National Institute Of Materials Physics - Romania

An amplification of near three orders of magnitude was observed in Pb(Zr,Ti)O-3 (PZT) thin films deposited on Pt/Si substrates when the Si substrate is included as an impedance in series with the PZT capacitor. The effect is present only at wavelengths below 1100 nm, where the incident light can be absorbed in the Si substrate with generation of free carriers. These carriers in turns modulate the internal electric field inside the ferroelectric layer leading to a much larger variation of the polarization compared to the one generated only by the temperature variation. This fact leads to a considerable enhancement of the pyroelectric signal. The finding can be useful in designing pyroelectric detectors with enhanced characteristics for visible and near infrared region of the electromagnetic spectrum.

The effects of strain field are studied in Si wafers implanted with heavy iodine and bismuth ions and in multi-quantum well structures. The experimental method of thermally stimulated currents without applied bias is used, and the trapping centres parameters are determined by modelling the discharge curves. In both cases, the strain field produces temperature-dependent parameters of trapping levels. So, due to the high strain field in the neighbourhood of implanted ions, energy levels broaden and cross sections become temperature dependent. In multilayer structures, for the trapping centres corresponding to strain-induced defects both concentrations and capture cross sections are temperature dependent.

Lamellar crystal objects such as straight, curved or kinked whiskers, bows and objects with missing stripes were grown in a static air atmosphere from melt-quenched substrates with starting composition Bi1.5Sr1Ca1Co0.6Oy. The average EDS composition of the objects is Bi2Sr0.75Ca1.8Co1.94Oy and the crystal structure is of the phase usually denoted in the literature as Bi-2(Sr,Ca)(2)Co2Oy (BiCO222). Objects of other phases were not found. Curvature is in the (ab)-plane. By scanning tunneling spectroscopy (STS) a semiconducting energy gap was determined at 2.41 eV.

We report the pressure vs area isotherms of Langmuir films of pure and doped with cholesterol (Ch) amyloid beta, A beta (1-40) and (1-42) at the air-water interface and, scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies of A beta (1-40) and (1-42) layers deposited from solution by drop cast and/or dipping and/or Langmuir-Blodgett on substrates of quartz and Si. The particularity of the substrate surface morphology determines the adhesion forces and plays an important role in the formation and stability of the multilayer films which are deposited on these substrates. The effect of cholesterol on the morphology of amyloids films and appearance of fibril structures is also analysed. AFM investigations have revealed the particularities of the aggregation process of the strongly hydrophobic A beta (1-42) on cholesterol films deposited by Langmuir-Blodgett on solid support of quartz and Si.

We investigate by different complementary methods the processes occurring when a polydimethylsiloxane film is used as interlayer for a silver doped hydroxyapatite coating. The X-ray diffraction and Fourier Transform Infrared Spectroscopy measurements show that the hydroxyapatite doped with silver is in a crystalline form and some SiO44- ions formation takes place at the surface and in the bulk of the new hydroxyapatite doped with silver/polydimethylsiloxane composite layer. The possibility of SiO44- ions incorporation in the structure of silver doped hydroxyapatite by the mechanism of SiO44-/PO43- ions substitution is analysed. The new formed silver doped hydroxyapatite/polydimethylsiloxane composite layer is compact, homogeneous, with no cracks as it was shown by Scanning Electron Microscopy and Glow Discharge Optical Emission Spectrometry.

Radar Cross Section (RCS) is a very important parameter of an aircraft. It is given by the overall signal reflected by the target when it is irradiated by electromagnetic waves in order to be detected and localized. The measurement of RCS for some aircrafts in real scenarios is a very complex and costly process because it needs a certain area for experiments, special equipment and a number of flights. Hence, in most cases the evaluation of RCS is made by measuring a scaled model aircraft in an anechoic chamber. This paper proposes a measurement scenario for IAR 99 and analysis the experimental data. This is the first evaluation of the IAR 99 radar cross section using measurements in time and frequency domain.

We study the generation of p-shell excitons in optically active disk-shaped quantum dots subjected to ultrafast optical pulses. The single-particle spectral properties are obtained from the four-band kp theory, whereas the Coulomb interaction is taken into account within the configuration-interaction approach, particular attention being payed to configuration mixing due to electron-hole correlations. The effect of intraband relaxation processes is included in the non-unitary dynamics derived from the von-Neumann Lindblad equation. We find that the fast hole relaxation processes drive the p-shell excitons to intermediate states which eventually evolve to s-shell excitons via slower electron relaxation.

A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 degrees C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

Samarium doped hydroxyapatite (Sm:HAp), Ca10-xSmx(PO4)(6)(OH)(2) (HAp), bionanoparticles with different x(Sm) have been successfully synthesized by coprecipitation method. Detailed characterization of samarium doped hydroxyapatite nanoparticles (Sm: HAp-NPs) was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The biocompatibility of samarium doped hydroxyapatite was assessed by cell viability. The antibacterial activity of the Sm: HAp-NPs was tested against Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) andGram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus). A linear increase of antimicrobial activity of P. aeruginosa has been observed when concentrations of Sm: HAp-NPs in the samples with x(Sm) = 0.02 were higher than 0.125 mg/mL. For Sm: HAp-NPs with x(Sm) = 0.05 a significant increase of antibacterial activity on E. coli was observed in the range 0.5-1 mg/mL. For low concentrations of Sm: HAp-NPs (x(Sm) = 0.05) from 0.031 to 0.125 mg/mL a high antibacterial activity on Enterococcus faecalis has been noticed. A growth of the inhibitory effect on S. aureus was observed for all concentrations of Sm: HAp-NPs with x(Sm) = 0.02.