1,721,036 research outputs found
Growth of photoluminescent cadmium sulphide quantum dots from soluble single source precursors in solution and in film
No full textPhotoluminescent cadmium sulphide (CdS) quantum dots (QDs) were successfully obtained by a single-source route via a non-injection one-pot approach using octadecene (ODE) as a non-coordinating solvent and myristic acid (MA) as capping agent. The synthetic scheme makes use of two metal-organic molecules belonging to the xanthate family, cadmium diethyl-xanthate (CdDEX) and cadmium dibutyl-xanthate (CdDBX) single-source precursors. The thermal conversion of both xanthates was explored in the temperature range of 150 °C-180 °C. Following this heat treatment material made from both precursors showed photoluminescence from the direct band gap having a PLQY from 5% (CdDEX) to 13% (CdDBX). The nucleation and growth of CdS nanoparticles in thin solid films was studied by transmission electron microscopy. The surface topography and morphology of the thin films was observed by atomic force microscopy
Fluorecence Microscopy Study of CdS quantum dots Obtained by Laser Irradiation from a Single Source Precursor in Polymeric Film
No full textRecently the quantum dots (QDs) synthesis from single source precursors (SSPs) showed a potential interest for patterning formation of nano-composites. In this approach the SSPs have to be mixed with a matrix that afterwards is treated selectively to obtain the desired nanocomposite. The study of the generation of the QDs from the SSPs is, therefore, crucial for the definition of its behaviour within the polymeric matrix. The formation of the CdS QDs via thermolysis of the cadmium diethyldithiocarbamate (CdDDTC) was performed and studied in the presence of a non coordinating solvent such as octadecene (ODE) in presence of myristic acid (MA) as ligand. The precursor is then studied in combination with the poly(methyl methacrylate) (PMMA) polymer for the generation of the CdS QDs under the laser irradiation within a film. The effect of the laser has been studied both on neat PMMA and on the polymer/precursor blend film with the aid of the fluorescence microscope. The results are used to identify the optimal laser parameters to obtain the decomposition of the precursor and to evaluate the effect of the laser irradiation on the polymer. © 2017 Elsevier Ltd
Photophysical and structural characterisation of in situ formed quantum dots
No full textConjugated polymer-semiconductor quantum dot (QD) composites are attracting increasing attention due to the complementary properties of the two classes of materials. We report a convenient method for in situ formation of QDs, and explore the conditions required for light emission of nanocomposite blends. In particular we explore the properties of nanocomposites of the blue emitting polymer poly[9,9-bis(3,5-di-tert-butylphenyl)-9H-fluorene] together with cadmium sulphide (CdS) and cadmium selenide (CdSe) precursors. We show the formation of emissive quantum dots of CdSe from thermally decomposed precursor. The dots are formed inside the polymer matrix and have a photoluminescence quantum yield of 7.5%. Our results show the importance of appropriate energy level alignment, and are relevant to the application of organic-inorganic systems in optoelectronic devices. © 2014 The Partner Organisations
Formation of quantum dots from precursors in polymeric films by ps-laser
No full textQuantum dots (QDs) of semiconductors are promising materials for light emission applications due to their size-tunable optoelectronic properties. We present results of direct quantum dot (QD) formation from precursors inside a polymer matrix using laser irradiation. The method is important because it provides a simple means of patterning nanocomposite material within selected regions of a polymer, as required for device design. Several combinations of polymer/precursors films were treated with a picosecond laser at wavelength of 266 nm in order to verify the formation of the QDs inside the polymeric matrix. Precursors for CdS and CdSe QDs were used in experiments. The structural studies of laser-irradiated samples carried out by means of transmission electron microscopy (TEM) showed the QD formation. The size of QDs and the clusters depended on the laser irradiation dose transferred to the film. The QDs were collected to clusters including 10-60 QDs of different size. The mean size of QDs was less than 10nm. The optical analysis carried out by means of UV-VIS and optical microscopy confirmed the formation of the QDs after laser processing. The time-resolved photoluminescence revealed the energy transfer from the organic host to QDs. However, the charge separation was present due to a certain energy level alignment. Modification of the polymer/precursor blends is still required to prevent imbalance of carrier injection to QDs. Photo-luminescent spectroscopy and fluorescence microscopy have revealed that even if the QDs are not emissive, in certain polymer/QDs combinations the PL emission of the polymer is restored after laser treatment. © 2013 Copyright SPIE
Direct Optical Patterning of Quantum Dots: One Strategy, Different Chemical Processes
Full text linkPatterning, stability, and dispersion of the semiconductor quantum dots (scQDs) are three issues strictly interconnected for successful device manufacturing. Recently, several authors adopted direct optical patterning (DOP) as a step forward in photolithography to position the scQDs in a selected area. However, the chemistry behind the stability, dispersion, and patterning has to be carefully integrated to obtain a functional commercial device. This review describes different chemical strategies suitable to stabilize the scQDs both at a single level and as an ensemble. Special attention is paid to those strategies compatible with direct optical patterning (DOP). With the same purpose, the scQDs’ dispersion in a matrix was described in terms of the scQD surface ligands’ interactions with the matrix itself. The chemical processes behind the DOP are illustrated and discussed for five different approaches, all together considering stability, dispersion, and the patterning itself of the scQDs
Film ordinati lipidi-proteine ottenuti per funzionalizzazione chimica e procedimento per la loro preparazione
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Verifiche combinate delle prestazioni dei Servizi NRTK tra Veneto e Friuli: Metodologia e risultati
No full textNRTK technology, in its different solutions, is today’s most advanced application of the topographical satellite positioning. Compared to the traditional solution of post-processing, it aims to offer the users accuracy independent from the base-rover distance, minimum occupation time at the point of observation, and immediate availability of the measurement result. Thanks to these merits, the NRTK services are rapidly spreading within the networks of permanent stations: between Veneto and Friuli, for example, a user can now choose between five distinct networks, capable of delivering a total of over 30 independent services.
This has suggested a series of tests carried out on the different network services available in the indicated area, designed primarily to ensure their reliability, both in terms of accessibility and availability of service, accuracy and repeatability.
The evaluation of these aspects is essential for the acceptance and for the establishment of a certification procedure of the NRTK measures, which hasn’t been universally recognized by the scientific and technical literature yet.
The tests described in this work consist of repeated determinations of the position of a vertex located at the intersection of the networks of Veneto and Friuli, by use of all the network services available, and was based on the making of 436 observations, divided into 25 sessions between January and April 2010.
The results are in agreement with the planimetric accuracies reported in literature, highlighting significant dispersion of the elevation component, however some critical issues in the reliability and availability of certain network services have been discovered, with possible repercussions on their use
Water Soluble CdTe Quantum Dots and their Laser Reverse Patterning in Polyvinyl Alcohol Films
No full textThe CdTe quantum dots of different size are obtained in water and are dispersed within a polyvinyl alcohol polymer. The nanocomposite is then irradiated with different UV laser to test the reverse laser patterning conditions
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