National Institute Of Materials Physics - Romania

Calcium phosphate ceramic powders were synthesized via sol-gel method. The powders were sintered at 600 and 1000 degrees C and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM and TEM), elemental microanalysis (EDS), infrared spectroscopy (FTIR), and thermal analysis (TGA and DTA). The XRD analysis revealed a well crystallized hydroxyapatite (HAp) structure at all temperatures. At 1000 degrees C a small amount of CaO (about 1.2 %) was detected. The average crystallite size increased from 19 nm at 80 degrees C to about 125 nm at 1000 degrees C. FTIR spectra showed the presence of various PO43- and OH- groups present in the powders. In order to verify the biocompatibility of HAP powders with hFOB 1.19 osteoblasts cells, an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was applied. It was noticed that the ceramics obtained at 1000 degrees C, increased the cell viability with 10%, 40% and 55% after 6, 12 respectively 24 h, whereas that obtained at 600 degrees C was less effective. Our results proved the high biocompatibility of calcium phosphate ceramic powders obtained by sol-gel and sintered at 1000 degrees C.

Highly oriented (001) AlN (wurtzite type) thin films have been successfully deposited on silicon, platinized silicon and glass substrates by reactive radio-frequency magnetron sputtering at low temperature (150 degrees C). X-ray diffraction, spectroscopic ellipsometry and scanning electron microscopy techniques have been employed to asses the structural characteristics of the AlN films. We have investigated both the influence of AlN film's thickness and of the substrate nature on crystallinity. The thicker films present a better c axis alignment, a minimum orientation dispersion of 3.5. being reached for 1 mu m AlN on silicon. The micro-and macrostrain of the AlN lattice relaxes as the film thickness increases. The film deposited onto platinum has the maximum value of tensile strain along c axis. The film on glass exhibited the poorest texturing and the highest defect concentration. From an optical point of view the film deposited on Pt is the denser one and that deposited on glass is the most rarefied. One can conclude that when using a low deposition temperature and a base pressure of similar to 10(-4) Pa the increase of film thickness leads to improved AlN structure on Si or Pt supports.

GeSiO nanosystems were obtained using two different preparation methods, sol-gel and magnetron-sputtering. Transmission electron microscopy measurements were performed to investigate the films structure. Amorphous and crystalline Ge dots embedded in amorphous silicon dioxide were observed. The Ge concentration in the GeSiO films was by Energy-dispersive X-ray spectroscopy.

Hydrogenated amorphous carbon (a-C: H) films were grown by radio-frequency (1.78 MHz) plasma enhanced chemical vapour deposition technique onto medical grade Ti6Al4V substrates. By varying the deposition pressure (13.33 Pa and 53.33 Pa, respectively) and methane dilution (20% and 60%, respectively) several types of carbonic films were obtained, presenting different bonding structures, surface energies and morphological features reflected in their biological behaviour. FTIR, Raman, UV-Vis, XPS and AFM measurements were used for characterizing these structures. The surface energy was determined by contact angle measurements, and their thrombogenicity was tested by the activated partial thromboplastin time (aPTT) method. We have noticed that at the same values of methane in argon dilution but at different pressure values, the film structure was totally changed: soft polymer-like carbon (PLC) type at the higher pressure and hard diamond-like carbon (DLC) type at the lower pressure. Raman spectroscopy and XPS suggested that the highest sp(3) ratio (similar to 52%), was found for DLC films prepared in a 60% methane dilution in argon. It has been found that for both PLC and DLC structures the surface energy has a decreasing tendency with the methane concentration increase in the deposition atmosphere. Excellent aPTT results were obtained for the DLC-60 (18.6.+/- 0.3 min) and PLC-20 (17.4 +/- 0.5 min) structures, superior to those recorded for Ti6Al4V and PMMA commercial materials. These values recommend the prepared carbonic structures for medical applications: harder coatings (DLC) for metal prostheses (heart valves, acetabular cups etc.), while softer and flexible coatings (PLC) for the textile vessels or stents biofunctionalization.

This work focuses on the investigation of radiation-induced defects responsible for the degradation of silicon detector performance. Comparative studies of the defects induced by irradiation with Co-60-gamma rays, 6 and 15 MeV electrons, 23 GeV protons and 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 is presented. In particular, it is shown that the changes in the Si device properties (depletion voltage and leakage current) after exposure to high levels of Co-60-gamma doses can be completely understood by the microscopically investigated formation of two point defects, a deep acceptor and a shallow donor, both depending strongly on the oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease (increase) the originally observed damage effects as seen by the changes of the depletion voltage and these effects are known as "beneficial" and "reverse" annealing, respectively. 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 silicon growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions. (C) 2009 Elsevier B.V. All rights reserved.

The fabrication and characterisation of surface acoustic wave resonators operating in the gigahertz frequency range are presented. The devices were fabricated on thin AlN layers deposited by magnetron sputtering on high resistivity (100) oriented silicon substrates. Using direct writing e-beam lithography, well defined interdigital transducers with 300 nm finger width and spacing have been obtained. On-wafer microwave measurements have demonstrated a narrow bandstop frequency characteristic with high rejection at approximately 5 GHz and an electromechanical coupling coefficient of 0.53%.

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric-antiferroelectric multilayers that take into account the long range dipolar interactions were simulated by a Monte-Carlo method. Simulations were carried out for a 1 + 1 bilayer and a 5 + 5 superlattice. Phase stabilities of components comprising the structures with an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field, can drive the ferroelectric layers toward 180A degrees domains with very flat domain interfaces mainly due to the competition between this term and the dipole-dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature. In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity that could be expected in the presence of anti-parallel dipoles, i.e., the switching takes place abruptly. Some recent experimental observations in ferroelectric-antiferroelectric multilayers are discussed where we conclude that the different electrical properties of bilayers and superlattices are not only due to strain effects alone but also due to long-range interactions. The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces.

We investigated the vortex dynamics in the noncentrosymmetric superconductor Li2Pt3B in the temperature range 0.1-2.8 K. Two different logarithmic creep regimes in the decay of the remanent magnetization from the Bean critical state have been observed. In the first regime, the creep rate is extraordinarily small, indicating the existence of an unconventional very effective pinning mechanism. At a certain time, a vortex avalanche occurs that increases the logarithmic creep rate by a factor of about 5 to 10 depending on the temperature. This may indicate that certain barriers against flux motion are present and they can be opened under increased pressure exerted by the vortices.