National Institute Of Materials Physics - Romania

The leakage current for a thin film metal-ferroelectric-metal device was modelled using an electron tunnelling approach. The potential energy through the device was obtained from an electrostatic argument and a balance equation was imposed for the incoming and outgoing currents. Using the obtained leakage current, experimental data was fitted in order to obtain qualitative values for the model parameters. Good agreement between the obtained dielectric constant and numerical calculations performed in the literature.

Bioactive materials play an increasingly important role in the biomaterials industry, and are extensively used in a range of applications, including biodegradable metallic implants. We report on Bioactive Glasses (BG) films deposition by pulsed laser techniques onto biodegradable substrates. The BG coatings were obtained using a KrF* excimer laser source (lambda= 248 nm, t(FWHM) <= 25 ns). Their thickness has been determined by Profilometry measurements, whilst their morphology has been analysed by Scanning Electron Microscopy (SEM). The obtained coatings fairly preserved the targets composition and structure, as revealed by Energy Dispersive X-Ray Spectroscopy, Grazing Incidence X-Ray Diffraction, and Fourier Transform Infra-Red Spectroscopy analyses.

Aluminum Nitride (AlN) films were deposited at 450 degrees C in nitrogen ambient at a pressure of 0.1 Pa and at a laser incident fluence of similar to 3 J/cm(2) and pulse repetition rate of 40 Hz. Grazing Incidence X-ray Diffraction patterns evidenced the presence of nanocrystallites in the amorphous AlN matrix. In the FTIR spectra the characteristic Reststrahlen band of AlN crystal with a hexagonal lattice is observed but it is quite broadened (950-550 cm(-1)). The angular dependence of the reflectance spectra in p-polarised incidence radiation demonstrates the sensitivity of the A(1)LO phonon mode of the AlN nanocrystallites to their orientation toward the normal to the substrate surface. With decrease of the incidence beam angle the intensity of the A(1)LO phonon mode diminishes and softening of the resonance frequency occurs.

The aim of this study was to evaluate the adhesion of different bioceramic coatings deposited by radio frequency magnetron sputtering on the biodegradable implant-type magnesium-calcium (MgCa) alloys. Hydroxyapatite (HA) and bioactive glass (BG) were chosen as coating materials, due to their remarkable biological potential. The morphology, composition, structure and adhesion of the deposited thin coatings was characterized by scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy and pull-out adherence measurements. A variation of the coating-to-substrate adhesion has been recorded and correlated with the physico-chemical results. The bonding strength values of the coatings were promising (being superior to the ISO13779-2:2008 fabrication standard for load-bearing biomedical coatings), and thus, encourage us to further proceed with the biological evaluation of the HA or BG coatings-MgCa substrate couples.

In this paper, the design of aperture-couplet rectangular dielectric resonator antennas arrays is illustrated. The effect of slot feed on the dielectric resonator antenna (DRA) and the effect of the spacing between array elements is observed. This paperwork can be useful for WLAN applications with the operating frequency 5.8 GHz.

A series of pyridinium salts with various counterions (Br-, NO3-, BF4-, PF6-, OTf- and SCN-) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4-hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

Fe and Fe-Cr-Al thin films, both as sputtered on Si substrates as well as after subsequent annealing treatments in hydrogen atmosphere, have been investigated by means of X-ray reflectometry, magneto-optic Kerr effect and Mossbauer spectroscopy with respect to structural and related magnetic characteristics. The as deposited films are showing chemically disordered bcc structures, assigned to Fe-Si and Fe-Cr-Al-Si phases, respectively, with soft magnetism and magnetic texture, both influenced by the presence of Si, Cr and Al atoms. The softness of the films as well as the magnetic texture are strongly modified via hydrogenation treatments. In addition, such treatments induce the expulsion of Si, Cr and Al atoms from the as deposited phases, providing almost pure Fe films of much well crystallized bcc structure.

Bioactive composites of bovine derived hydroxyapatite and boron containing bioactive glass were doped with 5, 10 and 15 wt.% lanthanum oxide (La2O3). Results showed that at low sintering temperatures (800 degrees C) the doping oxide of La2O3 promoted transformation to crystalline phases. Formation of secondary phases, such as rhenanite, NaCaPO4, and calcium silicate, Ca2SiO4, were also found. La was found to act as modifier and influenced the viscosity. The increase of La2O3 content led to decrease of pore size. Porosity amount 48.1 %, at 15-240 mu m size range were reduced, to 34.4 %, with 5-80 mu m size range and particle sizes of 0.3-6 mu m to 0.09-2 mu m, respectively. In addition to that compression strength (MPa) and microhardness (HV) of the performed composite bioceramics were in the range of 25 - 110 MPa, and 121 - 364 HV, respectively. Our investigations suggested that the porosity type has a strong influence on the compressive strength and microhardness properties of the final bioceramic products.

Restoration of damaged bone tissue involves two traditional approaches: tissue grafting and alloplastic replacement. Recently, their limitations led to the development of tissue engineering, which uses degradable porous supports named "scaffolds". These porous structures (used both for tissue engineering and classic bone substitution applications) with customizable designs may be constructed by solid freeform fabrication (SFF) techniques. SFF uses various synthetic materials and may be adapted for creating ceramic-based scaffolds, which became popular due to increased demands for bone substitution materials. Among these materials, naturally derived ceramics are suitable candidates for bone replacement due to their resemblance with the mineral bone. Innovative optimization routes for preparing naturally derived ceramics with modulated properties implies the management of key parameters involved in heat treatment of animal hard tissues: temperature, heating environment, and cooling conditions. Both powders and bulk pieces are evaluated with complementary techniques that focus on compositional, morphological, and structural features. Finally, qualitative and quantitative biological assay in relevant cell culture of the compacted powders may assist extensive testing programs for further evaluation of different ceramic scaffolds. All these results contribute to effective assessment of ceramics tuning strategies and to subsequent modulation of their enhanced properties and long-term functionality.