Detection and Removal of Long Scratch Lines in Aged Films

[[abstract]]Historical films usually have defects. We study the type of defects, and propose a series of solutions to detect defects before they are repaired by our inpainting algorithms. This paper focuses on a difficult issue to locate long vertical line defects in aged films. A progressive detection algorithm is proposed. We are able to detect more than 86% (recall rate) of effective line defects. These line defects are then removed step by step. The experiments use real historical video collected from national museum and public channel, instead of using computer generated noise. The results are visually pleasant based on our subjective evaluation by volunteers[[conferencetype]]國際[[conferencedate]]20060709~20060712[[iscallforpapers]]Y[[conferencelocation]]Toronto, Ont., Canad

Laser Surface Texturing, Crystallization and Scribing of Thin Films in Solar Cell Applications

Thin films have been considered for use in terrestrial solar cell applications because of their significantly reduced cost compared with bulk crystalline silicon. However, their overall efficiency and stability are less than that of their bulk crystalline counterpart. The work presented in this thesis seeks to investigate these issues via a series of experimental and numerical analysis of the influences of laser processing on microstructure, optical and electrical properties of two absorber materials, a-Si:H (hydrogenated amorphous silicon) and CdTe (cadmium telluride). a-Si:H thin film solar cells suffer from disadvantages of low efficiencies and light induced degradation. A one-step laser processing is investigated for introducing light-trapping structure and crystallization on a-Si:H thin films, which can potentially simultaneously alleviate the two weaknesses of a-Si:H. The nanoscale conical and pillar-shaped spikes formed on the surface of a-Si:H films by irradiation of both femtosecond (fs) infrared and nanosecond (ns) excimer lasers enhanced light absorption, while the formation of a mixture of hydrogenated nanocrystalline silicon (nc-Si:H) and a-Si:H after crystallization suggests that the overall material stability can potentially improve. It is shown that growth is a more dominant spike formation mechanism in excimer laser processing, rather than ablation which is dominant during fs laser texturing. Experimental and analytical approaches are also developed revealing the effect of hydrogen on texturing behavior and crystallization during excimer laser irradiation, and a step-by-step crystallization process is proposed to prevent the hydrogen from diffusing out in order to reduce the defect density. In addition, a comparison of absorptance spectra for various surface morphologies and crystallinity is developed and the absorptance across the solar spectrum shows that the combination of surface texturing and crystallization induced by laser processing is very promising for a-Si:H thin film solar cell applications. CdTe thin-film solar cells are the basis of a significant technology with major commercial impact on terrestrial photovoltaic production, since CdTe leads to substantial cost reduction. Laser scribing is a key process used to increase thin-film solar panel efficiency through the formation of serial interconnections to reduce photocurrent and resistance losses. Currently, scribing is performed using glass-side laser processes which have led to increased scribe quality. Defects formed during scribing such as micro cracks, film delamination, thermal effect and tapered sidewall geometries, however, still keep solar panels from reaching their theoretical efficiencies. In this study, a ns Nd:YAG laser operating at the fundamental (1064nm) or frequency-doubled (532nm) wavelengths is employed for pattern 1 (P1) and 2 (P2) scribing on CdTe thin-film solar cells. The experimental investigation shows that film removal mechanisms for different materials are due to laser-induced ablation, thermal stress and micro-explosion processes. The formation mechanisms and mitigation techniques of the defects during micro-explosion process are studied. A fully-coupled thermal and mechanical finite element model is developed to analyze the laser-induced spatio-temporal temperature and thermal stress distribution responsible for SnO2:F film removal, and a plasma expansion model is also investigated to simulate the film removal of CdTe/Cds multilayer due to the micro-explosion process. The characterization of removal qualities will enable the process optimization and design required to enhance solar module efficiency

Improved Sample Loading for Plutonium Analysis by Thermal Ionization Mass Spectrometry and Alpha Spectroscopy

Thermal ionization mass spectrometry (TIMS) and alpha spectroscopy are powerful analytical techniques for the detection and characterization of Pu samples. These techniques are important for efforts in environmental monitoring, nuclear safeguards, and nuclear forensics. Measurement sensitivity and accuracy are imperative for these efforts. TIMS is internationally recognized as the “gold standard†for Pu isotopic analysis. Detection of ultra-trace quantities of Pu, on the order of femtograms, is possible with TIMS. Alpha spectroscopy has a long history of use in the detection and isotopic analysis of actinides and can be a simpler and less expensive alternative to mass spectrometer based techniques. The sensitivity and accuracy of both techniques is highly dependent upon the method of sample loading. High quality sample loading is often tedious, time consuming, and expensive. In this work, we sought to simplify and improve high quality sample loading for TIMS in an effort to expand the utility and improve the sensitivity of this technique. During these efforts a promising sample loading method for alpha spectroscopy was developed. Three improvements were developed for sample loading procedures for isotope ratio measurements of ultra-trace quantities of Pu using (TIMS). Firstly, a new filament geometry, the “dimpleâ€, was developed. The bead loading method was used for these analyses. Beads were loaded with New Brunswick Laboratory certified reference material (NBL CRM) Pu128 (239Pu and 242Pu) from an 8M HNO3 matrix. Overall ion counts and isotopic ratios measured using the dimpled filament geometry were compared to those measured when using the established V-shaped filament geometry. The average number of Pu counts detected when using dimpled filaments was approximately 34% greater than ion counts detected using V-shaped filaments. The accuracy and precision of isotopic ratio measurements were unaffected by the use of dimpled filaments. The well-like geometry of dimpled filaments aids in sample loading and alignment. Additionally, the use of dimpled filaments was found to reduce sample losses inside the ion source. Over the course of 25 measurements, no sample losses were experienced on dimpled filaments, in contrast to 15% total sample loss experienced with v-shaped filaments. Secondly, a polymer fiber architecture for TIMS sample loading was developed using similar sample loading procedures as those used in bead loading. Fibers with diameter of approximately 100 μm were prepared from triethylamine-quaternized-poly(vinylbenzyl chloride) cross-linked with diazabicyclo[2.2.2]octane. Total ion counts (239Pu + 242Pu) and isotope ratios obtained from fiber-loaded filaments were compared to those measured bead loading. Fiber loading was found to improve sensitivity, accuracy, and precision of isotope ratio measurements of Pu compared to the established resin bead loading method, while maintaining its simplicity. The average number of detected Pu+ counts was 180% greater and there was a 72% reduction in standard deviation of ratio measurements when using fiber loading. An average deviation of 0.0003 (0.033%) from the certified isotope ratio value of NBL CRM Pu128 was measured when fiber loading versus a deviation of 0.0013 (0.133%) when bead loading. The fiber formation method can be extended to other anion-exchange polymer chemistries, and therefore offers a convenient platform to investigate the efficacy of novel polymer chemistries in sample loading for TIMS. Thirdly, a sample loading procedure was developed that is based on a polymer thin film architecture. Rhenium filaments were degassed, dip-coated with a thin (~180 nm) hydrophobic base layer of poly(vinylbenzyl chloride) (PVBC), and spotted with an aqueous solution of triethylamine-quaternized-PVBC and a cross-liking agent (diazabicyclo[2.2.2]octane). Spotting resulted in the formation of a toroidal, hydrophilic extractive polymer disk surrounded by the hydrophobic base polymer. Thin film coated filaments were direct loaded with NBL CRM Pu128 from a 9 M HCl matrix. Aqueous sample droplets adhered to the extractive polymer spot, facilitating sample loading. The influence of spot thickness upon ion production was investigated. Overall ion counts and isotopic ratios obtained from thin film coated filaments were compared to those produced by the established resin bead loading method. Isotopic ratios were within error of those measured using the bead loading method with few background interferences. The average number of detected Pu+ counts was 175% greater when using thin film coated filaments with 20-30 μm thick toroidal spots. The use of dimpled filaments further aided sample loading by providing a well-shaped substrate to deposit the sample droplet. No sample loss was experienced with the thin film loading method over the course of 65 sample analyses. Finally, thin films used in this design were found to slow filament aging under atmospheric conditions, facilitating the bulk production of filaments for future analyses. During this work, an unreported form of rhenium surface oxidation was discovered. Rhenium is the most common ionization filament material for Pu analysis by TIMS. Degassing is a common preparation technique for rhenium filaments and is performed to clean filaments before analysis. Degassing involves resistively heating the filaments under high vacuum to volatilize and degrade contaminants. Collaborators at Savannah River National Laboratory reported anecdotally that the use of excessively aged filaments (on the order of 2 months of aging in atmosphere after degassing) decreased the sensitivity and precision of TIMS analyses. Although optimization studies regarding degassing conditions have been reported, little work has been done to characterize filament aging after degassing. In this study, the effects of filament aging after degassing were explored to determine a “shelf-life†for degassed rhenium filaments, and methods to limit filament aging were investigated. Zone-refined rhenium filaments were degassed by resistance heating under high vacuum before exposure to ambient atmosphere for up to 2 months. After degassing, the nucleation and preferential growth of oxo-rhenium crystallites on the surface of polycrystalline rhenium filaments was observed by atomic force microscopy and scanning electron microscopy (SEM). Compositional analysis of the crystallites was conducted using SEM-Raman spectroscopy and SEM energy dispersive X-ray spectroscopy, and grain orientation at the metal surface was investigated by electron back-scatter diffraction mapping. Spectra collected by SEM-Raman suggest crystallites are composed primarily of perrhenic acid. The relative extent of growth and crystallite morphology were found to be grain dependent and affected by the dissolution of carbon into filaments during annealing (often referred to as carbonization or carburization). Crystallites were observed to nucleate in region specific modes and grow over time through transfer of material from the surface. The roles of atmospheric humidity and carburization on the oxidation characteristics (i.e. aging) of rhenium filaments were studied. Degassed and carburized filaments were aged for up to 79 days under dry and humid conditions, and the growth of oxo-rhenium crystallites was investigated intermittently by SEM to construct growth profiles. SEM images were analyzed to determine average crystallite size, number density, and percent surface coverage. Crystallite growth was found to be suppressed by both filament carburization and dry storage conditions (~13% relative humidity). Under humid conditions (75% relative humidity), crystallite growth progressed steadily over the investigatory period, reaching \u3e2.3% surface coverage within 79 days of aging. Atomic ion production of Pu+ was suppressed by approximately 20% and the standard deviation of isotope ratio measurements was increased by 170% when filaments with 1% oxide surface coverage were used in sample loading. Measurement sensitivity and reproducibility are imperative for applications involving ultra-trace analysis of Pu by TIMS. These findings offer validation for observations regarding the detrimental effect of excessive filament aging post-degassing, improve the understanding of conditions that impel the oxidation of rhenium filaments, and provide practical means to suppress the growth of oxides. PVBC nanolayers were found to slow the growth of oxo-rhenium crystallites on the filament surfaces and may serve as an alternative carbon source for filament carburization. A novel substrate for the simultaneous concentration of actinides and sample preparation for alpha spectroscopy was developed using thin films originally intended for TIMS sample loading. Substrate preparation involved forming ultrathin films (10-180 nm) of quaternary amine anion-exchange polymers on glass and silicon by dip-coating. Samples were loaded by submerging the polymer-coated substrates into acidified solutions of Pu or natural water with elevated uranium concentrations. High resolution (25-30 keV) alpha spectra were acquired from these substrates under certain loading conditions indicating that through further development they may be a useful, inexpensive, and potentially field deployable platform serving national security and environmental sampling applications

Photo defect detection for image inpainting

[[abstract]]Image inpainting (or image completion) techniques use textural or structural information to repair or fill damaged portion of a picture. However, most techniques request a human to identify the portion to be inpainted. We developed a new mechanism which can automatically detect defect portions in a photo, including damages by color ink spray and scratch drawing. The mechanism is based on several filters and structural information of damages. Old photos from the author's family are used for testing. Preliminary results show that most damages can be automatically detected without human involvement. The mechanism is integrated with our inpainting algorithms to complete a fully automatic photo defects repairing system.[[conferencetype]]國際[[conferencedate]]20051212~20051214[[conferencelocation]]Irvine, CA, US

[[alternative]]Photo Defect Detection and Inpainting

計畫編號：NSC94-2213-E032-017研究期間：200508~200607研究經費：398,000[[sponsorship]]行政院國家科學委員

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Synthesis, Design, and Environmental Fate of Metallic Nanoparticles

Rational design of nanoparticle surface chemistry offers the ability to control nanoparticle characteristics such as size, polydispersity, shape, dispersibility in various solvents, functionality and end fate. Ligand exchange has proved to be is a versatile method for modifying the surface of plasmonic nanoparticles. Ligand exchange has provided a “green” alternative to traditional biphasic syntheses that require large amounts of phase transfer catalysts. Ligand exchange can also be used to reduce the amount of post synthesis processing and waste when it is conducted on nanoparticles that have been synthesized with a method that affords control over nanoparticle size and polydispersity. Ligand exchange is also an important reaction to consider when determining the end fate of nanomaterials due to the fact that when nanoparticles enter the natural environment, they will be exposed to a variety of natural ligands and electrolytes. We have conducted a comprehensive review of ligand exchange literature and used isothermal titration calorimetry to investigate ligand binding and exchange on gold nanoparticles experimentally. We have also investigated the impact that citrate and natural organic matter surface chemistries have on the transport properties of silver nanoparticles. This work has led to a greater understanding of the influencing factors on the mechanism of nanoparticle ligand binding and exchange

Investigation and Propagation of Defects in the Membrane Electrode Assembly of Polymer Electrolyte Membrane Fuel Cells: Quality Control Analysis

Polymer electrolyte membrane fuel cells (PEMFC) have the potential to deliver high power density with a lower weight and volume compared to other fuel cells. However, some of the barriers to the successful commercialization of PEMFCs include problems associated with durability, stability and cost. Fuel cell defects that arise and propagate in the membrane electrode assembly (MEA) components during manufacturing and subsequent operation are the biggest factors limiting their durability and stability, leading to shortened lifetimes, reduced performance or cell failure. Defects in the production line must be minimized if PEMFCs are to become reliable electrochemical energy devices on a commercial scale. A conventional PEMFC electrode consists of layers (CL) of nanoscale Pt catalyst particles mixed with an ionomer on a high surface area carbon support deposited on the polymer electrolyte membrane (PEM) and sandwiched between gas diffusion media (GDM). The defects in these components originate from the raw materials used in the catalyst layers, process conditions during catalyst mixing, coating techniques, drying process, thickness variations in the casting substrate and the temperature and humidity of the processing environment. These defects can lead to reduced performance and can increase fuel cell degradation, specifically in the MEA components. Understanding the MEA component defects that affect fuel cell performance and lifetime is integral to the successful development of an on-line quality control strategy. Previous research studies have been conducted on defects in catalyst-coated membranes (CCMs) and gas diffusion layers (GDLs) with various dimensions that have been introduced artificially at specific locations, which does not satisfactorily mimic the situation with real manufacturing defects. Very few studies on real defects have been reported to date with limited work on localized effects on CL defects such as loss of catalyst, the morphology of defect growth or the effect of defect location within the CCM on the resulting cell performance. This has limited our fundamental and comprehensive understanding of the nature of defects in the beginning-of-life (BOL) state and the manner in which they may or may not propagate during PEMFC operation. The focus of this research is to analyze real catalyst layer defects and membrane pinholes on commercial CCMs that are developed during mass production. Specifically, the objectives of this study are to: (i) develop a non-destructive method to identify and quantify defects in CCM electrodes, (ii) implement a defect analysis framework to age CCMs using open-circuit voltage(OCV)- accelerated stress tests (AST), (iii) characterize the electrochemical performance of CCM/MEAs with varying extent of manufacturing defects (catalyst layer thickness, degree of catalyst non-uniformity) and compare this to a baseline, defect-free CCM/MEA using ASTs as well as in-situ and ex-situ methods and (iv) investigate defects on GDL-microporous layer (MPL) using infrared (IR) imaging and surface conductivity measurements. The first set of quality control experiments were performed on CCMs by using optical microscopy to characterize catalyst layer defects. Defects such as micro/macro cracks, catalyst clusters, missing catalyst layer defects (MCLDs), void/empty areas, CL delamination and pinholes in the CCM were characterized in terms of areal dimension (size, shape, and orientation) prior to electrochemical analysis. The OCV-AST protocol was developed to age defected CCMs in a custom-designed test cell and track defect propagation and behavior during aging. The geometric features of the defects were quantified and their growth measured at regular time intervals from beginning-of-life (BOL) to end-of-life (EOL) until the OCV had dropped by 20% from its initial value (as per the DOE-designed protocol). Overall, two types of degradation were observed: surface degradation caused by catalyst erosion and crack degradation caused by membrane mechanical deformation. Furthermore, the catalyst layer defects formed during the decal transfer process exhibited a higher growth rate at middle-of-life (MOL-1) before stabilizing by EOL. The results of the crack propagation analysis during AST showed that the defected area covered under cracks increased from 2.4% of the total CL area at BOL to 10.5% by EOL with a voltage degradation rate of 2.55mV/hr. This type of analysis should provide manufacturers with baseline information that will allow them to select and reject CCMs, increasing the lifetime of fuel cell stacks. Once the CCM defects were analyzed comprehensively, research was carried out on the MEA stack. MEAs containing defected CCMs (incomplete catalyst layer defects-MCLD), pinhole across sealant and artificial pinholes at inlet/middle/outlet were investigated using a cyclic open-circuit voltage (COCV)-AST. Different RH cycling periods from 80% RH to 20% RH with time delays from 5 mins to 30 mins were applied to the cathode to study the propagation of defects and their effect on overall cell performance. In-situ analysis included the measurement of polarization curves, linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) to measure electrode degradation. Non-destructive ex-situ analysis using IR thermography was conducted every 100 cycles to monitor the evolution of defects in the MEA. The growth of pinholes was studied on the basis on hydrogen crossover curves. Sealing defects were found to have a major impact on performance loss compared to catalyst layer defects. It was also observed that MCLDs degraded within a short period of time and developed pinholes although the extent of this degradation depended on defect thickness. The MCLD defects were unstable and observed to continually grow due to gradual loss of catalyst particles inside the defected areas that accelerated pinhole formation in CCMs. This effect was clearly reflected in the continuous decay of OCV during the fuel cell operation. Therefore, CCMs leaving the production line with missing and /or thin portions of CL are not recommended for MEA fabrication as they ultimately affect the long-term stability of PEMFC. The last set of quality control experiments was conducted on GDL-MPL defects in samples that were being aged by RH cycling in a custom-design test cell. Thermal image analysis using IR thermography was carried out by passing DC current through the GDL sheet mounted on a porous vacuum stage to identify hot and cold spots reflecting defective areas. The morphological features and surface conductivity of MPL cracks were characterized using optical microscopy and four-point probe conductivity measurements. Interestingly, the nature of defects/cracks propagation in the GDL-MPL was found to affect cell performance in the mass transfer region at high currents. Crack propagation in GDL-MPL increased mass transport losses due to water flooding on the cathode, which was clearly observed in the polarization curves. Finally, the overall effects of catalyst layer defects, membrane pinholes and GDL defects on cell performance were compared. MEA sealant defects (pinholes) had such a negative effect on cell performance that EOL was reached after only ~ 50 hours of COCV operation at 80% - 20% RH cycling. Thus, the detection of such a defect in a CCM should be sufficient cause to reject it for use in a commercial stack. We also observed that CCMs with defects that led to 70% reduced thickness of the CL failed faster than those with the same type of defects that had resulted in 30% reduced thickness of the CL, presumably due to less available catalyst for electrochemical reactions. Clearly, CL defects should be given high priority in quality control inspection strategies devised by CCM electrode manufacturers and PEMFC operators

Recent Advances in Thin Film Electronic Devices

This reprint is a collection of the papers from the Special Issue “Recent Advances in Thin Film Electronic Devices” in Micromachines. In this reprrint, 1 editorial and 11 original papers about recent advances in the research and development of thin film electronic devices are included. Specifically, three research fields are covered: device fundamentals (5 papers), fabrication processes (5 papers), and testing methods (1 paper). The experimental data, simulation results, and theoretical analysis presented in this reprint should benefit those researchers in flat panel displays, flat panel sensors, energy devices, memories, and so on