Matching Items (58)
Description
Photocatalytic water splitting has been proposed as a promising way of generating carbon-neutral fuels from sunlight and water. In one approach, water decomposition is enabled by the use of functionalized nano-particulate photocatalyst composites. The atomic structures of the photocatalysts dictate their electronic and photonic structures, which are controlled by synthesis methods and may alter under reaction conditions. Characterizing these structures, especially the ones associated with photocatalysts’ surfaces, is essential because they determine the efficiencies of various reaction steps involved in photocatalytic water splitting. Due to its superior spatial resolution, (scanning) transmission electron microscopy (STEM/TEM), which includes various imaging and spectroscopic techniques, is a suitable tool for probing materials’ local atomic, electronic and optical structures. In this work, techniques specific for the study of photocatalysts are developed using model systems.
Nano-level structure-reactivity relationships as well as deactivation mechanisms of Ni core-NiO shell co-catalysts loaded on Ta2O5 particles are studied using an aberration-corrected TEM. It is revealed that nanometer changes in the shell thickness lead to significant changes in the H2 production. Also, deactivation of this system is found to be related to a photo-driven process resulting in the loss of the Ni core.
In addition, a special form of monochromated electron energy-loss spectroscopy (EELS), the so-called aloof beam EELS, is used to probe surface electronic states as well as light-particle interactions from model oxide nanoparticles. Surface states associated with hydrate species are analyzed using spectral simulations based on a dielectric theory and a density of states model. Geometry-induced optical-frequency resonant modes are excited using fast electrons in catalytically relevant oxides. Combing the spectral features detected in experiments with classical electrodynamics simulations, the underlying physics involved in this excitation process and the various influencing factors of the modes are investigated.
Finally, an in situ light illumination system is developed for an aberration-corrected environmental TEM to enable direct observation of atomic structural transformations of model photocatalysts while they are exposed to near reaction conditions.
Nano-level structure-reactivity relationships as well as deactivation mechanisms of Ni core-NiO shell co-catalysts loaded on Ta2O5 particles are studied using an aberration-corrected TEM. It is revealed that nanometer changes in the shell thickness lead to significant changes in the H2 production. Also, deactivation of this system is found to be related to a photo-driven process resulting in the loss of the Ni core.
In addition, a special form of monochromated electron energy-loss spectroscopy (EELS), the so-called aloof beam EELS, is used to probe surface electronic states as well as light-particle interactions from model oxide nanoparticles. Surface states associated with hydrate species are analyzed using spectral simulations based on a dielectric theory and a density of states model. Geometry-induced optical-frequency resonant modes are excited using fast electrons in catalytically relevant oxides. Combing the spectral features detected in experiments with classical electrodynamics simulations, the underlying physics involved in this excitation process and the various influencing factors of the modes are investigated.
Finally, an in situ light illumination system is developed for an aberration-corrected environmental TEM to enable direct observation of atomic structural transformations of model photocatalysts while they are exposed to near reaction conditions.
ContributorsLiu, Qianlang (Author) / Crozier, Peter A. (Thesis advisor) / Chan, Candace (Committee member) / Buttry, Daniel (Committee member) / Liu, Jingyue (Committee member) / Nemanich, Robert (Committee member) / Arizona State University (Publisher)
Created2018
Description
Polycrystalline magnetite thin films were deposited on large area polymer substrates using aqueous solution based spin-spray deposition (SSD). This technique involved the hydrolysis of precursor salt solutions at low temperatures (70-100°C). The fundamental mechanisms and pathways in crystallization and evolution of the film microstructures were studied as a function of reactant chemistry and reactor conditions (rotation rate, flow rates etc.). A key feature of this method was the ability to constantly supply fresh solutions throughout deposition. Solution flow due to substrate rotation ensured that reactant depleted solutions were spun off. This imparted a limited volume, near two-dimensional restriction on the growth process. Film microstructure was studied as a function of process parameters such as liquid flow rate, nebulizer configuration, platen rotation rate and solution chemistry. It was found that operating in the micro-droplet regime of deposition was a crucial factor in controlling the microstructure.
Film porosity and substrate adhesion were linked to the deposition rate, which in-turn depended on solution chemistry. Films exhibited a wide variety of hierarchically organized microstructures often spanning length scales from tens-of-nanometers to a few microns. These included anisotropic morphologies such as nanoplates and nanoblades, that were generally unexpected from magnetite (a high symmetry cubic solid). Time resolved studies showed that the reason for complex hierarchy in microstructure was the crystallization via non-classical pathways. SSD of magnetite films involved formation of precursor phases that subsequently underwent solid-state transformations and nanoparticle self-assembly. These precursor phases were identified and possible reaction mechanisms for the formation of magnetite were proposed. A qualitative description of the driving forces for self-assembly was presented.
Film porosity and substrate adhesion were linked to the deposition rate, which in-turn depended on solution chemistry. Films exhibited a wide variety of hierarchically organized microstructures often spanning length scales from tens-of-nanometers to a few microns. These included anisotropic morphologies such as nanoplates and nanoblades, that were generally unexpected from magnetite (a high symmetry cubic solid). Time resolved studies showed that the reason for complex hierarchy in microstructure was the crystallization via non-classical pathways. SSD of magnetite films involved formation of precursor phases that subsequently underwent solid-state transformations and nanoparticle self-assembly. These precursor phases were identified and possible reaction mechanisms for the formation of magnetite were proposed. A qualitative description of the driving forces for self-assembly was presented.
ContributorsVadari Venkata, Kaushik Sridhar (Author) / Petuskey, William (Thesis advisor) / Carpenter, Ray (Committee member) / McCartney, Martha (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2018
Description
Two-dimensional transition metal dichalcogenides (TMDCs) such as
molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) are attractive for use in biotechnology, optical and electronics devices due to their promising and tunable electrical, optical and chemical properties. To fulfill the variety of requirements for different applications, chemical treatment methods are developed to tune their properties. In this dissertation, plasma treatment, chemical doping and functionalization methods have been applied to tune the properties of TMDCs. First, plasma treatment of TMDCs results in doping and generation of defects, as well as the synthesis of transition metal oxides (TMOs) with rolled layers that have increased surface-to-volume ratio and are promising for electrochemical applications. Second, chemical functionalization is another powerful approach for tuning the properties of TMDCs for use in many applications. To covalently functionalize the basal planes of TMDCs, previous reports begin with harsh treatments like lithium intercalation that disrupt the structure and lead to a phase transformation from semiconducting to metallic. Instead, this work demonstrates the direct covalent functionalization of semiconducting MoS2 using aryl diazonium salts without lithium treatments. It preserves the structure and semiconducting nature of MoS2, results in covalent C-S bonds on basal planes and enables different functional groups to be tethered to the MoS2 surface via the diazonium salts. The attachment of fluorescent proteins has been used as a demonstration and it suggests future applications in biology and biosensing. The effects of the covalent functionalization on the electronic transport properties of MoS2 were then studied using field effect transistor (FET) devices.
molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) are attractive for use in biotechnology, optical and electronics devices due to their promising and tunable electrical, optical and chemical properties. To fulfill the variety of requirements for different applications, chemical treatment methods are developed to tune their properties. In this dissertation, plasma treatment, chemical doping and functionalization methods have been applied to tune the properties of TMDCs. First, plasma treatment of TMDCs results in doping and generation of defects, as well as the synthesis of transition metal oxides (TMOs) with rolled layers that have increased surface-to-volume ratio and are promising for electrochemical applications. Second, chemical functionalization is another powerful approach for tuning the properties of TMDCs for use in many applications. To covalently functionalize the basal planes of TMDCs, previous reports begin with harsh treatments like lithium intercalation that disrupt the structure and lead to a phase transformation from semiconducting to metallic. Instead, this work demonstrates the direct covalent functionalization of semiconducting MoS2 using aryl diazonium salts without lithium treatments. It preserves the structure and semiconducting nature of MoS2, results in covalent C-S bonds on basal planes and enables different functional groups to be tethered to the MoS2 surface via the diazonium salts. The attachment of fluorescent proteins has been used as a demonstration and it suggests future applications in biology and biosensing. The effects of the covalent functionalization on the electronic transport properties of MoS2 were then studied using field effect transistor (FET) devices.
ContributorsChu, Ximo (Author) / Wang, Qing Hua (Thesis advisor) / Sieradzki, Karl (Committee member) / Green, Alexander (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2018
In-situ photoemission spectroscopy characterization of electronic states in semiconductor interfaces
Description
The electronic states of semiconductor interfaces have significant importance for semiconductor device performance, especially due to the continuing miniaturization of device technology.
The application of ultra high vacuum (UHV) enables the preparation and characterization of fresh and cleaned interfaces. In a UHV environment, photoemission spectroscopy (PES) provides a non-destructive method to measure the electronic band structure, which is a crucial component of interface properties.
In this dissertation, three semiconductor interfaces were studies to understand different effects on electronic states. The interfaces studied were freshly grown or pre-treated under UHV. Then in-situ PES measurements, including x-ray photoemission spectroscopy (XPS) and ultra-violet photoemission spectroscopy (UPS), were conducted to obtain electronic states information.
First, the CdTe/InSb (100) heterointerface was employed as a model interface for II-VI and III-V heterojunctions. It was suggested that an interface layer formed, which consisted of In-Te bonding. The non-octal bonding between In and Te atoms has donor-like behavior, which was proposed to result in an electron accumulation layer in InSb. A type-I heterointerface was observed. Second, Cu/ZnO interfaces were studied to understand the interface bonding and the role of polarization on ZnO interfaces. It was shown that on O-face ZnO (0001) and PEALD ZnO, copper contacts had ohmic behavior. However, on Zn-face ZnO (0001), a 0.3 eV Schottky barrier height was observed. The lower than expected barrier heights were attributed to oxygen vacancies introduced by Cu-O bonding during interface formation. In addition, it is suggested that the different barrier heights on two sides of ZnO (0001) are caused by the different behavior for the ZnO (0001) faces. Last, a pulse mode deposition method was applied for P-doped diamond growth on (100) diamond surfaces. Pretreatment effects were studied. It is suggested that an O/H plasma treatment or a short period of H-plasma and CH4/H2 plasma could yield a higher growth rate. PES measurements were conducted on H-terminated intrinsic diamond surface and P-doped/intrinsic diamond (100) interfaces. It was suggested that electronic states near the valence band maximum caused Fermi level pinning effects, independent of the diamond doping.
The application of ultra high vacuum (UHV) enables the preparation and characterization of fresh and cleaned interfaces. In a UHV environment, photoemission spectroscopy (PES) provides a non-destructive method to measure the electronic band structure, which is a crucial component of interface properties.
In this dissertation, three semiconductor interfaces were studies to understand different effects on electronic states. The interfaces studied were freshly grown or pre-treated under UHV. Then in-situ PES measurements, including x-ray photoemission spectroscopy (XPS) and ultra-violet photoemission spectroscopy (UPS), were conducted to obtain electronic states information.
First, the CdTe/InSb (100) heterointerface was employed as a model interface for II-VI and III-V heterojunctions. It was suggested that an interface layer formed, which consisted of In-Te bonding. The non-octal bonding between In and Te atoms has donor-like behavior, which was proposed to result in an electron accumulation layer in InSb. A type-I heterointerface was observed. Second, Cu/ZnO interfaces were studied to understand the interface bonding and the role of polarization on ZnO interfaces. It was shown that on O-face ZnO (0001) and PEALD ZnO, copper contacts had ohmic behavior. However, on Zn-face ZnO (0001), a 0.3 eV Schottky barrier height was observed. The lower than expected barrier heights were attributed to oxygen vacancies introduced by Cu-O bonding during interface formation. In addition, it is suggested that the different barrier heights on two sides of ZnO (0001) are caused by the different behavior for the ZnO (0001) faces. Last, a pulse mode deposition method was applied for P-doped diamond growth on (100) diamond surfaces. Pretreatment effects were studied. It is suggested that an O/H plasma treatment or a short period of H-plasma and CH4/H2 plasma could yield a higher growth rate. PES measurements were conducted on H-terminated intrinsic diamond surface and P-doped/intrinsic diamond (100) interfaces. It was suggested that electronic states near the valence band maximum caused Fermi level pinning effects, independent of the diamond doping.
ContributorsWang, Xingye (Author) / Nemanich, Robert J (Thesis advisor) / Chan, Candace (Committee member) / Ponce, Fernando (Committee member) / Holman, Zachary (Committee member) / Arizona State University (Publisher)
Created2018
Description
Diamond and cubic boron nitride (c-BN) are ultra wide band gap semiconductors (Eg>3.4 eV) and share similar properties in various aspects, including being isoelectronic, a 1% lattice mismatch, large band gap, high thermal conductivity. Particularly, the negative electron affinity (NEA) of diamond and c-BN is an unusual property that has led to effects such as p-type surface conductivity, low temperature thermionic emission, and photon enhanced thermionic emission. In this dissertation, the interface chemistry and electronic structure of dielectrics on diamond and c-BN are investigated with X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). The first study established that the surface conductive states could be established for thin Al2O3 on diamond using a post deposition H-plasma process. At each step of the atomic layer deposition (ALD) and plasma processing, the band alignment was characterized by in situ photoemission and related to interface charges. An interface layer between the diamond and dielectric layer was proposed to explain the surface conductivity. The second study further investigated the improvement of the hole mobility of surface conductive diamond. A thin layer of Al2O3 was employed as an interfacial layer between surface conductive hydrogen-terminated (H-terminated) diamond and MoO3 to increase the distance between the hole accumulation layer in diamond and negatively charged states in acceptor layer. With an interfacial layer, the ionic scattering, which was considered to limit the hole mobility, was reduced. By combining two oxides (Al2O3 and MoO3), the hole mobility and concentration were modulated by altering the thickness of the Al2O3 interfacial layer. The third study focused on the electronic structure of vanadium-oxide-terminated c-BN surfaces. The vanadium-oxide-termination was formed on c-BN by combining vanadium deposition using molecular beam deposition (MBD) and oxygen plasma treatment. After thermal annealing, a thermally stable NEA was achieved on c-BN. A model was proposed based on the deduced interface charge distribution to explain the establishment of an NEA.
ContributorsYang, Yu (Author) / Nemanich, Robert J (Thesis advisor) / McCartney, Martha (Committee member) / Ponce, Fernando (Committee member) / Qing, Quan (Committee member) / Arizona State University (Publisher)
Created2018
Description
Zinc oxide nanowires ( NWs) have broad applications in various fields such as nanoelectronics, optoelectronics, piezoelectric nanogenerators, chemical/biological sensors, and heterogeneous catalysis. To meet the requirements for broader applications, the growth of high-quality ZnO NWs and functionalization of ZnO NWs are critical. In this work, specific types of functionalized ZnO NWs have been synthesized and correlations between specific structures and properties have been investigated. Deposition of δ-Bi2O3 (narrow band gap) epilayers onto ZnO (wide band gap) NWs improves the absorption efficiency of the visible light spectrum by 70%. Furthermore, the deposited δ-Bi2O3 grows selectively and epitaxially on the {11-20} but not on the {10-10} facets of the ZnO NWs. The selective epitaxial deposition and the interfacial structure were thoroughly investigated. The morphology and structure of the Bi2O3/ZnO nanocomposites can be tuned by controlling the deposition conditions.
Various deposition methods, both physical and chemical, were used to functionalize the ZnO NWs with metal or alloy nanoparticles (NPs) for catalytic transformations of important molecules which are relevant to energy and environment. Cu and PdZn NPs were epitaxially grown on ZnO NWs to make them resistant to sintering at elevated temperatures and thus improved the stability of such catalytic systems for methanol steam reforming (MSR) to produce hydrogen. A series of Pd/ZnO catalysts with different Pd loadings were synthesized and tested for MSR reaction. The CO selectivity was found to be strongly dependent on the size of the Pd: Both PdZn alloy and single Pd atoms yield low CO selectivity while Pd clusters give the highest CO selectivity.
By dispersing single Pd atoms onto ZnO NWs, Pd1/ZnO single-atom catalysts (SACs) was synthesized and their catalytic performance was evaluated for selected catalytic reactions. The experimental results show that the Pd1/ZnO SAC is active for CO oxidation and MSR but is not desirable other reactions. We further synthesized ZnO NWs supported noble metal (M1/ZnO; M=Rh, Pd, Pt, Ir) SACs and studied their catalytic performances for CO oxidation. The catalytic test data shows that all the fabricated noble metal SACs are active for CO oxidation but their activity are significantly different. Structure-performance relationships were investigated.
Various deposition methods, both physical and chemical, were used to functionalize the ZnO NWs with metal or alloy nanoparticles (NPs) for catalytic transformations of important molecules which are relevant to energy and environment. Cu and PdZn NPs were epitaxially grown on ZnO NWs to make them resistant to sintering at elevated temperatures and thus improved the stability of such catalytic systems for methanol steam reforming (MSR) to produce hydrogen. A series of Pd/ZnO catalysts with different Pd loadings were synthesized and tested for MSR reaction. The CO selectivity was found to be strongly dependent on the size of the Pd: Both PdZn alloy and single Pd atoms yield low CO selectivity while Pd clusters give the highest CO selectivity.
By dispersing single Pd atoms onto ZnO NWs, Pd1/ZnO single-atom catalysts (SACs) was synthesized and their catalytic performance was evaluated for selected catalytic reactions. The experimental results show that the Pd1/ZnO SAC is active for CO oxidation and MSR but is not desirable other reactions. We further synthesized ZnO NWs supported noble metal (M1/ZnO; M=Rh, Pd, Pt, Ir) SACs and studied their catalytic performances for CO oxidation. The catalytic test data shows that all the fabricated noble metal SACs are active for CO oxidation but their activity are significantly different. Structure-performance relationships were investigated.
ContributorsXu, Jia, Ph.D (Author) / Liu, Jingyue (Thesis advisor) / Smith, David (Committee member) / Chan, Candace (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2017
Description
Dealloying, the selective electrochemical dissolution of an active component from an alloy, often results in nanoscale bi-continuous solid/void morphologies. These structures are attracting attention for a wide range of applications including catalysis, sensing and actuation. The evolution of these nanoporous structures has been widely studied for the case at low homologous temperature, TH, such as in Ag-Au, Cu-Au, Cu-Pt, etc. Since at low TH the solid-state mobility of the components is of order 10-30 cm2s-1 or less, percolation dissolution is the only mechanism available to support dealloying over technologically relevant time scales. Without the necessity of solid-state mass transport, percolation dissolution involves sharp transitions based on two key features, the parting limit and critical potential.
Dealloying under conditions of high TH, (or high intrinsic diffusivity of the more electrochemically reactive component) is considerably more complicated than at low TH. Since solid-state mass transport is available to support this process, a rich set of morphologies, including negative or void dendrites, Kirkendall voids and bi-continuous porous structures, can evolve. In order to study dealloying at high TH we have examined the behavior of Li-Sn and Li-Pb alloys. The intrinsic diffusivities of Li were measured in these alloys using electrochemical titration and time of flight measurements. Morphology evolution was studied with varying alloy composition, host dimension and imposed electrochemical conditions. Owing to diffusive transport, there is no parting limit for dealloying, however, there is a compositional threshold (pPD) as well as a critical potential for the operation of percolation dissolution and the formation of bi-continuous structures. Negative or void dendrite morphologies evolve at compositions below pPD and at large values of the applied electrochemical potential when the rate of dealloying is limited by solid-state mass transport. This process is isomorphic to dendrite formation in electrodeposition. Kirkendall voiding morphologies evolve below the critical potential over the entire range of alloy compositions.
We summarize our results by introducing dealloying morphology diagrams that we use to graphically illustrate the electrochemical conditions resulting in various morphologies that can form under conditions of low and high TH.
Dealloying under conditions of high TH, (or high intrinsic diffusivity of the more electrochemically reactive component) is considerably more complicated than at low TH. Since solid-state mass transport is available to support this process, a rich set of morphologies, including negative or void dendrites, Kirkendall voids and bi-continuous porous structures, can evolve. In order to study dealloying at high TH we have examined the behavior of Li-Sn and Li-Pb alloys. The intrinsic diffusivities of Li were measured in these alloys using electrochemical titration and time of flight measurements. Morphology evolution was studied with varying alloy composition, host dimension and imposed electrochemical conditions. Owing to diffusive transport, there is no parting limit for dealloying, however, there is a compositional threshold (pPD) as well as a critical potential for the operation of percolation dissolution and the formation of bi-continuous structures. Negative or void dendrite morphologies evolve at compositions below pPD and at large values of the applied electrochemical potential when the rate of dealloying is limited by solid-state mass transport. This process is isomorphic to dendrite formation in electrodeposition. Kirkendall voiding morphologies evolve below the critical potential over the entire range of alloy compositions.
We summarize our results by introducing dealloying morphology diagrams that we use to graphically illustrate the electrochemical conditions resulting in various morphologies that can form under conditions of low and high TH.
ContributorsGeng, Ke (Author) / Sieradzki, Karl (Thesis advisor) / Crozier, Peter (Committee member) / Chan, Candace (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2017
Description
As selenium is toxic at low levels, treatment methods to remove selenium from industrial waste waters are needed. In this work, three groups of sorbent materials were investigated in detail for their effectiveness for selenium and arsenic removal from water: 1) nanostructured carbon-based materials, 2) layered double hydroxide (LDH)-based materials, and 3) biopolymer-based sorbents. The materials were investigated in spiked de-ionized water and waters collected from different locations at Salt River Project’s (SRP) Santan Generating Station in Gilbert, AZ. The results show that nanostructured carbon-based materials removed ~80% and up to 100% selenium and arsenic, respectively in spiked DI water. Heat treated layered double hydroxides removed close to 100% removal in selenium and arsenic spiked DI water. Isotherms conducted in spiked DI water fit the Langmuir model and showed a maximum selenate adsorption capacity of 67 mg/g for the calcined LDH powder. Results from SRP waters showed that certain LDH sorbents were effective for removing the selenium, but that higher pH and existence of competing ions affected the removal efficiencies. The functionalized biopolymer sorbent from Crystal Clear Technologies: CCT-149/OCI-B showed good removal efficiencies for both selenate and selenite in DI water. Isotherms conducted in spiked DI water for CCT-149 fit the Langmuir model and showed a maximum selenate adsorption capacity of 90.9 mg/g. Column tests using spiked DI water and waters obtained from SRP wells were investigated using both LDH and CCT-149/OCI-B. Removal of sulfate using chemical pre-treatment of the water with barium chloride resulted in about three times higher selenate loading onto the granular LDH and doubled the water volume that can be treated using CCT-149/OCI-B. The results from the column tests are being used to guide the pilot testing investigating the implementation of LDH sorbents at pilot scale at the Santan plant. The good results in the cooling tower #5 blowdown water and combined discharge waste water of SRP provide valuable information about the efficacy and efficiency of adsorptive media for the removal of selenium. Composites comprising LDH nanosheets with different substrates were successfully synthesized that were able to retain the performance in removing selenate of nanosheet LDH.
ContributorsLi, Man (Author) / Chan, Candace (Thesis advisor) / Lind, Mary Laura (Committee member) / Perreault, Francois (Committee member) / Arizona State University (Publisher)
Created2017
Description
Delamination of solar module interfaces often occurs in field-tested solar modules after decades of service due to environmental stressors such as humidity. In the presence of water, the interfaces between the encapsulant and the cell, glass, and backsheet all experience losses of adhesion, exposing the module to accelerated degradation. Understanding the relation between interfacial adhesion and water content inside photovoltaic modules can help mitigate detrimental power losses. Water content measurements via water reflectometry detection combined with 180° peel tests were used to study adhesion of module materials exposed to damp heat and dry heat conditions. The effect of temperature, cumulative water dose, and water content on interfacial adhesion between ethylene vinyl acetate and (1) glass, (2) front of the cell, and (3) backsheet was studied. Temperature and time decreased adhesion at all these interfaces. Water content in the sample during the measurement showed significant decreases in adhesion for the Backsheet/Ethylene vinyl acetate interface. Water dose showed little effect for the Glass/ Ethylene vinyl acetate and Backsheet/ Ethylene vinyl acetate interfaces, but there was significant adhesion loss with water dose at the front cell busbar/encapsulant interface. Initial tensile test results to monitor the effects of the mechanical properties ethylene vinyl acetate and backsheet showed water content increasing the strength of ethylene vinyl acetate during plastic deformation but no change in the strength of the backsheet properties. This mechanical property change is likely inducing variation along the peel interface to possibly convolute the adhesion measurements conducted or to explain the variation seen for the water saturated and dried peel test sample types.
ContributorsTheut, Nicholas (Author) / Bertoni, Mariana (Thesis advisor) / Holman, Zachary (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2020
Description
Flexible conducting materials have been in the forefront of a rapidly transforming electronics industry, focusing on wearable devices for a variety of applications in recent times. Over the past few decades, bulky, rigid devices have been replaced with a surging demand for thin, flexible, light weight, ultra-portable yet high performance electronics. The interconnects available in the market today only satisfy a few of the desirable characteristics, making it necessary to compromise one feature over another. In this thesis, a method to prepare a thin, flexible, and stretchable inter-connect is presented with improved conductivity compared to previous achievements. It satisfies most mechanical and electrical conditions desired in the wearable electronics industry. The conducting composite, prepared with the widely available, low cost silicon-based organic polymer - polydimethylsiloxane (PDMS) and silver (Ag), is sandwiched between two cured PDMS layers. These protective layers improve the mechanical stability of the inter-connect. The structure can be stretched up to 120% of its original length which can further be enhanced to over 250% by cutting it into a serpentine shape without compromising its electrical stability. The inter-connect, around 500 µm thick, can be integrated into thin electronic packaging. The synthesis process of the composite material, along with its electrical and mechanical and properties are presented in detail. Testing methods and results for mechanical and electrical stability are also illustrated over extensive flexing and stretching cycles. The materials put into test, along with conductive silver (Ag) - polydimethylsiloxane (PDMS) composite in a sandwich structure, are copper foils, copper coated polyimide (PI) and aluminum (Al) coated polyethylene terephthalate (PET).
ContributorsNandy, Mayukh (Author) / Yu, Hongbin (Thesis advisor) / Chan, Candace (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2020