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School of Energy and Chemical Engineering (Chemical Engineering)Optoelectronic devices are essential components that exploit electromagnetic radiation based on light-matter interactions and have been developed with the advance of nanotechnology. In particular, communication between materials at interfaces is crucial because optoelectronic devices are made up of multilayer structures. Interface/surface engineering allows the regulation of physical stress, energy barrier, interfacial band alignment, and defect passivation, all of which are directly related to the performance of devices. The arrangement of energy levels affects charge transport and can be adjusted by the dipole moment on the surface of nanomaterials. Defect passivation on the interface/surface of the materials reduces trap states that induce charge accumulation as a charge injection barrier or act as nonradiative recombination centers. These effects are prominent in nanomaterials because of their high surface-area-to-volume ratio. Furthermore, since the nanomaterial layer of optoelectronics is a microscopic assembly, surface engineering can regulate the communication between nanomaterials by changing the interparticle distance and packing density. This dissertation describes surface engineering strategies for semiconductor nanomaterials to improve the efficiency of optoelectronic devices. Chapter 2 demonstrates the interface engineering between the graphene electrode and the hole transport layer for organic solar cells. A thin layer of norepinephrine, an amphiphilic catecholamine derivative, is applied to the graphene electrode as a hydrophilic surface modifier to enable efficient surface modification without significantly decreasing the optical transmittance or the electrical conductivity. The power conversion efficiency of organic solar cells fabricated with this poly(norepinephrine)-coated graphene electrode is 7.93%, close to that of the ITO-based reference device with a power conversion efficiency of 8.73%. In Chapter 3, we demonstrate the surface engineering of InP@ZnSeS quantum dots for a color filter. Phenylethyl mercaptan ligands are used as surface modifiers, substituting the original oleic acid ligands. In the propylene glycol monomethyl ether acetate solvent, more than 75% of photoluminescence quantum yields are retained without a peak shift in the emission spectrum during the ligand exchange procedure. Surface-engineered quantum dots show high colloidal stability in propylene glycol monomethyl ether acetate for more than one month under ambient conditions. Chapter 4 demonstrates the interface engineering between CsPbBr3 and Cs4PbBr6 perovskite nanocrystals for blue light-emitting diodes. Highly emissive blue CsPbBr3 quantum dots are developed by controlling the reactivity of metal precursors. In situ generated Cs4PbBr6 nanocrystals eliminate the surface defects of CsPbBr3 quantum dots, resulting in high colloidal and thermal stability. The fabricated blue light-emitting diode shows an external quantum efficiency of 4.65% at 480 nm and excellent spectral stability under operational conditions. As previously discussed, we have developed a catechol-based nanocoating method, a thiol-based ligand exchange method, and a surface reconstruction strategy for perovskite materials. Our strategies can accelerate the development of a wide range of optoelectronic applications thanks to their versatility.ope

Nutrient removal and microalgal biomass production from different anaerobic digestion effluents with Chlorella species

Potential of microalgal cultivation as an alternative approach to the treatment of anaerobic digestion (AD) effluents was examined using two representative Chlorella species, Chlorella vulgaris (CV) and Chlorella protothecoides (CP). Both species effectively removed NH 4 + -N from the AD effluents from four digesters treating different wastes under different operating conditions. In all experimental cultures on the AD effluents, NH 4 + -N (initial concentration, 40 mg/L) was completely removed within 10 days without residual NO 3 ??? -N or NO 2 ??? -N in batch mode. Compared to CP, CV showed greater biomass and lipid yields (advantageous for biodiesel production), regardless of the media used. Prolonged nitrogen starvation significantly increased the lipid accumulation in all cultures on the AD effluents, and the effect was more pronounced in the CV than in the CP cultures. On the other hand, compared to CV, CP showed significantly faster settling (advantageous for biomass harvesting) in all media. Our results suggest that the Chlorella cultivation on AD effluents under non-sterile, mixed-culture conditions may provide a viable way to manage and valorize the problematic effluents. Diverse bacteria derived from the AD effluents co-existed and presumably interacted with the Chlorella species in the cultures. ?? 2019, The Author(s)

Bandgap Modulation of Cs2AgInX6 (X = Cl and Br) Double Perovskite Nano- and Microcrystals via Cu2+ Doping

Recently, the double perovskite Cs2AgInCl6, which has high stability and low toxicity, has been proposed as a potential alternative to Pb-based perovskites. However, the calculated parity-allowed transition bandgap of Cs2AgInCl6 is 4.25 eV; this wide bandgap makes it difficult to use as an efficient solar absorber. In this study, we explored the effect of Cu doping on the optical properties of Cs2AgInCl6 double perovskite nano- and microcrystals (MCs), particularly in its changes of absorption profile from the ultraviolet (UV) to near-infrared (NIR) region. Undoped Cs2AgInCl6 showed the expected wide bandgap absorbance, but the Cu-doped sample showed a new sharp absorption peak at 419 nm and broad absorption bands near 930 nm, indicating bandgap reduction. Electron paramagnetic resonance (EPR) spectroscopy demonstrated that this bandgap reduction effect was due to the Cu doping in the double perovskite and confirmed that the Cu2+ paramagnetic centers were located on the surface of the nanocrystals (NCs) and at the center of the perovskite octahedrons (g(parallel to) > g(perpendicular to) > g(e)). Finally, we synthesized Cu-doped Cs2AgInCl6 MCs and observed results similar to those of the NCs, showing that the application range could be expanded to multidimensions

Eco-Friendly Synthesis of Water-Glass-Based Silica Aerogels via Catechol-Based Modifier

Silica aerogels have attracted much attention owing to their excellent thermal insulation properties. However, the conventional synthesis of silica aerogels involves the use of expensive and toxic alkoxide precursors and surface modifiers such as trimethylchlorosilane. In this study, cost-effective water-glass silica aerogels were synthesized using an eco-friendly catechol derivative surface modifier instead of trimethylchlorosilane. Polydopamine was introduced to increase adhesion to the SiO2 surface. The addition of 4-tert-butyl catechol and hexylamine imparted hydrophobicity to the surface and suppressed the polymerization of the polydopamine. After an ambient pressure drying process, catechol-modified aerogel exhibited a specific surface area of 377 m(2)/g and an average pore diameter of approximately 21 nm. To investigate their thermal conductivities, glass wool sheets were impregnated with catechol-modified aerogel. The thermal conductivity was 40.4 mWm(-1)K(-1), which is lower than that of xerogel at 48.7 mWm(-1)K(-1). Thus, by precisely controlling the catechol coating in the mesoporous framework, an eco-friendly synthetic method for aerogel preparation is proposed

Treatment of Axillary Osmidrosis Using a Subcutaneous Pulsed Nd-YAG Laser

BackgroundAxillary osmidrosis is characterized by an unpleasant odor, profuse sweating, and in some instances, staining of clothes that may socially and psychologically impair affected individuals. Various types of surgical procedures have been developed for the treatment of axillary osmidrosis. This study was undertaken to evaluate the effectiveness of subcutaneous pulsed neodymium: yttrium-aluminum-garnet (Nd-YAG) laser treatment for the treatment of axillary osmidrosis.MethodsTwenty-nine patients with axillary osmidrosis were included in this study. Patients were categorized according to the results of an axillary malodor grading system, and a subcutaneous pulsed Nd-YAG laser was applied to all patients. The treatment area for the appropriate distribution of laser energy was determined using the iodine starch test (Minor's test) against a grid pattern composed of 2×2 cm squares. The endpoint of exposure was 300 to 500 J for each grid, depending on the preoperative evaluation results. The results were evaluated by measurement of axillary malodor both pre- and postoperatively using the grading system and iodine starch test.ResultsThe average follow-up period was 12.8 months. Nineteen patients had a fair-to-good result and ten patients had poor results. The postoperative Minor's test demonstrated that there were remarkable improvements for patients with mild to moderate symptoms. Complications including superficial second degree burns (n=3) were treated in a conservative manner. A deep second degree burn (n=1) was treated by a surgical procedure.ConclusionsSubcutaneous pulsed Nd-YAG laser has many advantages and is an effective noninvasive treatment for mild to moderate axillary osmidrosis

Deposition of Crystalline GdIG Samples Using Metal Organic Decomposition Method

Fabrication of high quality ferrimagnetic insulators is an essential step for ultrafast magnonics, which utilizes antiferromagnetic exchange of the ferrimagnetic materials. In this work, we deposit high-quality GdIG thin films on a (111)-oriented GGG substrate using the Metal Organic Decomposition (MOD) method, a simple and high throughput method for depositing thin film materials. We postannealed samples at various temperatures and examined the effect on structural properties such as crystallinity and surface morphology. We found a transition in the growth mode that radically changes the morphology of the film as a function of annealing temperature and obtained an optimal annealing temperature for a uniform thin film with high crystallinity. Optimized GdIG has a high potential for spin wave applications with a low damping parameter in the order of 10(-3), which persists down to cryogenic temperatures

Eco-Friendly Synthesis of Water-Glass-Based Silica Aerogels via Catechol-Based Modifier

Silica aerogels have attracted much attention owing to their excellent thermal insulation properties. However, the conventional synthesis of silica aerogels involves the use of expensive and toxic alkoxide precursors and surface modifiers such as trimethylchlorosilane. In this study, cost-effective water-glass silica aerogels were synthesized using an eco-friendly catechol derivative surface modifier instead of trimethylchlorosilane. Polydopamine was introduced to increase adhesion to the SiO2 surface. The addition of 4-tert-butyl catechol and hexylamine imparted hydrophobicity to the surface and suppressed the polymerization of the polydopamine. After an ambient pressure drying process, catechol-modified aerogel exhibited a specific surface area of 377 m2/g and an average pore diameter of approximately 21 nm. To investigate their thermal conductivities, glass wool sheets were impregnated with catechol-modified aerogel. The thermal conductivity was 40.4 mWm−1K−1, which is lower than that of xerogel at 48.7 mWm−1K−1. Thus, by precisely controlling the catechol coating in the mesoporous framework, an eco-friendly synthetic method for aerogel preparation is proposed

Potential of mixed-culture microalgae enriched from aerobic and anaerobic sludges for nutrient removal and biomass production from anaerobic effluents

This study examines the potential of the mixed-culture microalgal consortia enriched from aerobic sludge (AeS) and anaerobic sludge (AnS) with regard to nutrient removal and biomass production from four different anaerobic digestion (AD) effluents. Both the inocula achieved the complete removal of the NH 4 + -N (initial concentration of 40 mg/L) within 14 days from all the effluents. The AeS cultures showed faster and greater microalgal growth, although the NH 4 + -N removal rate was comparable or higher in the case of the AnS cultures. Further, the AeS and AnS cultures showed significantly different lipid production characteristics in terms of the fatty acid composition and the response to nitrogen deficiency. Nitrogen starvation caused changes in the microbial community structures in all the experimental cultures, which may have influenced the lipid metabolism and the microalgal growth. The overall results suggest that both the inocula exhibit good potential with regard to the treatment of AD effluents