A Comprehensive Review and Analysis of Nanosensors for Structural Health Monitoring in Bridge Maintenance: Innovations, Challenges, and Future Perspectives

This paper presents a thorough review and detailed analysis of nanosensors for structural health monitoring (SHM) in the context of bridge maintenance. With rapid advancements in nanotechnology, nanosensors have emerged as promising tools for detecting and assessing the structural integrity of bridges. The objective of this review is to provide a comprehensive understanding of the various types of nanosensors utilized in bridge maintenance, their operating principles, fabrication techniques, and integration strategies. Furthermore, this paper explores the challenges associated with nanosensor deployment, such as signal processing, power supply, and data interpretation. Finally, the review concludes with an outlook on future developments in the field of nanosensors for SHM in bridge maintenance.publishedVersio

Development and Life Cycle Assessment of Advanced-Concept III-V Multijunction Photovoltaics

III-V semiconductors make for highly efficient solar cells, but are expensive to manufacture. However, there are many mechanisms for improving III-V photovoltaics in order to make them more competitive with other photovoltaic (PV) technologies. One possible method is to design cells for high efficiency under concentrated sunlight, effectively trading expensive III-V material for cheaper materials such as glass lenses. Another approach is to reduce the amount of III-V material necessary for the same power output, which can be achieved by removing the substrate and installing a reflector on the back of the cell, while also adding quantum structures to the cell to permit absorption of a greater portion of the solar spectrum. Regarding the first approach, this dissertation focused on the development of an InAlAsSb material for a mulitjunction design with the potential of achieving 52.8% efficiency under 500 suns. First, development of a single-junction InAlAs cell lattice-matched to InP was executed as a preliminary step. The InAlAs cell design was optimized via simulation, then grown via metal organic vapor phase epitaxy (MOVPE) and fabricated resulting in 17.9% efficiency under 1-sun AM1.5, which was unprecedented for the InAlAs material. Identical InAlAs cells were grown using alternative MOVPE precursors to study the effects of necessary precursors for InAlAsSb. Fits to experimental device results showed longer lifetimes when grown with the alternative aluminum precursor. InAlAsSb grown using these alternative precursors targeted a 1.8 eV bandgap required for the multijunction design. Ultimately, InAlAsSb material with the desired bandgap was confirmed by photoreflectance spectroscopy. For the second approach, this dissertation studied the integration of InAs quantum dots (QDs) in a GaAs solar cell in conjunction a back surface reflector (BSR). A quantum dot solar cell (QDSC) with a BSR has the potential to increase short-circuit current by 2.5 mA/cm2 and also increase open-circuit voltage due to photon recycling. In this study, multiple textured BSRs were fabricated by growing inverted QDSCs on epitaxial lift-off templates and then texturing the rear surface before removing the device from the substrate. Identical cells with a flat BSR served as controls. Optimization of inverted QDSC growth conditions was also performed via a cell design study. Device results showed increased open-circuit voltage with increasing optical path length, and the greatest improvement in sub-band current over a flat BSR control device was 40%. In the final chapter, a life cycle assessment (LCA) of these technologies was performed to identify the hypothetical optimum at which energy investments in cell performance (such as the two described above) no longer correspond to improvements in the overall life cycle performance of the PV system. Four cell designs with sequentially increasing efficiencies were compared using a functional unit of 1 kWp. The first is a commercially available and has been studied in previous LCAs. The second is the design containing InAlAsSb mentioned above. The third represents the most material-intensive option, which bonds two substrates to create a five-junction cell. The fourth is a six-junction cell that uses a metamorphic grade between subcells and represents the most energy-intensive option. A thorough literature review of existing LCAs of high-concentration photovoltaic (HCPV) systems was performed, which obviated the need for data on the manufacture of MOVPE precursors and substrates. LCAs for the most common III-V substrate (GaAs) and precursors were executed prior to conducting the HCPV system LCA, due to the absence of detailed information on the life cycle impacts of these compounds in literature. Ultimately, both the cumulative energy demand and greenhouse gas emissions of the HCPV system decreased proportionally with increasing cell efficiency, even for the most energy and material-intensive cell designs. It was found that the substrates and precursors corresponded to less than 2% of system impacts. This implies that current mechanisms to increase cell efficiency are environmentally viable in HCPV applications without the need for material reduction, and would make III-V HCPV more environmentally competitive with dominant silicon PV technologies

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Statistical Methods for Semiconductor Manufacturing

In this thesis techniques for non-parametric modeling, machine learning, filtering and prediction and run-to-run control for semiconductor manufacturing are described. In particular, algorithms have been developed for two major applications area: - Virtual Metrology (VM) systems; - Predictive Maintenance (PdM) systems. Both technologies have proliferated in the past recent years in the semiconductor industries, called fabs, in order to increment productivity and decrease costs. VM systems aim of predicting quantities on the wafer, the main and basic product of the semiconductor industry, that may be physically measurable or not. These quantities are usually ’costly’ to be measured in economic or temporal terms: the prediction is based on process variables and/or logistic information on the production that, instead, are always available and that can be used for modeling without further costs. PdM systems, on the other hand, aim at predicting when a maintenance action has to be performed. This approach to maintenance management, based like VM on statistical methods and on the availability of process/logistic data, is in contrast with other classical approaches: - Run-to-Failure (R2F), where there are no interventions performed on the machine/process until a new breaking or specification violation happens in the production; - Preventive Maintenance (PvM), where the maintenances are scheduled in advance based on temporal intervals or on production iterations. Both aforementioned approaches are not optimal, because they do not assure that breakings and wasting of wafers will not happen and, in the case of PvM, they may lead to unnecessary maintenances without completely exploiting the lifetime of the machine or of the process. The main goal of this thesis is to prove through several applications and feasibility studies that the use of statistical modeling algorithms and control systems can improve the efficiency, yield and profits of a manufacturing environment like the semiconductor one, where lots of data are recorded and can be employed to build mathematical models. We present several original contributions, both in the form of applications and methods. The introduction of this thesis will be an overview on the semiconductor fabrication process: the most common practices on Advanced Process Control (APC) systems and the major issues for engineers and statisticians working in this area will be presented. Furthermore we will illustrate the methods and mathematical models used in the applications. We will then discuss in details the following applications: - A VM system for the estimation of the thickness deposited on the wafer by the Chemical Vapor Deposition (CVD) process, that exploits Fault Detection and Classification (FDC) data is presented. In this tool a new clustering algorithm based on Information Theory (IT) elements have been proposed. In addition, the Least Angle Regression (LARS) algorithm has been applied for the first time to VM problems. - A new VM module for multi-step (CVD, Etching and Litography) line is proposed, where Multi-Task Learning techniques have been employed. - A new Machine Learning algorithm based on Kernel Methods for the estimation of scalar outputs from time series inputs is illustrated. - Run-to-Run control algorithms that employ both the presence of physical measures and statistical ones (coming from a VM system) is shown; this tool is based on IT elements. - A PdM module based on filtering and prediction techniques (Kalman Filter, Monte Carlo methods) is developed for the prediction of maintenance interventions in the Epitaxy process. - A PdM system based on Elastic Nets for the maintenance predictions in Ion Implantation tool is described. Several of the aforementioned works have been developed in collaborations with major European semiconductor companies in the framework of the European project UE FP7 IMPROVE (Implementing Manufacturing science solutions to increase equiPment pROductiVity and fab pErformance); such collaborations will be specified during the thesis, underlying the practical aspects of the implementation of the proposed technologies in a real industrial environment

Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final Report. Volume III: Silicon sheet: wafers and ribbons

The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development. The primary objective of the Silicon Sheet Task of the FSA Project was the development of one or more low-cost technologies for producing silicon sheet suitable for processing into cost-eompetitive solar cells. Silicon sheet refers to high-purity crystalline silicon of size and thickness for fabrication into solar cells. The Task effort began with state-of-the-art sheet technologies and then solicited and supported any new silicon sheet alternatives that had the potential to achieve the Project goals. A total of 48 contracts were awarded that covered work in the areas of ingot growth and casting, wafering, ribbon growth, other sheet technologies, and programs of supportive research. Periodic reviews of each sheet technology were held, assessing the technical progress and the long-range potential. Technologies that failed to achieve their promise, or seemed to have lower probabilities for success in comparison with others, were dropped. A series of workshops was initiated to assess the state of the art, to provide insights into problems remaining to be addressed, and to support technology transfer. The Task made and fostered significant improvements in silicon sheet including processing of both ingot and ribbon technologies. An additional important outcome was the vastly improved understanding of the characteristics associated with high-quality sheet, and the control of the parameters required for higher efficiency solar cells. Although significant sheet cost reductions were made, the technology advancements required to meet the Task cost goals were not achieved. This FSA Final Report (JPL Publication 86-31, 5101-289, DOE/JPL 1012-125, October 1986) is composed of eight volumes, consisting of an Executive Summary and seven technology reports: Volume I: Executive Summary. Volume II: Silicon Material. Volume III: Silicon Sheet: Wafers and Ribbons Volume IV: High-Efficiency Solar Celis. Volume V: Process Development. Volume VI: Engineering Sciences and Reliability. Volume VII: Module Encapsulation. Volume VIII: Project Analysis and Integration. Two supplemental reports included in the final report package are: FSA Project: 10 Years of Progress, JPL Document 400-279. 5101-279, October 1985. Summary of FSA Project Documentation: Abstracts of Published Documents, 1975 to 1986, JPL Publication 82-79 (Revision 1),5101-221, DOE/JPL-1 012-76, September 1986

Understanding and Optimization of III-V nanowire growth in Aerotaxy

III-V semiconductor nanowires are high aspect ratio nanostructures with superior properties that can potentially enhance the functionality of next-generation opto-electronic devices. At present, the most reliable method for fabricating III-V semiconductor nanowires is the particle-assisted vapor-liquid-solid growth using a substrate-based growth process. However, a substrate-based process limits the number of nanowires that can be produced per cycle and is an obstacle to the industrial production of III-V nanowires. A viable alternative technology for the high-throughput synthesis of III-V nanowires is vital to exploit the true potential of III-V semiconductor nanowires. Aerotaxy is a gas-phase vapor-liquid-solid growth technology that can mass-produce III-V semiconductor nanowires without a substrate. It reduces the cost of production by eliminating the need for a crystalline substrate and can produce nanowires at a phenomenal rate.This thesis explores the fundamental limits of the Aerotaxy technology in producing III-V nanowires. GaAs and GaAsP material systems were adopted to explore the fundamentals of Aerotaxy nanowire growth. Growth experiments were designed to probe the growth parameter dependence of nanowire properties like morphology, crystal structure and composition. In addition to that, the efficiency of in situ doping (p- and n- type) in Aerotaxy was evaluated using optical and electrical characterization techniques. The growth parameter space was explored to demonstrate the reproducibility and efficiency of Aerotaxy nanowire growth. To better understand the growth, a pseudo-particle continuum model for Aerotaxy growth was developed. The results from the model shows good agreement with experimental quantitative and qualitative observations.The studies presented in the thesis also explores the fabrication of complex nanostructures like branched GaAsP nanowires. By tuning the diameter of the initial catalytic particle, we were able to induce branching in GaAsP nanowires. Apart from that, GaAs nanowires grown from alternative metal particles like Ga, AuAg and Ag in Aerotaxy shows promising initial results. Mass-producing III-V nanowires using alternative seed metals that are compatible with Si could bring novel functionalities while reducing production costs. The importance nano-safety is also highlighted in the context of a high-throughput production environment