1,720,968 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Time Domain Optical Coherence Tomography (OCT) for MEMS-based Endoscopic Application
No full textThesis (Master's)--University of Washington, 2014As an innovative bio-tissue imaging modality, Optical Coherence Tomography (OCT) endoscope remains attractive due to its high resolution, capability of subepithelial morphology imaging, compact size and low cost of system. Recently, a MEMS-based endoscope scanner is demonstrated to have the ability of focus-tracking and 2D lateral scanning. A time-domain OCT employing Rapid Scanning Optical Delay Line (RSOD) is constructed based on the need of this new MEMS scanner. The effect of dispersion compensation is discussed. An axial resolution of 20 μm and a lateral resolution of 30 μm is demonstrated
Large Infrared Optical Tweezer Array
No full textThesis (Master's)--University of Washington, 2012A summary of an attempt to build a large optical tweezer array for trapping cancer cell nuclei is described. Our system was ultimately unable to trap a large array of cell nuclei but was able to trap a large array of polystyrene beads. Our optical trap array method is described as well as its drawbacks and advantages and the potential modifications that could improve the systems performance. The system utilized an amplitude-modulated spatial light modulator to generate an array of individually addressable optical traps. The optical source for trapping radiation was a neodymium-doped yttrium vanadate crystal laser (Nd:YVO4) which produces light at a wavelength of 1064 nm. (The system utilized a Texas Instruments digital micro-mirror device as a spatial light modulator, a Zeiss Axio-Imager microscope to view the sample and focus the laser light, and a Spectra-Physics CW, Nd:YVO4,1064 nm laser.
Design and Fabrication of Perovskite Micro-Cavity Lasers
No full textThesis (Master's)--University of Washington, 2016-08Over the past several years, research of methylammonium trihalide perovskite solar cells has led to a rapid increase in the efficiency of single p-n junction perovskite solar cells, from 6.5% in 2012 to 22.1% in 2016. Favorable optical properties make CH3NH3PbI3 perovskite a promising candidate for performing at the Shockley-Queisser limit; the theoretical maximum efficiency of single p-n junction solar cells, and a commonly cited goal for photovoltaics researchers. To operate at this limit, the gain material must exhibit purely radiative recombination. Thus, research in photovoltaics is actively trying to improve the quality of thin-film perovskite in order to maximize its efficiency not only as a light absorber, but as a light emitting material. A high-quality optical micro-cavity requires patterning of microstructures, which is made difficult by perovskite’s sensitivity to chemicals used in conventional fabrication processes. This thesis describes three designs of a perovskite laser: 1) a silicon nitride photonic crystal cavity coupled to a perovskite gain medium, 2) whispering-gallery mode lasers made by chemically reflowing perovskite, and 3) an electrically-pumped distributed feedback laser
Metal Halide Perovskite Light-Emitting Materials and Devices
No full textThesis (Ph.D.)--University of Washington, 2020Metal halide perovskites were first rediscovered for photovoltaic applications in 2009. The performance of perovskite solar cells has undergone a rapid advancement with power conversion efficiency (PCE) increasing from 3.8% to over 25%, comparable to state-of-art commercial solar cells. Recent findings on excellent optoelectronic properties of perovskites like high photoluminescence quantum yield (PLQY), good charge transport and bandgap tunability motivate researchers to explore their applications in light-emitting devices such as light-emitting diodes (LEDs), multicolor displays and laser diodes. In this dissertation, I first introduce the development of perovskite LEDs (PeLEDs) and analyze key factors affecting the external quantum efficiency (EQE). The high refractive index of perovskites limits the light outcoupling efficiency to 20-25%. The next step to further increase EQEs should be focused on enhancing light extraction. Through an optical simulation, I found the emitter dipole orientation plays an important role. This finding may provide guidance on further performance boost of PeLEDs. CsPbI3 is the lowest bandgap all-inorganic perovskite, targeted for covering the red corner of CIE chromaticity diagram. However, CsPbI3 bulk films transition to undesirable orthorhombic phase at room temperature. CsPbI3 QDs are much more phase stable due to the reduced surface energy. Based on CsPbI3 QDs, I demonstrate a stable red-emission PeLED. To push perovskite materials towards commercialized display applications, I developed a high-resolution photolithographic approach to pattern multicolor perovskite thin films. This approach is based on a dry lift-off process, addressing the incompatibility of perovskites to common polar solvents. Using this approach, we fabricated a multicolor pixel array for liquid crystal displays (LCDs) and a prototype perovskite mirco-LED display. Besides great potential in display applications, perovskites have renewed people’s hope for achieving the long-standing goal of solution-processable electrically pumped laser diodes. I first demonstrate perovskite lasers integrated with distributed Bragg (DBR) and distributed feedback (DFB) cavities under optical pumping. Towards electrically pumped laser diodes, I suppressed the efficiency roll-off (droop) of perovskite LEDs by applying combined strategies. Finally, devices could be operated at high current densities up to 1 kA/cm2. Future work will be integrating DFB cavities with perovskite LEDs to approach the ultimate goal
FAIR Modeling for Perovskite Solar Cells: An Open Source Machine Learning Pipeline
Get PDFThesis (Master's)--University of Washington, 2023Perovskite solar cells (PSCs) show great promise for commercialization, rivaling traditional silicon-crystal solar cell efficiency despite their comparatively short research lifetime. This efficiency is achieved while being manufactured at low temperatures and in ambient conditions, lowering fabrication costs dramatically. Machine learning (ML) promises to significantly expedite further optimization by recommending novel configurations based on insight from existing literature. This paper utilizes the Perovskite Database Project (PDP), an open source PSC database consisting of over 43,000 entries from published literature, to train three ML architectures with short circuit current density (J) as a target. Using the XGBoost architecture, an RMSE of 3.73 , R-value of 0.63, and MPE of 10.35% were achieved. This performance is comparable to the results reported in literature and through further investigation could likely be improved. To overcome the challenges of manual database creation, an open-sourced data cleaning-pipeline was created to leverage the PDP. Through the creation of these tools this research aims to increase the availability of ML as a tool to promote improvement in novel device configurations for PSC while showing the already promising performance achieved
Efficient, stable perovskite solar cells enabled by electrode interface engineering and nanoscale phase stabilization
No full textThesis (Ph.D.)--University of Washington, 2017-08Semiconducting metal halide perovskites have emerged as a promising solution-processable, photovoltaic material with research cell power conversion efficiencies now exceeding 22% under simulated sunlight. The prototypical composition of this “ABX3” semiconductor is CH3NH3PbI3, in which organic methylammonium cations charge stabilize lead iodide octahedra. Research is underway on mixed component systems with A-site cation combinations of methylammonium, formamidinium, cesium, and rubidium; B-site cations of Pb2+ and Sn2+; and iodide, bromide and chloride anions. Although perovskite solar cells with low-cost fabrication methods have demonstrated impressive power conversion efficiencies, device durability remains a key concern of the technology. In this dissertation, the effect of the anode electrode material on the device lifetime is characterized under constant operating conditions. It is demonstrated that MoOx/Al electrodes are more stable than commonly used Au or Ag electrodes. Interestingly, the enhanced stability of MoOx/Al electrodes is due to the formation of an oxide at the MoOx/Al interface, which likely prevents ion migration between the device layers, as opposed to encapsulation from environmental agents. I also demonstrate a more stable photoactive layer comprised of CsPbI3 quantum dots (QDs). CsPbI3 is the lowest bandgap, all-inorganic lead halide perovskite, and has shown remarkable chemical and thermal stability up to 400 °C. However, bulk and thin film CsPbI3 transitions to the undesired orthorhombic phase when cooled to room temperature. CsPbI3 QDs have unique surface properties which alter the phase transitions and successfully maintain the photoactive cubic phase at room temperature and even well below. In addition to reporting the first demonstration of an all-inorganic CsPbX3 nanocrystal solar cell, I also detail new QD surface treatments that improve the short circuit current density of the devices by doubling the QD film mobility. These advancements led to an NREL-certified QD solar cell efficiency of 13.43% that is currently the record efficiency reported for a QD solar cell of any material system. In this dissertation, I assess operational stability of thin film organic-inorganic perovskite solar cells, fabricate more durable electrodes, develop novel CsPbI3 QD photovoltaic devices and discover new surface modifications to improve charge transport in efficient perovskite QD solar cells
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Flexible Colloidal Quantum Dot Photodetection with Cellulose Structures
No full textThesis (Ph.D.)--University of Washington, 2016-08This thesis will outline a new way of fabricating flexible photodetectors. Solution-processable colloidal quantum dots (QDs, or nanocrystals(NCs)) are incorporated into cellulose structures to form a composite structure that can be used for photodetection. This enables new ways of device fabrication and also makes ultrathin, ultraflexible and even transparent optoelectronic devices possible. Inkjet printing with an office inkjet printer is introduced and applied towards PEDOT:PSS transparent electrode deposition. This offers a low cost method for material deposition. Flexible photoconductors are fabricated with these electrodes and CdSe quantum dot embedded tracing paper by utilizing the porous cellulose structure. Consistent photoresponse is achieved with such a structure under 550nm light illumination. After further realizing the shortcomings of tracing paper for its large thickness and low porosity, which both deteriorate the performance of these devices, natural plant-membranes are chosen as an alternative and offer superb properties for optoelectronic device fabrication. Visible-blind self-powered ultra-violet detectors are designed and fabricated with the incorporation of ZnO NCs on reed membrane. Schottky junction devices are fabricated with the use of gold and aluminum as the electrodes. Sub-second responses are observed at a bias of zero, which is superior than most of the flexible photoconductors in the literature. An external quantum efficiency of over 3% is discovered with the device at 350nm light illumination under zero bias. A great performance enhancement is also observed on the devices fabricated on reed membrane comparing to the ones on tracing paper. Nanofibrillated cellulose(NFC) can be readily used to fabricate transparent papers. ZnO NC-NFC composite structure is prepared and fabricated into ultrathin transparent papers with a thickness less than 1 micrometer. Self-powered Schottky photodiodes are fabricated on such papers and relatively fast response is observed at zero bias
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