dimensional materials for memristor improvement(2022-07-29) Gu, Yuqian; Akinwande, Deji; Lee, Jack C.; Liechti, Kenneth M.; Incorvia, Jean Anne; Register, Leonard F.The non-volatile resistive switching phenomenon has been widely observed recently in the Two-dimensional (2D) materials down to monolayer, with promising memristor applications. However, many fundamental challenges for 2D memristors remain towards industrialization, including large-scale growth of 2D thin films and device reliability. This dissertation presents a feasible method for wafer-scale synthesis of MoS₂ and WS₂ films and multiple strategies to improve the reliability of 2D memristor. In Chapter 2, a significant improvement in yield and endurance has been demonstrated with defect engineering. The E-beam irradiation effect on MoS₂ is detailed studied with material characterization and Montre Carlo simulations. Chapter 3 presents a simple one-step low-temperature sulfurization process to synthesize wafer-scale few-layer MoS₂ and WS₂. The sulfurized film-based memristors show stable non-volatile switching and a satisfactory on/off current ratio. The impact of sulfurization parameters on film quality has been systematically studied to guide device optimization. The performance of memristors based on MoS₂ grown with sulfurization parameters is evaluated and compared. A qualitative model is proposed to provide more insight on reliability improvement with sulfurization parameters adjustment. In Chapter 5, MoS₂ memristors under fabrication configurations are comprehensively compared. Considerable reliability (yield and endurance) improvements are achieved by reducing top electrode deposition rate and increasing MoS₂ thickness. The statistical analysis further reveals an intriguing convergence of switching metrics, despite the reliability difference. The reliability improvements and independence switching metrics can be understood with a proposed general-purpose “active layer” model. Monte Carlo simulations have been performed to provide a more intuitive understanding of endurance failure mode associated with the formation of clusters in the active layer.Item Resistance training as a modality to enhance muscle regeneration in a rat skeletal muscle defect(2009-12) Taylor, Daniel Ryan; Farrar, Roger P.; Suggs, LauraTraumatic skeletal muscle injuries that include loss of large amounts of muscle mass are becoming more common in today’s warfare. Traditional treatments often do not prevent long term functional impairments. Using a decellularized extracellular matrix (ECM) as scaffolding to replace lost muscle tissue allows for transmission of force through the injury site, and provides a suitable microenvironment receptive to myofiber growth. Seeding the ECM with progenitor cells improves cellular content in the defect area. Exercise exposes the muscle to improved blood flow as well as higher than normal loading. This results in increased blood vessel density as well as higher levels of cellular content, and near complete restoration of function.