Chalcogenide Sol-Gel Assembly: Controlling The Kinetics Of Nanocrystal Aggregation And Film Formation For Applications In Optoelectronics

The dissertation work is focused on 1) optimization of gelation conditions in order to tune the properties of the resultant gel structures with the aim of addressing application-specific needs; 2) incorporation of gel materials into device architectures for evaluation of intrinsic properties and assessment of suitability for optoelectronic applications. Sol-gel assembly of CdSe/ZnS core/shell NCs typically results in opaque gel materials, which is one of the major obstacles for their use in optoelectronic applications such as LEDs. Macroscopic properties (i.e. transparency) of CdSe/ZnS gel structures were tuned by controlling the aggregation and gelation kinetics by means of oxidant concentration. The mechanism and kinetics of aggregation of 11-mercaptoundecanoic acid (MUA)-capped CdSe/ZnS NCs, as a function of oxidant concentration (tetranitromethane, (TNM)), were studied by means of time resolved dynamic light scattering (TRDLS). The structural characteristics of the resultant gels were probed by optical transmission, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). Transparent gel structures were achieved for small NCs (~4.5 nm) at relatively low NC concentration (~4 × 10-7 M) and oxidant concentration (~4-10 μL) enabling the tuning of macroscopic properties for application-specific needs in optoelectronics. In order to incorporate chalcogenide gel materials into device architectures, it is essential to fabricate gel materials in film form. The synthesis of transparent micron-thick xerogel films of CdSe/ZnS NCs was achieved by employing similar gelation conditions that resulted in transparent gel structures. Films were deposited by immersing a glass substrate horizontally in the pre-oxidized sols, gelling and drying under ambient conditions. CdSe/ZnS xerogel films exhibited strong photoluminescence and high conductivities (~10-3 S*cm-1). However, the films were rough, and attempts to make crack-free thinner films by this approach were not successful. High quality thin (ca 70 nm) sol-gel NC films were deposited by spin coating sols of thioglycolic acid-capped CdSe and CdSe/ZnS NCs onto substrates and dipping the films into an oxidizing solution (TNM in acetone). Optical, structural and electrical properties of the sol-gel films were evaluated and the films were found to exhibit superior charge transport properties, as shown by a dramatic enhancement of electrochemical photocurrent under white light illumination relative to thin films composed of ligand-capped NCs. This suggests that the sol-gel approach may yield NC thin films suitable for a range of optoelectronic applications. Composite films of poly(3-hexylthiophene) (P3HT) with either CdSe and CdSe/ZnS aerogels, with were evaluated for hybrid photovoltaic devices by analyzing the variation of morphology and photocurrent generation with the composition of the hybrid film. Compared to films composed of ligand capped, physically aggregated NCs and P3HT, aerogel/P3HT films showed increased photocurrent and charge generation attributed to the interconnected NC network. These data suggest the use of chalcogenide aerogel materials for hybrid photovoltaic applications is feasible

Transparent conducting films of CdSe(ZnS) core(shell) quantum dot xerogels

A method of fabricating sol–gel quantum dot (QD) films is demonstrated, and their optical, structural and electrical properties are evaluated. The CdSe(ZnS) xerogel films remain quantum confined, yet are highly conductive (10−3 S cm−1). This approach provides a pathway for the exploitation of QD gels in optoelectronic applications

A Time-Sensitive IoT Data Analysis Framework

This paper proposes a Time-Sensitive IoT Data Analysis (TIDA) framework that meets the time-bound requirements of time-sensitive IoT applications. The proposed framework includes a novel task sizing and dynamic distribution technique that performs the following: 1) measures the computing and network resources required by the data analysis tasks of a time-sensitive IoT application when executed on available IoT devices, edge computers and cloud, and 2) distributes the data analysis tasks in a way that it meets the time-bound requirement of the IoT application. The TIDA framework includes a TIDA platform that implements the above techniques using Microsoft’s Orleans framework. The paper also presents an experimental evaluation that validates the TIDA framework’s ability to meet the time-bound requirements of IoT applications in the smart cities domain. Evaluation results show that TIDA outperforms traditional cloud-based IoT data processing approaches in meeting IoT application time-bounds and reduces the total IoT data analysis execution time by 46.96%

Antinociceptive and antipyretic activities of methanol extract Amaranthus caudatus linn

The methanolic extract of whole plant of Amaranthus caudatus Linn. (MEAC), was tested for antinociceptive (using hot plate method, acetic acid writhing and tail immersion) and antipyretic (using yeast induced pyrexia) activities using mice and rats at doses of 200 and 400 mg/kg body weight. MEAC significantly (p < 0.05) inhibited acetic acid induced writhing and also significantly delayed the reaction time of mice to thermal stimulation produced by the hot plate and hot water in tail immersion test. MEAC significantly (p < 0.01) reduced fever induced by yeast. These results suggest that the MEAC has exhibited significant antinociceptive and antipyretic effects, which were comparable with standard drugs.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Aggregation Kinetics of Metal Chalcogenide Nanocrystals: Generation of Transparent CdSe (ZnS) Core (Shell) Gels

Transparent CdSe (ZnS) core (shell) sol–gel materials have potential uses in optoelectronic applications such as light-emitting diodes (LEDs) due to their strong luminescence properties and the potential for charge transport through the prewired nanocrystal (NC) network of the gel. However, typical syntheses of metal chalcogenide gels yield materials with poor transparency. In this work, the mechanism and kinetics of aggregation of two sizes of CdSe (ZnS) core (shell) NCs, initiated by removal of surface thiolate ligands using tetranitromethane (TNM) as an oxidant, were studied by means of time-resolved dynamic light scattering (TRDLS); the characteristics of the resultant gels were probed by optical absorption, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). At low concentrations of NCs (ca. 4 × 10^–7 M), the smaller, green-emitting NCs aggregate faster than the larger, orange-emitting NCs, for a specific oxidant concentration. The kinetics of aggregation have a significant impact on the macroscopic properties (i.e., transparency) of the resultant gels, with the transparency of the gels decreasing with the increase of oxidant concentration due the formation of larger clusters at the gel point and a shift away from a reaction-limited cluster-aggregation (RLCA) mechanism. This is further confirmed by analyses of the gel structures by SAXS and TEM. Likewise, the larger orange-emitting particles also produce larger aggregates at the gel point, leading to lower transparency. The ability to control the transparency of chalcogenide gels will enable their properties to be tuned in order to address application-specific needs in optoelectronics

Nature of the gabbro in central anatolia: Geological observation and spectroscopic applications, Turkey

*Güllü, Bahattin ( Aksaray, Yazar )Central Anatolia is bounded by the Izmir Ankara Erzincan (IAE) Suture Zone dipping northward beneath the Pontides at the north and the Inner Tauride (IT) Suture Zone with NE-dipping Central part of Turkey with triangular shaped structure. The Paleozoic metamorphic rocks are formed the basement of the Central Anatolia and obducted by the remnant of Inner Tauride ophiolitic products. Both of the units injected by Late Cretaceous age of the felsic and mafic intrusive unit. The mafic products mainly composed of gabbroic rocks and formed the less exposure crystalline magmatic rocks in comparison to the felsic crystalline magmatic rocks. The gabbroic rocks have a wide range in the exposure and mainly exposed at the eastern and far eastern part of Central Anatolia. They are ranging from a few meters up to kilometer square in dimension. The largest outcrops mostly accumulated with felsic intrusion in Central Anatolia. Different geographical distribution, colour, texture and mineral chemistry led to evaluate different source and nature in the region. MORB normalized elemental pattern of most of the gabbroic rocks of the Central Anatolian are enriched with the LIL elements with respect to HFS elements. Whole rock, trace and rare earth element results reveal that most of these mafic rocks are almost reveal almost similar geochemical behavior and patterns. The Raman spectra of the ophiolitic, intrusive and alkaline gabbroic rocks pyroxene mainly composed of augite, augite-diopside and augite- hedenbergite in composition respectively. The Electron Probe Micro Analysis (EPMA) results reveal that the pyroxene of the ophiolitic gabbro, intrusive gabbro and alkaline gabbro may crystalized at 178, 77 and 80 km depth with 46, 20 and 19 kilo bar pressure. Although the mineralogical, whole rock geochemical compositions are not able to differentiate between these gabbro the crystallization conditions of the pyroxene may be used in the classification of the gabbro types in Central Anatolia...

Enhanced Conductivity in CZTS/Cu_2–<i>x</i>Se Nanocrystal Thin Films: Growth of a Conductive Shell

Poor charge transport in Cu₂ZnSnS₄ (CZTS) nanocrystal (NC) thin films presents a great challenge in the fabrication of solar cells without postannealing treatments. We introduce a novel approach to facilitate the charge carrier hopping between CZTS NCs by growing a stoichiometric Cu₂Se shell that can be oxidized to form a conductive Cu_2–<i>x</i>Se phase when exposed to air. The CZTS/Cu₂Se core/shell NCs with varying numbers of shell monolayers were synthesized by the successive ionic layer adsorption and reaction (SILAR) method, and the variation in structural and optical properties of the CZTS NCs with varying shell thicknesses was investigated. Solid-phase sulfide ligand exchange was employed to fabricate NC thin films by layer-by-layer dip coating and a 2 orders of magnitude rise in dark conductivity (∼10^–3 S cm^–1 at 0 monolayer and ∼10^–1 S cm^–1 at 1.5 monolayers) was observed with an increase in the number of shell monolayers. The approach described herein is the first key step in achieving a significant increase in the photoconductivity of as-deposited CZTS NC thin films

Connecting the (quantum) dots: towards hybrid photovoltaic devices based on chalcogenide gels

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CdSe(ZnS) core(shell) aerogels were prepared from the assembly of quantum dots into mesoporous colloidal networks. The sol-gel method produces inorganic particle interfaces with low resistance to electrical transport while maintaining quantum-confinement. The photoelectrochemical properties of aerogels and their composites with poly(3-hexylthiophene) are reported for the first time.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.14431518015184Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)INEORoyal SocietyUK Engineering and Physical Sciences Research Council (EPSRC)Revolutionary Materials for Solid State Energy ConversionEnergy Frontier Research CenterU.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-SC0001054]National Institutes of Health, National Cancer Institute via a subcontract from Weinberg Medical Physics, LLC [R44 CA138013-03]NSF Grant [DMR0216084]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2009/15428-0]U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-SC0001054]National Institutes of Health, National Cancer Institute via a subcontract from Weinberg Medical Physics, LLC [R44 CA138013-03]NSF Grant [DMR0216084