National Institute Of Materials Physics - Romania

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations < 100 > and < 111 > produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60 degrees C and 80 degrees C on MOS capacitors and gate-controlled diodes irradiated to 5MGy and the annealing kinetics of oxide charges and surface current determined.

The hysteretic properties of metal-ferroelectric-semiconductor (MFS) structures based on Pb(Zr0.2Ti0.8)O-3 (PZT) and ZnO films were studied with respect of the quality of the PZT-ZnO interface. The films were grown by pulsed laser deposition (PLD) on platinized silicon (Pt/Si) substrate and on single crystal, (001) oriented SrTiO3 (STO) substrates. The structural analysis has revealed that the PZT-ZnO stack grown on single crystal STO is epitaxial, while the structure grown on Pt/Si has columnar texture. The temperature change of the capacitance-voltage (C-V) hysteresis direction, from clockwise at low temperatures to counter clockwise at high temperatures, was observed at around 300K in the case of the MFS structure grown by PLD on Pt/Si substrate. This temperature is lower than the one reported for the case of the PZT-ZnO structure grown by sol-gel on Pt/Si substrate (Pintilie et al., Appl. Phys. Lett. 96, 012903 (2010)). In the fully epitaxial structures the C-V hysteresis is counter clockwise even at 100K. These findings strongly points out that the quality of the PZT-ZnO interface is essential for having a C-V hysteresis of ferroelectric nature, with negligible influence from the part of the interface states and with a memory window of about 5V at room temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765723]

Ba(Zn1/3Ta2/3)O-3 (BZT) thin films were grown on Pt-coated Si substrates at 500 degrees C substrate temperatures by pulsed electron beam deposition method and post-annealed at 600 and 650 degrees C for 1 h. The X-ray diffraction patterns indicate that the as-grown films are partially crystallized but single-phase cubic perovskite structure was formed in annealed films. The temperature dependence of the dielectric constant of the BZT films was recorded in the -100 to + 100 degrees C range. The annealing treatment induces a decrease of the temperature coefficient of the dielectric permittivity with an order of magnitude, from 2000 to 100 ppm/degrees C. The influence of the annealing treatments on the temperature behavior of the BZT films was evidenced; a dielectric constant of about 21 at room temperature was obtained for the films annealed at 650 degrees C. (C) 2012 Elsevier B. V. All rights reserved.

The influence of target-substrate distance during pulsed laser deposition of indium zinc oxide (IZO), indium tin oxide (ITO) and aluminium-doped zinc oxide (AZO) thin films grown on polyethylene terephthalate (PET) substrates was investigated. It was found that the properties of such flexible transparent conductive oxide (TCO)/PET electrodes critically depend on this parameter. The TCO films that were deposited at distances of 6 and 8 cm exhibited an optical transmittance higher than 90% in the visible range and electrical resistivities around 5 x 10(-4) Omega cm. In addition to these excellent electrical and optical characteristics the films grown at 8 cm distance were homogenous, smooth, adherent, and without cracks or any other extended defects, being suitable for opto-electronic device applications. (C) 2012 Elsevier B. V. All rights reserved.

High permittivity materials allow good miniaturization of microwave components, but the dielectric resonator antenna using these materials has the drawback of a reduced bandwidth. To overcome this disadvantage we wanted to obtain a relatively wideband high permittivity DRA using the superior modes. Using HFSS simulations, we identified some of the superior modes that appear in cylindrical DRAs situated on a conductor ground plane and excited by a symmetric rectangular slot made in the ground plane. We identified seven superior modes and, for all of them, the measured and theoretically calculated resonant frequencies did not differ by more than 6%. Knowing the possible excited modes in the antenna and the relations for their resonant frequencies, one can predict the operating frequencies of a cylindrical DRA excited by a central rectangular slot.

In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by amagnetic field in NiCl2 center dot 4SC(NH2)(2) (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z = d; moreover the correlation length exponent is found to be nu = 0.75(10), and the order parameter exponent to be beta = 0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher et al. [Phys. Rev. B 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

Smooth and adherent bioactive coatings with similar to 0.5 mu m thickness were deposited onto Si substrates by the radiofrequency-magnetron sputtering method at 150 degrees C under 0.4 Pa of Ar atmosphere using a bioglass powder as target with a composition in the SiO2-CaO-MgO-P2O5-CaF2-B2O3-Na2O system. The bioactivity of the as-prepared bioglass samples was assessed by immersion in simulated body fluid for different periods of time up to 30 days. Grazing incidence X-ray diffraction, Fourier transform infra-red spectrometry and energy dispersive spectroscopy revealed that important structural and compositional changes took place upon immersing the samples in SBF. Whilst the excellent biomineralisation capability of the BG thin films was demonstrated by the in vitro induction of extensive and homogenous crystalline hydroxyapatite in-growths on their surfaces, a series of bioactivity process kinetics peculiarities (derogations from the classical model) were emphasised and thoroughly discussed. (C) 2012 Elsevier B. V. All rights reserved.

Bi1.5-xZn0.92-yNb1.5O6.92-delta thin films have the potential to be implemented in microwave devices. This work aims to establish the effect of the substrate and of the grain size on the optical and dielectric properties. Bi1.5-xZn0.92-yNb1.5O6.92-delta thin films were grown at 700 degrees C via pulsed-laser deposition on R-plane sapphire and (100)(pc) LaAlO3 substrates at various oxygen pressures (30, 50, and 70 Pa). The structure, morphology, dielectric and optical properties were investigated. Despite bismuth and zinc deficiencies, with respect to the Bi1.5Zn0.92Nb1.5O6.92 stoichiometry, the films show the expected cubic pyrochlore structure with a (100) epitaxial-like growth. Different morphologies and related optical and dielectric properties were achieved, depending on the substrate and the oxygen pressure. In contrast to thin films grown on (100)(pc) LaAlO3, the films deposited on R-plane sapphire are characterized by a graded refractive index along the layer thickness. The refractive index (n) at 630 nm and the relative permittivity (epsilon(t)) measured at 10 GHz increase with the grain size: on sapphire, n varies from 2.29 to 2.39 and epsilon(r) varies from 85 to 135, when the grain size increases from 37 nm to 77 nm. On the basis of this trend, visible ellipsometry can be used to probe the characteristics in the microwave range quickly, nondestructively, and at a low cost.

Samarium is deposited on Si(001) at various temperatures (room temperature to 400 A degrees C), and the surface structure, interface reactivity, electron configuration, and magnetic properties are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and magneto-optical Kerr effect (MOKE), respectively. It is found that metal Sm is present on samples prepared at room temperature with an interface layer containing mostly Sm2+ and a lower amount of Sm3+. When samples are prepared at high temperature, much less Sm-0 is found with an increasing amount of Sm2+. Freshly prepared Sm-0 and SmSi2 layers react strongly with oxygen from the residual gas, promoting formation of Sm2O3 at the expense of both metal Sm and SmSi2. Room temperature ferromagnetism is observed for all prepared layers with a decrease of the saturation magnetisation when samples are prepared at high temperature. It is found that ferromagnetism implies mostly Sm3+ and Sm metal. In addition to these findings, this work proposes a new assignment of the Sm 3d chemically shifted components. Also, a noticeable variation of the XPS Sm 3d spin-orbit splitting is found as a function of the Sm ionization state.

Thin films with the composition [(Bi0.5Na0.5)TiO3](0.92)-[BaTiO3](0.08) (hereafter BNT-BT0.08) were deposited on Pt-Si by spin-coating from a stable sol precursor. The BNT-BT0.08 film, crystallized on the Bi0.5Na0.5TiO3 rhombohedral lattice, was obtained after annealing the film-gel at 700 A degrees C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT-BT0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (epsilon (r)) was 243 and the loss tangent (tan delta) was 0.38. The remnant polarization (P (r)) was 0.87 mu C/cm(2) and the coercive field (E (c)) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 x 10(-5) A/cm(2) at low electric fields (100 kV/cm). BNT-BT0.08 thin films shown piezoelectric properties (d (33eff) = 100 pm/V) comparable to those of PZT thin films.