R. Vlastou

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.

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.

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.

Characterization of magnetron sputtering deposited thin films of TiN for use as a metal electrode on TiN/SiO2/Si metal–oxide–semiconductor devices

Titanium nitride (TiN) thin films were deposited by dc magnetron sputtering on SiO2/n-Si substrates in order to study their use as gate electrodes in metal–oxide–semiconductor (MOS) devices. Rutherford backscattering spectroscopy was used to determine the composition of the films and the results were correlated to those obtained by electrical measurements of the constructed MOS devices. Oxygen contamination of the TiN layers was observed, with percentage and spatial variations depending on the various deposition parameters such as the deposition temperature and the substrate bias. The best electrical performance was achieved for devices where the exposed TiN surface had low oxygen contamination. From these samples, the TiNx–Si barrier height was calculated to be equal to 0.52 eV.

Heavy-ion induced damage of crystalline Ge and W in the 0.5–8 A MeV range

Abstract High energy heavy-ion induced damage of Ge and W crystals was studied by blocking and channeling. Beams of ions from C to Au with energies from 12 to 266 MeV were used both for damaging the crystal and for “in-situ” measurement of lattice disordering. The blocking minimum yield and angular half-width have been measured as a function of dose, and it is shown that the relative ion damaging efficiency for Ge decreases at high electronic energy-loss values. The mechanism of microannealing along the ion path is discussed. The saturation and dose-rate dependence of damage are explained in terms of defect mobility and recombination processes. For a W crystal the initial damaging power is proportional to the number of displacements predicted by TRIM and a disorder saturation is observed at high doses.

High-spin properties of 173Re

Abstract The high-spin structure of 173 Re has been investigated by in-beam γ-ray spectroscopy. Strongly coupled bands based on the 5 2 + [402] and 9 2 − [514] Nilsson proton states and decoupled bands based on the h 11 2 and i 13 2 intruder proton orbitals have been established. The alignment of an i 13 2 neutron pair has been identified at h ω c = 0.25–0.29 MeV . The detailed behaviour of the neutron crossing shows a marked dependence on the proton configuration. Ratios of the reduced transition rates B (M1)/ B (E2) have been extracted for the ΔI = 1 bands and have been used to confirm the neutron origin of the alignment. The results are interpreted within the total routhian surface (TRS) approach.