National Institute Of Materials Physics - Romania

In this paper we investigate the properties of two-dimensional photonic crystals (2D PhCs) with both hexagonal and square symmetry for applications in optoelectronics and telecommunication. An efficient way of manipulating the light is to make use of the defects introduced within the periodic structure, which consequently break the symmetry of the crystal, resulting in linear waveguides or resonant cavities. We calculate using finite-difference time-domain and finite-difference frequency-domain methods the properties associated with several kinds of defects, conveniently selected, performed in 2D PhCs with square and hexagonal symmetry.

Electrophoretic deposition (EPD) method is employed to obtain a thick ZnO layer on a ZnO nanorod array prepared in a hydrothermal-electrochemical process. ZnO nanorods have the role to improve the mechanical stability and adherence of ZnO layer deposited by electrophoretic technique. D149 dye is used as sensitizer for ZnO semiconductor. The thus prepared ZnO layer is used for the photoanode of dye-sensitized solar cell (DSC). Performance parameters were extracted from standard current-voltage characteristic (I-V) and charge transfer phenomena occurring at ZnO/dye/electrolyte was evaluated by electrochemical impedance spectroscopy (EIS).

Sol-gel HfO2 thin films, prepared from etoxid precursor, were deposited onto silicon wafer substrates by dipcoating. Low fluence multipulse excimer laser processing was used for sol-gel film densification. The small duration of the laser pulse heating limits the quantity of oxygen atoms arriving from the surface at the HfO2/Si interface. Laser irradiations were performed using a XeCl (308 nm) excimer laser, with a homogeneous laser beam. The nanostructure evolution of the laser irradiated films, using different laser fluences between 30 and 120 mJ/cm(2) and different number of pulses, was studied by systematic cross section transmission electron microscope (XTEM) observations. Dielectric constant measurements were performed on the sol-gel HfO2 films samples after laser annealing. The optimum laser processing conditions were found to be a laser fluence of 80 mJ/cm(2) and 5000 to 10000 laser pulses. In these conditions, uniform densified HfO2 amorphous films with a dielectric constant of about 25 were obtained.

Commercially pure titanium (CP-Ti) offers a good corrosion resistance and tissue tolerance. The interfacial phenomena between biomaterial and biological fluids depend especially on surface chemistry, energy, roughness and topography of the implant Different methods are used to modify CP-Ti surface in order to improve its bonding properties to bone tissue. Besides the mechanical approaches, chemical etching and chemical oxidation, there are also other procedures improving the biocornpatibility. One of the most important involves the deposition of a bioceramic thin layer on the metallic surface. A bioceramics frequently used is hydroxyapatite (HA), the mineral component of the bone. In this paper. the main objective was to study the effects of different surface pretreatments on adherence of hydroxyapatite layer obtained by electrochemical method. The CP-Ti substrate was used in different treated states of the surface. The applicability of the electrochemical technique is relieved by the fact that it is a very rapid method, requires relatively low temperatures, being also very versatile. The obtained coatings were studied by scanning electron microscopy (SEM) associated with EDX (Energy dispersive X-ray spectroscopy, X-ray diffraction method (XRD). The adherence of the layers was evaluated by the "pull-out" test. The quality of the coating (morphology and adhesion properties) is decisively influenced by the electrochemical parameters and also by the surface state.

We present a careful analysis of field characteristics in two-dimensional photonic crystals with square and hexagonal symmetry designed in a Si/SiO2/Cu heterostructure. A special attention is devoted to frequencies close to photonic band gap. Following the symmetry classification in odd and even modes, their field characteristics are studied. The material prepared in a dedicated deposition chamber in ultra-high vacuum by annealing the Si/SiO2 substrate and subsequent deposition of 10 angstrom copper in order to prevent the sample oxidation, allows the study of the photonic characteristics of the copper/silicon oxide/silicon interface. The chemical state of the Cu/SiO/Si system is addressed by photoelectron spectroscopy which allows us to deduce the amount of crystalline Si and amorphous oxide. In this manner a precise estimation of the dielectric constant of the materials is possible. It is expected that at the interface with copper, a strong confinement of radiation should appear due to high reflectivity of copper.

Fourier transform infrared spectroscopy (FT-IR) analysis was conducted on europium-doped hydroxyapatite, Ca10-xEux (PO4)(6)(OH)(2) nanocrystalline powders (Eu:HAp) with 0 < x(Eu) < 0.2. Antimicrobial studies were also performed for the first time on Eu: HAp. The antimicrobial properties of Eu: HAp nanoparticles with 0 < x(Eu) <= 0.2 on Gram-negative (E. coli ATCC 25922, Pseudomonas aeruginosa 1397) andGram-positive (Staphylococcus aureus 0364, Enterococcus faecalis ATCC 29212) bacteria systems and a species of fungus (Candida albicans ATCC 10231) were reported. Our study demonstrates that the antimicrobial activity of Eu: HAp nanoparticles is dependent on the europium concentration.

The synthesis of multifunctional magnetic nanoparticles (MF-MPs) is one of the most active research areas in advanced materials as their multifunctional surfaces allow conjugation of biological and chemical molecules, thus making it possible to achieve target-specific diagnostic in parallel to therapeutics. We report here a simple strategy to integrate in a one-step reaction several reactive sites onto the particles. The preparation of MF-MPs is based on their simultaneous modification with differently functionalized dopamine derivatives using simple solution chemistry. The formed MF-MPs show comparable magnetic properties to those of naked nanoparticles with almost unaltered particle size of around 25 nm. The different termini, amine, azide and maleimide functions, enable further functionalization of MF-MPs by the grafting-on approach. Michael addition, Cu(I) catalyzed << click >> chemistry and amidation reactions are performed on the MF-MPs integrating subsequently 6-(ferrocenyl)-hexanethiol, horseradish peroxidase (HRP) and mannose.

Iron layers are grown on GaAs(001) single crystal wavers by magnetron sputtering and characterized by magneto-optical Kerr effect (MOKE) and X-ray photoelectron spectroscopy (XPS). It is found that all deposited layers, starting with 2 nm thickness, are ferromagnetic at room temperature with a relatively high coercitive field (500 to 750 Oe). The average Fe magnetic moment is larger for the thinnest Fe film deposited, of about 0.52 Bohr magnetons per Fe atom. The average Fe magnetic moment decreases to 0.26 Bohr magnetons, then to 0.17 Bohr magnetons for 4 and 8 nm, resepctively. XPS evidenced that the outermost Fe layers are oxidized; however, the thinnest Fe film presented the lower oxidation state. We may connect this reaction with Fe-As bonds, resulting in a nonferromagnetic interface compound. Indeed, XPS depth profiling of the 8 nm sample evidenced the formation of a very thin (about 1.4 nm) Fe metal layer immediately at the interface with GaAs. In this layer, Fe may reach an atomic magnetic moment as high as 1 Bohr magneton.

The fast decomposition of hydrozincite [Zn-5(CO3)(2)(OH)(6)] into ZnO observed in the transmission electron microscope could be slowed down and investigated in situ by operating the microscope at very low electron beam current densities and cooling the specimen down to -160 degrees C. Thus, it was possible to observe and pursue the distinct structural steps of the disruption of the hydrozincite lattice due to the energetic emission of H2O and CO2 gases. The initially formed disordered ZnO phase was found to further crystalize resulting in a mesoporous structure of small ZnO nanocrystals.