Matching Items (75)
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
ABSTRACT An Ensemble Monte Carlo (EMC) computer code has been developed to simulate, semi-classically, spin-dependent electron transport in quasi two-dimensional (2D) III-V semiconductors. The code accounts for both three-dimensional (3D) and quasi-2D transport, utilizing either 3D or 2D scattering mechanisms, as appropriate. Phonon, alloy, interface roughness, and impurity scattering mechanisms are included, accounting for the Pauli Exclusion Principle via a rejection algorithm. The 2D carrier states are calculated via a self-consistent 1D Schrödinger-3D-Poisson solution in which the charge distribution of the 2D carriers in the quantization direction is taken as the spatial distribution of the squared envelope functions within the Hartree approximation. The wavefunctions, subband energies, and 2D scattering rates are updated periodically by solving a series of 1D Schrödinger wave equations (SWE) over the real-space domain of the device at fixed time intervals. The electrostatic potential is updated by periodically solving the 3D Poisson equation. Spin-polarized transport is modeled via a spin density-matrix formalism that accounts for D'yakanov-Perel (DP) scattering. Also, the code allows for the easy inclusion of additional scattering mechanisms and structural modifications to devices. As an application of the simulator, the current voltage characteristics of an InGaAs/InAlAs HEMT are simulated, corresponding to nanoscale III-V HEMTs currently being fabricated by Intel Corporation. The comparative effects of various scattering parameters, material properties and structural attributes are investigated and compared with experiments where reasonable agreement is obtained. The spatial evolution of spin-polarized carriers in prototypical Spin Field Effect Transistor (SpinFET) devices is then simulated. Studies of the spin coherence times in quasi-2D structures is first investigated and compared to experimental results. It is found that the simulated spin coherence times for GaAs structures are in reasonable agreement with experiment. The SpinFET structure studied is a scaled-down version of the InGaAs/InAlAs HEMT discussed in this work, in which spin-polarized carriers are injected at the source, and the coherence length is studied as a function of gate voltage via the Rashba effect.
ContributorsTierney, Brian David (Author) / Goodnick, Stephen (Thesis advisor) / Ferry, David (Committee member) / Akis, Richard (Committee member) / Saraniti, Marco (Committee member) / Vasileska, Dragica (Committee member) / Arizona State University (Publisher)
Created2011
Description
ABSTRACT The relationships between adaptive and maladaptive aspects of gender roles in predicting substance use were examined in a sample of 955 (450 boys, 505 girls) Mexican American 7th and 8th grade adolescents participating in a school-based substance use intervention. The moderating effect of linguistic acculturation, the mediating effects of antisociality, depressive symptoms, and adaptive and avoidant coping on gender role-substance use relationships were examined. Correlational and path analyses supported the Functional Model of Gender Roles that considers these roles as adaptive or maladaptive social coping strategies. For boys, the path analyses yielded significant direct paths from aggressive masculinity to composite alcohol, cigarette, and marijuana use measures, with all other effects of gender roles on substance use operating through the mediators. Bootstrapped mediation tests yielded significant indirect paths, where for boys the positive relationships between assertive and aggressive masculinity with substance use and the negative relationship of affective femininity with substance use were mediated through antisociality, which is predictive of increased substance use. For girls, the positive relationship between aggressive masculinity with cigarette and alcohol use and the negative relationship of affective femininity with alcohol and cigarette use were also mediated by adaptive coping, which is predictive of decreased substance use. A different set of significant indirect paths through avoidant coping connected assertive masculinity and submissive femininity to alcohol use for boys. For boys, the paths from affective femininity to antisociality and adaptive coping were found to be moderated by linguistic acculturation, with the negative correlation of affective femininity with antisociality and positive correlation of this gender role with adaptive coping being stronger in boys low in acculturation. In turn, the pathway from this acculturation by affective femininity interaction to substance use was found to be mediated by antisociality. The present analyses confirmed the importance of gender roles and their interaction with acculturation in predicting substance use in Mexican American adolescents. The analyses also were important in delineating functional mechanisms through which these gender roles have their effects, with implications for the design of interventions to reduce substance use in this population.
ContributorsNagoshi, Julieann Lynn (Author) / Kulis, Stephen (Thesis advisor) / Marsiglia, Flavio (Committee member) / Gillmore, Mary (Committee member) / Arizona State University (Publisher)
Created2012
Description
This dissertation used the risk and resilience framework to examine the associations between perceived racial discrimination, family racial socialization, nativity status, and psychological distress. Regression analyses were conducted to test the links between perceived racial discrimination and psychological distress and the moderation on these associations by family racial socialization and nativity status. Results suggest, for U.S.-born adolescents, cultural socialization strengthened the relation between subtle racial discrimination and anxiety symptoms. In addition, promotion of mistrust buffered the relations of both subtle and blatant racial discrimination on depressive symptoms. For foreign-born adolescents, promotion of mistrust exacerbated the association between blatant racial discrimination and depressive symptoms. Overall, the findings revealed the detrimental effects of perceived racial discrimination on the mental health of Asian American adolescents, how some family racial socialization strategies strengthen or weaken the relation between perceived racial discrimination and psychological distress, and the different ways foreign-born and U.S-born adolescents may interpret racial discrimination and experience family racial socialization.
ContributorsBurrola, Kimberly S (Author) / Yoo, Hyung Chol (Thesis advisor) / Umaña-Taylor, Adriana J. (Thesis advisor) / Eggum, Natalie (Committee member) / Kulis, Stephen (Committee member) / Updegraff, Kimberly (Committee member) / Arizona State University (Publisher)
Created2012
Description
The purpose of this study is to first investigate the role of political socialization on young men and women and what motivates them to become politically active and make the ultimate decision to run for elected office. These effects include parental attitudes, exposure to political shows and news sources, participation in voluntary organizations, and overall community involvement. After understanding these direct and indirect effects of political socialization, I can attempt to explain the causes for the gender gap in political ambition \u2014 meaning that significantly more men are running for elected office compared to women.
ContributorsOsgood, Shannon Marie (Author) / Woodall, Gina (Thesis director) / Herrera, Richard (Committee member) / Barrett, The Honors College (Contributor) / College of Public Service and Community Solutions (Contributor) / School of Public Affairs (Contributor) / School of Politics and Global Studies (Contributor)
Created2015-05
Description
The Undoing Project is an ongoing educational feminist YouTube channel that serves as an introduction to feminism and feminist theory. The objective for this project is to present feminist theory and feminist ideology in an accessible and entertaining way. Through this project I sought to accomplish three goals: to challenge the negative image of feminism, bridge the gap between the language of academia and the public, and to acknowledge and unlearn ingrained prejudices. The videos focus on theory, history, legislation, current events, and pop culture. The initial project consists of ten videos addressing the feminist wave models, a brief history of the feminist movement, and discussions of concepts like hegemony, intersectionality, masculinity, femininity, and race.
ContributorsBuchholtz, Kaylee Marie (Author) / Brian, Jennifer (Thesis director) / Grzanka, Patrick (Committee member) / Brouwer, Dan (Committee member) / Barrett, The Honors College (Contributor) / College of Public Service and Community Solutions (Contributor) / School of Social Transformation (Contributor) / Department of English (Contributor)
Created2015-05
Description
Previous research has found improvements in motor and cognitive measures following Assisted Cycle Therapy (AC) in adolescence with Down syndrome (DS). Our study investigated whether we would find improvements in older adults with DS on measures of leisure physical activity (GLTEQ) and sleep, which are early indicators of Alzheimer's disease (AD) in persons with Down syndrome. This study consisted of eight participants with Down syndrome between 31 and 51 years old that cycled for 30 minutes 3 x/week for eight weeks either at their voluntary cycling rate (VC) or approximately 35% faster with the help of a mechanical motor (AC). We predicted that, based on pilot data (Gomez, 2015), GLTEQ would either maintain or improve after AC, but would decrease after VC and would stay the same after NC. We predicted that the sleep score may improve after both VC or AC or it may improve more after VC than AC based on pilot data related to leisure activity. Our results were consistent with our prediction that GLTEQ will either maintain or improve after AC but will decrease after VC. Our results were not consistent with our prediction that sleep may improve after both VC or AC or it may improve more after VC than AC, possibly because we did not pre-screen for sleep disorders. Future research should focus on recruiting more participants and using both objective and subjective measures of sleep and physical activity to improve the efficacy of the study.
ContributorsParker, Lucas Maury (Author) / Ringenbach, Shannon (Thesis director) / Buman, Matthew (Committee member) / Holzapfel, Simon (Committee member) / School of Social and Behavioral Sciences (Contributor) / School of Nutrition and Health Promotion (Contributor) / College of Public Service and Community Solutions (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Graphene, a one atomic thick planar sheet of carbon atoms, has a zero gap band structure with a linear dispersion relation. This unique property makes graphene a favorite for physicists and engineers, who are trying to understand the mechanism of charge transport in graphene and using it as channel material for field effect transistor (FET) beyond silicon. Therefore, an in-depth exploring of these electrical properties of graphene is urgent, which is the purpose of this dissertation. In this dissertation, the charge transport and quantum capacitance of graphene were studied. Firstly, the transport properties of back-gated graphene transistor covering by high dielectric medium were systematically studied. The gate efficiency increased by up to two orders of magnitude in the presence of a high top dielectric medium, but the mobility did not change significantly. The results strongly suggested that the previously reported top dielectric medium-induced charge transport properties of graphene FETs were possibly due to the increase of gate capacitance, rather than enhancement of carrier mobility. Secondly, a direct measurement of quantum capacitance of graphene was performed. The quantum capacitance displayed a non-zero minimum at the Dirac point and a linear increase on both sides of the minimum with relatively small slopes. The findings - which were not predicted by theory for ideal graphene - suggested that scattering from charged impurities also influences the quantum capacitance. The capacitances in aqueous solutions at different ionic concentrations were also measured, which strongly suggested that the longstanding puzzle about the interfacial capacitance in carbon-based electrodes had a quantum origin. Finally, the transport and quantum capacitance of epitaxial graphene were studied simultaneously, the quantum capacitance of epitaxial graphene was extracted, which was similar to that of exfoliated graphene near the Dirac Point, but exhibited a large sub-linear behavior at high carrier density. The self-consistent theory was found to provide a reasonable description of the transport data of the epitaxial graphene device, but a more complete theory was needed to explain both the transport and quantum capacitance data.
ContributorsXia, Jilin (Author) / Tao, N.J. (Thesis advisor) / Ferry, David (Committee member) / Thornton, Trevor (Committee member) / Tsui, Raymond (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2010
Description
Surrounded by a developmental boom in downtown Phoenix, Roosevelt Row fights to maintain the local art influence and historic character. An earthy community of street artists, coffee drinkers, band tees, nose rings, vinyl collectors and rolled denim, the people are facing dramatic urbanization. The hum of drills, hammers, cranes and alarms sound throughout the viscidity, echoing the construction of a new era downtown. In the interest of better understanding the developmental process, resident needs and community, this research project evaluates successful public spaces and similar downtown areas in the United States, synthesized their elements of prosperity in comparison to general attributes of quality public spaces, and implemented the concepts and ideas into Roosevelt Row. This provided the researcher with knowledge of quality public spaces, why public space is important, and how placemaking is routinely accomplished. This also equipped the researcher with the tools to participate in ethnography and collect observational data to learn about Roosevelt Row. The researcher then combined learned material with what she observed on the Row, to condense the artists' district developmental needs into nine proposals for bettering the Row in the immediate, near and long-term future. The study begs to answer the question: is Roosevelt Row a Place or a place? Observation, residential and visitor engagement with the space; locality, pleasurability, inclusiveness and safety of the public spaces; and relationship between residents and quality of space all contribute to the space's qualifications. While Roosevelt Row has the potential and assets to become a Place, especially if the nine proposals are implemented. However, at the time of research, the space is between place and Place.
ContributorsStobbe, Brooke Elizabeth (Author) / Larsen, Dale (Thesis director) / Knopf, Richard (Committee member) / College of Public Service and Community Solutions (Contributor) / Walter Cronkite School of Journalism and Mass Communication (Contributor) / Barrett, The Honors College (Contributor)
Created2015-12
Description
Background
Weight gain during the childbearing years and failure to lose pregnancy weight after birth contribute to the development of obesity in postpartum Latinas.
Methods
Madres para la Salud [Mothers for Health] was a 12-month, randomized controlled trial exploring a social support intervention with moderate-intensity physical activity (PA) seeking to effect changes in body fat, fat tissue inflammation, and depression symptoms in sedentary postpartum Latinas. This report describes the efficacy of the Madres intervention.
Results
The results show that while social support increased during the active intervention delivery, it declined to pre-intervention levels by the end of the intervention. There were significant achievements in aerobic and total steps across the 12 months of the intervention, and declines in body adiposity assessed with bioelectric impedance.
Conclusions
Social support from family and friends mediated increases in aerobic PA resulting in decrease in percent body fat.
Weight gain during the childbearing years and failure to lose pregnancy weight after birth contribute to the development of obesity in postpartum Latinas.
Methods
Madres para la Salud [Mothers for Health] was a 12-month, randomized controlled trial exploring a social support intervention with moderate-intensity physical activity (PA) seeking to effect changes in body fat, fat tissue inflammation, and depression symptoms in sedentary postpartum Latinas. This report describes the efficacy of the Madres intervention.
Results
The results show that while social support increased during the active intervention delivery, it declined to pre-intervention levels by the end of the intervention. There were significant achievements in aerobic and total steps across the 12 months of the intervention, and declines in body adiposity assessed with bioelectric impedance.
Conclusions
Social support from family and friends mediated increases in aerobic PA resulting in decrease in percent body fat.
ContributorsKeller, Colleen (Author) / Ainsworth, Barbara (Author) / Records, Kathryn (Author) / Todd, Michael (Author) / Belyea, Michael (Author) / Vega Lopez, Sonia (Author) / Permana, Paska (Author) / Coonrod, Dean (Author) / Williams, Allison (Author) / Arizona State University. College of Nursing & Healthcare Innovation (Contributor) / College of Health Solutions (Contributor) / School of Nutrition and Health Promotion (Contributor) / College of Public Service and Community Solutions (Contributor) / Southwest Interdisciplinary Research Center (Contributor)
Created2014-09-19