Matching Items (3)
154755-Thumbnail Image.png
Description
High-performance III-V semiconductors based on ternary alloys and superlattice systems are fabricated, studied, and compared for infrared optoelectronic applications. InAsBi is a ternary alloy near the GaSb lattice constant that is not as thoroughly investigated as other III-V alloys and that is challenging to produce as Bi has a

High-performance III-V semiconductors based on ternary alloys and superlattice systems are fabricated, studied, and compared for infrared optoelectronic applications. InAsBi is a ternary alloy near the GaSb lattice constant that is not as thoroughly investigated as other III-V alloys and that is challenging to produce as Bi has a tendency to surface segregate and form droplets during growth rather than incorporate. A growth window is identified within which high-quality droplet-free bulk InAsBi is produced and Bi mole fractions up to 6.4% are obtained. Photoluminescence with high internal quantum efficiency is observed from InAs/InAsBi quantum wells. The high structural and optical quality of the InAsBi materials examined demonstrates that bulk, quantum well, and superlattice structures utilizing InAsBi are an important design option for efficient infrared coverage.

Another important infrared material system is InAsSb and the strain-balanced InAs/InAsSb superlattice on GaSb. Detailed examination of X-ray diffraction, photoluminescence, and spectroscopic ellipsometry data provides the temperature and composition dependent bandgap of bulk InAsSb. The unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattice is measured and found to significantly impact the analysis of the InAs/InAsSb band alignment. In the analysis of the absorption spectra, the ground state absorption coefficient and transition strength of the superlattice are proportional to the square of the electron-hole wavefunction overlap; wavefunction overlap is therefore a major design parameter in terms of optimizing absorption in these materials. Furthermore in addition to improvements through design optimization, the optical quality of the materials studied is found to be positively enhanced with the use of Bi as a surfactant during molecular beam epitaxy growth.

A software tool is developed that calculates and optimizes the miniband structure of semiconductor superlattices, including bismide-based designs. The software has the capability to limit results to designs that can be produced with high structural and optical quality, and optimized designs in terms of maximizing absorption are identified for several infrared superlattice systems at the GaSb lattice constant. The accuracy of the software predictions are tested with the design and growth of an optimized mid-wave infrared InAs/InAsSb superlattice which exhibits superior optical and absorption properties.
ContributorsWebster, Preston Thomas (Author) / Johnson, Shane R (Thesis advisor) / Zhang, Yong-Hang (Committee member) / Menéndez, Jose (Committee member) / Vasileska, Dragica (Committee member) / Arizona State University (Publisher)
Created2016
154768-Thumbnail Image.png
Description
Silicone compounds have a very low surface energy due to highly flexible Si-O-Si backbone and large number of –CH3 groups, but these compounds are extremely hydrophobic and thus have limited applications in aqueous formulations. Modification of such silicone compounds by grafting hydrophilic chains provides a wide range of silicone products

Silicone compounds have a very low surface energy due to highly flexible Si-O-Si backbone and large number of –CH3 groups, but these compounds are extremely hydrophobic and thus have limited applications in aqueous formulations. Modification of such silicone compounds by grafting hydrophilic chains provides a wide range of silicone products called "Silicone Surfactants". Silicone surfactants are surface active agents which get adsorbed at the air-water interface thereby, reducing the interfacial tension. Some of the larger applications of silicone surfactant are in the manufacture of plastic foams, in personal care products and as spreading and wetting agents (Hill, R.M, 2002).

In this thesis, a series of silicone surfactant graft copolymers were synthesized via hydrosilylation reaction. Poly(ethylene glycol) (PEG) of different chain length was grafted to a hydrophobic Poly(methylhydrosiloxane) (PMHS) backbone to improve the final hydrophilicity. Also, a positively charged quaternary ammonium salt (allyltriethylammonium bromide) was grafted to the PMHS backbone. The objective of this thesis was to synthesize polymers in predefined ratios of the above mentioned side groups and utilize these polymers to-

1) Study the effect of PEG chain length and its composition on the hydrophilicity of the polymer.

2) Study the effect of PEG: ammonium salt ratio on the surface tension of aqueous systems.

Analysis of FT-IR and 1H NMR spectra of the polymers confirmed the predicted structure. The absence of characteristic Si-H absorbance peak at 2160 cm-1 in FT-IR spectra indicates consumption of silane groups along the polymer backbone. The actual moles of the side chain grafted on the backbone are calculated by 1H NMR peak integration. The results of contact angle studies indicated an increase in hydrophilicity with an increase in the composition of PEG in molecule. A 2*2 factorial DOE analysis reported that the fraction of Si-H bonds converted to PEG grafts was the critical factor towards increasing the hydrophilicity (p value of 0.015). Surface tension studies report that the air-water interfacial tension of the synthesized polymers is between 28mN/m – 45mN/m. The amount of Si-H was concluded to be the deciding factor in lowering the surface tension.
ContributorsSingh, Pummy (Author) / Green, Matthew (Thesis advisor) / He, Ximin (Committee member) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2016
189203-Thumbnail Image.png
Description
Both molecular structure of macromolecular materials and subsequent processing of these materials dictate resulting material properties. In this work novel synthetic strategies combined with detailed analytical methodology reveal fundamental structure-processing-property relationships in thermoplastic polyesters, thermoplastic polyurethanes, covalently crosslinked acetal functionalized networks, and small molecule surfactants. 4,4’ dimethyloxybisbenzoate afforded a series

Both molecular structure of macromolecular materials and subsequent processing of these materials dictate resulting material properties. In this work novel synthetic strategies combined with detailed analytical methodology reveal fundamental structure-processing-property relationships in thermoplastic polyesters, thermoplastic polyurethanes, covalently crosslinked acetal functionalized networks, and small molecule surfactants. 4,4’ dimethyloxybisbenzoate afforded a series of novel polyester structures, and the incorporation of this monomer both increased the Tg and decreased the crystallinity in cyclohexane dimethanol based polyesters. Solubility and dynamic light scattering experiments combined with oscillatory rheology techniques provided methodology to validate polyurethane extrusion in commercial polyurethanes. Acid catalyzed hydroxyl addition to vinyl ethers provided two families of acetal functionalized poly(ethylene glycol hydrogels). Stoichiometric control of binary thiol-acrylate polymerizations afforded hydrogels with both tunable mechanical properties and predictable degradation profiles. Following this work, a photoacid generator catalyzed cationic catalysis provided acetal functionalized organogels whose mechanical properties were predicted by excess vinyl ether monomers which underwent cationic polymerization under the same reaction conditions that yielded acetal functionalization. Time resolved FT-IR spectroscopy provided new understanding in hydroxyl vinyl ether reactions, where both hydroxyl addition to a vinyl ether and vinyl ether cationic polymerization occur concurrently. This work inspired research into new reactive systems for photobase generator applications. However, current photobase generator technologies proved incompatible for carbon-Michael reactions between acetoacetate and acrylate functionalities as a result of uncontrollable acrylate free radical polymerization. The fundamental knowledge and synthetic strategies afforded by these investigations were applied to small molecule surfactant systems for fire-fighting applications. Triethylsilyl-containing zwitterionic and cationic surfactants displayed surface tensions lower than hydrocarbon surfactants, but larger than siloxane-containing surfactants. For the first time, oscillatory rheology and polarized optical light imagine rheology highlighted shear-induced micelle alignment in triethylsilyl surfactants, which provided more stable foams than zwitterionic analogues. The knowledge gained from these investigations provided fundamental structure-processing-property relationships in small molecule surfactant solutions applied as fire-fighting foams. This discovery regarding the effect of self-assembled structures in foam solutions informs the design and analysis of next generation surfactants to replace fluorocarbon surfactants in fire-fighting foam applications.
ContributorsBrown, James Robert (Author) / Long, Timothy E (Thesis advisor) / Bortner, Michael J (Committee member) / Biegasiewicz, Kyle F (Committee member) / Jin, Kailong (Committee member) / Arizona State University (Publisher)
Created2023