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In recent years, ultra-wide bandgap semiconductors have increasingly moved into scientific focus due to their outstanding material properties, making them promising candidates for future applications within high-power electronics or solar-blind photo detectors. The group-III-sesquioxides can appear in various polymorphs, which influences, for instance, the energy of the optical bandgap. In gallium oxide, the optical bandgap ranges between 4.6 and 5.3 eV depending on the polymorph. For each polymorph it can be increased or decreased by alloying with aluminum oxide (8.8 eV) or indium oxide (2.7–3.75 eV), respectively, enabling bandgap engineering and thus leading to an extended application field. For this purpose, an overview of miscibility limits, the variation of bandgap and lattice constants as a function of the alloy composition are reviewed for the rhombohedral, monoclinic, orthorhombic and cubic polymorph. Further, the effect of formation and desorption of volatile suboxides on growth rates is described with respect to chemical trends of the discussed ternary materials.

Desorption electrospray ionization (DESI) is an ambient ionization technique for mass spectrometry. This solvent based desorption ion source has wide applicability in surface analysis with minimal sample preparation. Interest in improving detection limits, broadening applications, and increasing the spatial resolution for chemical imaging has led to studies of the DESI mechanism. An inverted microscope has been used to image interactions between the DESI spray and test analytes on a glass surface. Microscopic images recorded with millisecond time resolution have provided important insights into the processes governing analyte transport and desorption. These insights are the basis of a rivulet-based model for desorption that differs significantly from the widely-accepted momentum transfer model.

Recently there has been a surge in the field of mass spectrometry centered around the concept of rapid analysis of target analytes with minimal or no sample preparation. The target analyte undergoes desorption from its surface of origin and is subsequently ionized under ambient conditions. The technique is termed ambient desorption/ionization mass spectrometry (ADI-MS). Since the introduction of ADI-MS in 2004, there has been an explosion of research based around the development of novel ambient desorption/ionization (ADI) sources with the capability of desorbing and ionizing a variety of target analytes from various sampling surfaces. One type of ADI source uses the properties of an electrical discharge, typically a helium gas plasma, for desorption and ionization. For electrical-discharge-based sources, ionization is the result of an atmospheric pressure chemical ionization (APCI) process. The initiation of the APCI process it generally attributed to the Penning ionization of atmospheric nitrogen (N2) by highly energetic helium metastable species (Hem). In this work, I describe the direct imaging of the densities of helium metastable atoms in atmospheric pressure plasma jet (APPJ) of a helium-based dielectric-barrier discharge (DBD) using collisionally-assisted laser-induced fluorescence. Axial Hem distributions are compared to the emission of excited helium (He*) and nitrogen ion (N2+*) species in the plasma. A correlation is found between Hem densities and the performance of the ionization source in ADI-MS. Fluorescence images also show that Hem densities increase substantially when a glass slide is placed 10 mm from the discharge capillary in a geometry typical for desorption/ionization experiments. Advantage is taken of the time-varying nature of the plasma to produce axial profiles of temporally and spectrally resolved fluorescence images of Hem atoms and ground state nitrogen ions in the plasma jet. The axial distribution and similarities in the temporal behavior of the helium metastable and ground state nitrogen ion species give strong evidence that nitrogen ion species are created via Penning ionization by helium metastable atoms. Although axial distributions of He*,N2+*, and N2* emission support the fluorescence data, temporally-resolved emission measurements show that emission from key plasma species is almost entirely the result of excitation by a temporal energy wave. The effect that hydrogen (H2) has on the helium metastable atom densities is also presented. The addition of hydrogen to the discharge gas severely quenches the metastable state, leaving it virtually undetectable. The addition of 0.9% H2 to the helium in the source provides an order of magnitude increase in ADI-MS signal for target analytes despite the quenching of the Hem population.

Green adsorption media with the inclusion of renewable and recycled materials can be applied as a stormwater best management practice for copper removal. A green adsorption media mixture composed of recycled tire chunk, expanded clay aggregate, and coconut coir was physicochemically evaluated for its potential use in an upflow media filter. The results found that the use of the green adsorption media mixture in isolation or the coconut coir with an expanded clay filtration chamber could be an effective and reliable stormwater best management practice for copper removal. A suite of tests were conducted on the media mixture and the individual media components including studies of isotherm, reaction kinetics, column adsorption and reaction kinetics. Batch adsorption tests revealed that the media and media mixture follow both the Freundlich and Langmuir isotherm models and that the coconut coir had the highest affinity for copper. A screening of desorbing agents revealed that hydrochloric acid has good potential for copper desorption, while batch tests for desorption with hydrochloric acid as the desorbing agent showed the data fit the Freundlich isotherm model. Reaction kinetics revealed that the adsorption reaction took less than 1 hour to reach equilibrium and that it followed pseudo-second order kinetics for the mixture and coconut. Desorption kinetic data had high correlation with the pseudo-second order model and revealed a rapid desorption reaction. Batch equilibrium data over 3 adsorption/desorption cycles found that the coconut coir and media mixture were the most resilient and demonstrated that they could be used through 3 or more adsorption/desorption cycles. The coconut coir also performed the best under dynamic conditions, having an equilibrium uptake of 1.63 mg?g-1, compared to 0.021 mg?g-1 at an influent concentration of 1.0 mg?L-1 and a hydraulic retention time of 30 minutes. A physical evaluation of the media found the macro-scale properties, such as particle size distribution and mass-volume relationships, and observed the micro-scale properties such as surface and pore microstructures, crystalline structures, and elemental composition. FE-SEM imaging found a strong correlation between the porosity of the micro pore structure and the adsorptive capacity. The equilibrium and dynamic adsorption testing results were confirmed by elemental analysis, which showed measureable quantities of copper in the coconut coir and media mixture after adsorption followed by partial desorption. A new scaling-up theory was developed through a joint consideration of the Damköhler and Péclet numbers for a constant media particle size such that a balance between transport-controlled and reaction-controlled kinetics can be harmonized. A series of column breakthrough tests at varying hydraulic residence times revealed a clear peak adsorptive capacity for the media mixture at a Damköhler number of 2.7. The Péclet numbers for the column breakthrough tests indicated that mechanical dispersion is an important effect that requires further consideration in the scaling-up process. However, perfect similitude of the Damköhler number cannot be maintained for a constant media particle size, and relaxation of hydrodynamic similitude through variation of the Péclet number must occur.

No description available.

No description available.

No description available.

No description available.