Radiation Induced Point and Cluster-Related Defects with Strong Impact to Damage Properties of Silicon Detectors

This work focuses on the investigation of radiation induced defects responsible for the degradation of silicon detectors. Comparative studies of the defects induced by irradiation with 60Co- rays, 6 and 15 MeV electrons, 23 GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of point defects and cluster related centers having a strong impact on damage properties of Si diodes. The detailed relation between the microscopic reasons as based on defect analysis and their macroscopic consequences for detector performance are presented. In particular, it is shown that the changes in the Si device properties after exposure to high levels of 60Co- doses can be completely understood by the formation of two point defects, both depending strongly on the Oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease resp. increase the originally observed damage effects as seen by the changes of the depletion voltage. A group of three cluster related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the Oxygen content or Si growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions.Comment: 14 pages, 15 figure

Quinolone Compounds with Activity Against Multidrug- Resistant Gram-Positive Microorganisms

The emergence of resistance to antimicrobial agents is a global public health problem. Some microorganisms may develop resistance to a single antimicrobial agent (or related class of agent), while others develop resistance to several antimicrobial agents or classes. These organisms are often referred to as multidrug-resistant or MDR strains. Identification of new molecules that show activity against multidrug-resistant microorganisms and its development on a new antimicrobial drug, would be an important step in the fight against antimicrobial resistance. This paper presents experimental data regarding the synthesis of several quinolones. The novel compounds having quinolone structure were synthesized by Gould-Jacobs method. Their structure has been determined and confirmed by the following physicochemical methods: elemental analysis, IR spectral analysis, H-NMR, C-NMR, UV, thin layer chromatography. The new compounds have been evaluated for „in vitro” activity by determining minimum inhibitory concentration against a variety of bacteria Some of new quinolones, which showed a good activity, have been tested against 30 strains of methicillin resistant Staphylococcus aureus isolated in the Microbiology Laboratory of INBI Prof. “Dr. Matei Bals” during 2012 The minimum inhibitory concentration (MIC) of the isolates have been determined by agar plate Mueller Hinton (bioMerieux) dilution method using the reference strain Staphylococcus aureus ATCC 29213. The 30 strains of isolated have been also tested for susceptibility to ciprofloxacin, levofloxacin and imipenem by Etest method. Base on the “in vitro” studies, the quinolone FPQ-30 appears to be an promising compound, all strains isolates were inhibited at a concentration of 8 μg/ml

Field-effect-assisted photoconductivity in PbS films deposited on silicon dioxide

Cataloged from PDF version of article.Lead sulfide (PbS) thin films were deposited from a chemical bath onto SiO2/Si (n-type) substrates. Pseudo-metal-oxide-semiconductor devices were obtained by evaporating source and drain gold electrodes on a PbS surface and aluminum gate electrode on a Si substrate. Field-effect-assisted photoconductivity in the PbS layer was investigated at room temperature, in the 800-2700-nm-wavelength domain for different values and polarities of the drain and gate voltages. The best results were obtained for a positive gate, when both semiconductors are in depletion. An enhancement of about 25% of the photoconductive signal is obtained compared with the case when the gate electrode is absent or is not used. A simple model is proposed that explains the behavior of the dark current and photoconductive signal in PbS film with changing the gate voltage. (C) 2002 American Institute of Physics

Molecular Descriptors and Properties of Organic Molecules

The main goal of this chapter is to reveal the importance of molecular structure analysis with specific computational tools using quantum chemistry methods based on density functional theory (DFT) with focus on pharmaceutical compounds. A wide series of molecular properties and descriptors related with chemical reactivity is discussed and compared for small organic molecules (e.g., quinolones, oxazolidinones). Structural and physicochemical information, important for quantitative structure-property relationships (QSPR) and quantitative structure-activity relationships (QSAR) modeling analysis, obtained using Spartan 14 software Wavefunction, are reported. Thus, by a computational procedure including energy minimization and predictive calculations, values of quantum chemical parameters and molecular properties related with electronic charge distribution are reported and discussed. Frontier molecular orbitals energy diagram and their bandgap provide indications about chemical reactivity and kinetic stability of the molecules. Derived parameters (ionization potential (I), electron affinity (A), electronegativity (χ), global hardness (η), softness (σ), chemical potential (μ) and global electrophilicity index (ω)) are given. Also, graphic quantities are reported: electrostatic potential maps, local ionization potential maps and LUMO maps, as visual representation of the chemically active sites and comparative reactivity of different constitutive atoms

Investigation of X-ray induced radiation damage at the Si-SiO2 interface of silicon sensors for the European XFEL

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations and produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100 MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60 and 80 degree C on MOS capacitors and gate-controlled diodes irradiated to 5 MGy and the annealing kinetics of oxide charges and surface current determined.Comment: 10 pages, 6 figures, 3 table

Docking Studies on Novel Analogues of 8-Chloro-Quinolones against Staphylococcus aureus

Molecular docking studies have been carried out for a better understanding of the drug-receptor interactions. All the synthesized compounds have been subjected to molecular docking against targets that have been chosen based on the specific mechanism of action of the quinolones used in the antibacterial activity screening. A study of the characteristics and molecular properties of the small molecule known as ligand has been realized. In the first stage of the study, the 2D and 3D structures have been generated. The most stable conformer for each structure was obtained by geometry optimization and energy minimization. A series of topological, conformational characteristics and QSAR properties, important to assess the flexibility and the ability of the studied conformer to bind to the protein receptor, were determined and analyzed. These properties were discussed in order to assess the flexibility and the binding ability of studied conformers to bind to the receptor protein. The docking studies have been carried out. The score and hydrogen bonds formed with the amino acids from group interaction atoms are used to predict the binding modes, the binding affinities and the orientation of the docked quinolones in the active site of the protein receptor