Publications

A short description of approaches for carbon nanostructures synthesis is made and the advantages of using plasma during the growth are presented. As a particular example of a plasma based technique we detail the process of downstream carbon nanowall (CNW) synthesis by a radiofrequency expanding plasma beam. The technique combines magnetron sputtering for catalyst deposition and plasma enhanced chemical vapor deposition (main gas: argon, active gas: hydrogen, precursor gas: acetylene) for carbon growth in a single reactor. The analysis focuses on the correlation between the material properties and the plasma characteristics measured at different points along the flow axis, aiming to reveal the importance of plasma species in the growth process. The material properties were investigated by scanning and transmission electron microscopy, whereas the plasma data were obtained by optical emission spectroscopy, Langmuir probes and mass spectrometry. CNWs with a large area and well isolated from each other are obtained at an optimum distance from the precursor injection point where the plasma presents an enhanced content of carbon nanoclusters. The possible processes responsible for the growth are discussed.

Functionalized implants represent an advanced approaching in implantology, aiming to improve the biointegration and the long-term success of surgical procedures. We report on the synthesis of hydroxyapatite (HA) thin films on polymethylmetacrylate (PMMA) substrates - used as cranio-spinal implant-type structures - by two alternative methods: pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (MS). The deposition parameters were optimized in order to avoid the substrate overheating. Stoichiometric HA structures were obtained by PLD with incident laser fluences of 1.4-2.75 J/cm(2), pressures of 30-46.66 Pa and 10 Hz pulses repetition rate. The MS depositions were performed at constant pressure of 0.3 Pa in inert and reactive atmospheres. SEM-EDS, XRD, FTIR and pull-out measurements were performed assessing the apatitic-type structure of the prepared films along with their satisfactory mechanical adhesion. Cell viability, proliferation and adhesion tests in osteosarcoma SaOs2 cell cultures were performed to validate the bioactive behaviour of the structures and to select the most favourable deposition regimes. For PLD, this requires a low thence of 1.4 J/cm2, reduced pressure of water vapours and a 100 degrees C/4 h thermal treatment. For MS, the best results were obtained for 80% Ar + 20% O-2 reactive atmosphere at low RF power (similar to 75 W). Cells grown on these coatings exhibit behaviour similar to those grown on the standard borosilicate glass control: increased viability, good proliferation, and optimal cell adhesion. In vitro tests proved that HA/PMMA neurosurgical structures prepared by PLD and MS are compatible for the interaction with human bone cells. (C) 2010 Elsevier B.V. All rights reserved.

Implant type coatings were prepared by magnetron sputtering (MS) technique onto medical grade Ti6Al4V alloy substrates starting from biological 45S5 glass system powders. The as-deposited thin layers were annealed 2 h at 700 degrees C in ambient air, followed by a slow cooling (2 degrees C/min) in order to induce crystallization. The behavior of the coatings was investigated by soaking the samples in simulated body fluids (SBF) and extracting them after 24 and 72 h. The changes in the films' structure were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) analysis and by Fourier transform infrared spectroscopy (FTIR). A pitched, pore free microstructure with 6 mu m agglomerates of submicron grains in a continuous matrix was revealed by the SEM images of the annealed samples. Complex silicates as Na(4)Ca(4)Si(6)O(18)-combeite and phosphates NaCaPO(4) as crystalline phases were identified in the XRD diffraction patterns. In-growths after 24 h show the enrichment in Si-O (s) non-bonding oxygen (NBO). The polymerization reaction in the surface layer appears for the sample immersed 72 h in SBF. No crystalline hydroxyapatite (HA) was evidenced for those samples. Subsequent dissolution processes of the surface layers were noticed from XRD patterns and SEM images. (c) 2010 Elsevier B.V. All rights reserved.

A diode end-pumped Nd:YAG microlaser passively Q-switched by Cr4+:YAG with performances controlled by a volume Bragg grating (VBG) output coupler has been developed. Compared with operation at room temperature, the Q-switched laser pulse energy was increased, by a factor of 2 or more, by elevating the Nd:YAG temperature and locking the wavelength of emission with the VBG. Furthermore, the emission wavelength was tuned over 0.7 nm bandwidth by changing the VBG temperature while maintaining laser pulses of millijoule-level energy and short (less than 4 ns) duration. (C) 2010 Optical Society of America

We use a generalized master equation (GME) to describe the nonequilibrium magnetotransport of interacting electrons through a broad finite quantum wire with an embedded ring structure. The finite quantum wire is weakly coupled to two broad leads acting as reservoirs of electrons. The mutual Coulomb interaction of the electrons is described using a configuration interaction method for the many-electron states of the central system. We report some nontrivial interaction effects both at the level of time-dependent filling of states and on the time-dependent transport. We find that the Coulomb interaction in this nontrivial geometry can enhance the correlation of electronic states in the system and facilitate it's charging in certain circumstances in the weak coupling limit appropriate for the GME. In addition, we find oscillations in the current in the leads due to the correlations oscillations caused by the switched-on lead-system coupling. The oscillations are influenced and can be enhanced by the external magnetic field and the Coulomb interaction.

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for biosensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (lambda = 248 nm, tau(FWHM) congruent to 30 ns, nu = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm(2). Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition. (C) 2010 Elsevier B.V. All rights reserved.

A theoretical description for a single quantum-dot emitter in a microcavity is developed. We analyze for increasing steady-state pump rate the transition from the strong-coupling regime with photon antibunching to the weak-coupling regime with coherent emission. It is demonstrated how Coulomb interaction of excited carriers and excitation-induced dephasing can strongly modify the emission properties. Our theoretical investigations are based on a direct solution of the Liouville-von Neumann equation for the coupled carrier-photon system. We include multiple carrier excitations in the quantum dot, their Coulomb interaction, as well as excitation-induced dephasing and screening. Similarities and differences to atomic systems are discussed and results in the regime of recent experiments are interpreted. (C) 2010 Optical Society of America

Zinc oxide (ZnO) is a semiconductor with a wurtzite-type structure, useful for a variety of optical, optoelectronic and piezoelectric applications. We report here on the post deposition treatment (Rapid Thermal Annealing at 400 and 550 degrees C) impact on the microstructural properties of N-doped ZnO (ZnO:N) thin films grown on silicon substrate by r.f. magnetron sputtering of ZnN target. The ZnO:N films have been characterized by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning (SEM) and Transmission (TEM) Electron Microscopy coupled with Energy Dispersive X-ray (EDX) and Selected Area Electron Diffraction (SAED) respectively and Fourier Transform Infrared (FTIR) Spectroscopy. XRD confirms that ZnO:N films are polycrystalline in the as deposited state. SEM, TEM and XRD measurements revealed a polycrystalline film with preferentially oriented columnar crystals. AFM studies reveal a drastic change of ZnO surface morphology upon RTA and the existence of areas with different roughness in the sample thermally treated at 400 degrees C. FTIR, XRD and TEM results shows that disorder associated mainly with grain boundary defects decreases as the annealing temperature increases.

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 A degrees C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 A degrees C for 3 h is proposed for synthesis of dense Ba(Ti0.87Sn0.13)O-3 ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300-500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti0.87Sn0.13)O-3 ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of similar to 2 mu m. The apparent densities of the sintered pellets at temperature of 1400 A degrees C were similar to 92% of the theoretical value of Ba(Ti0.87Sn0.13)O-3. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan delta) = 0.078 at Curie temperature of 63 A degrees C and 10 Hz.