National Institute Of Materials Physics - Romania

In the aim to improve the adherence of the nanostructured gold layers onto glass substrate, gold deposition has been first time performed onto a polystyrene (PS) layer. The PS layer of ca. 50nm was spin-coated onto glass plates from a toluene solution. Gold layers of 10-20nm were vacuum deposited at small incidence angle. We found that at variance from the plates with gold deposited directly on the glass, the plates with an intermediate PS layer do not peel under overnight treatment in ethanol solution. The layers were characterized by several methods. X-ray diffraction (XRD) measurements showed that gold peaks have the position corresponding to the face-centered cubic structure: However, the crystallites on the sample with PS layer seem to be a little bit smaller than those with gold deposited directly onto the glass. XR reflectometry measurements have given the thickness of the gold layer in good agreement with the value estimated from quartz monitor readings and with the ellipsometric data as well, Liquid crystal cells were obtained to observe the molecular alignment imposed by the nanostructured gold layer deposited onto PS film. A rather strong interaction of gold atoms with the substrate molecules can be considered on the basis of the XRD and ellipsometry measurements.

Multiferroic composite materials, consisting of piezoelectric and piezomagnetic phases, show electric polarization in the presence of a magnetic field and magnetization on applying an electric field, i.e. piezomagnetic phase causes polarization while piezoelectric phase causes changes in magnetization. The figure of merit of such multiferroic particulate composites is the magnetoelectric voltage coefficient representing the amount of polarization induced by a given magnetic field. In the present investigation we prepared and studied the properties of bulk particulate composites made from cobalt ferrite (COF) and a soft piezoelectric material (PZT). Composite samples, according to the formula xCOF center dot(1-x)PZT with 0 <= x <= 1 were prepared by mixing the COF and PZT powders, pressing them as discs and then sintered at 1200 degrees C for 3 hours. Structural, magnetic, piezoelectric and magnetoelectric characteristics of the sintered composites were determined as a function of the mass fraction of COF into PZT and magnetic field. The ME coefficient shows a maximum value of about 70 mV/cm.Oe for composites containing 40 % COF and 60 % PZT, in a DC magnetic field of 3 kOe at a frequency of 1 KHz of the ac magnetic field. Some of the dielectric and piezoelectric properties of the composite samples, as a function of the mass fraction x, were also determined.

A high quality soft type PZT material was designed and produced in order to be used as sensor for a high intensity air siren, Two thin disks from this material were assembled into a parallel bimorph type sensor with an intermediate metallic plate for the siren. This assembly behaves like an acoustic resonator in the high frequency audio range. This structure transforms the radial mode of vibration into a flexural one, with a much lower frequency. A mechanical impedance adapter was used in order to assure a good match between the oscillating ceramic and the surrounding air. A theoretical approach was outlined, which allows the evaluation of the resonance frequency for the working transducer. The theoretical and experimental data agree to a satisfactory degree up to the input errors assumed by the model. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. The bimorph necessary for making the siren was designed as a parallel structure and the corresponding transducer was measured and evaluated. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

This work deals with the influence of neutron and proton induced cluster related defects on the properties of n-type silicon detectors. Defect concentrations were obtained by means of Deep Level Transient Spectroscopy (DLTS) and Thermally Stimulated Current (TSC) technique, while the full depletion voltage and the reverse current were extracted from capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The annealing behaviour of the reverse current can be correlated with the annealing of the cluster related defect levels labeled E4a and E4b by making use of their bistability. This bistability was characterised by isochronal and isothermal annealing studies and it was found that the development with increasing annealing temperature is similar to that of divacancies. This supports the assumption that E4a and E4b are vacancy related defects. In addition we observe an influence of the disordered regions on the shape and height of the DLTS or TSC signals corresponding to point defects like the vacancy-oxygen complex. (C) 2009 Elsevier B.V. All rights reserved.

Pt-ZnO-Pb(Zr0.2Ti0.8)O-3-Pt (PZT-ZnO) heterostructures were fabricated by using a sol-gel process. Capacitance-voltage measurements performed on a wide temperature range (20-450 K) have revealed the presence of a hysteresis that undergo a change of direction from clockwise at temperatures below 350 K to counter-clockwise at higher temperatures. In the first case, the hysteresis is produced by charge injection, similar to the case of classical metal-oxide-semiconductor capacitors. In the last case, the hysteresis is the fingerprint of polarization reversal, as reported for metal-ferroelectric-semiconductor (MFS) structures based on n-Si. The memory window at 450 K is about 6 V. This result suggests that PZT-ZnO MFS heterostructures can be used for memory devices working at elevated temperatures, in which the ZnO plays the role of the semiconductor.

We report on the vortex dynamics of a single crystal of the noncentrosymmetric heavy-fermion superconductor CePt3Si. Decays of the remnant magnetization display a logarithmic time dependence with rates that follow the temperature dependence expected from the Kim-Anderson theory. The creep rates are lower than observed in any other centrosymmetric superconductor and are not caused by high critical currents. On the contrary, the critical current in CePt3Si is considerably lower than in other superconductors with strong vortex pinning indicating that an alternative impediment on the flux-line motion might be at work in this superconductor.

A growing need for eco-friendly energy sources have led recently to a frantic search of new compositional systems for photovoltaic applications. The nanocomposite titania-germanium (TiO2-Ge) systems represent a new viable family of optoelectronic materials. Their structural, optical and electronic properties can be easily tailored by customizing the density and size of Ge dots in the TiO2 matrix. Early studies on TiO2-Ge nanocomposites have shown promises for their use as an alternative in photovoltaic applications. In this study we report the TiO2-Ge films synthesis by reactive magnetron co-sputtering. Their properties were evaluated by compositional (EDS), structural (XRD, FTIR) and optical (UV-Vis) characterizations.

We report on the versatility of pulsed laser deposition and radio frequency magnetron sputtering deposition methods to synthesize highly adherent bioactive hydroxyapatite thin layers on cranio-spinal implants as appropriate biofixation alternatives.

In this study, Fourier Transform Infrared Spectroscopy (FTIR) in Attenuated Total Reflectance mode was employed as main characterization technique to investigate the reaction mechanisms in vitro (SBF) of bioglass and glass-ceramic sputtered coatings. Two bioglass compositional systems are compared in order to gain more information regarding their in vitro bioreactivity. Important correlations between the concentration of non-bridging silicon-oxygen (Si-O-NBO) groups and the content of network modifiers were found. FTIR revealed that the high concentrations of Si-O-NBO groups are promoting the enhancing of coatings' reactivity. This information could be very useful for the development and tailoring of new bioactive glasses with an optimum biological behaviour. By varying the compositional features and the structural state, the sputtered glassy coatings exhibited different in vitro behaviour: inertness, resorbability and bioactivity.

The application area of piezoceramic materials and devices based on such materials is continuously extended. The working conditions for such devices and structures may be sometimes very hard such as low and high temperatures, nuclear radiation, high pressure and so on. Such conditions may affect to some extent the transducer performances due to the changes of the basic properties of piezoceramic materials used as sensors. In this regard we have investigated the changes of the main piezoelectric properties of two typically hard and soft piezoceramics within a large temperature range from 2 to 600 K. All parameters measured showed a rather steady increase or decrease with increasing temperature. The results were discussed in terms of intrinsic and domain wall contribution to the dielectric and piezoelectric response of materials.