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Why Does CuFeS2 Resemble Gold?
No full textWhile several potential applications of CuFeS2 quantum dots have already been reported, doubts regarding their optical and physical properties persist. In particular, it is unclear if the quantum dot material is metallic, a degenerately doped semiconductor, or else an intrinsic semiconductor material. Here we examine the physical properties of CuFeS2 quantum dots in order to address this issue. Specifically, we study the bump that is observed in the optical spectra of these quantum dots at similar to 500 nm. Using a combination of structural and optical characterization methods, ultrafast spectroscopy, as well as electronic structure. calculations, we ascertain that the unusual purple color of CuFeS2 quantum dots as well the golden luster of CuFeS2 films arise from the existence of a plasmon resonance in these materials. While the presence of free carriers causes this material to resemble gold, surface treatments are also described to suppress the plasmon resonance altogether
Synthesis, characterisation and optical studies of new tetraethyl-rubyrin-graphene oxide covalent adducts
No full textTetrathia-rubyrin and graphene oxide (GO) covalent adduct was synthesized, characterised and optical properties were studied. GO-Rubyrin adducts showed fluorescence quenching of rubyrin clue to electron or energy transfer from rubyrin to graphene oxide, which also reflected in UV-vis absorbance spectroscopy. The non-linear optical responses were measured through Z scan technique in nano-second regime. The enhanced optical non-linearity was observed after attachment of GO with rubyrin, can be ascribed to the photo-induced electron or energy transfer from the electron rich rubyrin moiety to the electron deficient GO. (C) 2017 Elsevier B.V. All rights reserved
A Call to Introduce Structured Zika Surveillance in India
No full textIndia has the climatic conditions conducive to year-round transmission of Zika virus, and a structured disease surveillance program should be implemented to prevent an outbreak. Such a program should (i) start screening before an outbreak arises; (ii) collect baseline data to assess future disease risk and monitor potential birth defects; and (iii) provide new insights into the ecology of the disease and inform public health policy following the one health concept
Compact Model for Low Effective Mass Channel Common Double-Gate MOSFET
No full textIn the spirit of quantum drift-diffusion formalism, we propose a core compact model for low-effective mass channel common double-gate MOSFET. In contrast to the existing models, carriers in each subband are treated to be in locally thermal equilibrium within that subband, but not with the carriers in a different subband. We observe quasi-linear relationship between energy eigenvalue, quasi-Fermi level, and carrier density in each subband and exploit it to obtain closed-form expressions for drain current and terminal charges. Proposed model, which is free from any unphysical model parameter or interpolating function, captures the essential device physics (strong transverse confinement, wave function penetration, multisubband occupancy, bias-dependent diffusivity, and Fermi-Dirac distribution of the carriers) while preserving the mathematical simplicity of industry standard Silicon MOSFET models. Drain current, conductance, and capacitances calculated from the proposed model are found to be in good agreement with numerical device simulation for a wide range of channel thickness, effective mass, oxide thickness asymmetry, and bias voltages
C2N/WS2 van der Waals type-II heterostructure as a promising water splitting photocatalyst
No full textPhotocatalytic water splitting has long been considered as a source of pollution-free clean energy and finding an efficient photocatalyst for this reaction has remained a major challenge. Here, we study C2N/WS2 van der Waals heterostructure as a possible photocatalyst for water splitting. Using first principles calculations, we find that band edges of the heterostructure are found to satisfy both water oxidation and reduction energy levels, ensuring the occurrence of these two reactions. Additionally, it is found to be a type-II heterostructure, that enables the separation of electrons and holes in two different layers upon light irradiation and thereby facilitates water oxidation on WS2 layer and water reduction on C2N layer. The charge transfer occurs from WS2 to C2N monolayer, which serves dual purpose of separating photoinduced charge carriers and extending their lifetimes. The heterostructure also shows high charge carrier mobilities, indicating their efficient utilization in reduction and oxidation reactions before recombination. Most importantly, light absorption in visible range for the heterostructure is significantly enhanced compared to the constituent monolayers, rendering it to be a suitable photocatalyst for water splitting. Thermodynamic analysis for redox reactions suggest facile hydrogen generation on the heterostructure. Our study explains the underlying mechanism of the enhanced photocatalytic activity of C2N/WS2 heterostructure, which could further lead to designing of wider range of 2D heterostructured photocatalysts. (C) 2018 Elsevier Inc. All rights reserved
An independent race model involving an abort and re-plan strategy explains reach redirecting movements during planning and execution
No full textAlthough race models have been extensively used to study inhibitory control, the mechanisms that enable change of reach plans in the context of race models remain unexplored. We used a redirect task in which targets occasionally changed their locations to study the control of reaching movements during movement planning and execution phases. We tested nine different race model architectures that could explain the redirect behavior of reaching movements. We show that an independent GO-STOP-GO model that reflects a plan-abort-re-plan strategy involving non-interacting elements successfully explained the various behavioral measures such as the compensation function and the pattern of error response reaction times. By extending the same race model to the execution phase, we could explain the extent and the pattern of hypometric trials. Interestingly, the race model also provided evidence that redirecting a movement during planning and execution shared the same inhibitory mechanism. Taken together, this study demonstrates the applicability of an independent race model to understand the computational mechanisms underlying the control of reach movements
Understanding the photoluminescence behaviour in nano CaZrO3:Eu3+ pigments by Judd-Ofelt intensity parameters
No full textCaZrO3 ceramic pigment exhibits high chemical, thermal and structural stability. However, its application as a host for various luminophores/activators has not been clearly explored. In the present investigation, CaZrO3 doped with Eu3+, as a potential orange-red phosphor has been demonstrated. Ca1-xZrO3:Eu-x (x = 0.01-0.09) nanophosphor is prepared here through a low temperature, one pot solution combustion synthesis approach using glycine as the fuel. X-ray diffraction results show that all the samples are stabilized in orthorhombic crystal structure without any impurity phases. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM are carried out to determine the microstructure of the phosphor. The particles are found to be significantly agglomerated and in the nano-regime (similar to 40 nm). The observed excitation spectrum suggests that Ca1-xEuZrO3 can be efficiently excited using ultra-violet (UV), near-UV and UV blue (UVB), making it immediately relevant for current solid state lighting technologies. In fact with every similar to 1 at% doping increase, the primary excitation line intensity increases by a factor of similar to 1.5; this provides a simple parameter to enhance the UV excitability of the phosphor. The color coordinates are deduced using the Commission International De Eclairage (CIE) co-ordinates (x, y = 0.58, 0.40). The critical distance of energy transfer in this system is determined to be similar to 10.7 angstrom, making multipole-multipole interactions as the plausible reason for concentration quenching beyond 7 mol.% Eu doping. The luminescence behaviour of the material is evaluated using Judd-Offelt (JO) intensity parameters. Judd-Ofelt (JO) intensity parameters (Omega(2) and Omega(4)) are calculated for the sample Ca1-xZrO3:Eu-x (x = 0.01-0.09), in order to understand the local structure around the activator. Irrespective of the concentration of Eu3+, Omega(2) is found to be greater than Omega(4), indicating asymmetric environment around the activator. Furthermore, with increase in Eu3+, Omega(2) increases suggesting an increase in covalency of Eu-O bonds with significant effect of host crystal field on Eu3+
Augmented photocatalytic and electrochemical activities of Ag tailored LaCoO3 perovskite semiconductor
No full textInorganic perovskite materials have drawn significant interest in photocatalytic application owing to their excellent photo absorbing nature. In this regard, we have synthesized pristine and silver (Ag) modified lanthanum cobaltite (LaCoO3) perovskite by hydrothermal method and characterized by multitechnique approaches. The structural, absorption and emission studies reveal that addition of Ag influences the crystallite size, absorption co-efficient and electron hole recombination rate of LaCoO3. Morphological analysis shows that tetragonal morphology of the pure LaCoO3 is changed to square shape morphology on addition of Ag, which reveals the dispersion of Ag into LaCoO3. Electrochemical analysis demonstrates the possible electrochemical activity of the materials and confirms that Ag provides higher charge transfer kinetics and stability to LaCoO3. In addition, Ag-LaCoO3 degrades methylene blue (MB) in higher rate (99% in 10 min) compared to LaCoO3 (75% in 10 min). Mechanism behinds the photocatalytic activity has been discussed. Hence, the present investigation explores Ag modified LaCoO3 as a newpotential candidate for the application in photocatalytic activity under sunlight irradiation. (C) 2018 Elsevier B.V. All rights reserved
A pH-Triggered Synthesis of Blue-Emitting Au Nanoclusters and Their Luminescence Enhancement in a Metallohydrogel: Selective Detection of Pb2+ through Luminescence Quenching
No full textThe synthesis and stabilization of blue-emitting nanoclusters (Au, Cu or Ag) are very challenging. We have developed a facile, acid-induced protocol to synthesize blue-emitting Au NCs (B-NCs) in aqueous medium at room temperature from green-emitting ones (G-NCs). The rapid quenching of the blue emission was successfully arrested, and in fact enhanced, by the incorporation of the NCs in a bile acid derived metallohydrogel, demonstrating the special effect of the gel medium. The NCs in both solution and gel were characterized in detail using microscopic and photophysical techniques, including a detailed analysis of the excited state relaxation pathway. We have demonstrated that this NC can be switched back to G-NCs reversibly upon the reaction with a base. We have also shown that the B-NC can be efficiently applied towards detection of Pb2+. This simple approach towards B-NC synthesis and its stabilization can contribute to application of this material in LEDs, bioimaging, and energy transfer