National Institute Of Materials Physics - Romania

Triglycine sulphate crystal (TGS) is one of the most studied ferroelectric materials, having a second order transition around 49 degrees C. The complex dielectric constant we have measured on the frequency range 1-10(7) Hz and on a large temperature range, in ferroelectric phase after the para - ferro transition. Temperature was monitored from room temperature to 65 degrees C, were for 30min it was kept constant and then was lowered down at a rate of 0.6 degrees C/min. Both component of permittivity were automatically registered. This study was focused on the dielectric relaxation processes. Three fundamental relaxation mechanisms (LF, MF, and HF) were found and analyzed with the Cole-Cole functions. The activation energy of these relaxation mechanisms have been estimated in the ferroelectric phase

In this work we present the deposition of amorphous SiC thin films by radiofrequency dual magnetron sputtering. The dependence of the deposited films properties over the discharges electrical power and the effect of hydrogenous species (H-2 and/or D-2) addition to main discharge gas (Ar) were investigated. Accurate elemental analysis of the samples, including detection of hydrogen and deuterium, was performed by ion beam analysis (IBA) techniques: RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). SiCx thin films with thicknesses between 1700 and 4500 angstrom and C/Si ratio between 0.2/1 and 1.25/1 were obtained in different deposition conditions. The results prove that thin films of amorphous SiC with well controlled properties can be produced using radiofrequency dual magnetron sputtering. (C) 2015 Elsevier B.V. All rights reserved.

We report in this paper on the deposition and characterization of CeO2 nanostructured thin films with hierarchical morphology. Micro -sized ceria powder (CeO2, 99.9% purity) was pressed to obtain a ceramic target. An ArF laser working at 193 nm irradiated the target in controlled oxygen gas flow at constant pressure (0.1 mbar). Silicon wafers used as substrates for thin films were heated at different temperatures, up to 773 K. The influence of substrate temperature on the structure and surface morphology of ceria thin films was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and scanning electron microscopy (SEM). The refractive indices and information about roughness and thickness were revealed by spectroellipsometry. Crystalline cubic ceria thin films exhibiting a hierarchical structure that combines columnar and dendritic growth were obtained at temperatures above 473 K. For the samples obtained at 773 K, columns ending in pyramidal formations with sharp edges and sizes of hundreds of nanometers were observed, indicating a high crystallinity of the layer. XRD analysis reveals a consistent increase of the X-ray coherence length/crystallite size along the [111] direction with increasing temperature. Using a semi -empirical formula, Raman crystallites sizes were calculated and it was found that size increases with the temperature increasing. The spectroellipsometry investigations evidenced the increasing of refractive index with the substrate temperature increase. High surface roughness and pyramidal structures were noticed from the atomic force microscopy images for layers deposited at substrate temperature above 473 K. (C) 2015 Elsevier B.V. All rights reserved.

This paper presents some investigations on the optical and morphological properties of the polymer (matrix): monomer (inclusion) composite materials obtained from blends of bisphenol A polycarbonate and amidic monomers. For the preparation of the composite films, we have selected monomers characterised by a maleamic acid structure and synthesised them starting from maleic anhydride and aniline derivatives with -COOH, -NO2, -N(C2H5)(2) functional groups attached to the benzene ring. The composite films have been deposited by spin coating using a mixture of two solutions, one containing the matrix and the other the inclusion, both components of the composite system being dissolved in the same solvent. The optical transmission and photoluminescence properties of the composite films have been investigated in correlation with the morphology of the films. The scanning electron microscopy and atomic force microscopy have revealed a non-uniform morphology characterised by the development of two distinct phases. We have also investigated the generation of some optical non-linear (ONL) phenomena in these composite systems. The composite films containing as inclusions monomers characterised by the presence of one -COOH or two -NO2 substituent groups to the aromatic nucleus have shown the most intense second-harmonic generation (SHG). The second-order optical non-linear coefficients have been evaluated for these films, and the effect of the laser power on the ONL behaviour of these materials has also been emphasised.

Surface layers have already been observed by broadband dielectric spectroscopy for composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species n(s) was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees.

We report a study on the biocompatibility vs. thickness in the case of titanium nitride (TiN) films synthesized on 410 medical grade stainless steel substrates by pulsed laser deposition. The films were grown in a nitrogen atmosphere, and their in vitro cytotoxicity was assessed according to ISO 10993-5 [1]. Extensive physical-chemical analyses have been carried out on the deposited structures with various thicknesses in order to explain the differences in biological behavior: profilometry, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and surface energy measurements. XPS revealed the presence of titanium oxynitride beside TiN in amounts that vary with the film thickness. The cytocompatibility of films seems to be influenced by their TiN surface content. The thinner films seem to be more suitable for medical applications, due to the combined high values of bonding strength and superior cytocompatibility.

Glassy nanocomposites containing Eu3+-doped LaOCl nanocrystals of about tens of nm size embedded in a silica matrix have been prepared by using sol-gel route followed by controlled crystallization of the xerogel. Crystallization behavior of LaOCl nanocristalline phase was discussed on the basis of thermal analysis, X-ray diffraction and photoluminescence measurements. LaOCl nanocrystalline phase precipitation is the result of lanthanum chloride hydrolytic and oxidative reactions. As the annealing temperature increases nanocrystallites size grows up to tens of nm; Eu3+-ions are gradually incorporated during the nanocrystals growth. Structural changes were studied using the Eu3+ as probe ion and the luminescence properties were analysed by using Judd-Ofelt theory. (C) 2015 Elsevier Ltd. All rights reserved.

This paper presents some investigations of the effect of nanopatterning on the properties of aluminum layer deposited by sputtering. UV-Nanoimprint Lithography technique has been used for the realization of a 2D array of nanostructures (pillars) in aluminum film characterized by cylindrical shape and the following structural parameters: diameter between 400 nm and 490 nm, depth between 320 nm and 420 nm and periodicity of 1.1 mu m, which have been revealed by SEM and AFM measurements. The UV-Vis transmission, reflection and photoluminescence measurements have evidenced the effect of the nanopatterning on the optical properties of the A1 layer.

Eu-doped CaF(2)nanocrystalline powders have been prepared by using co-precipitation technique. Structural and morphological modifications induced by annealing are followed by using Eu3+-ion probe. Theluminescence properties are changing gradually together with the morphology of doped CaF2 nanoparticles accompanied by anEu(3+)-> Eu2+ conversion. Cathodoluminescence measurements show uniform distribution of the europium dopant ions in the annealed samples accompanied by a strong increase of the integral photoluminescence signal. During annealing the cubic structure of CaF2 nanoparticles is altered going to the spherical morphology due to the Eu3+ ions incorporation. In the annealed samples Eu3+ ions are incorporated as Eu3+-O dimer centres with the coordination symmetry (C-2 nu); in the sintered samples there are two non-equivalent Eu3+ sites. The thermoluminescence peaks have been assigned to the recombination of the Eu3+ related traps in these sites.

Up-conversion properties of the glass-ceramics microrods containing (Er3+, Yb3+)-doped LiYF4 nanocrystals have been studied. Under 980 nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 samplesshow green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion luminescences explained by a two-photon processes. The luminescence decay time of the green luminescence is much shorter in the glass-ceramics microrods (0.9 mu s) compared to the bulk powder (15 mu s) indicating the enhancement of the non-radiative relaxation rate due to the cross-relaxation effects between Er3+-ions. The quantum efficiencies were estimated for the green luminescence being much smaller in the glass-ceramic rods (eta = 0.15%) compared the bulk powder (eta = 2%) or pellet (eta = 46%).