Die quantitative Bestimmung von Quecksilber in thierischen Geweben

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Origins of Photoluminescence Decay Kinetics in CdTe Colloidal Quantum Dots

Recent experimental studies have identified at least two nonradiative components in the fluorescence decay of solutions of CdTe colloidal quantum dots (CQDs). The lifetimes reported by different groups, however, differed by orders of magnitude, raising the question of whether different types of traps were at play in the different samples and experimental conditions and even whether different types of charge carriers were involved in the different trapping processes. Considering that the use of these nanomaterials in biology, optoelectronics, photonics, and photovoltaics is becoming widespread, such a gap in our understanding of carrier dynamics in these systems needs addressing. This is what we do here. Using the state-of-the-art atomistic semiempirical pseudopotential method, we calculate trapping times and nonradiative population decay curves for different CQD sizes considering up to 268 surface traps. We show that the seemingly discrepant experimental results are consistent with the trapping of the hole at unsaturated Te bonds on the dot surface in the presence of different dielectric environments. In particular, the observed increase in the trapping times following air exposure is attributed to the formation of an oxide shell on the dot surface, which increases the dielectric constant of the dot environment. Two types of traps are identified, depending on whether the unsaturated bond is single (type I) or part of a pair of dangling bonds on the same Te atom (type II). The energy landscape relative to transitions to these traps is found to be markedly different in the two cases. As a consequence, the trapping times associated with the different types of traps exhibit a strikingly contrasting sensitivity to variations in the dot environment. Based on these characteristics, we predict the presence of a sub-nanosecond component in all photoluminescence decay curves of CdTe CQDs in the size range considered here if both trap types are present. The absence of such a component is attributed to the suppression of type I traps

Reuse of terminological resources for efficient ontological engineering in Life Sciences

This paper is intended to explore how to use terminological resources for ontology engineering. Nowadays there are several biomedical ontologies describing overlapping domains, but there is not a clear correspondence between the concepts that are supposed to be equivalent or just similar. These resources are quite precious but their integration and further development are expensive. Terminologies may support the ontological development in several stages of the lifecycle of the ontology; e.g. ontology integration. In this paper we investigate the use of terminological resources during the ontology lifecycle. We claim that the proper creation and use of a shared thesaurus is a cornerstone for the successful application of the Semantic Web technology within life sciences. Moreover, we have applied our approach to a real scenario, the Health-e-Child (HeC) project, and we have evaluated the impact of filtering and re-organizing several resources. As a result, we have created a reference thesaurus for this project, named HeCTh

Laparotomie bei Extrauterinschwangerschaft, 21/2 Jahre nach dem Tode der ausgetragenen Frucht: mit vollständiger Entfernung des Fruchtsackes und glücklichem ausgange für die Mutter

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Charge transfer from CdTe quantum dots into a CdS thin layer

AbstractElectron injection from CdTe quantum dots (CdTe-QDs) into ultra-thin CdS layers has been demonstrated bytransient and spectral dependent surface photovoltage (SPV) methods while the thickness of the CdS layer was variedsystematically between several nm and tens on nm. Signal heights and decay times at half maximum were correlatedwith the thickness of the CdS layer. The decay times increased by several orders of magnitude for electronstransferred across the charge-selective CdS/CdTe-QD contact in comparison to electrons photo-generated in the CdSlayer

Role of ligand exchange at CdSe quantum dot layers for charge separation

Layers of CdSe quantum dots QDs with fixed diameter 4.5 nm and various ligands were deposited on ITO substrates and investigated by photoluminescence PL and surface photovoltage SPV techniques. The distance between QDs decreased after washing and ligand exchange. The PL signals in the first excitonic peak as well as in the defect range strongly decreased with successive ligand exchange. In contrast to multilayer deposition, no PL signal related to CdSe QDs has been observed for a monolayer of QDs with pyridine surfactants on ITO. Neither modulated nor transient SPV signals were found for pristine CdSe QD layers. The modulated SPV signals strongly increased with successive ligand exchange. SPV transients became longer with successive ligand exchange. The experiments gave evidence for strong generation of surface defect states with ongoing ligand exchange and for fast initial charge separation of electrons from the first monolayer of CdSe QDs to the ITO surface. SPV transients could be described within a single QD approximation model, in which the number of surface defect states per QD, the energy distributions of defect states, hopping and distant dependent recombination were considere

Formation of a heterojunction by electrophoretic deposition of CdTe CdSe nanoparticles from an exhaustible source

Fast and well controlled electrophoretic deposition of CdTe and CdSe nanoparticle CdTe np and CdSe np layers and nanoparticle layer systems from an exhaustible source has been demonstrated. Using a small volume of pyridine based nanoparticle suspensions with varying concentrations, these were completely drained of nanoparticles during deposition. Our proposed approach is well suited to a practical realization of engineering materials with different band gaps for various promising applications such as fabrication of nanodevices. The formation of a charge selective contact across the CdTe np CdSe np heterojunction was investigated by surface photovoltage methods and evidence of the separation of charge carriers at a CdTe CdSe np heterojunction in amp; 8208;between was demonstrate