National Institute Of Materials Physics - Romania

N-doping is often used to improve the photocatalytic properties of TiO2, films in order to achieve visible light response. In this work, we study the effect of annealing treatment (temperature and atmosphere) on the structural and optical properties of undoped and N-doped TiO2, films by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE) and UV-VIS optical transmission spectroscopy. Porous five-layer TiO2, films were deposited by sol-gel method on quartz substrate and thermally treated in oxygen or NH3 flow at 500 and 600 degrees C. Significant doping effect was achieved after annealing at 600 degrees C in NH3 and a shift in optical bandgap value down to visible range (2.69 eV) was observed. (C) 2008 Elsevier B.V. All rights reserved.

Hydroxyapatite (HA) biocoatings were obtained using two different deposition methods: sol-gel and sputtering. A direct comparison of films obtained using different techniques is necessary because of possible formation of multi-phases and components in HA films. HA films were investigated using spectroscopic ellipsometry (SE) as a powerful method to evaluate composition and structural properties of the films. For both types of films, sputtering and sol-gel, a weak dispersion of the refractive index within the wavelength range 0.4-0.7 pm was found. This corresponds to a high energy bandgap and a high optical transparency in the UV-VIS range. The internal porosity varying in a wide range in the sol-gel films was evaluated using a modeling of SE data. Additionally to SE Studies, structural, chemical and optical characterizations of the Films were performed using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Two absorption bands observed in the wavelength ranges 550-600 cm(-1) and 1000-1200 cm(-1) can be attributed to the major absorption modes associated with HA in agreement with published data. Prom XPS analysis, the atom ratio Ca/P was found for sol-gel films close to the stoichiometric value 1.67. For sputtering films, a higher Ca/P ratio of about 2.1 was estimated. However, similar FTIR spectra have been recorded for both sputtering and sol-gel films. XRD Studies show also similar crystallization conditions by annealing at temperatures higher than 500 degrees C. (C) 2008 Elsevier B.V. All rights reserved.

Nano-scale ordering may be revealed in transmission electron microscopy (TEM) by at least three techniques that will be presented in this work: selected area electron diffraction, conventional TEM and high-resolution TEM. Digital image processing is used to extract additional information from the high-resolution micrographs. The described methods are illustrated in a microstructural and compositional study of a 90%Pb(Mg1/3Nb2/3)O-3-10%PbTiO2 ceramic sample. High-resolution images reveal the presence of ordered compositional nano-domains, observable in two specific crystallographic orientations. Antiphase boundaries lying in the (111) planes separate them, while (100) and (111) facets separate the ordered domains from the disordered matrix.

In this work we report the synthesis and characterization of the polypyrrole - porous silicon nanocomposites. Our main goal is to control the growth of conducting polypyrrole into the alveolar pores of porous silicon, in order to get a functionalized nanocomposite with the required properties for application as electrode in microfluidic devices. Porous silicon was electrochemically etched from (100) p-type silicon wafers. Different silicon resistivities (from 1.8 to 11 Omega cm) and preparation conditions (different electrolyte concentrations and current densities) were used. The electrodeposition of polypyrrole into porous silicon was carried out galvanostatically, at a constant current density 2.5 mA/cm(2) from a solution containing acetonitrile, the monomer, pyrrole and p-toluensulfonic acid as electrolyte. The polymerization time was varied in order to investigate the growing process of polypyrrole into the pores. The morphology and of the as-prepared nanocomposites was investigated by SEM. The existence of PPY into porous silicon is evidenced by the EDX spectra of the nanocomposite. The electrical characterization evidences the relative contributions of the polypyrrole and the substrate resistivity, respectively.

Water-soluble gold nanoparticles, capped with captopril, have been synthesized and characterized. Their average size is 2.3 nm, with a spherical shape. These gold nanoparticles can be easily labeled with stable free radicals (4-amino-tempo) by a coupling reaction performed in the presence of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ). Both synthesized and spin-labeled gold nanoparticles can be incorporated into much bigger (100 nm) silica nanoparticles using the Stober method, thus forming hybrid metal (gold)-inorganic (silica) nanoparticles. These hybrid silica nanoparticles (containing or not spin-labeled gold nanoparticles) can be easily spin-labeled with another stable free radical (4-isocyanato-tempo), leading to the formation of a double spin-labeled material. In this way, some stable free radicals are attached on the gold surface while others are attached on the silica surface. Three types of EPR spectra were recorded and discussed for the hybrid gold-silica nanoparticles: (1) where the spin labels are attached to the embedded gold nanoparticles, (2) where the spin labels are attached to the silica nanoparticles, and (3) in the case of the double spin labeled material where both gold and silica nanoparticles are spin-labeled. Influence of different solvents on the EPR spectra is also discussed.

The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.

This paper investigates the conduction mechanism in Cr2O3 gas sensing thick films. A citrate combustion method was used for the preparation of the metal oxide and ethanol vapour as a test gas. The manner in which surface reactions induced electrical changes are affecting the sensor signals inputs was explored by simultaneous dc and work function changes (Kelvin probe method). The identification of the contributions to conduction of the different sensing layer elements was made possible by ac impedance spectroscopy measurements. A conduction model, which qualitatively explains the experimental findings, was elaborated on the basis of the acquired experimental data and the information provided in literature. The model validity should apply, besides Cr2O3, to all p-type metal oxides used as gas sensitive materials. (C) 2008 Elsevier B.V. All rights reserved.

Several hole trapped centres, namely Tl2+, self-trapped hole and A-type centres, were observed by ESR in PbBr2:Tl single crystals after X-ray irradiation at 77 K. The corresponding spectra are visible up to 200 K for all three defect centres. The STH centres are observed at higher temperatures than in the undoped PbBr2 single crystals, probably due to the stabilising effect of the Tl+ impurities. The ESR parameters of the Tl2+ centre point to stronger covalency effects in PbBr2 than in the isostructural PbCl2 crystals. All hole trapped centres started decaying around 160 K, probably due to recombination with nonparamagnetic electron trapped centres. Besides a small concentration of self-trapped electron centres, no other electron trapped centres were observed. (c) 2008 Elsevier B.V. All rights reserved.

Single crystallites of superhard, semiconducting, n-type, amber colored and p-type, blue colored, Be-doped cubic boron nitride have been irradiated either with UV (350 nm) light or with an intense beam of accelerated (1 MeV) electrons. The examination of the irradiated samples at low temperatures by high frequency W (95 GHz)-band electron spin resonance reveals several new, radiation-induced, isotropic paramagnetic centers. The UV irradiation of both types of crystals yields centers involving very likely protons. In the amber c-BN crystals the irradiation with I MeV electrons results in the formation of vacancy associated paramagnetic defects and quasi-free electrons in colloidal particles. (C) 2008 Elsevier B.V. All rights reserved.

Mono and multilayer TiO2(Fe, PEG(600)) films were deposited by the dip-coating on SiO2/glass substrate using sol-gel method. In an attempt to improve the antibacterial properties of doped TiO2 films, the influence of the iron oxides and polyethilenglycol (PEG(600)) on the morphological, optical, surface chemical composition and biological properties of nanostructured layers was studied. Complementary measurements were performed including Spectroscopic Ellipsometry (SE), Scanning Electron Microscopy (SEM) coupled with the fractal analysis, X-Ray Photoelectron Spectroscopy (XPS) and antibacterial tests. It was found that different concentrations of Fe and PEG(600) added to coating solution strongly influence the porosity and morphology at nanometric scale related to fractal behaviour and the elemental and chemical states of the surfaces as well. The thermal treatment under oxidative atmosphere leads to films densification and oxides phase stabilization. The antibacterial activity of coatings against Escherichia Coli bacteria was examined by specific antibacterial tests.