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We calculate charge transition levels of various defects at the SiC/SiO2 interface within a scheme based on hybrid density functionals, which accurately reproduce the involved band gaps and band offsets. The defect levels are first evaluated in bulk models of the interface components and then aligned with respect to the interface band diagram through the use of a model interface showing good structural and electronic properties. Interface-specific polarization effects are evaluated separately through classical electrostatics. We considered carbon-related defects involving single atoms and dimers in both the crystalline SiC substrate and the amorphous SiO2 oxide. Our investigation also comprises oxygen- and hydrogen-related defects, including the Si-Si bond (O vacancy), the Si2-C-O structure, the peroxy linkage, and the hydrogen bridge (Si-H-Si). Among the defects studied, the Si2-C-O structure represents the best candidate for the high defect density measured near the conduction band of SiC. [ABSTRACT FROM AUTHOR]

We investigate carbon single-atom and pair defects at the SiC/SiO2 interface as candidate defects for the density of defect states in the SiC band gap. In order to accurately describe the electronic defect levels with respect to the SiC band edges, we use a hybrid density functional which reproduces the experimental band gap of SiC. The carbon pair defect consisting of two neighboring sp2 hybridized carbon atoms is modeled in various configurations within a SiC/SiO2 model interface showing good structural parameters and an oxide density typical of amorphous SiO2. The carbon pair defect is found to contribute to the density of defect states not only in the lower and/or mid band gap of SiC, but also in the upper band gap, in contrast with previous studies. The carbonpair defect is also investigated via molecular models to achieve insight into the energy range spanned by its defect levels when the relative orientation of its sp2 hybridization planes and the chemical nature of its neighbors are varied. Carbon single-atom defects on the oxide side of the interface are also modeled and found to contribute to the defect density in the band gap in a similar way as carbonpair defects. Comparison to the experimental defect density suggests that defects involving one or two carbon atoms cannot account for the high defect density observed in the vicinity of the SiC conduction band. [ABSTRACT FROM AUTHOR]

Abstract: Through the sequential use of classical molecular dynamics and first-principles relaxation methods, we generate an abrupt model interface for the 4H(0001)SiC-SiO2 interface showing regular structural parameters without any coordination defect. The bond density reduction at the interface is achieved through the use of two interfacial structural units which connect the disordered oxide to the abrupt crystalline substrate. The present model demonstrates that the sole topological constraints at SiC substrates do not preclude the occurrence of oxides of similar quality as compared to those found on Si substrates. [Copyright &y& Elsevier]

Background: 99mTc-mercaptoacetyl-triglycine (99mTc-MAG3) has been used for dynamic renal imaging since about 30 years. Free pertechnetate (99mTcO4), colloidal 99mTc ((99mTcO2)n), 99mTc-tartrate (precursor), precomplexes (99mTc-(MAG3)x) and lipophilic 99mTc-MAG2 are the main radiochemical impurities that may occur in the preparation. The total amount of these impurities has to be identified before release of the product for patient administration to guarantee patient safety and good image quality. The European Pharmacopoeia suggests a method based on high-pressure liquid chromatography analysis in combination with a paper chromatography. This analytical method is time consuming, expensive and requires specially trained technicians. As a consequence, it is not widely applied in nuclear medicine radiopharmacies.Results: We developed a simple method for radiochemical purity testing of 99mTc-MAG3. The method is based on thin layer chromatography with two strips to be developed in parallel. Method validation was carried out in comparison to the official methods of the companies and to the European Pharmacopoeia method. It was tested on specificity, accuracy, robustness and precision.Conclusion: The proposed method is able to identify and quantify the sum of all impurities occurring in the preparation, respecting the acceptance criteria for the radiochemical purity defined by the official methods. Hydrophilic and lipophilic compounds are identified separately and results are obtained within less than 20 minutes. Our method is simple, cost effective, fast and is suitable for employing dose calibrators or radiometric scanners. [ABSTRACT FROM AUTHOR]