National Institute Of Materials Physics - Romania

Europium doped zinc oxide (Eu:ZnO) thin films have been obtained by pulsed laser deposition (PLD). 002 textured thin films were achieved on glass and silicon substrates, while hetero-epilayers and homo-epilayers have been attained on single crystal SrTiO3 and ZnO, respectively. X-ray Diffraction (XRD) was employed to characterize the Eu:ZnO thin films. Extended XRD studies confirmed the different thin film structural properties as function of chosen substrates.

The aim of the paper is to identify the modes that can be excited by a wide microstrip line, in a cylindrical DRA situated symmetrically above it, to study the radiating performances of these modes and to present their radiating patterns. We managed to identify thirteen high-order modes; among these modes, four of them: HEM112, TMme(311), TEme(112), and TEme(121) have high transmission performances.

In this work we report our studies concerning the synthesis and characterisation of a series of imine derivatives that incorporate the 2-phenylpyridine (2-ppy) core. These derivatives were used in the cyclo-metalating reactions of platinum(II) or palladium(II) in order to prepare several complexes with liquid crystalline properties. Depending on the starting materials used as well as the solvents employed, different metal complexes were obtained, some of them showing both liquid crystalline behaviour and luminescence properties at room temperature. It was found that, even if there are two competing coordination sites, the cyclometalation process takes place always at the 2-ppy core with (for Pt) or without (for Pd) the imine bond cleavage. We successfully showed that it is possible to prepare emissive room temperature liquid crystalline materials based on double cyclopalladated heteroleptic complexes by varying the volume fraction of the long flexible alkyl tails on the ancillary benzoylthiourea (BTU) ligands.

Oxide materials are becoming of increasing interest due to their large variety of physical properties such as dielectric, magnetism, superconductivity, conductivity, ferroelectricity, multiferroism, etc. In addition, interfacing oxides with other materials is conferring new or better device functionalities. The main physical properties of oxides interfaces and their impact on the electrical properties of interest for microelectronic applications are presented. Further on, this subchapter is also devoted to the investigation and understanding of interface effects observed in heterostructures containing linear (SiO2) and non-linear (ferroelectrics) dielectrics in combination with wide-band gap semiconductor materials (e.g. ZnO and SiC) with special emphasis on size effects, interface quality and the opportunity to control the emergent phenomena in Metal-Oxide-Semiconductor (MOS) and Metal-Ferroelectric-Semiconductor (MFS) materials systems.

A series of bis(imidazolium) salts with different mesogenic groups (cyanobiphenyl or cholesteryl) and their silver carbene complexes with Br- anion has been designed and prepared. The liquid crystalline behaviour of these ionic liquids and their corresponding silver-carbene complexes was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The silver complexes are thermally stable on a broad temperature range with accessible transition temperatures close to ambient temperature. The compounds with cholesteryl groups show higher transition temperatures than the compounds possessing cyanobiphenyl mesogenic groups, but their thermal stability is limited by a slight decomposition before reaching the isotropic state. Interestingly, the bis(imidazolium) salt with two cyanobiphenyl groups at each side shows an enantiotropic nematic phase on a short range, being one of the few examples of ILC displaying nematic phase.

We report on the synthesis by PLD of bioactive glass (BG) films onto ultra high molecular weight polyethylene acetabular cups, and their preliminarily characterization after immersion in simulated body fluid. Fourier Transform Infrared spectra evidenced the strong depolymerization of the BG coatings. Scanning Electron Microscopy evidenced that the typical PLD film surface was converted after soaking in SBF to a rough one consisting of acicular crystals. Energy Dispersive Spectroscopy analysis demonstrated a remarkable conservation of the targets stoichiometry. The functionalization of acetabular cups with BG films by PLD should allow for the fabrication of implant coatings with improved osteoinductive characteristics.

The high intensity and high repetition rate of the European X-Ray Free Electron Laser, presently under construction in Hamburg, will require pixel sensors which can stand X-ray doses up to 1 GGy for 3 years of operation. Within the AGIPD Collaboration the Hamburg group has systematically studied X-ray damage in silicon sensors for the dose range between 1 kGy and 1 GGy using strip sensors and test structures fabricated on high-ohmic n-type silicon from four different vendors. The densities of oxide charges, interface traps and surface current as function of dose and annealing conditions have been determined. The results have been implemented in TCAD simulations, and the radiation performance of strip sensors and guard-ring structures has been simulated and compared to experimental results. Finally, with the help of detailed TCAD simulations, the layout and technological parameters of the AGIPD pixel sensor have been optimized. It is found that the optimization for silicon sensors exposed to high X-ray doses is significantly different from that for non-irradiated sensors, and that the specifications of the AGIPD sensor can be met. (C) 2013 Elsevier B.V. All rights reserved.

Epitaxial Pb(Zr0.2Ti0.8)O-3 layers of good structural quality were grown on single crystal SrTiO3 substrates. The pyroelectric coefficient was estimated from the signal generated by the ferroelectric film working as a pyroelectric detector in the voltage mode, without pre-poling procedure. The obtained value is as high as 1.9 x 10(-3) C/m(2) K. The large value is attributed to the presence of 90 degrees ferroelectric domains and to the compressive misfit strain, leading to an enhanced ferroelectric polarization. (C) 2013 AIP Publishing LLC.

A systematic experimental study of the main challenges for silicon-pixel sensors at the European XFEL is presented. The high instantaneous density of X-rays and the high repetition rate of the XFEL pulses result in signal distortions due to the plasma effect and in severe radiation damage. The main parameters of X-ray-radiation damage have been determined and their impacton p(+)n sensors is investigated. These studies form the basis of the optimized design of a pixel-sensor for experimentation at the European XFEL. (C) 2013 Elsevier B.V. All rights reserved.

Radiation damage in silicon, caused by the creation of point and cluster defects due to energetic charged hadrons and neutrons, results in a serious degradation of silicon-sensor performance and limits their lifetime. So far not all the defects are understood. The work presented here focuses on the study of radiation damage by electrons of different kinetic energies, from 1.5 MeV to 15 MeV, in order to study the differences between point- and cluster-related defects. The introduction rate of vacancy-related point defects and of so-called clustered regions was investigated as a function of electron energy. It is shown that the ratio between cluster dominated and point defect formation increases with increasing electron energy. 1.5 MeV electrons create only point defects, and the formation of cluster defects starts already at 3.5 MeV. To study the defect kinetics, isothermal annealing at 80 degrees C and isochronal annealing measurements were performed. (C) 2013 Elsevier B.V. All rights reserved.