Publications

Experimental demonstration of low power laser induced optical nonlinearities in two different types of specially designed materials: dye doped liquid crystals and copolymers with new pendant azobenzene moieties, is presented. Saturation of the nonlinear refractive index change is observed for some of the samples. The origin of the huge nonlinearity and its saturation in the continuous wave laser regime and at low power levels are analyzed.

Tl+-doped lithium fluoride crystals exhibit very interesting properties concerning the formation of colour centres after X-rays irradiation. The presence of Tl+ ions, even in small concentrations, increases the number of traps which stabilize the H-centre aggregates. These H-centre aggregates become smaller and their number increases, inducing two sets of trapping levels. Photoluminescence measurements after subsequent thermal bleaching of the thermoluminescence peaks show a faster decreasing of the F-3(+) centres, in three steps, compared with the F-2 ones. The F-H recombination processes may induce the excitation-emission transitions of Tl+-ions.

Sucrose is a natural osmolyte accumulated in cells of organisms as they adapt to environmental stress. In vitro sucrose increases protein stability and forces partially unfolded structures to refold. Thin films of sucrose (C12H22O11) were deposited on thin cut glass substrates by thermal evaporation technique (p similar to 10(-5) torr). Characteristics of thin films were putted into evidence by Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM) and differential thermal analysis and thermal gravimetric analysis (TG/DTA). The experimental results confirm a uniform deposition of an adherent layer.

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.

Nanoparticles of interest in nanotechnology (design of nanodevices) and medicine (controlled-release of drugs) can be produced both by anorganic and organic synthesis. The biogenetic production is now of high interest due to simplicity of the procedures and their versatility. Several species of bacteria and plants are able to synthesize nanoparticles or to help in the process of their production. The paper gives an overview on the biogenetic production of nanomaterials.

The ability of a sol-gel route for the synthesis of cobalt doped ZnO (Zn 1-xCoxO, x = 0.04-0.11) films grown on Si (100) and glass substrates is investigated. A homogeneous and stable Zn (1-x) CoxO sol was prepared by dissolving zinc nitrate hexahydrate and cobalt acetate tetrahydrate in a PVP (polyvinylpyrrolidone) solution, followed by annealing at 800 degrees C. Local structure studies of the Zn1-xCoxO thin films by XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) proved the co-existence of a few amount of small metal cobalt aggregates with Co in non-stoichiometric ConOm aggregates, with n > m, and m similar to 4. Low temperature magneto-optical Kerr effect (Faraday rotation) measurements of the magnetization versus field give a direct proof of a superparamagnetic behavior of the magnetic aggregates and allowed an estimate of the number of magnetically active atoms in Co aggregates, which is close to the number of Co excess atoms inferred from XANES and EXAFS considerations: n - m similar to 3 atoms per aggregate. To this main superparamagnetic phase, a weak ferromagnetic phase with coercitive field of similar to 50 Oe is superimposed, most probably due to metal cobalt nanoclusters.

The difficulty to stabilize a definite crystalline structure or phase, due to a large gradient of defects along the particle diameter, is unfortunately specific to particles of nanometer size. Therefore, atypical spin configurations and magnetic anisotropies as well as enhanced magnetic relaxations via thermal excitations are expected in systems of fine nano-particles. The actual work reports on various possibilities for a comprehensive characterization of the magnetic configuration and magnetic relaxation mechanisms of nano-particles, by corroborating the powerful method of Mossbauer spectroscopy with complementary magnetic and structural techniques. The capabilities of temperature and field dependent Mossbauer spectroscopy to provide valuable information about spin blocking temperatures, effective anisotropy constants, amount of uncompensated spins inside of particle and magnetic phase composition are critically discussed for both powder like systems and nano-particles dispersed in different solvents.

Tin chalcogenides SnX(2) and SnX, where X = S, Se and Te present a particularly interest for their electronic properties and applications in gas sensors. The state of tin in these materials is important for understanding of the sensing effect and improvement of the sensor performances. Mossbauer spectroscopy is a widely used technique for the analysis of the local electronic structure or chemical bonding in solids. In this paper we applied Mossbauer technique for the investigation of bulk and thin films of SnSe(2) chalcogenide. The films of SnSe2 chalcogenide were obtained by the methods: PLD ("Pulsed laser deposition") and PED ("Pulsed electron deposition"). Mossbauer measurements were performed by transmission (TMS), respectively conversion electron spectroscopy (CEMS). By CEMS spectroscopy surfaces, coatings and thin films containing Sn can be studied on substrates and to various depths up to 1000 nanometers.

Computer Material Science is a branch of material sciences that uses theoretical concepts and models from chemistry, physics, geology, mineralogy, as well as biology and includes them into software applications in order to calculate the structure and the properties of molecules, gases, liquids, soft and condensed matter. This paper presents the estimated performances of the HPC-ICF cluster of the Institute of Physical Chemistry "Ilie Murgulescu" of the Romanian Academy and the NCIT-UPB Cluster developed by the Computer Science Department of the University Politehnica of Bucharest, with the run in the parallel mode on these systems of the HPL - High Performance Linpack Benchmark as well as of the electronic structure codes GAMESS and ONETEP. The results of the study show that both clusters break the Teraflop barrier, thus making available a valuable tool for the Romanian scientific community in Computing Materials Science.