Embedding PbS Quantum Dots (QDs) in Pb-Halide Perovskite Matrices: QD Surface Chemistry and Antisolvent Effects on QD Dispersion and Confinement Properties

Hybrid materials of metal chalcogenide colloidal quantum dots (QDs) embedded in metal halide perovskites (MHPs) have led to composites with synergistic properties. Here, we investigate how QD size, surface chemistry, and MHP film formation methods affect the resulting optoelectronic properties of QD/MHP “dot-in-matrix” systems. We monitor the QD absorption and photoluminescence throughout synthesis, ligand exchange, and transfer into the MHP ink, and we characterize the final QD/MHP films via electron microscopy and transient absorption. In addition, we are the first to globally map how PbS QDs are distributed on the micrometer scale within these dot-in-matrix systems, using three-dimensional (3D) tomography time-of-flight secondary ion mass spectrometry. The surface chemistry imparted during synthesis directly affects the optical properties of the dot-in-matrix composites. Pb-halide passivation leads to QD/MHP dot-in-matrix samples with optical properties that are well-described by a theoretical model, based on a Type I finite-barrier heterostructure between the PbS QD and the MHP matrix. Samples without Pb-halide passivation show complicated size-dependent behavior, indicating a transition from a Type I heterostructure between the PbS QD wells and MHP barriers for small-sized QDs to PbS QDs that are electronically decoupled from the MHP matrix for larger QDs. Furthermore, the choice in perovskite antisolvent crystallization method leads to a difference in the spatial QD distribution within the perovskite matrix, differences in carrier lifetime, and photoluminescence shifts of up to 180 meV for PbS in methylammonium lead iodide. This work establishes an understanding of such emerging synergistic systems relevant for technologies such as photovoltaics, infrared emitters and detectors, and other unexplored technological applications

The effect of Zn excess on kesterite solar cells

a b s t r a c t Accuracy in composition control has been one of the top issues for fabricating high-performance kesterite (Cu 2 ZnSn(Se,S) 4 ) solar cells. A detailed understanding of the effect of Zn excess on device performance has not yet been demonstrated. Thus, specific criteria for high-performance devices, in particular discriminating between the effects of Zn-rich features at the front versus the back of the absorber, are desired. In this study, we report that co-evaporated kesterite absorbers can demonstrate high device efficiency despite the presence of large quantities of ZnSe. However, the benign presence of ZnSe is found to be conditional. While large ZnSe grains on the back of the absorbers are not harmful to device performance, the ZnSe grains produced by excess Zn near the end of the deposition degrade the cell efficiency from 8% level to 6% level (without anti-reflection coatings). The other effect related to excess Zn on the front of absorber is the facilitation of breakdown in lower reverse bias. The breakdown indicated here occurs only under the illumination of blue photons, and to our best knowledge has not been reported before. The exact mechanism of the breakdown remains open, but it is demonstrated to be related to the photoconductivity of CdS, and is thus possibly a symptom of lateral defect issues in the absorber, caused by the overdose of Zn. The same type of issue contributing to the breakdown may also be responsible for part of the parasitic loses at the working voltage, and therefore warrants further research

Optical transitions in magnetoelectric Ga0.6Fe1.4O3 from 0.73 to 6.45 eV

The optical properties of polycrystalline Ga0.6Fe1.4O3 bulk are determined by spectroscopic ellipsometry from 0.73 to 6.45 eV. Complex dielectric function epsilon = epsilon(1) + i epsilon(2) spectra are obtained from the multilayer analysis. The ellipsometric data exhibit numerous optical structures, and the transition energies are accurately obtained by analyzing the second-energy derivatives of the data. The origins of the optical structures are explained in terms of Fe3+ ligand field transitions and ligand-to-metal charge transfer transitions. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4721649

Discutindo a educação ambiental no cotidiano escolar: desenvolvimento de projetos na escola formação inicial e continuada de professores

A presente pesquisa buscou discutir como a Educação Ambiental (EA) vem sendo trabalhada, no Ensino Fundamental e como os docentes desta escola compreendem e vem inserindo a EA no cotidiano escolar., em uma escola estadual do município de Tangará da Serra/MT, Brasil. Para tanto, realizou-se entrevistas com os professores que fazem parte de um projeto interdisciplinar de EA na escola pesquisada. Verificou-se que o projeto da escola não vem conseguindo alcançar os objetivos propostos por: desconhecimento do mesmo, pelos professores; formação deficiente dos professores, não entendimento da EA como processo de ensino-aprendizagem, falta de recursos didáticos, planejamento inadequado das atividades. A partir dessa constatação, procurou-se debater a impossibilidade de tratar do tema fora do trabalho interdisciplinar, bem como, e principalmente, a importância de um estudo mais aprofundado de EA, vinculando teoria e prática, tanto na formação docente, como em projetos escolares, a fim de fugir do tradicional vínculo “EA e ecologia, lixo e horta”.Facultad de Humanidades y Ciencias de la Educació

Correlates of Protective Motivation Theory (PMT) to Adolescents’ Drug Use Intention

Early onset and increasing proliferation of illicit adolescent drug-use poses a global health concern. This study aimed to examine the correlation between Protective Motivation Theory (PMT) measures and the intention to use drugs among adolescents. An exploratory quantitative correlation design and convenience sampling were adopted. A total of 318 students completed a self-reported questionnaire that solicited information related to their demographics and activities, measures of threat appraisal and coping appraisal, and the intention to use drugs. Logistic regression analysis showed that intrinsic and extrinsic rewards were significant predictors of intention. The odds ratios were equal to 2.90 (p < 0.05) and 8.04 (p < 0.001), respectively. The logistic regression model analysis resulted in a high Nagelkerke R2 of 0.49, which suggests that PMT related measures could be used in predicting drug use intention among adolescents. Further research should be conducted with non-school adolescents to confirm the application

With an Additional Open Problem By

on the occasion of his 60th birthday The success of the symbolic mathematical computation discipline is striking. The theoretical advances have been continuous and significant: Gröbner bases, the Risch integration algorithm, integer lattice basis reduction, hypergeometric summation algorithms, etc. From the beginning in the early 1960s, it has been the tradition of our discipline to create software that makes our ideas readily available to scientists, engineers, and educators: SAC-1, Reduce, Macsyma, etc. The commercial viability of our system products is proven by Maple and Mathematica. Today’s user communities of symbolic computation systems are diverse: educators, engineers, stock market analysts, etc. The mathematics and computer science in the design and implementation of our algorithms are sophisticated. The research challenges in symbolic computation at the close of the twentieth century are formidable. I state my favorite eight open problems in symbolic computation. They range from problems in symbolic/numeric computing, symbolic algorithm synthesis, to system component construction. I have worked on seven of my problems and borrowed one from George Collins. I present background to each of my problems and a clear-cut test that evaluates whether a proposed attack has solved one of my problems. An additional ninth open problem by Rob Corless and David Jeffrey on complex function semantics is given in an appendix