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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

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
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ABSTRACT The purpose of this study was to determine the energy cost of four modes of resistance training (push-ups, pull-ups, curl-ups, lunges). Twelve well trained men aged 23.6 (SD=2.84) years were recruited to participate in the study. Each of the 12 men completed three trials of each of

ABSTRACT The purpose of this study was to determine the energy cost of four modes of resistance training (push-ups, pull-ups, curl-ups, lunges). Twelve well trained men aged 23.6 (SD=2.84) years were recruited to participate in the study. Each of the 12 men completed three trials of each of the four exercises on one visit to the laboratory lasting slightly over one hour (M=72 min, SD=5.9 min). The oxygen consumption of the men was monitored constantly throughout the trial and data was recorded every five seconds. Mean VO2 values were calculated for each exercise. The values for push-ups (M=11.57 ml/kg/min, SD=1.99), curl-ups (M=10.99 ml/kg/min, SD=1.48), pull-ups (M=10.87 ml/kg/min, SD=2.51), and lunges (M=14.18 ml/kg/min, SD=1.78) were converted to METs (Metabolic Equivalents). The MET values (3.31, 3.14, 3.11, and 4.05 respectively) all fall within the range of moderate intensity activity. The findings of this study show that a single set of any of the above exercises will qualify as a moderate intensity activity and can be used to meet recommendations on daily physical activity.
ContributorsVezina, Jesse (Author) / Ainsworth, Barbara (Thesis advisor) / Campbell, Kathryn (Committee member) / Woodruff, Larry (Committee member) / Arizona State University (Publisher)
Created2011
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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

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
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Description
Introduction: Several faith-based or faith-placed programs have focused on the physical dimension of wellness in efforts to improve health by increasing physical activity and improving diet behaviors. However, these programs were not designed to intervene on the mental dimension of wellness which is critical for stress reduction and health behavior

Introduction: Several faith-based or faith-placed programs have focused on the physical dimension of wellness in efforts to improve health by increasing physical activity and improving diet behaviors. However, these programs were not designed to intervene on the mental dimension of wellness which is critical for stress reduction and health behavior change. Purpose: To evaluate the feasibility of a spirituality-based stress reduction and health behavior change intervention using the Spiritual Framework of Coping (SFC) model. Methods: This study was a quasi-experimental one group pretest posttest design. The study was a total of eight weeks conducted at a non-denominational Christian church. Participants were recruited from the church through announcements and flyers. The Optimal Health program met once a week for 1.5 hours with weekly phone calls during an additional four week follow-up period. Feasibility was assessed by the acceptability, demand, implementation, practicality, integration, and limited efficacy of the program. Analysis: Frequencies for demographics were assessed. Statistical analyses of feasibility objectives were assessed by frequencies and distribution of responses to feasibility evaluations. Limited efficacy of pretest and posttest measures were conducted using paired t-test (p <.05). Results: The Optimal Health Program was positively accepted by participants. The demand for the program was shown with average attendance of 78.7%. The program was successfully implemented as shown by meeting session objectives and 88% homework completion. The program was both practical for the intended participants and was successfully integrated within the existing environment. Limited efficacy changes within the program were mostly non-significant. Conclusion: This study tested the feasibility of implementing the Optimal Health program that specifically targeted the structural components of the Spiritual Framework of Coping Model identified to create meaning making and enhance well-being. This program may ultimately be used to help individuals improve and balance the spiritual, mental, and physical dimensions of wellness. However, length of study and limited efficacy measures will need to be reevaluated for program success.
ContributorsWalker, Jenelle R (Author) / Swan, Pamela (Thesis advisor) / Ainsworth, Barbara (Committee member) / Chisum, Jack (Committee member) / Fleury, Julie (Committee member) / Hooker, Steven (Committee member) / Arizona State University (Publisher)
Created2012
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The health enhancing effects of physical activity are well documented in the literature. However, women continue to report lower participation in exercise and physical activity (PA) compared to men. As women age an overall trend in decreased activity is observed. The primary place of activity reported in women is the

The health enhancing effects of physical activity are well documented in the literature. However, women continue to report lower participation in exercise and physical activity (PA) compared to men. As women age an overall trend in decreased activity is observed. The primary place of activity reported in women is the home and one of the most commonly reported reasons for lack of physical activity is the lack of time. Few instruments have been developed that focus on the activity patterns of women. The Cross Cultural Physical Activity Study that this study was based on targeted women of color to assess the types of activity and constraints to activity experienced by African American and Native American women over 40 years old. This secondary data analysis focused on the psychometric properties of two scales used in the above study, The Physical Recreation Questionnaire (PRQ) and The Typical Week Physical Activity Survey (TWPAS). An exploratory factor analysis (EFA) was conducted on the 18 items from the Physical Recreation Questionnaire (PRQ) which focused on constraints to PA. The results of the EFA were a poor fit of a two factor model. The three factor model had a favorable fit in the EFA. Confirmatory factor analysis (CFA) was then conducted on the 18 items in the PRQ. Results of the CFA supported the presence of three latent variables: enjoyment of PA, constraints to PA, and negotiation of constraints to PA. The Typical Week Physical Activity Survey (TWPAS) is a 35 item measure of moderate PA that includes the activities most often reported by women. The purpose of the TWPAS was to capture habitual PA that might not be recorded in other PA questionnaires. The TWPAS was correlated with criterion measures of PA records, treadmill, accelerometer, and BMI. Although correlations were small, they were in the expected direction with the criterion measures. The evaluation of the instruments supported the presence of the construct of constraints to PA in the PRQ and the measurement of moderate intensity PA in the TWPAS.
ContributorsBishop, Jewel (Author) / Ainsworth, Barbara (Thesis advisor) / Komnenich, Pauline (Committee member) / Arizona State University (Publisher)
Created2012
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Health care providers (HCPs) are an important source of physical activity (PA) information. Two studies were conducted to qualitatively and quantitatively examine nurse practitioners'(NPs) and physician assistants' current PA counseling practices, knowledge and confidence to provide PA counseling and providers' perceptions about their current PA counseling practices. The specific aims

Health care providers (HCPs) are an important source of physical activity (PA) information. Two studies were conducted to qualitatively and quantitatively examine nurse practitioners'(NPs) and physician assistants' current PA counseling practices, knowledge and confidence to provide PA counseling and providers' perceptions about their current PA counseling practices. The specific aims for these two studies included quantitatively and qualitatively identifying the prevalence of PA counseling, perceived counseling knowledge and confidence, and educational training related to counseling. In study 1, survey respondents were currently practicing NPs and physician assistants. Participants completed a modified version of the Promotion of Physical Activity by Nurse Practitioners Questionnaire either online or in person during a population specific conference. The majority of both NP and physician assistant respondents reported routinely counseling patients about PA. There were no differences in perceived knowledge or confidence to provide PA counseling between the two populations. Approximately half of all respondents reported receiving training to provide PA counseling as part of their educational preparation for becoming a health practitioner. Nearly three-quarters of respondents reported interest in receiving additional PA counseling training. In study 2, five focus groups (FGs), stratified by practice type, were conducted with NPs and physician assistants. Both NPs and physician assistants reported discussing PA with their patients, particularly those with chronic illness. Participants reported that discussing lifestyle modifications with patients was the most common type of PA counseling provided. Increased confidence to counsel was associated with having PA knowledge and providing simple counseling, such as lifestyle modifications. Barriers to counseling included having more important things to discuss, lack of time during appointments, the current healthcare system, lack of reimbursement and perceived patient financial barriers. PA recommendation knowledge was highly variable, with few participants reporting specific guidelines. FG participants, while not familiar with the American College of Sports Medicines' "Exercise is Medicine" initiative indicated interest in its use and learning more about it. The findings of these two studies indicate that while NPs and physician assistants are knowledgeable, confident and currently providing some amount of PA counseling to patients, additional training in PA counseling is needed and desired.

ContributorsGrimstvedt, Megan (Author) / Der Ananian, Cheryl (Thesis advisor) / Ainsworth, Barbara (Committee member) / Keller, Colleen (Committee member) / Sebren, Ann (Committee member) / Woolf, Kathleen (Committee member) / Arizona State University (Publisher)
Created2011
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It is broadly accepted that physical activity provides substantial health benefits. Despite strong evidence, approximately 60% to 95% of US adults are insufficiently active to obtain these health benefits. This dissertation explored five projects that examined the measurement properties and methodology for a variety of physical activity assessment methods. Project

It is broadly accepted that physical activity provides substantial health benefits. Despite strong evidence, approximately 60% to 95% of US adults are insufficiently active to obtain these health benefits. This dissertation explored five projects that examined the measurement properties and methodology for a variety of physical activity assessment methods. Project one identified validity evidence for the new MyWellness Key accelerometer in sixteen adults. The MyWellness Key demonstrated acceptable validity evidence when compared to a criterion accelerometer during graded treadmill walking and in free-living settings. This supports the use of the MyWellness Key accelerometer to measure physical activity. Project two evaluated validity (study 1) and test-retest reliability evidence (study 2) of the Global Physical Activity Questionnaire (GPAQ) in a two part study. The GPAQ was compared to direct and indirect criterion measures including object and subjective physical activity instruments. These data provided preliminary validity and reliability evidence for the GPAQ that support its use to assess physical activity. Project three investigated the optimal h.d-1 of accelerometer wear time needed to assess daily physical activity. Using a semi-simulation approach, data from 124 participants were used to compare 10-13 h.d-1 to the criterion 14 h.d-1. This study suggested that a minimum accelerometer wear time of 13 h.d-1 is needed to provide a valid measure of daily physical activity. Project four evaluated validity and reliability evidence of a novel method (Movement and Activity in Physical Space [MAPS] score) that combines accelerometer and GPS data to assess person-environment interactions. Seventy-five healthy adults wore an accelerometer and GPS receiver for three days to provide MAPS scores. This study provided evidence for use of a MAPS score for future research and clinical use. Project five used accelerometer data from 1,000 participants from the 2005-2006 National Health and Nutrition Examination Study. A semi-simulation approach was used to assess the effect of accelerometer wear time (10-14 h.d-1) on physical activity data. These data showed wearing for 12 h.d-1 or less may underestimate time spent in various intensities of physical activity.
ContributorsHerrmann, Stephen (Author) / Ainsworth, Barbara (Thesis advisor) / Gaesser, Glenn (Committee member) / Der Ananian, Cheryl (Committee member) / Kang, Minsoo (Committee member) / Vega-Lopez, Sonia (Committee member) / Arizona State University (Publisher)
Created2011
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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

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
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"Globesity," as defined by the World Health Organization, describes obesity as a pandemic affecting at least 400 million people worldwide. The prevalence of obesity is higher among women than men; and in non-Hispanic black and Hispanic populations. Obesity has been significantly associated with increased all-cause mortality, and mortality from cardiovascular

"Globesity," as defined by the World Health Organization, describes obesity as a pandemic affecting at least 400 million people worldwide. The prevalence of obesity is higher among women than men; and in non-Hispanic black and Hispanic populations. Obesity has been significantly associated with increased all-cause mortality, and mortality from cardiovascular disease, obesity-related cancers, diabetes and kidney disease. Current strategies to curb obesity rates often use an ecological approach, suggesting three main factors: biological, behavioral, and environmental. This approach was used to develop four studies of obesity. The first study assessed dietary quality, using the Healthy Eating Index (HEI)-2005, among premenopausal Hispanic and non-Hispanic white women, and found that Hispanic women had lower total HEI-2005 scores, and lower scores for total vegetables, dark green and orange vegetables and legumes, and sodium. Markers of obesity were negatively correlated with total HEI-2005 scores. The second study examined the relationship between reported screen time and markers of obesity among premenopausal women and found that total screen time, TV, and computer use were positively associated with markers of obesity. Waist/height ratio, fat mass index, and leptin concentrations were significantly lower among those who reported the lowest screen time versus the moderate and high screen time categories. The third study examined the relationship between screen time and dietary intake and found no significant differences in absolute dietary intake by screen time category. The fourth study was designed to test a brief face-to-face healthy shopping intervention to determine whether food purchases of participants who received the intervention differed from those in the control group; and whether purchases differed by socioeconomic position. Participants in the intervention group purchased more servings of fruit when compared to the control group. High-income participants purchased more servings of dark green/deep yellow vegetables compared to those in the low-income group. Among those who received the intervention, low-income participants purchased foods of lower energy density, and middle-income participants purchased food of higher fat density. The findings of these studies support policy changes to address increasing access and availability of fruits and vegetables, and support guidelines to limit screen time among adults.
ContributorsMilliron, Brandy-Joe (Author) / Woolf, Kathleen (Thesis advisor) / Vaughan, Linda (Committee member) / Ainsworth, Barbara (Committee member) / Wharton, Chris (Committee member) / Der Ananian, Cheryl (Committee member) / Appelhans, Bradley (Committee member) / Arizona State University (Publisher)
Created2010
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Features of the built environment (BE) are related to a wide range of health factors, including leisure-time physical activity (PA) and active forms of transportation. For working adults, worksite neighborhood is likely an important BE to better understand the impact of various factors on PA patterns. Compared to home neighborhood

Features of the built environment (BE) are related to a wide range of health factors, including leisure-time physical activity (PA) and active forms of transportation. For working adults, worksite neighborhood is likely an important BE to better understand the impact of various factors on PA patterns. Compared to home neighborhood walkability research, worksite walkability has received relatively less attention. The objective of this project was to identify if worksite walkability was significantly associated with PA behavior.

Aims: to evaluate 1) the PA variation explained by work walkability, 2) the moderating effects of person-level characteristics to the relationship between PA and work walkability, and 3) the differences in the rate of change in PA over time by worksite walkability.

Methods: self-report and accelerometer measured PA at baseline (aim 1, 2); longitudinal accelerometer PA during the initial 56 days of a behavioral intervention (aim 3). Adults were generally healthy and reported part- or full-time employment with a geocodeable address outside the home. Geographic Information Systems (GIS) measured walkability followed established techniques (i.e., residential, intersection, and transit densities, and land-use-mix).

Results: On average, worksite walkability did not show direct relationships with PA (aim 1); yet certain person-level characteristics moderated the relationships: sex, race, and not having young children in the household (aim 2). During 56 days of intervention, the PA rate of change over time showed no evidence of a moderating effect by worksite walkability.

Discussion: Worksite walkability was generally not shown to relate to the overall PA. However, specific subgroups (women, those without young children) appeared more responsive to their worksite neighborhood walkability. Prior literature shows certain demographics respond differently with various BE exposures, and this study adds a potentially novel moderator of interest regarding young children at home. Understanding who benefits from access to walkable BE may inform targeted interventions and policy to improve PA levels and foster health equity.
ContributorsHurley, Jane Cathleen (Author) / Adams, Marc A (Thesis advisor) / Todd, Mike (Committee member) / Hooker, Steven P (Committee member) / Ohri-Vachaspati, Punam (Committee member) / Ainsworth, Barbara (Committee member) / Arizona State University (Publisher)
Created2019