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- Genre: Academic theses
- Creators: Yu, Hongbin
- Creators: Norton, Kay
Description
This dissertation aims to demonstrate a new approach to fabricating solar cells for spectrum-splitting photovoltaic systems with the potential to reduce their cost and complexity of manufacturing, called Monolithically Integrated Laterally Arrayed Multiple Band gap (MILAMB) solar cells. Single crystal semiconductor alloy nanowire (NW) ensembles are grown with the alloy composition and band gap changing continuously across a broad range over the surface of a single substrate in a single, inexpensive growth step by the Dual-Gradient Method. The nanowire ensembles then serve as the absorbing materials in a set of solar cells for spectrum-splitting photovoltaic systems.
Preliminary design and simulation studies based on Anderson's model band line-ups were undertaken for CdPbS and InGaN alloys. Systems of six subcells obtained efficiencies in the 32-38% range for CdPbS and 34-40% for InGaN at 1-240 suns, though both materials systems require significant development before these results could be achieved experimentally. For an experimental demonstration, CdSSe was selected due to its availability. Proof-of-concept CdSSe nanowire ensemble solar cells with two subcells were fabricated simultaneously on one substrate. I-V characterization under 1 sun AM1.5G conditions yielded open-circuit voltages (Voc) up to 307 and 173 mV and short-circuit current densities (Jsc) up to 0.091 and 0.974 mA/cm2 for the CdS- and CdSe-rich cells, respectively. Similar thin film cells were also fabricated for comparison. The nanowire cells showed substantially higher Voc than the film cells, which was attributed to higher material quality in the CdSSe absorber. I-V measurements were also conducted with optical filters to simulate a simple form of spectrum-splitting. The CdS-rich cells showed uniformly higher Voc and fill factor (FF) than the CdSe-rich cells, as expected due to their larger band gaps. This suggested higher power density was produced by the CdS-rich cells on the single-nanowire level, which is the principal benefit of spectrum-splitting. These results constitute a proof-of-concept experimental demonstration of the MILAMB approach to fabricating multiple cells for spectrum-splitting photovoltaics. Future systems based on this approach could help to reduce the cost and complexity of manufacturing spectrum-splitting photovoltaic systems and offer a low cost alternative to multi-junction tandems for achieving high efficiencies.
Preliminary design and simulation studies based on Anderson's model band line-ups were undertaken for CdPbS and InGaN alloys. Systems of six subcells obtained efficiencies in the 32-38% range for CdPbS and 34-40% for InGaN at 1-240 suns, though both materials systems require significant development before these results could be achieved experimentally. For an experimental demonstration, CdSSe was selected due to its availability. Proof-of-concept CdSSe nanowire ensemble solar cells with two subcells were fabricated simultaneously on one substrate. I-V characterization under 1 sun AM1.5G conditions yielded open-circuit voltages (Voc) up to 307 and 173 mV and short-circuit current densities (Jsc) up to 0.091 and 0.974 mA/cm2 for the CdS- and CdSe-rich cells, respectively. Similar thin film cells were also fabricated for comparison. The nanowire cells showed substantially higher Voc than the film cells, which was attributed to higher material quality in the CdSSe absorber. I-V measurements were also conducted with optical filters to simulate a simple form of spectrum-splitting. The CdS-rich cells showed uniformly higher Voc and fill factor (FF) than the CdSe-rich cells, as expected due to their larger band gaps. This suggested higher power density was produced by the CdS-rich cells on the single-nanowire level, which is the principal benefit of spectrum-splitting. These results constitute a proof-of-concept experimental demonstration of the MILAMB approach to fabricating multiple cells for spectrum-splitting photovoltaics. Future systems based on this approach could help to reduce the cost and complexity of manufacturing spectrum-splitting photovoltaic systems and offer a low cost alternative to multi-junction tandems for achieving high efficiencies.
ContributorsCaselli, Derek (Author) / Ning, Cun-Zheng (Thesis advisor) / Tao, Meng (Committee member) / Yu, Hongbin (Committee member) / Vasileska, Dragica (Committee member) / Arizona State University (Publisher)
Created2014
Description
The thrill of a live performance can enhance endorphin, serotonin, dopamine, and adrenaline levels in the body. This mixture of heightened chemical levels is a result of "performance adrenaline." This phenomenon can positively and/or negatively affect a performing singer. A singer's body is her instrument, and therefore, any bodily change can alter the singing voice. The uptake of these chemicals can especially influence a central aspect of singing: breath. "Performance adrenaline" can induce shallow or clavicular breathing, alter phonation, and affect vibrato. To optimize the positive effects and counteract the negative, diaphragmatic breathing, yoga, and beta-blockers are explored as viable management tools. When managed properly, the boost offered by "performance adrenaline" can aid the singer in performing and singing. After a review of medical and psychological studies that reveal the physiological and emotional effects of endorphins, serotonin, dopamine, and adrenaline, this paper will explore the biological changes specific to vocalists and methods to optimize these effects in performance.
ContributorsPaige, Belinda Roseann (Author) / FitzPatrick, Carole (Thesis advisor) / Dreyfoos, Dale (Committee member) / Norton, Kay (Committee member) / Arizona State University (Publisher)
Created2015
Description
"Recontextualizing Music for Social Change" proposes alternative ways through which the traditional setup of a vocal recital may be transformed into a multidisciplinary performance with a specific social purpose. This task might be achieved by the conscious use and merging of elements such as innovation, ritualistic significance of music, and hopes for social change.
Rather than exclusively analyzing the nature of these three elements, this document seeks to exemplify the artistic use of these tools through the description of two doctoral recitals. These performances focus on the portrayal of two specific social issues concerning gender identity: the femme fatale, and sexual identity.
The first performance, "Defatalizing the Femme Fatale: The Voice behind a Stereotype," reflects on the negative connotations of the French femme fatale stereotype. This dangerous image has been perpetuated through popular and mass media since the nineteenth century. The femme fatale has achieved an iconic status thanks to her appealing, damaging, unrealistic, and hypersexualized traits. Nevertheless, this male-constructed stereotype was actually conceived as a parody of female emancipation. "Defatalizing the Femme Fatale" seeks to create awareness of this image through a staged approach of Shostakovich's Michelangelo Suite, feminist poetry and prose, and euphonium music.
The second performance, "Un-Labelling Love: A Scientific Study of Romantic Attachment in Four Seasons," analyses the biological nature of love. According to this perspective, "Un-Labelling Love" transforms a vocal recital into a scientific lecture. This lecture examines four developmental stages of romantic love through the performance of art songs and the inclusion of a narrator, who describes the biological and psychological changes experienced by two research subjects--the performers--during these love stages. Through a plot-twist at the end of the performance, "Un-Labelling Love" also questions the patriarchal assumption that heterosexual kinship represents, by default, the unmarked category of adult pair-bonding. In summary, and based on scientific facts, this vocal performance seeks to encourage social assimilation of non-heterosexual kinship systems.
Rather than exclusively analyzing the nature of these three elements, this document seeks to exemplify the artistic use of these tools through the description of two doctoral recitals. These performances focus on the portrayal of two specific social issues concerning gender identity: the femme fatale, and sexual identity.
The first performance, "Defatalizing the Femme Fatale: The Voice behind a Stereotype," reflects on the negative connotations of the French femme fatale stereotype. This dangerous image has been perpetuated through popular and mass media since the nineteenth century. The femme fatale has achieved an iconic status thanks to her appealing, damaging, unrealistic, and hypersexualized traits. Nevertheless, this male-constructed stereotype was actually conceived as a parody of female emancipation. "Defatalizing the Femme Fatale" seeks to create awareness of this image through a staged approach of Shostakovich's Michelangelo Suite, feminist poetry and prose, and euphonium music.
The second performance, "Un-Labelling Love: A Scientific Study of Romantic Attachment in Four Seasons," analyses the biological nature of love. According to this perspective, "Un-Labelling Love" transforms a vocal recital into a scientific lecture. This lecture examines four developmental stages of romantic love through the performance of art songs and the inclusion of a narrator, who describes the biological and psychological changes experienced by two research subjects--the performers--during these love stages. Through a plot-twist at the end of the performance, "Un-Labelling Love" also questions the patriarchal assumption that heterosexual kinship represents, by default, the unmarked category of adult pair-bonding. In summary, and based on scientific facts, this vocal performance seeks to encourage social assimilation of non-heterosexual kinship systems.
ContributorsVázquez Morillas, Mario (Author) / Norton, Kay (Thesis advisor) / Reber, William F. (Thesis advisor) / Kopta, Anne (Committee member) / Bowditch, Rachel (Committee member) / Arizona State University (Publisher)
Created2014
Description
In this work, a highly sensitive strain sensing technique is developed to realize in-plane strain mapping for microelectronic packages or emerging flexible or foldable devices, where mechanical or thermal strain is a major concern that could affect the performance of the working devices or even lead to the failure of the devices. Therefore strain sensing techniques to create a contour of the strain distribution is desired.
The developed highly sensitive micro-strain sensing technique differs from the existing strain mapping techniques, such as digital image correlation (DIC)/micro-Moiré techniques, in terms of working mechanism, by filling a technology gap that requires high spatial resolution while simultaneously maintaining a large field-of-view. The strain sensing mechanism relies on the scanning of a tightly focused laser beam onto the grating that is on the sample surface to detect the change in the diffracted beam angle as a result of the strain. Gratings are fabricated on the target substrates to serve as strain sensors, which carries the strain information in the form of variations in the grating period. The geometric structure of the optical system inherently ensures the high sensitivity for the strain sensing, where the nanoscale change of the grating period is amplified by almost six orders into a diffraction peak shift on the order of several hundred micrometers. It significantly amplifies the small signal measurements so that the desired sensitivity and accuracy can be achieved.
The important features, such as strain sensitivity and spatial resolution, for the strain sensing technique are investigated to evaluate the technique. The strain sensitivity has been validated by measurements on homogenous materials with well known reference values of CTE (coefficient of thermal expansion). 10 micro-strain has been successfully resolved from the silicon CTE extraction measurements. Furthermore, the spatial resolution has been studied on predefined grating patterns, which are assembled to mimic the uneven strain distribution across the sample surface. A resolvable feature size of 10 µm has been achieved with an incident laser spot size of 50 µm in diameter.
In addition, the strain sensing technique has been applied to a composite sample made of SU8 and silicon, as well as the microelectronic packages for thermal strain mappings.
The developed highly sensitive micro-strain sensing technique differs from the existing strain mapping techniques, such as digital image correlation (DIC)/micro-Moiré techniques, in terms of working mechanism, by filling a technology gap that requires high spatial resolution while simultaneously maintaining a large field-of-view. The strain sensing mechanism relies on the scanning of a tightly focused laser beam onto the grating that is on the sample surface to detect the change in the diffracted beam angle as a result of the strain. Gratings are fabricated on the target substrates to serve as strain sensors, which carries the strain information in the form of variations in the grating period. The geometric structure of the optical system inherently ensures the high sensitivity for the strain sensing, where the nanoscale change of the grating period is amplified by almost six orders into a diffraction peak shift on the order of several hundred micrometers. It significantly amplifies the small signal measurements so that the desired sensitivity and accuracy can be achieved.
The important features, such as strain sensitivity and spatial resolution, for the strain sensing technique are investigated to evaluate the technique. The strain sensitivity has been validated by measurements on homogenous materials with well known reference values of CTE (coefficient of thermal expansion). 10 micro-strain has been successfully resolved from the silicon CTE extraction measurements. Furthermore, the spatial resolution has been studied on predefined grating patterns, which are assembled to mimic the uneven strain distribution across the sample surface. A resolvable feature size of 10 µm has been achieved with an incident laser spot size of 50 µm in diameter.
In addition, the strain sensing technique has been applied to a composite sample made of SU8 and silicon, as well as the microelectronic packages for thermal strain mappings.
ContributorsLiang, Hanshuang (Author) / Yu, Hongbin (Thesis advisor) / Poon, Poh Chieh Benny (Committee member) / Jiang, Hanqing (Committee member) / Zhang, Yong-Hang (Committee member) / Arizona State University (Publisher)
Created2014
Description
Bohuslav Martinù (1890-1959) was a prolific composer who wrote nearly 100 works for piano. His highly imaginative and eclectic style blends elements of the Baroque, Impressionism, Twentieth-century idioms and Czech folk music. His music is fresh and appealing to the listener, yet it remains intriguing as to how all the elements are combined in a cohesive manner. Martinù himself provides clues to his compositional process. He believed in pure musical expression and the intensity of the musical idea, without the need for extra-musical or programmatic connotations. He espoused holistic and organic views toward musical perception and composition, at times referring to a work as an "organism." This study examines Martinù's piano style in light of his many diverse influences and personal philosophy. The first portion of this paper discusses Martinù's overall style through several piano miniatures written throughout his career. It takes into consideration the composer's personal background, musical influences and aesthetic convictions. The second portion focuses specifically on Martinù's first large-scale work for piano, the Fantasie et Toccata, H. 281. Written during a time in which Martinù was black-listed by the Nazis and forced to flee Europe, this piece bears witness to the chaotic events of WWII through its complexity and intensity of character. The discussion and analysis of the Fantasie et Toccata intends to serve as a guide to interpretation for the performer or listener and also seeks to promote the piano music of Bohuslav Martinù to a wider audience.
ContributorsCrane-Waleczek, Jennifer (Author) / Hamilton, Robert (Thesis advisor) / Hackbarth, Glenn (Committee member) / Meyer Thompson, Janice (Committee member) / Norton, Kay (Committee member) / Campbell, Andrew (Committee member) / Arizona State University (Publisher)
Created2011
Description
Works for clarinet in the twentieth century exist in abundance; furthermore, the number of extant works from the Classical period is substantial. However, works for solo clarinet in the late-Romantic style are lacking; most of the significant literature for clarinet is contained in orchestral works. Therefore, the purpose of this project is to add to the solo clarinet repertoire of the late Romantic-style through the transcription of works written originally for viola. The four works transcribed for this project are by York Bowen. Bowen was a British composer and pianist who taught at the Royal Academy of Music in England. Although his career flourished in the twentieth century, his music reflects the music of the late-Romantic style. The project includes a transcription of Bowen's Sonata No. 1 in C minor, Op. 18 for viola and piano, Sonata No. 2 in F major, Op. 22 for viola and piano, Romance in D-flat for viola and piano, and Phantasy in F, Op. 54 for viola and piano. Additionally, a brief examination of Bowen's life, an overview of each piece, details regarding transcription parts, a list of changes made to the original part, and a recording of each transcription is included in the document.
ContributorsDeBoer, Andrew Caleb (Author) / Spring, Robert S (Thesis advisor) / Hill, Gary (Committee member) / Norton, Kay (Committee member) / McAllister, Timothy (Committee member) / Stauffer, Sandra (Committee member) / Arizona State University (Publisher)
Created2011
Description
Semiconductor devices are generally analyzed with relatively simple equations or with detailed computer simulations. Most text-books use these simple equations and show device diagrams that are frequently very simplified and occasionally incorrect. For example, the carrier densities near the pinch-off point in MOSFETs and JFETs and the minority carrier density in the base near the reverse-biased base-collector junction are frequently assumed to be zero or near zero. Also the channel thickness at the pinch-off point is often shown to approach zero. None of these assumptions can be correct. The research in thesis addresses these points. I simulated the carrier densities, potentials, electric fields etc. of MOSFETs, BJTs and JFETs at and near the pinch-off regions to determine exactly what happens there. I also simulated the behavior of the quasi-Fermi levels. For MOSFETs, the channel thickness expands slightly before the pinch-off point and then spreads out quickly in a triangular shape and the space-charge region under the channel actually shrinks as the potential increases from source to drain. For BJTs, with collector-base junction reverse biased, most minority carriers diffuse through the base from emitter to collector very fast, but the minority carrier concentration at the collector-base space-charge region is not zero. For JFETs, the boundaries of the space-charge region are difficult to determine, the channel does not disappear after pinch off, the shape of channel is always tapered, and the carrier concentration in the channel decreases progressively. After simulating traditional sized devices, I also simulated typical nano-scaled devices and show that they behave similarly to large devices. These simulation results provide a more complete understanding of device physics and device operation in those regions usually not addressed in semiconductor device physics books.
ContributorsYang, Xuan (Author) / Schroder, Dieter K. (Thesis advisor) / Vasileska, Dragica (Committee member) / Yu, Hongbin (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
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
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