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Description
This dissertation presents research findings on the three materials systems: lateral Si nanowires (SiNW), In2Se3/Bi2Se3 heterostructures and graphene. The first part of the thesis was focused on the growth and characterization of lateral SiNW. Lateral here refers to wires growing along the plane of substrate; vertical NW on the other hand grow out of the plane of substrate. It was found, using the Au-seeded vapor – liquid – solid technique, that epitaxial single-crystal SiNW can be grown laterally along Si(111) substrates that have been miscut toward [11− 2]. The ratio of lateral-to-vertical NW was found to increase as the miscut angle increased and as disilane pressure and substrate temperature decreased. Based on this observation, growth parameters were identified whereby all of the deposited Au seeds formed lateral NW. Furthermore, the nanofaceted substrate guided the growth via a mechanism that involved pinning of the trijunction at the liquid/solid interface of the growing nanowire.
Next, the growth of selenide heterostructures was explored. Specifically, molecular beam epitaxy was utilized to grow In2Se3 and Bi2Se3 films on h-BN, highly oriented pyrolytic graphite and Si(111) substrates. Growth optimizations of In2Se3 and Bi2Se3 films were carried out by systematically varying the growth parameters. While the growth of these films was demonstrated on h-BN and HOPG surface, the majority of the effort was focused on growth on Si(111). Atomically flat terraces that extended laterally for several hundred nm, which were separated by single quintuple layer high steps characterized surface of the best In2Se3 films grown on Si(111). These In2Se3 films were suitable for subsequent high quality epitaxy of Bi2Se3 .
The last part of this dissertation was focused on a recently initiated and ongoing study of graphene growth on liquid metal surfaces. The initial part of the study comprised a successful modification of an existing growth system to accommodate graphene synthesis and process development for reproducible graphene growth. Graphene was grown on Cu, Au and AuCu alloys at varioua conditions. Preliminary results showed triangular features on the liquid part of the Cu metal surface. For Au, and AuCu alloys, hexagonal features were noticed both on the solid and liquid parts.
Next, the growth of selenide heterostructures was explored. Specifically, molecular beam epitaxy was utilized to grow In2Se3 and Bi2Se3 films on h-BN, highly oriented pyrolytic graphite and Si(111) substrates. Growth optimizations of In2Se3 and Bi2Se3 films were carried out by systematically varying the growth parameters. While the growth of these films was demonstrated on h-BN and HOPG surface, the majority of the effort was focused on growth on Si(111). Atomically flat terraces that extended laterally for several hundred nm, which were separated by single quintuple layer high steps characterized surface of the best In2Se3 films grown on Si(111). These In2Se3 films were suitable for subsequent high quality epitaxy of Bi2Se3 .
The last part of this dissertation was focused on a recently initiated and ongoing study of graphene growth on liquid metal surfaces. The initial part of the study comprised a successful modification of an existing growth system to accommodate graphene synthesis and process development for reproducible graphene growth. Graphene was grown on Cu, Au and AuCu alloys at varioua conditions. Preliminary results showed triangular features on the liquid part of the Cu metal surface. For Au, and AuCu alloys, hexagonal features were noticed both on the solid and liquid parts.
ContributorsRathi, Somilkumar J (Author) / Drucker, Jeffery (Thesis advisor) / Smith, David (Committee member) / Chen, Tingyong (Committee member) / Arizona State University (Publisher)
Created2014
Description
A primary motivation of research in photovoltaic technology is to obtain higher efficiency photovoltaic devices at reduced cost of production so that solar electricity can be cost competitive. The majority of photovoltaic technologies are based on p-n junction, with efficiency potential being much lower than the thermodynamic limits of individual technologies and thereby providing substantial scope for further improvements in efficiency. The thesis explores photovoltaic devices using new physical processes that rely on thin layers and are capable of attaining the thermodynamic limit of photovoltaic technology. Silicon heterostructure is one of the candidate technologies in which thin films induce a minority carrier collecting junction in silicon and the devices can achieve efficiency close to the thermodynamic limits of silicon technology. The thesis proposes and experimentally establishes a new theory explaining the operation of silicon heterostructure solar cells. The theory will assist in identifying the optimum properties of thin film materials for silicon heterostructure and help in design and characterization of the devices, along with aiding in developing new devices based on this technology. The efficiency potential of silicon heterostructure is constrained by the thermodynamic limit (31%) of single junction solar cell and is considerably lower than the limit of photovoltaic conversion (~ 80 %). A further improvement in photovoltaic conversion efficiency is possible by implementing a multiple quasi-fermi level system (MQFL). A MQFL allows the absorption of sub band gap photons with current being extracted at a higher band-gap, thereby allowing to overcome the efficiency limit of single junction devices. A MQFL can be realized either by thin epitaxial layers of alternating higher and lower band gap material with nearly lattice matched (quantum well) or highly lattice mismatched (quantum dot) structure. The thesis identifies the material combination for quantum well structure and calculates the absorption coefficient of a MQFl based on quantum well. GaAsSb (barrier)/InAs(dot) was identified as a candidate material for MQFL using quantum dot. The thesis explains the growth mechanism of GaAsSb and the optimization of GaAsSb and GaAs heterointerface.
ContributorsGhosha, Kuṇāla (Author) / Bowden, Stuart (Thesis advisor) / Honsberg, Christiana (Thesis advisor) / Vasileska, Dragica (Committee member) / Goodnick, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
The research described in this dissertation has involved the use of transmission electron microcopy (TEM) to characterize the structural properties of II-VI and III-V compound semiconductor heterostructures and superlattices. The microstructure of thick ZnTe epilayers (~2.4 µm) grown by molecular beam epitaxy (MBE) under virtually identical conditions on GaSb, InAs, InP and GaAs (100) substrates were compared using TEM. High-resolution electron micrographs revealed a highly coherent interface for the ZnTe/GaSb sample, and showed extensive areas with well-separated interfacial misfit dislocations for the ZnTe/InAs sample. Lomer edge dislocations and 60o dislocations were commonly observed at the interfaces of the ZnTe/InP and ZnTe/GaAs samples. The amount of residual strain at the interfaces was estimated to be 0.01% for the ZnTe/InP sample and -0.09% for the ZnTe/GaAs sample. Strong PL spectra for all ZnTe samples were observed from 80 to 300 K. High quality GaSb grown by MBE on ZnTe/GaSb (001) virtual substrates with a temperature ramp at the beginning of the GaSb growth has been demonstrated. High-resolution X-ray diffraction (XRD) showed clear Pendellösung thickness fringes from both GaSb and ZnTe epilayers. Cross-section TEM images showed excellent crystallinity and smooth morphology for both ZnTe/GaSb and GaSb/ZnTe interfaces. Plan-view TEM image revealed the presence of Lomer dislocations at the interfaces and threading dislocations in the top GaSb layer. The defect density was estimated to be ~1 x107/cm2. The PL spectra showed improved optical properties when using the GaSb transition layer grown on ZnTe with a temperature ramp. The structural properties of strain-balanced InAs/InAs1-xSbx SLs grown on GaSb (001) substrates by metalorganic chemical vapor deposition (MOCVD) and MBE, have been studied using XRD and TEM. Excellent structural quality of the InAs/InAs1-xSbx SLs grown by MOCVD has been demonstrated. Well-defined ordered-alloy structures within individual InAs1-xSbx layers were observed for samples grown by modulated MBE. However, the ordering disappeared when defects propagating through the SL layers appeared during growth. For samples grown by conventional MBE, high-resolution images revealed that interfaces for InAs1-xSbx grown on InAs layers were sharper than for InAs grown on InAs1-xSbx layers, most likely due to a Sb surfactant segregation effect.
ContributorsOuyang, Lu (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha (Committee member) / Ponce, Fernando (Committee member) / Chamberlin, Ralph (Committee member) / Menéndez, Jose (Committee member) / Arizona State University (Publisher)
Created2012
Description
Recently a new materials platform consisting of semiconductors grown on GaSb and InAs substrates with lattice constants close to 6.1 A was proposed by our group for various electronic and optoelectronic applications. This materials platform consists of both II-VI (MgZnCdHg)(SeTe) and III-V (InGaAl)(AsSb) compound semiconductors, which have direct bandgaps spanning the entire energy spectrum from far-IR (~0 eV) up to UV (~3.4 eV). The broad range of bandgaps and material properties make it very attractive for a wide range of applications in optoelectronics, such as solar cells, laser diodes, light emitting diodes, and photodetectors. Moreover, this novel materials system potentially offers unlimited degrees of freedom for integration of electronic and optoelectronic devices onto a single substrate while keeping the best possible materials quality with very low densities of misfit dislocations. This capability is not achievable with any other known lattice-matched semiconductors on any available substrate. In the 6.1-A materials system, the semiconductors ZnTe and GaSb are almost perfectly lattice-matched with a lattice mismatch of only 0.13%. Correspondingly, it is expected that high quality ZnTe/GaSb and GaSb/ZnTe heterostructures can be achieved with very few dislocations generated during growth. To fulfill the task, their MBE growth and material properties are carefully investigated. High quality ZnTe layers grown on various III-V substrates and GaSb grown on ZnTe are successfully achieved using MBE. It is also noticed that ZnTe and GaSb have a type-I band-edge alignment with large band offsets (delta_Ec=0.934 eV, delta_Ev=0.6 eV), which provides strong confinement for both electrons and holes. Furthermore, a large difference in refractive index is found between ZnTe and GaSb (2.7 and 3.9, respectively, at 0.7 eV), leading to excellent optical confinement of the guided optical modes in planar semiconductor lasers or distributed Bragg reflectors (DBR) for vertical-cavity surface-emitting lasers. Therefore, GaSb/ZnTe double-heterostructure and ZnTe/GaSb DBR structure are suitable for use in light emitting devices. In this thesis work, experimental demonstration of these structures with excellent structural and optical properties is reported. During the exploration on the properties of various ZnTe heterostructures, it is found that residual tensile strains exist in the thick ZnTe epilayers when they are grown on GaAs, InP, InAs and GaSb substrates. The presence of tensile strains is due to the difference in thermal expansion coefficients between the epilayers and the substrates. The defect densities in these ZnTe layers become lower as the ZnTe layer thickness increases. Growth of high quality GaSb on ZnTe can be achieved using a temperature ramp during growth. The influence of temperature ramps with different ramping rates in the optical properties of GaSb layer is studied, and the samples grown with a temperature ramp from 360 to 470 C at a rate of 33 C/min show the narrowest bound exciton emission peak with a full width at half maximum of 15 meV. ZnTe/GaSb DBR structures show excellent reflectivity properties in the mid-infrared range. A peak reflectance of 99% with a wide stopband of 480 nm centered at 2.5 um is measured from a ZnTe/GaSb DBR sample of only 7 quarter-wavelength pairs.
ContributorsFan, Jin (Author) / Zhang, Yong-Hang (Thesis advisor) / Smith, David (Committee member) / Yu, Hongbin (Committee member) / Menéndez, Jose (Committee member) / Johnson, Shane (Committee member) / Arizona State University (Publisher)
Created2012
Description
This dissertation offers three essays that investigate consumers’ health-related food choices and behaviors from three different, yet complementary, angles. The first essay uses an eye-tracking experiment to examine consumers’ visual attention to the Nutrition Facts Panels for healthy and unhealthy products. In this essay, I focus on how involvement and familiarity affect consumers’ attention toward the Nutrition Facts panel and how these two psychological factors interact with new label format changes in attracting consumers’ attention. In the second essay, I demonstrate using individual-level scanner data that nutritional attributes interact with marketing mix elements to affect consumers’ nutrition intake profiles and their intra-category substitution patterns. My findings suggest that marketing-mix sensitivities are correlated with consumers’ preferences for nutrient attributes in ways that depend on the “healthiness” of the nutrient. For instance, featuring promotes is positively correlated with “healthy” nutritional characteristics such as high-protein, low-fat, or low-carbohydrates, whereas promotion and display are positively correlated with preferences for “unhealthy” characteristics such as high-fat, or high-carbohydrates. I use model simulations to show that some marketing-mix elements are able to induce consumers to purchase items with higher maximum-content levels than others. The fourth chapter shows that dieters are not all the same. I develop and validate a new scale that measures lay theories about abstinence vs. moderation. My findings from a series of experiments indicate that dieters’ recovery from recalled vs. actual indulgences depend on whether they favor abstinence or moderation. However, compensatory coping strategies provide paths for people with both lay theories to recover after an indulgence, in their own ways. The three essays provide insights into individual differences that determine approaches of purchase behaviors, and consumption patterns, and life style that people choose, and these insights have potential policy implications to aid in designing the food-related interventions and policies to improve the healthiness of consumers’ consumption profiles and more general food well-being.
ContributorsXie, Yi (Author) / Richards, Timothy (Thesis advisor) / Mandel, Naomi (Committee member) / Grebitus, Carola (Committee member) / Arizona State University (Publisher)
Created2018
Description
This article can be divided into six parts.
The first chapter analyzes the background, theatrical and particle reasons of this research. The author argues that the management of law firm needs a set of good system. The first one is operating the law firm in scale, and the other on is corporate management model, which shall be constructed in detail in the paper and will be put into practice by the law firm in which the author is worked.
The second chapter will introduce modern management theory, combining the situation of management in our law firm to analyze, raising some reasonable suggestions and instructions to promote our law firm to achieve the corporate management.
In the third chapter, the first chapter, starting with the review of the development process of foreign and our law firms, listing the organizational forms and the characteristics of our law firm, analyzing the situation and the drawbacks of the law firm management.
The fourth and fifth chapter introduce he background, the connotation of the corporate management model, listing the development and successful experience of some typical cases in respect of corporate management.
In the last chapter, the construction of corporate management model will be introduced in terms of organization form, human resource management and informationizing development.
The corporate management model is not mature in china. Though it is not easy to reform the existing model, but it should be believed that the development benefiting the legal industry will be achieved.
The first chapter analyzes the background, theatrical and particle reasons of this research. The author argues that the management of law firm needs a set of good system. The first one is operating the law firm in scale, and the other on is corporate management model, which shall be constructed in detail in the paper and will be put into practice by the law firm in which the author is worked.
The second chapter will introduce modern management theory, combining the situation of management in our law firm to analyze, raising some reasonable suggestions and instructions to promote our law firm to achieve the corporate management.
In the third chapter, the first chapter, starting with the review of the development process of foreign and our law firms, listing the organizational forms and the characteristics of our law firm, analyzing the situation and the drawbacks of the law firm management.
The fourth and fifth chapter introduce he background, the connotation of the corporate management model, listing the development and successful experience of some typical cases in respect of corporate management.
In the last chapter, the construction of corporate management model will be introduced in terms of organization form, human resource management and informationizing development.
The corporate management model is not mature in china. Though it is not easy to reform the existing model, but it should be believed that the development benefiting the legal industry will be achieved.
ContributorsZhu, Ping (Author) / Gu, Bin (Thesis advisor) / Chang, Chun (Thesis advisor) / Zhu, Ning (Committee member) / Arizona State University (Publisher)
Created2017
Description
Due to the booming young mothers and fathers in the new era as well as the changes in the concept of parenting and the favorable liberalization of China's second child policy, the maternal-baby nursing market continues to grow, and it has become a must for businesses nowadays. In 2020, the size of the maternal-baby nursing market will reach 3.6 trillion. (Data: Yibang Power China's Maternal and Child Industry White Paper 2017).
The rapid development of mobile Internet, highly transparent information, consumers grasp the sovereignty, along with the rise of the middle class, consumption increase encouraged personalized, customized needs. The boundaries between online and offline are becoming increasingly blurred. Consumers are more inclined to choose multi-category with service channel providers. If the retailers still rely on good market resources, and the difference between the sales and purchase of commodities, they will face a huge challenge of the decrease in passenger flow and a decline in performance.
The paper takes the relationship between maternal-baby nursing retailers and targets customers as the study object, based on customer service of maternal-baby nursing retailer data, empirical studies, we found that this particular group, mothers and babies, especially value safety, quality, public praise and community review. If the retail enterprise attaches importance to establishing relationships with customers and enhances the relational viscosity through mutual trust, emotional formation and spread of public praise, it will help to increase the traffic volume and increase the output value of single customers.
The maternal-baby nursing retailers form a strong relationship between enterprises and customers by establishing a strong relationship between products and customers, employees and customers, and customers to customers. Maternal-baby nursing retailers operate single-customer value deeply, build a heavy membership system and manage customer assets, thereby enhancing their brand and performance.
The research on the method of establishing the strong tie can be considered as an analysis of feasibility. The research results of this paper will help to improve the overall customer service experience and satisfaction of the mother and infant retail industry, enhance the development of the whole industry and draw significance lessons from other service industries.
The rapid development of mobile Internet, highly transparent information, consumers grasp the sovereignty, along with the rise of the middle class, consumption increase encouraged personalized, customized needs. The boundaries between online and offline are becoming increasingly blurred. Consumers are more inclined to choose multi-category with service channel providers. If the retailers still rely on good market resources, and the difference between the sales and purchase of commodities, they will face a huge challenge of the decrease in passenger flow and a decline in performance.
The paper takes the relationship between maternal-baby nursing retailers and targets customers as the study object, based on customer service of maternal-baby nursing retailer data, empirical studies, we found that this particular group, mothers and babies, especially value safety, quality, public praise and community review. If the retail enterprise attaches importance to establishing relationships with customers and enhances the relational viscosity through mutual trust, emotional formation and spread of public praise, it will help to increase the traffic volume and increase the output value of single customers.
The maternal-baby nursing retailers form a strong relationship between enterprises and customers by establishing a strong relationship between products and customers, employees and customers, and customers to customers. Maternal-baby nursing retailers operate single-customer value deeply, build a heavy membership system and manage customer assets, thereby enhancing their brand and performance.
The research on the method of establishing the strong tie can be considered as an analysis of feasibility. The research results of this paper will help to improve the overall customer service experience and satisfaction of the mother and infant retail industry, enhance the development of the whole industry and draw significance lessons from other service industries.
ContributorsWang, Jianguo (Author) / Gu, Bin (Thesis advisor) / Chen, Hong (Thesis advisor) / Cui, Haitao (Committee member) / Arizona State University (Publisher)
Created2018
Description
This study examines the 3 key questions of media budget allocation, to find our a better invest model. Including spending share of traditional media and digital media, program selection strategy and duration mix optimization to analyse the trend of sample A (a global cosmetic brand) . Based on every test media campaign, we do research of media performance and sales volumn, add youth consumer behavior result, to develop a media investment ROI model for this brand. Create the evaluation system according to past big data and find the learnings of different length TVC usage. Of course all relavant findings and implications will be summarized after every section.
ContributorsXu, Jin (Author) / Gu, Bin (Thesis advisor) / Chen, Xinlei (Thesis advisor) / Shao, Benjamin (Committee member) / Arizona State University (Publisher)
Created2018
Description
Most advanced economies have evolved into service economies with the majority of their activity and jobs being in the service sector. The manufacturing sector is also going through a similar shift towards services. Manufacturers are increasingly complementing their products with new services in order to satisfy a broader array of customer needs and increase the value of their offerings. This shift has offered significant opportunities to the sector and the success of major firms such as IBM, Caterpillar, and Rolls-Royce in competing through services has been remarkable.
Despite the increased importance of services in the manufacturing sector, the academic literature is yet to investigate the many questions that arise under this new manufacturing paradigm. Perhaps for the same reason study of servitization is listed as a research priority in recent publications both in the field of service operations management and in the field services marketing. This dissertation covers three essays aimed at disentangling multiple aspects of the role of services in the manufacturing sector. The literature on the drivers and implications of transition towards services in manufacturing firms is limited. The three studies in this dissertation aim at shedding light on this issue.
Specifically, the first essay looks at the innovation benefits of service transactions with customers. This paper demonstrate the value of services in getting manufacturers closer to customers and allowing them glean useful information from their service interactions. The second essay investigates the antecedents of service strategy adoption. We suggest that the extant diversification theory does not fully explain servitization and this phenomenon represents a unique type of diversification, which is likely driven by different factors. Through econometric analysis of financial data over a 27-year period, this study explores characteristics of product, firm resources, competition, and industry that encourage adoption of service strategies in manufacturing sector. Finally, the third essay takes a deeper dive and focuses on dealerships, as service centers, in the automobile industry. It investigates the role of dealerships in the success of automakers and explores dealership traits that are critical for market success of an automobile brand.
Despite the increased importance of services in the manufacturing sector, the academic literature is yet to investigate the many questions that arise under this new manufacturing paradigm. Perhaps for the same reason study of servitization is listed as a research priority in recent publications both in the field of service operations management and in the field services marketing. This dissertation covers three essays aimed at disentangling multiple aspects of the role of services in the manufacturing sector. The literature on the drivers and implications of transition towards services in manufacturing firms is limited. The three studies in this dissertation aim at shedding light on this issue.
Specifically, the first essay looks at the innovation benefits of service transactions with customers. This paper demonstrate the value of services in getting manufacturers closer to customers and allowing them glean useful information from their service interactions. The second essay investigates the antecedents of service strategy adoption. We suggest that the extant diversification theory does not fully explain servitization and this phenomenon represents a unique type of diversification, which is likely driven by different factors. Through econometric analysis of financial data over a 27-year period, this study explores characteristics of product, firm resources, competition, and industry that encourage adoption of service strategies in manufacturing sector. Finally, the third essay takes a deeper dive and focuses on dealerships, as service centers, in the automobile industry. It investigates the role of dealerships in the success of automakers and explores dealership traits that are critical for market success of an automobile brand.
ContributorsGolara, Sina (Author) / Dooley, Kevin J (Thesis advisor) / Rogers, Dale (Committee member) / Kull, Thomas (Committee member) / Arizona State University (Publisher)
Created2018
Description
This dissertation details a study of wide-bandgap molecular beam epitaxy (MBE)-grown single-crystal MgxCd1-xTe. The motivation for this study is to open a pathway to reduced $/W solar power generation through the development of a high-efficiency 1.7-eV II-VI top cell current-matched to low-cost 1.1-eV silicon. This paper reports the demonstration of monocrystalline 1.7-eV MgxCd1-xTe/MgyCd1-yTe (y>x) double heterostructures (DHs) with a record carrier lifetime of 560 nanoseconds, along with a 1.7-eV MgxCd1-xTe/MgyCd1-yTe (y>x) single-junction solar cell with a record active-area efficiency of 15.2% and a record open-circuit voltage (VOC) of 1.176 V. A study of indium-doped n-type 1.7-eV MgxCd1-xTe with a carrier activation of up to 5 × 1017 cm-3 is presented with promise to increase device VOC. Finally, this paper reports an epitaxial lift-off (ELO) technology using water-soluble MgTe for the creation of free-standing MBE-grown II-VI single-crystal CdTe and 1.7-eV MgxCd1-xTe solar cells freed from lattice-matched InSb(001) substrates. Photoluminescence (PL) spectroscopy measurements comparing intact and free-standing films reveal the survival of optical quality in CdTe DHs after ELO. This technology opens up several possibilities to drastically increase cell conversion efficiency through improved light management and transferability into monolithic multijunction devices. Lastly, this report will present considerations for future work in each of the study areas mentioned above.
ContributorsCampbell, Calli Michele (Author) / Zhang, Yong-Hang (Thesis advisor) / Chan, Candance K (Committee member) / King, Richard R (Committee member) / Arizona State University (Publisher)
Created2019