Because of their lower toxicity, indium phosphide (InP) quantum dots (QDs) are replacing cadmium selenide QDs in applications that require narrowband luminescence across the visible spectrum. ...However, InP QDs generally suffer from lower size tunability and broader ensemble emission linewidths because of imperfect synthetic control of nucleation and growth. Despite evidence that InP QDs do not follow the mechanisms that hot-injection and heat-up syntheses were designed to facilitate, these methods are still used, at least as the first step, in most syntheses of InP QDs. In this article, we describe a new method to synthesize large InP QDs with low size dispersity that does not require a hot-injection or heat-up step. Instead, nucleation, growth, and size focusing all take place continuously during a slow syringe-pump-mediated continuous injection of precursors into the reaction mixture. In refining our method, we monitored the photoluminescence (PL) and absorption spectra to find indirect evidence for the role of persistent intermediates in the formation of a secondary population of smaller QDs. We then developed a growth model that is consistent with our observations, and we used it to improve our method with a variable-rate injection that controls the concentration of intermediates to extend growth and prevent secondary nucleation. The result was InP QDs with an absorption peak at 631 nm with a half width at half-maximum of 81 meV. Growth of a thin zinc selenide shell on these InP QDs revealed a PL peak centered at 655 nm with a full width at half-maximum of 53 nm. These values are indicative of large QDs with low size dispersity. This work demonstrates a new method to synthesize large InP QDs that may be attractive to large-scale industrial processes because of its simplicity and potential scalability.
The formation of sub-surface defects during friction stir welding has limited the adoption of the process in high volume production. A potential exists to eliminate/reduce the need for costly post ...weld inspection of such defects through the development of an in-process defect detection method based on a measured process output. The current state of in-process defect detection consists primarily of applying “black box” methods of correlating process outputs to defect occurrence without a fundamental physical understanding of what is producing the change in the output. This approach constrains the application of such methods when altering any aspect of the friction stir welding process. The current study seeks to provide a fundamental physical explanation as to what is driving the oscillation of friction stir welding process forces at the tool rotational frequency, as well as what is occurring when the tool interacts with defects and the oscillatory process forces are altered. A novel understanding was enabled through the synchronization of force measurements with angular position measurements of tool features. The results suggest that the eccentric motion of the tool and/or the rotation of a slanted shoulder surface are the primary drivers of process force oscillations. A fundamental explanation of the interaction between features on the tool probe and defective volumes has been proposed. The physical understanding helps to explain how altering the process will alter the force transients on which the detection method is based, which will enable a more robust and transferable method.
Clusters have been identified as important growth intermediates during group III–V quantum dot (QD) formation. Here we report a one-solvent protocol that integrates synthesis, purification, and mass ...characterization of indium phosphide (InP) QD growth mixtures. The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) successfully tracks the evolution of clusters and the formation of QDs throughout the synthesis. Similar clusters are observed during the formation of large particles, suggesting that these clusters serve as a reservoir for QD formation. Combining MALDI and NMR techniques further enables us to extract extinction coefficients and construct sizing curves for cluster-free InP QDs. The use of MALDI MS opens new opportunities for characterization and mechanistic studies of small-sized air-sensitive clusters or QDs.
Next-generation optoelectronic applications centered in the near-infrared (NIR) and short-wave infrared (SWIR) wavelength regimes require high-quality materials. Among these materials, colloidal InAs ...quantum dots (QDs) stand out as an infrared-active candidate material for biological imaging, lighting, and sensing applications. Despite significant development of their optical properties, the synthesis of InAs QDs still routinely relies on hazardous, commercially unavailable precursors. Herein, we describe a straightforward single hot injection procedure revolving around In(I)Cl as the key precursor. Acting as a simultaneous reducing agent and In source, In(I)Cl smoothly reacts with a tris(amino)arsenic precursor to yield colloidal InAs quantitatively and at gram scale. Tuning the reaction temperature produces InAs cores with a first excitonic absorption feature in the range of 700–1400 nm. A dynamic disproportionation equilibrium between In(I), In metal, and In(III) opens up additional flexibility in precursor selection. CdSe shell growth on the produced cores enhances their optical properties, furnishing particles with center emission wavelengths between 1000 and 1500 nm and narrow photoluminescence full-width at half-maximum (FWHM) of about 120 meV throughout. The simplicity, scalability, and tunability of the disclosed precursor platform are anticipated to inspire further research on In-based colloidal QDs.
New developments in the program package ATSAS (version 2.4) for the processing and analysis of isotropic small‐angle X‐ray and neutron scattering data are described. They include (i) multiplatform ...data manipulation and display tools, (ii) programs for automated data processing and calculation of overall parameters, (iii) improved usage of high‐ and low‐resolution models from other structural methods, (iv) new algorithms to build three‐dimensional models from weakly interacting oligomeric systems and complexes, and (v) enhanced tools to analyse data from mixtures and flexible systems. The new ATSAS release includes installers for current major platforms (Windows, Linux and Mac OSX) and provides improved indexed user documentation. The web‐related developments, including a user discussion forum and a widened online access to run ATSAS programs, are also presented.
Control of quantum dot (QD) precursor chemistry has been expected to help improve the size control and uniformity of III–V QDs such as indium phosphide and indium arsenide. Indeed, experimental ...results for other QD systems are consistent with the theoretical prediction that the rate of precursor conversion is an important factor controlling QD size and size distribution. We synthesized and characterized the reactivity of a variety of group‐V precursors in order to determine if precursor chemistry could be used to improve the quality of III–V QDs. Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution. This result disproves the widely accepted explanation for the shortcoming of current III–V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth.
It’s different: Experimental results for II–VI and IV–VI quantum dots (QDs) imply that the rate of precursor conversion during QD synthesis plays a key role for controlling QD size and size distribution. While these results agree with predictions from kinetic growth models, the current study shows that precursor chemistry and conversion rates have a much weaker influence on the growth of III–V QDs.
The economic transformation in the Czech Republic in the 1990s triggered a dramatic increase in economic disparities. In the 2000s a new spatial economic pattern established itself and the increased ...mobility of people into better jobs reinforced the preceding inequality in growth. This article reveals spatial changes based on an analysis of quantitative and qualitative data from the national censuses in 2001 and 2011. The correlations of data with particular types of regions and micro-regions are also presented, and several typical groups of micro-regions are identifi ed on the basis of analyses of changes in the population, education levels, demographic age, economic activity, and housing stock. The booming suburbia of Prague and Brno and their large hinterlands contrast with the decline of remote rural areas and regions with outdated industries such as mining, heavy industry and energy. The spatial economic disparities of the 1990s turned into spatial social polarisation, which will in turn lead to the further polarisation of regions in a future economy be based on knowledge and information. This increasing polarisation lends confirmation to theories that regional divergence is the prevailing trend in current and also future spatial change, the effects of which are contrary to the EU’s objectives of territorial cohesion.
Homodimerization is an essential step for membrane type 1 matrix metalloproteinase (MT1-MMP) to activate proMMP-2 and to degrade collagen on the cell surface. To uncover the molecular basis of the ...hemopexin (Hpx) domain-driven dimerization of MT1-MMP, a crystal structure of the Hpx domain was solved at 1.7 Å resolution. Two interactions were identified as potential biological dimer interfaces in the crystal structure, and mutagenesis studies revealed that the biological dimer possesses a symmetrical interaction where blades II and III of molecule A interact with blades III and II of molecule B. The mutations of amino acids involved in the interaction weakened the dimer interaction of Hpx domains in solution, and incorporation of these mutations into the full-length enzyme significantly inhibited dimer-dependent functions on the cell surface, including proMMP-2 activation, collagen degradation, and invasion into the three-dimensional collagen matrix, whereas dimer-independent functions, including gelatin film degradation and two-dimensional cell migration, were not affected. These results shed light on the structural basis of MT1-MMP dimerization that is crucial to promote cellular invasion.
Este trabalho discute a questão do acesso à geoinformação e a sua importância para a Administração Pública. Dados e informações associados ao espaço geográï¬co são insumos importantes para as ...políticas públicas, uma vez que podem se tornar sinalizadores de uma situação problemática ou identiï¬cadores de uma oportunidade de atuação em um determinado espaço territorial. Estes problemas ou oportunidades poderão, então, ser objeto de uma intervenção mais precisa, ágil e eï¬ciente do poder público. No entanto, historicamente, a Administração Pública tem enfrentado diï¬culdades na gestão da geoinformação que produz e que adquire, o que tem restringido a sua utilização de forma plena por todos os seus órgãos. Nesse sentido, é feita uma análise dos avanços recentes relacionados à ampliação do uso, do compartilhamento e da disseminação da geoinformação no Brasil. Para isso, são detalhadas três importantes iniciativas: a implantação da Infraestrutura Nacional de Dados Espaciais (INDE), a elaboração da Política Nacional de Geoinformação (PNGeo) e as iniciativas de aquisição conjunta de geoinformação. Nessa análise, são abordados os seus principais aspectos, identiï¬cando os desaï¬os enfrentados e apontando caminhos para superá-los.
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imaging, the short-wavelength infrared region (SWIR; 1000-2000 nm) provides several advantages over the visible and near-infrared regions: general lack of autofluorescence, low light absorption ...by blood and tissue, and reduced scattering. However, the lack of versatile and functional SWIR emitters has prevented the general adoption of SWIR imaging by the biomedical research community. Here, we introduce a class of high-quality SWIR-emissive indium-arsenide-based quantum dots (QDs) that are readily modifiable for various functional imaging applications, and that exhibit narrow and size-tunable emission and a dramatically higher emission quantum yield than previously described SWIR probes. To demonstrate the unprecedented combination of deep penetration, high spatial resolution, multicolor imaging and fast-acquisition-speed afforded by the SWIR QDs, we quantified, in mice, the metabolic turnover rates of lipoproteins in several organs simultaneously and in real time as well as heartbeat and breathing rates in awake and unrestrained animals, and generated detailed three-dimensional quantitative flow maps of the mouse brain vasculature.
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