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)…
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.
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This study examined the effect of the amino acid composition of protein capsids on virus inactivation using ultraviolet (UV) irradiation and titanium dioxide photocatalysis, and physical removal via enhanced coagulation using ferric chloride. Although genomic damage is likely more extensive…
This study examined the effect of the amino acid composition of protein capsids on virus inactivation using ultraviolet (UV) irradiation and titanium dioxide photocatalysis, and physical removal via enhanced coagulation using ferric chloride. Although genomic damage is likely more extensive than protein damage for viruses treated using UV, proteins are still substantially degraded. All amino acids demonstrated significant correlations with UV susceptibility. The hydroxyl radicals produced during photocatalysis are considered nonspecific, but they likely cause greater overall damage to virus capsid proteins relative to the genome. Oxidizing chemicals, including hydroxyl radicals, preferentially degrade amino acids over nucleotides, and the amino acid tyrosine appears to strongly influence virus inactivation. Capsid composition did not correlate strongly to virus removal during physicochemical treatment, nor did virus size. Isoelectric point may play a role in virus removal, but additional factors are likely to contribute.
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Recent studies indicate the presence of nano-scale titanium dioxide (TiO[subscript 2]) as an additive in human foodstuffs, but a practical protocol to isolate and separate nano-fractions from soluble foodstuffs as a source of material remains elusive. As such, we developed…
Recent studies indicate the presence of nano-scale titanium dioxide (TiO[subscript 2]) as an additive in human foodstuffs, but a practical protocol to isolate and separate nano-fractions from soluble foodstuffs as a source of material remains elusive. As such, we developed a method for separating the nano and submicron fractions found in commercial-grade TiO[subscript 2] (E171) and E171 extracted from soluble foodstuffs and pharmaceutical products (e.g., chewing gum, pain reliever, and allergy medicine). Primary particle analysis of commercial-grade E171 indicated that 54% of particles were nano-sized (i.e., < 100 nm). Isolation and primary particle analysis of five consumer goods intended to be ingested revealed differences in the percent of nano-sized particles from 32%‒58%. Separation and enrichment of nano- and submicron-sized particles from commercial-grade E171 and E171 isolated from foodstuffs and pharmaceuticals was accomplished using rate-zonal centrifugation. Commercial-grade E171 was separated into nano- and submicron-enriched fractions consisting of a nano:submicron fraction of approximately 0.45:1 and 3.2:1, respectively. E171 extracted from gum had nano:submicron fractions of 1.4:1 and 0.19:1 for nano- and submicron-enriched, respectively. We show a difference in particle adhesion to the cell surface, which was found to be dependent on particle size and epithelial orientation. Finally, we provide evidence that E171 particles are not immediately cytotoxic to the Caco-2 human intestinal epithelium model. These data suggest that this separation method is appropriate for studies interested in isolating the nano-sized particle fraction taken directly from consumer products, in order to study separately the effects of nano and submicron particles.
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