Matching Items (106)
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- Genre: Academic theses
- Creators: Yu, Hongbin
Description
As the 3rd generation solar cell, quantum dot solar cells are expected to outperform the first 2 generations with higher efficiency and lower manufacture cost. Currently the main problems for QD cells are the low conversion efficiency and stability. This work is trying to improve the reliability as well as the device performance by inserting an interlayer between the metal cathode and the active layer. Titanium oxide and a novel nitrogen doped titanium oxide were compared and TiOxNy capped device shown a superior performance and stability to TiOx capped one. A unique light anneal effect on the interfacial layer was discovered first time and proved to be the trigger of the enhancement of both device reliability and efficiency. The efficiency was improved by 300% and the device can retain 73.1% of the efficiency with TiOxNy when normal device completely failed after kept for long time. Photoluminescence indicted an increased charge disassociation rate at TiOxNy interface. External quantum efficiency measurement also inferred a significant performance enhancement in TiOxNy capped device, which resulted in a higher photocurrent. X-ray photoelectron spectrometry was performed to explain the impact of light doping on optical band gap. Atomic force microscopy illustrated the effect of light anneal on quantum dot polymer surface. The particle size is increased and the surface composition is changed after irradiation. The mechanism for performance improvement via a TiOx based interlayer was discussed based on a trap filling model. Then Tunneling AFM was performed to further confirm the reliability of interlayer capped organic photovoltaic devices. As a powerful tool based on SPM technique, tunneling AFM was able to explain the reason for low efficiency in non-capped inverted organic photovoltaic devices. The local injection properties as well as the correspondent topography were compared in organic solar cells with or without TiOx interlayer. The current-voltage characteristics were also tested at a single interested point. A severe short-circuit was discovered in non capped devices and a slight reverse bias leakage current was also revealed in TiOx capped device though tunneling AFM results. The failure reason for low stability in normal devices was also discussed comparing to capped devices.
ContributorsYu, Jialin (Author) / Jabbour, Ghassan E. (Thesis advisor) / Alford, Terry L. (Thesis advisor) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2011
Description
The increasing isolation and segregation of children in American cities and suburbs is of special significance. This has meant a loss of freedom for children to explore their neighborhood and city as they get older, their exclusion from varied contacts with diverse adults in a variety of settings, and their consequent inability to learn from personal experience and observation, so essential to social and emotional development. The purpose of this study is to measure the differences in child-friendliness between neighborhoods with different income levels by developing an indicator framework that can be used by planning departments and other local authorities based on available data. The research also focus on what other factor (besides income) influences child-friendliness in a city at the neighborhood level. If a relationship does exist, how big is the difference in terms of child-friendliness between low-income and high-income neighborhoods, and what indicators play the most important role in creating the difference? Neighborhoods in the city of Glendale, Arizona serve as case studies to aid in refining the assessment method, and show the potential for how cities can become more child-friendly. The neighborhoods were selected based on income, same size and different location.
ContributorsRakhimova, Nelya (Author) / Stein, Jay (Thesis advisor) / Pijawka, David (Committee member) / Crewe, Katherine (Committee member) / Arizona State University (Publisher)
Created2011
Description
The United States has a long history of providing public parks and amenities, especially for children. Unfortunately, children today are spending less time in public parks, less time getting physical activity and more time being indoors and sedentary. While multiple factors may be responsible for this lack of activity, multiple researchers have found the availability of parks is a significant influence on the physical activity levels of children as well as on the occurrence of obesity related illness. Public parks are ideal locations for children to get physical activity, however they are not always equitably distributed within communities. Income and race/ethnicity especially are common variables found to impact availability of parks. Such socioeconomic variables typically have an impact on the availability of public parks within a community. Such variables may also impact the quality of the parks provided. A case study of Scottsdale, Arizona was conducted analyzing the availability of public parks within the City between the years of 1990 and 2000 and the current quality of the parks. Statistical analysis and observation were utilized to assess the amount of park space available (in acres) and the quality of the parks in comparison to selected socioeconomic variables including ethnicity, income and total percent housing type (single family or multi-family). All analysis was conducted using U.S. Census data from the years 1990 and 2000 and was at the tract level. The results of the analysis indicate that in contrast to the initial hypothesis and past research, within the City of Scottsdale, lower income neighborhoods actually have more public park space available to them than higher income neighborhoods. Between 1990 and 2000 the difference in park space between the lowest and highest income quartiles increased considerably, approximately 230% over the ten years. The quality analysis results indicate that the overall quality of parks is slightly higher in the highest income neighborhoods, which also have no parks that could be considered of poor quality. Given the atypical results of this analysis, further research is necessary to better understand the impacts of socioeconomic characteristics on park, especially regarding children.
ContributorsSamples, Samantha (Author) / Crewe, Katherine (Thesis advisor) / Booze, Randy (Committee member) / Pijawka, David (Committee member) / Arizona State University (Publisher)
Created2011
Description
Semiconductor nanowires are featured by their unique one-dimensional structure which makes them promising for small scale electronic and photonic device applications. Among them, III-V material nanowires are particularly outstanding due to their good electronic properties. In bulk, these materials reveal electron mobility much higher than conventional silicon based devices, for example at room temperature, InAs field effect transistor (FET) has electron mobility of 40,000 cm2/Vs more than 10 times of Si FET. This makes such materials promising for high speed nanowire FETs. With small bandgap, such as 0.354 eV for InAs and 1.52 eV for GaAs, it does not need high voltage to turn on such devices which leads to low power consumption devices. Another feature of direct bandgap allows their applications of optoelectronic devices such as avalanche photodiodes. However, there are challenges to face up. Due to their large surface to volume ratio, nanowire devices typically are strongly affected by the surface states. Although nanowires can be grown into single crystal structure, people observe crystal defects along the wires which can significantly affect the performance of devices. In this work, FETs made of two types of III-V nanowire, GaAs and InAs, are demonstrated. These nanowires are grown by catalyst-free MOCVD growth method. Vertically nanowires are transferred onto patterned substrates for coordinate calibration. Then electrodes are defined by e-beam lithography followed by deposition of contact metals. Prior to metal deposition, however, the substrates are dipped in ammonium hydroxide solution to remove native oxide layer formed on nanowire surface. Current vs. source-drain voltage with different gate bias are measured at room temperature. GaAs nanowire FETs show photo response while InAs nanowire FETs do not show that. Surface passivation is performed on GaAs FETs by using ammonium surfide solution. The best results on current increase is observed with around 20-30 minutes chemical treatment time. Gate response measurements are performed at room temperature, from which field effect mobility as high as 1490 cm2/Vs is extracted for InAs FETs. One major contributor for this is stacking faults defect existing along nanowires. For InAs FETs, thermal excitations observed from temperature dependent results which leads us to investigate potential barriers.
ContributorsLiang, Hanshuang (Author) / Yu, Hongbin (Thesis advisor) / Ferry, David (Committee member) / Tracy, Clarence (Committee member) / Arizona State University (Publisher)
Created2011
Description
There is a conflict in the profession of interior design over regulation through legislation. For some organizations and individuals, regulation via legislation is the next perceived step in the professionalization process which has been evolving for over 40 years and is needed to protect the health, safety and welfare (HSW) of the public. For other organizations and individuals, legislation is deemed unnecessary and an affront to the free trade market and serves only to create anti-competitive barriers resulting in the formation of a "design cartel" (Campo-Flores, 2011; Carpenter, 2007). Research exists on the professionalization of interior design and on the reasons stated for and against legislation (ASID, 2010, Anderson, Honey, Dudek, 2007, Martin, 2008). However, there is little research on understanding how the actual stake-holders view legislation. For the purpose of this research, the stake-holders are the professional interior designers themselves. The purpose of this study was to examine the current status of relevant issues to the subject of regulation in interior design and to pose the question if there is an option to legislation. If so, could third party certification be an acceptable alternative? An on-line survey was developed and posted on interior design networking sites on LinkedIn. The results of the survey suggest that interior designers are completely divided on the issue of legislation but favorably view certification. The survey has also revealed the lack of understanding of the legislative process in interior design and confusion in the role that interior design organizations play. The study has also revealed that interior designers identify the distorted view the public has of this industry as a problem. Interior designers surveyed in this study see a need to separate commercial and residential interior design. Overall, this study has concluded that interior designers would actually prefer a certification process to legislation.
ContributorsPliess, Catherine (Author) / Bender, Diane (Thesis advisor) / Crewe, Katherine (Committee member) / Kroelinger, Michael D. (Committee member) / Arizona State University (Publisher)
Created2011
Description
A workload-aware low-power neuromorphic controller for dynamic power and thermal management in VLSI systems is presented. The neuromorphic controller predicts future workload and temperature values based on the past values and CPU performance counters and preemptively regulates supply voltage and frequency. System-level measurements from stateof-the-art commercial microprocessors are used to get workload, temperature and CPU performance counter values. The controller is designed and simulated using circuit-design and synthesis tools. At device-level, on-chip planar inductors suffer from low inductance occupying large chip area. On-chip inductors with integrated magnetic materials are designed, simulated and fabricated to explore performance-efficiency trade offs and explore potential applications such as resonant clocking and on-chip voltage regulation. A system level study is conducted to evaluate the effect of on-chip voltage regulator employing magnetic inductors as the output filter. It is concluded that neuromorphic power controller is beneficial for fine-grained per-core power management in conjunction with on-chip voltage regulators utilizing scaled magnetic inductors.
ContributorsSinha, Saurabh (Author) / Cao, Yu (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Yu, Hongbin (Committee member) / Christen, Jennifer B. (Committee member) / Arizona State University (Publisher)
Created2011
Description
This study addresses the landscape connectivity pattern at two different scales. The county-level analysis aims to understand how urban ecosystem structure is likely to evolve in response to the proposed development plans in Maricopa County, Arizona. To identify the spatio-temporal land pattern change, six key landscape metrics were quantified in relative to the urban development scenarios based on the certainty of the proposed urban plans with different level of urban footprints. The effects of future development plans from municipalities on landscape connectivity were then analyzed in the scaled temporal and spatial frame to identify in which urban condition the connectivity value would most likely to decrease. The results demonstrated that tremendous amount of lands will be dedicated to future urbanization, and especially urban agricultural lands will be likely to be vulnerable. The metro-level analysis focuses on a group of species that represent urban desert landscape and have different degrees of fragmentation sensitivity and habitat type requirement. It hypothesizes that the urban habitat patch connectivity is impacted upon by urban density. Two underlying propositions were set: first, lower connectivity is predominant in areas with high urbanization cover; second, landscape connectivity will be impacted largely on the interfaces between urban, suburban, and rural areas. To test this, a GIS-based connectivity modeling was employed. The resultant change in connectivity values was examined for exploring the spatial relation to predefined spatial frames, such as urban, suburban, and rural zones of which boundaries were delineated by buffering method with two criteria of human population density and urban cover proportion. The study outcomes provide a practical guidance to minimize connectivity loss and degradation by informing planners with more optimal alternatives among various policy decisions and implementation. It also gives an inspiration for ecological landscape planning in urbanized or urbanizing regions which can ultimately leads urban landscape sustainability.
ContributorsPak, So-hyŏn (Author) / Cook, Edward (Thesis advisor) / Crewe, Katherine (Committee member) / Wu, Jianguo (Jingle) (Committee member) / Arizona State University (Publisher)
Created2011
Description
CMOS technology is expected to enter the 10nm regime for future integrated circuits (IC). Such aggressive scaling leads to vastly increased variability, posing a grand challenge to robust IC design. Variations in CMOS are often divided into two types: intrinsic variations and process-induced variations. Intrinsic variations are limited by fundamental physics. They are inherent to CMOS structure, considered as one of the ultimate barriers to the continual scaling of CMOS devices. In this work the three primary intrinsic variations sources are studied, including random dopant fluctuation (RDF), line-edge roughness (LER) and oxide thickness fluctuation (OTF). The research is focused on the modeling and simulation of those variations and their scaling trends. Besides the three variations, a time dependent variation source, Random Telegraph Noise (RTN) is also studied. Different from the other three variations, RTN does not contribute much to the total variation amount, but aggregate the worst case of Vth variations in CMOS. In this work a TCAD based simulation study on RTN is presented, and a new SPICE based simulation method for RTN is proposed for time domain circuit analysis. Process-induced variations arise from the imperfection in silicon fabrication, and vary from foundries to foundries. In this work the layout dependent Vth shift due to Rapid-Thermal Annealing (RTA) are investigated. In this work, we develop joint thermal/TCAD simulation and compact modeling tools to analyze performance variability under various layout pattern densities and RTA conditions. Moreover, we propose a suite of compact models that bridge the underlying RTA process with device parameter change for efficient design optimization.
ContributorsYe, Yun, Ph.D (Author) / Cao, Yu (Thesis advisor) / Yu, Hongbin (Committee member) / Song, Hongjiang (Committee member) / Clark, Lawrence (Committee member) / Arizona State University (Publisher)
Created2011
Description
As a significant level of the reformation and transformation of our society has been provoked by environmental deterioration, ecological approaches in environmental design have drawn much attention from professionals as an alternative world view and also as a practical design approach. Particularly in landscape architecture, ecological understanding has been at the very core of the profession since its emergence and plays an important role in the decision making processes. While ecology supports the profession with an objective rationale, aesthetics plays another major role in providing various understandings about the aesthetic experience of people, which is rather subjective. However, the ways to seek the balance between them are still controversial. Furthermore, the conventional aesthetic value system of landscape appears to have limitations for guiding us to an appropriate appreciation, especially in dealing with newly emerging urban landscape patterns such as regeneration of post-industrial landscapes. Understanding these issues, there have been continuous attempts to describe the relation between ecology and aesthetics, suggesting that a new approach known as "ecological aesthetics," can bring us a new set of viewpoints seeking a reunion of nature and culture, and science and art. It asserts that "there is a type of beauty" in the landscape associated with its ecological health which people could aesthetically appreciate; and therefore, revealing the "hidden" beauty of nature in more visible ways should be the primary concern of today's ecological designers. This research mainly consists of extensive literature research and a case study on two landscape restructuring projects of post-industrial landscapes in Seoul, Korea. The literature research redefines the tasks of landscape architecture based on the idea of ecological aesthetics, and the case study seeks the potentials and limitations of current design projects. This research proposes a framework for landscape perception and reflects on the lessons that would be useful for better practice and research.
ContributorsMin, Byoung Wook (Author) / Cook, Edward (Thesis advisor) / Crewe, Katherine (Committee member) / Pijawka, David (Committee member) / Arizona State University (Publisher)
Created2011
Description
Semiconductor nanowires (NWs) are one dimensional materials and have size quantization effect when the diameter is sufficiently small. They can serve as optical wave guides along the length direction and contain optically active gain at the same time. Due to these unique properties, NWs are now very promising and extensively studied for nanoscale optoelectronic applications. A systematic and comprehensive optical and microstructural study of several important infrared semiconductor NWs is presented in this thesis, which includes InAs, PbS, InGaAs, erbium chloride silicate and erbium silicate. Micro-photoluminescence (PL) and transmission electron microscope (TEM) were utilized in conjunction to characterize the optical and microstructure of these wires. The focus of this thesis is on optical study of semiconductor NWs in the mid-infrared wavelengths. First, differently structured InAs NWs grown using various methods were characterized and compared. Three main PL peaks which are below, near and above InAs bandgap, respectively, were observed. The octadecylthiol self-assembled monolayer was employed to passivate the surface of InAs NWs to eliminate or reduce the effects of the surface states. The band-edge emission from wurtzite-structured NWs was completely recovered after passivatoin. The passivated NWs showed very good stability in air and under heat. In the second part, mid-infrared optical study was conducted on PbS wires of subwavelength diameter and lasing was demonstrated under optical pumping. The PbS wires were grown on Si substrate using chemical vapor deposition and have a rock-salt cubic structure. Single-mode lasing at the wavelength of ~3000-4000 nm was obtained from single as-grown PbS wire up to the temperature of 115 K. PL characterization was also utilized to demonstrate the highest crystallinity of the vertical arrays of InP and InGaAs/InP composition-graded heterostructure NWs made by a top-down fabrication method. TEM-related measurements were performed to study the crystal structures and elemental compositions of the Er-compound core-shell NWs. The core-shell NWs consist of an orthorhombic-structured erbium chloride silicate shell and a cubic-structured silicon core. These NWs provide unique Si-compatible materials with emission at 1530 nm for optical communications and solid state lasers.
ContributorsSun, Minghua (Author) / Ning, Cun-Zheng (Thesis advisor) / Yu, Hongbin (Committee member) / Carpenter, Ray W. (Committee member) / Johnson, Shane (Committee member) / Arizona State University (Publisher)
Created2011