National Institute Of Materials Physics - Romania

Photoactive europium doped titanium dioxide (Eu: TiO2) thin films were grown by a matrix assisted pulsed laser evaporation technique. TiO2 and Eu cation-adsorbed TiO2 nanoparticles (NPs) sols were used as starting materials. The sols were synthesized by a colloidal sol-gel route. In order to obtain solid targets, the sols were cooled down until solidification in liquid nitrogen. The irradiation of the solid targets was performed in a controlled oxygen atmosphere using an UV KrF* (lambda = 248 nm, tau(FWHM) nu 25 ns, n = 10 Hz) excimer laser source. The NPs were transferred and deposited onto solid substrates placed in the front of the frozen targets, forming continuous thin films. The as-grown undoped and Eu: TiO2 thin films were submitted to post-deposition thermal treatments. The surface morphology, crystalline structure, and chemical composition of the thin films were characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Functional optical properties of the films were investigated by UV-VIS-NIR spectroscopy, spectroscopic ellipsometry, and photoluminescence as a function of dopant concentration in the TiO2 host and annealing temperature. A direct correlation was established between the processing conditions, films structure, chemical composition and oxidation states studied both at the top surface and in-depth as well as their functional, optical properties. Eu doping induces a blue-shift of the absorption edge with respect to the as-grown samples. Under visible light excitation (lambda = 488 nm, emitted by an Ar+ laser source), the Eu: TiO2 samples show characteristic photoluminescence corresponding to the D-5(0) -> F-7(i) (i = 0, 1, 2, 3, 4) transitions of Eu+ ions in the visible spectral range. The samples treated at the highest annealing temperature are characterized by strong photoluminescence emission, high transmittance in the VIS-NIR spectral regions, and high refractive index.

The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO2 cap/(GeSi/TiO2)(2) multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO2 cap/GeSi/TiO2 (TL) were also deposited using reactive high power impulse MS (HiPIMS) for TiO2 layers and dc MS for the GeSi layer. For TL samples a two-step annealing was employed, one before and the second after depositing TiO2 cap. Structure and morphology characterization (X-ray diffraction, scanning and transmission electron microscopy) was carried out and photocurrent measurements (voltage dependences, spectral curves) were performed. The annealed ML samples are formed of GeSi NCs with 5 - 10 nm sizes, while in the annealed TL samples, the GeSi NCs are larger (20 - 30 nm). These morphologies determine the multilayers photosensing properties in VIS-NIR of ML structures and in UV in TL ones, respectively.

SnO2 loaded with 1 wt.% NiO based gas sensors, have been tested under humid background towards different H2S concentrations when operated at 350 degrees C. Knowing that water dissociation takes place, leading to the formation of strongly bonded surface hydroxyl groups, usually hindering the subsequent gas detection, it is of highly importance to understand the role of NiO as "OH groups trapper" element. By using complementary phenomenological investigations (simultaneous electrical resistance and work function measurements) we could emphasize the role of loading element in mitigating the water effects, further reflected through the different H2S interaction mechanisms. As such, the exposure of the SnO2 - 1 wt.% NiO sensors to different relative humidity levels was mirrored through a decrease in surface band bending due to the water donor effect and to a minor increase in the electronic affinity explained by the low adsorption of surface OH groups.

Investigations on antenna array for 5.8 GHz frequency band applications are presented in this paper. In order to enhance the characteristics of the dielectric resonator antenna elements, a pair of resonators with different sizes and dielectric constants is used. The antenna elements are connected to four daughter-boards of Universal Software Radio Peripherals, which perform the signal processing required by the sources detection and beamforming.

Cobalt ferrites nanoparticles (CoFe2O4) were synthesized through self-combustion method using aqueous extracts of ginger root and cardamom seeds. X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and Mossbauer spectroscopy were used for the characterization of the cobalt ferrite nanoparticles. X-ray diffraction patterns indicated the formation of the cubic phase CoFe2O4. SEM micrographs revealed different morphological features of obtained cobalt ferrites. The Mossbauer parameters together with the inversion parameter and the cationic distribution were obtained from Mossbauer spectra recorded at room temperature.

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid-implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials' structure-dissolution behavior. This will contribute to "upgrade" our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic-organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials.

The recent progress in the theory of generalised Lambert functions makes possible to solve exactly the Weiss equation of ferromagnetism. However, this solution is quite inconvenient for practical purposes. Precise approximate analytical solutions are obtained, giving the temperature dependence of the spontaneous magnetization, and also the dependence of the magnetization on both temperature and external magnetic field. The experimental relevance of these results, mainly for the determination of the Curie temperature, is discussed.

This contribution is a review of recent aspects connected with photoelectron spectroscopy of free ferroelectric surfaces, metals interfaced with these surfaces, graphene-like layers together with some exemplifications concerning molecular adsorption, dissociations and desorptions occurring from ferroelectrics. Standard photoelectron spectroscopy is used nowadays in correlation with other characterization techniques, such as piezoresponse force microscopy, high resolution transmission electron spectroscopy, and ferroelectric hysteresis cycles. In this work we will concentrate mainly on photoelectron spectroscopy and spectro-microscopy characterization of ferroelectric thin films, starting from atomically clean ferroelectric surfaces of lead zirco-titanate, then going towards heterostructures using this material in combination with graphene-like carbon layers or with metals. Concepts involving charge accumulation and depolarization near surface will be revisited by taking into account the newest findings in this area.