M. Kokkoris

Study of Antibacterial Composite Cu/SiO2 Thin Coatings

In the present work, composite copper containing silicate thin coatings (Cu/SiO2) were prepared on glass substrates by the sol-gel route. The preparation process included hydrolysis and subsequent polycondensation of corresponding alkoxide under refluxing and addition of soluble salt of antibacterial metal to the resulting sol. The coatings deposited by dipping process, were thermally treated in oxidative and reductive conditions up to 500°C for metal nanoparticles formation. The coating structure and the nanoparticles formation were studied by the X-ray Diffraction (XRD), UV-VIS and Heavy Ion Rutherford Backscattering (HIRBS) Spectroscopies. The antibacterial activity against Escherichia Coli was examined by the so-called antibacterial-drop test. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity was considered and analyzed. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was decreased with the increase of temperature of thermal treatment and metal nanoparticles formation.

RBS and HIRBS studies of nanostructured AgSiO2 sol–gel thin coatings

In the present work, composite AgSiO2 thin coatings, containing metal nanoparticles, were prepared on glass substrates by the sol–gel route. The coatings were thermally treated in oxidative and reductive conditions up to 500 C for metal nanoparticle formation. The coating structure and the nanoparticle formation were studied by atomic force microscopy and Rutherford backscattering spectroscopy (RBS) techniques. In the case of RBS, 1.4 MeV 4 He þ ions were used for all samples, and low energy 16 O and 12 C ions in selected ones (heavy ion RBS, HIRBS), in order to improve the depth resolution for the profiling of the metal component. The antibacterial activity against Escherichia coli is examined by antibacterial drop test. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was reduced with the increase of the particle size of the metal nanoparticles. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity is examined and analyzed. Although further studies are required, RBS and HIRBS seem to be excellent tools for the quality control in the production of sol–gel thin coatings. 2002 Elsevier Science B.V. All rights reserved.

Void formation in Ge induced by high energy heavy ion irradiation

Abstract Ge wafer irradiated at room temperature with high energetic heavy ions ranging from 165 MeV Ni to 266 MeV Au show a swelling of the bombarded region. The corresponding volume expansion reaches values up to 30% of the irradiated volume. In cross section SEM as well as cross section TEM measurements it is found that the volume expansion is due to a buried porous layer with a sponge-like structure. The dose dependence of the swelling of the germanium samples and the void formation in amorphous Ge will be discussed.

Dielectric properties of CVD grown SiON thin films on Si for MOS microelectronic devices

The bulk properties of SiON films grown on n-Si substrates by CVD are examined by means of electrical measurements and Rutherford backscattering spectroscopy (RBS). The main aim of this project was to investigate the performance of the films in order to test their suitability for the construction of CMOS devices with SiON being the gate insulator. The CVD technique was used to produce the films and subsequent metallization leads to the creation of MOS devices. Rutherford backscattering spectroscopy (RBS) was used to verify the film bulk properties. Electrical measurements including current–voltage, capacitance–conductance–voltage (C–G–V) measurements and admittance spectroscopy were performed allowing determination of the bulk trapped charges and the dielectric constant of the films. These charges were calculated to have values between 0.76 nCb and 2.54 nCb, while the dielectric constant of the films was found to be quite high, with values greater than 5 and as high as 34. The RBS concluded that the films were uniform, and the nitrogen concentration was not higher than 10%.

Determination of marine gamma activity and study of the minimum detectable activity (MDA) in 4pi geometry based on Monte Carlo simulation.

Monte Carlo simulations were performed using the GEANT4 code for the investigation of γ-ray absorption in water in different spherical geometries and of the efficiency of a NaI(Tl) detector for different radionuclides in the aquatic environment. In order to test the reliability of these simulations, experimental values of the NaI(Tl) detector efficiency were deduced and seem to be in good agreement with the simulated ones. In addition, using the simulated efficiency, an algorithm was developed to determine the minimum detectable activity in becquerels per cubic meter in situ as a function of energy for typical freshwater and seawater spectra.

The elastic scattering of 6Li+28Si at near-barrier energies

The 6 Li + 28 Si elastic scattering was studied at near-barrier energies with the aim to probe the threshold anomaly. Angular distributions were measured over a wide angular range (θlab = 25 ◦ to 150 ◦ ) at 4 energies, namely, 7.5, 9, 11 and 13 MeV. The present data together with previous ones at higher energies, as well as elastic scattering data of 6 Li on various targets at near barrier energies, were analyzed by using optical potentials obtained in a double-folding framework. It was found that the strength of the real part of the potential remains almost independent of energy down to, and possible even below, barrier, while the strength of the imaginary part presents an increase at near barrier energies. The results are discussed.  2003 Elsevier Science B.V. All rights reserved.

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from   kT=5-100  keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

Proton induced reaction cross section measurements on Se isotopes for the astrophysical p process

As a continuation of a systematic study of reactions relevant to the astrophysical p process, the cross sections of the Se-74,Se-76(p,gamma) Br-75,Br-77 and Se-82(p,n) Br-82 reactions have been measured at energies from 1.3 to 3.6 MeV using an activation technique. The results are compared to the predictions of Hauser-Feshbach statistical model calculations using the NON-SMOKER andMOST codes. The sensitivity of the calculations to variations in the optical proton potential and the nuclear level density was studied. Good agreement between theoretical and experimental reaction rates was found for the reactions Se-74(p,gamma) Br-75 and Se-82(p,n) Br-82 .

Radioactivity measurements in the aquatic environment using in-situ and laboratory gamma-ray spectrometry

The in-situ underwater gamma-ray spectrometry method is validated by inter-comparison with laboratory method. Deployments of the spectrometer KATERINA on a submarine spring and laboratory measurements of water samples with HPGe detector were performed. Efficiency calibrations, Monte Carlo simulations and the Minimum Detectable Activity (MDA) estimations were realized. MDAs varied from 0.19 to 10.4 (lab) and 0.05 to 0.35 (in-situ) Bq/L, while activity concentrations differed from 7% (for radon progenies) up to 10% (for (40)K), between the two methods.

Neutron cross-section measurements in the Th–U cycle by the activation method

The 232 Th(n,2n) 231 Th reaction cross-section was measured relative to the 56 Fe(n,p) 56 Mn and 27 Al(n,a) 24 Na reaction cross-sections with the activation method for neutron energies up to 11 MeV. Neutrons were produced by the 2 H(d,n) reaction in the 5.5 MV Tandem accelerator of the NCSR ‘‘Demokritos’’. The characteristic g lines of the product nuclei 231 Th (25.646 keV) and 56 Mn (846.771 keV) or 24 Na (1368 keV) were measured with an 80 mm 2 Si(Li) and a 20% reverseelectrode coaxial germanium detector, respectively. The results indicate that our values are in agreement with the JEF2 and BROND2 database values up to 9 MeV and slightly higher than those from all the libraries for higher energies. r 2003 Elsevier Science B.V. All rights reserved.