National Institute Of Materials Physics - Romania

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.

The new opportunities introduced by the large development of the IoT (internet of things) are increasing the demand for sensors to be located as close as possible to the supervised process. The Aluminum Nitride (AIN) is one of the most promising materials for sensors due to its piezoelectric, excellent mechanical properties, chemical inertness and high melting point. Due to these material properties, the AlN sensors are suitable to operate in high temperature and harsh environment conditions and therefore are very promising to be employed in industrial applications. In this article are presented the studies conducted on several Aluminum Nitride-Coated Steel structures with the goal of producing sensors embedded in the ball bearings, bearings and other mobile parts of machine tools. The experiments were conducted on simple coatings structures without lubricating materials and the obtained results are promising, demonstrating that, with some limitations the AIN could be used in such applications.

Iron and nitrogen doped TiO2 nanoparticles were synthesized and investigated with the aim to obtain photocatalytic systems with enhanced visible light efficiency. In a first step, commercially available Degussa P25 was impregnated with iron (0.3, 0.5, and 1 at. %) and nitrogen under hydrothermal conditions. In the second step, Fe-N doped TiO2 was synthesized by a hydrothermal route starting with TiCl3, FeCl3 center dot 6H(2)O and Urea, at 200 degrees C for 2 h. All samples were post annealed at 400 degrees C for 2h. The X-ray diffraction (XRD) revealed a two phase nanoscaled composition (Anatase and Rutile) of Degussa P25 and a single phase-nanoscaled Anatase content of the hydrothermally synthesized (1at.%) Fe-N doped TiO2 sample. The presence of Fe and nitrogen in samples was confirmed by Mossbauer and X-ray photoelectron spectroscopy measurements (XPS). Transmission electron microscopy (TEM) revealed the structure, particle dimension and morphology. The photocatalytic measurements (based on degradation of Methylene Blue) evidenced the most efficient composition in TiO2 Degussa P25 series as corresponding to 1 at.% Fe, in both UV and visible spectrum. At the same time, the hydrothermal synthesized sample (1at.%) Fe-N doped TiO2 exhibits the best activity in visible spectral region. The nanoscaled systems were synthesized in view of tests on textile materials.

Samples of Ni57-xNdxFe18Ga25 with x=2 and 4 were prepared in ribbon form by rapid quenching via melt spinning route. The samples were analyzed by X-ray diffraction (XRD), magnetic measurements and Mossbauer spectroscopy, both in the as-quenched form and after thermal annealing at 900 degrees C for 2 min and 400 degrees C for 2 hours. For x=2 the Nd atoms are completely dissolved in the Ni-Fe-Ga matrix, while for x=4 the additional occurrence of the secondary 2:17 phase could be resolved. These findings were supported by the analysis of hyperfine magnetic field distributions obtained from the non-linear least-squares fitting of the Mossbauer spectra.

The elastic and structural properties of thermal barrier coatings of Cr2AlC DC sputtered from elemental targets onto Si(100) substrate at 200 degrees C are studied. The material was subsequently submitted to re-crystallization procedure by annealing the film at 650 degrees C and 700 degrees C in high vacuum and in air for 30 min. As-deposited and annealed films are shown to be homogeneous and dense over large areas. The re-crystallization process was monitored using X-ray diffraction and Raman spectroscopy. As-deposited films have an amorphous-like Cr-C-Al solid solution structure and annealed samples crystallize into single-phase hexagonal Cr2AlC. While XRD analysis and Raman spectroscopy of samples annealed in-air show the presence of 5% Cr2O3, the high vacuum samples annealed at 650 degrees C and 700 degrees C are fully crystallized and comprise only single-phase Cr2AlC hexagonal structure. Oxygen presence in the in-air annealed sample is shown to cause an elongation of the hexagonal unit cell along the c axis which coincides with the direction of stacking of Cr6C octahedral building blocks with alternate Al layers. Whereas the average grain size is shown to increase upon annealing, lattice microstrain, calculated using the integral breadth method, is seen to decrease by almost 70% in the annealed films. Raman spectra of as-deposited films show characteristic MAX-phase bands with broad, overlapping peaks in the region of 120-400 cm(-1) but also peaks in the range of 550-900 cm(-1), attributed to other Raman-active modes of the Cr2AlC structure. After annealing, the Raman peaks corresponding to Cr2AlC single-phase are narrower, more intense and better defined than in the as-deposited case. The occurrence of the disorder-induced D carbon band is observed in the Raman spectrum of the as-deposited film while, after high vacuum annealing, a sharp and relatively intense peak attributed to the carbon G band is observed that suggests that there may be carbon nanoclustering in the coatings upon annealing. This observation is consistent with and comes as a confirmation of previously reported ab initio modelling of possible Cr2AlC off-stoichiometric structures.

In the present work we study the optical, struc-tural and morphological properties of CdS-doped glass films, deposited by Pulsed Laser Deposition (PLD) method. The glass target used for ablation was prepared by conventional melt-quenching technique and the semiconductor dopant, CdS powder, was embedded in the borosilicate melt glass host by continuous stirring. In order to improve the properties of the films, the laser wavelength was modified. Photoluminescence emission (PL) of CdSdoped glass films revealed a broad band located in the visible range. The structural analysis was carried out by micro-Raman spectroscopy, pointing out specific vibration modes for Si-O-Si bonds as well as for CdS dopant. The morphology and the chemical characterization of the films were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Atomic Force Microscopy (AFM).