2,000 research outputs found
Radiation detection properties of 4H-SiC Schottky diodes irradiated up to 10(16) n/cm(2) by 1 MeV neutrons
No full textWe report the results of an experimental study on the radiation hardness of 4H-SiC diodes used as alpha-particle detectors with 1 MeV neutrons up to a fluence of 8 x 10(15) n/cm(2). As the irradiation level approaches the range 10(15) n/cm(2), the material behaves as intrinsic due to a very high compensation effect and the diodes are still able to detect with a reasonable good Charge Collection Efficiency (CCE = 80%).For fluences > 10(15) n/cm(2) CCE decreases monotonically to approximate to 20 % at the highest fluence. Heavily irradiated SiC diodes have been studied, by means of Photo Induced Current Transien
Deep Levels in 4H Silicon Carbide Epilayers Induced by Neutron-Irradiation up to 1016 n/cm2
No full textNeutron irradiation effects on standard and oxygenated silicon diodes
No full textSilicon diodes processed on standard and oxygenated silicon substrates by two different manufacturers have been irradiated by neutrons in a nuclear reactor and by the 9Be(d,n)10B nuclear reaction. The leakage current density (JD) increase is linear with the neutron fluence. JD and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. On the contrary, standard devices from one manufacturer present the lowest acceptor introduction rate (β) for the effective substrate doping concentration (Neff), showing that the β dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the Neff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons
Thermodynamic and MD studies of anion complexation by cyclopentaleucine in acetonitrile and dimethyl sulfoxide
No full textComplexation affinity of cyclic pentaleucine for halogen anions, thiocyanate and oxoanions was studied in acetonitrile and dimethyl sulfoxide. Equilibrium constants and derived Gibbs energies, as well as enthalpies and entropies of the corresponding reactions were determined by means of microcalorimetric and H-1 NMR titrations. To get more detailed insight into the binding of anions by the cyclopeptide, classical molecular dynamics simulations were carried out. The preorganization of cyclopentaleucine binding site by inclusion of solvent molecules was observed in acetonitrile by these simulations. The investigated receptor showed larger affinity for all anions in acetonitrile than in dimethyl sulfoxide. The results of H-1 NMR studies and those of molecular dynamics simulations indicated that the bound anions were coordinated by the amide groups of cyclopeptide. The stoichiometry of most of the complexes was 1:1 (receptor:anion), with the exception of dihydrogen phosphate and hydrogen sulfate complexes, where higher stoichiometries (1:2 and 2:1, respectively) were also observed. In the case of complexes with H2PO4- anion, in both acetonitrile and dimethyl sulfoxide the binding of dihydrogen phosphate dimer was observed, whereas the species in which two ligands coordinate one HSO4- ion was observed in acetonitrile. The obtained thermodynamic reaction parameters and the observed rather strong solvent effect on the studied equilibria were discussed regarding anions and receptor structural properties as well as solvation abilities of the solvents used
Chloride-Assisted Peptide Macrocyclization
No full textThe role of the Cl− anion as a templating agent for the synthesis of cyclopeptides was assessed through the preparation of three new homocyclolysines and other six cyclic peptides by head-to-tail lactamization. Isolated yields of products obtained by chloride-templating approach were considerably higher than those gained by a cation-promoted procedure, whereby, in some cases, only the anion-assisted synthesis yielded the desired cyclopeptides
Metal-ion-assisted synthesis of cyclic homopeptides
No full textIn the recent years cyclic peptides have attracted attention since they find applications in many fields from drug discovery to nanomaterials. These compounds have been difficult to prepare due to the fact that the activated peptide must adopt an entropically disfavoured conformation before forming the desired product[1]. The most important factor for successful peptide macrocyclization is ring size. Peptides that contain less than seven aminoacids are troublesome to cyclize[2]. In this work we will describe synthesis of small homocyclopeptides containig 4-6aminoacids.
Cyclic peptides are also known as versatile ion-binders[3] but their binding affinities are often reduced by the inadequate orientation of amide functional group. To overcome these problems, cyclopeptides will be conjugated to a molecules with rigid geometry, such as calixarenes. Homocyclolysine and homocycloserine will be bind, , to calixarenes exploiting functional groups via amide bond on peptide's side chain. Influence of lenght of side chains on affinities of this conjugates towards different anions will be investigated.
Linear precursors were sinthesized using standard solution phase peptide synthesis and HOBt, HBTU as a coupling reagents. A three-dimensional orthogonal protection scheme was required to built the linear peptides, to deprotect the N- and C-termini and to cyclize them in a head-to-tail fashion. To promote the cyclization,different alkali metal ions were used depending on a the size of the desired cyclic peptide. These ions coordinate amidic oxygen atoms along the chain forcing the linear peptide to form a strong turn structure and to bring the N- and C-termini closer, allowing helping in that way cyclization to occur
Experimental Determination of the Impact Ionization Coefficients in Irradiated Silicon
No full textWe present new results on the influence of radiationinduced
damage on the electron Impact Ionization (I.I.) coefficient
, suggesting a small but distinct reduction of at high fluence
with respect to unirradiated silicon. Experiments on thick (1.5 m)
and thin (1 m) epitaxial silicon samples confirm that such a reduction
of is expected even in cases where impact ionization is not
simply a field driven process because of strongly non local transport
conditions.
A consistent increase on the breakdown voltage of a 3D radiation
detector has been evaluated by means of TCAD simulations using
the experimentally extracted I.I. coefficient for irradiated silicon.
These results clarify the impact of radiation damage on some
of the key model parameters for TCAD simulations and allow for
improved accuracy toward predictive breakdown simulations of
silicon particle detectors, e.g., for the ATLAS experiment
Polycrystalline diamond detectors with three-dimensional electrodes
No full textThe three-dimensional concept in diamond detectors has been applied, so far, to high quality single-crystal material, in order to test this technology in the best available conditions. However, its application to polycrystalline chemical vapor deposited diamond could be desirable for two reasons: first, the short inter-electrode distance of three-dimensional detectors should improve the intrinsically lower collection efficiency of polycrystalline diamond, and second, at high levels of radiation damage the performances of the poly-crystal material are not expected to be much lower than those of the single crystal one. We report on the fabrication and test of three-dimensional polycrystalline diamond detectors with several inter-electrode distances, and we demonstrate that their collection efficiency is equal or higher than that obtained with conventional planar detectors fabricated with the same material
Characterization of bulk damage in CMOS MAPS with deep N-well collecting electrode
No full textMonolithic active pixel sensors in CMOS technology, featuring a deep N-well as the collecting electrode (so called DNW MAPS), have been exposed to neutrons from a nuclear reactor,
up to a total 1 MeV neutron equivalent fluence of about 3.7E13 cm^-2. The irradiation campaign was aimed at studying the effects of radiation induced displacement damage on the charge collection properties of the device, which was conceived for applications to charged particle tracking in high energy physics experiments. A number of different techniques, including electrical characterization of the front-end electronics and of DNW diodes, laser stimulation of the sensors and tests with Fe and Sr radioactive
sources, has been employed for evaluating the device operation before and after irradiation. This paper discusses the measurement results and their relation with the bulk damage mechanisms underlying performance degradation in DNW MAPS
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