Publications

Nano-hydroxyapatite bio-ceramics were synthesized by sol-gel method. The gel was dried at 80 degrees C for 96 h. The dried gels were individually heated at a rate of 5 degrees C/min up to 600 degrees C, 800 degrees C, and 1000 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for to characterize the composition, morphology and particle size of samples. At 800 degrees C a small amount of CaO (about 0.3 wt%) was detected in which increased after annealing at 1000 degrees C (about 1.1 wt%). The crystallites are elongated along the c crystallographic axis, but the size anisotropy decreases with increasing temperature above 800 degrees C. The size along the elongation axis increased from 43 nm at 80 degrees C to about 143 nm at 1000 degrees C, as determined by XRD, and from 120 to 280 nm, as measured by TEM. The functional groups were analyzed using Fourier transform infrared (FTIR) and Raman spectroscopies confirming the presence of various and PO43 and OH- bands in the samples. After calcination at 1000 degrees C the bands are more intense which indicates an increase in the cristallynity. The photoluminescence (PL) of HAp treated at various temperatures (80, 600, 800, 1000 degrees C) was also studied. hFOB 1.19 osteoblats cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics. To evaluate cell proliferation rate quantitative by the hFOB 1.19 cells on HAp samples were cultured to 4 days. Cellular morphology was investigated using FESEM to obtain qualitative information of osteoblast cells on HAp samples. The number of hFOB 1.19 cells on control HAp_80, HAp_600, HAp_800 and HAp_1000 was 400 +/- 30, 360 +/- 25, 350 +/- 21, 320 +/- 16 and 300 +/- 10 after 4 days. Our results proved that the HAp sintered at 1000 degrees C promoted osteoblast cell attachment and adhesion.

By taking advantage of the unique and unusual properties of the recent composite right-/left-handed metamaterial transmission line, we have designed a small-sized resonant antenna that can operate in three different frequency bands. The antenna is well matched to the outer network by the use of a compact matching circuit and the resulting radiation characteristics make it suitable for short-range wireless communication systems.

The combined investigation techniques, electron probe microanalysis (EPMA), Mossbauer spectroscopy (NGR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD),) evidenced the third level of the inclusions at nanosize scale for specific minerals of different Romanian metamorphic deposits. So, NGR technique reveals the contribution of the (Mn, Fe) oxides - small particles at standard (RT) and at very low temperature (LHeT) in the Fe-52 gamma - ray signal of manganoan-fayalites (Razoare deposit). The EM analysis techniques confirmed the presence of the nanometric Fe and Mn oxides inclusions in manganoan fayalites, as well as of pyroxferroite (Razoare deposit). On the other hand, an extensive investigation of the gold ores in the South Carpathians (Costesti, Valea lui Stan and Jidostita) has been performed by using a fruitful combination among the above mentioned complementary mineralogical and structural methods. The investigation of the representative sulfide samples by the structural techniques relieved new minerals in the gold ores, the presence of submicroscopic inclusions of uytenbogaardtite, cobaltite and loellingite as well as the "coral like" aggregates of nanometric gold.

By taking advantage of the unique and unusual properties of the recent composite right/left-handed metamaterial transmission line, we have designed a shunt mode resonant antenna with a multi-band operation, and a series mode zero order resonant antenna, which is frequency independent. The antennas are well matched to the external network by using compact matching circuits. The resulting radiation characteristics make these antennas suitable for short-range wireless communications systems.

This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.

Three pyridine 2,3-dicarboxylate complexes have been synthesized and characterized by IR spectroscopy, thermal analysis and single crystal X-ray diffractometry. Their magnetic properties have also been studied by EPR and magnetisation measurements. The decomposition of such complexes in air leads to the generation of mixed metal oxides, as confirmed by powder X-ray diffraction.

The direct mixing of aqueous ferric chloride and o-phenylenediamine (OPD) solution at room temperature in the absence and presence of carbon nanotubes (CNTs) has been used to prepare poly(o-phenylenediamine) (POPD) micro-fibers and composites of the type CNTs/POPD having nanotubes incorporated in polymer fiber mass. Using surface enhanced infrared absorption (SEIRA) spectroscopy significant modifications in the low frequency range of the polymer spectrum are revealed when Au is used as metallic support. Similar variations are reported for the POPD samples prepared by the electropolymerization of OPD onto rough Au electrode. A covalent functionalization of CNTs with POPD and a doping process of POPD with radical anions of CNTs is proved by surface enhanced resonant Raman scattering and SEIRA spectroscopy. The X-ray diffraction (XRD) studies indicate a high crystallinity both for POPD and CNTs/POPD composites prepared by chemical or electrochemical methods. (C) 2011 Elsevier B.V. All rights reserved.

This paper presents the very first surface physics experiment performed in ultrahigh vacuum (UHV) in Romania, using a new molecular beam epitaxy (MBE) installation. Cleaning of a Si(001) wafer was achieved by using a very simple technique: sequences of annealing at 900-1000 degrees C in ultrahigh vacuum: low 10(-8) mbar, with a base pressure of 1.5 x 10(-10) mbar. The preparation procedure is quite reproducible and allows repeated cleaning of the Si(001) after contamination in ultrahigh vacuum. The Si(001) single crystal surface is characterized by low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), and Auger electron spectroscopy (AES). The latter technique is utilized in order to investigate the sample contamination by the residual gas in the UHV chamber, as determined by a residual gas analyzer (RGA). Unambiguous assignment of oxidized and unoxidized silicon is provided; also, an important feature is that the LVV Auger peak at 90-92 eV cannot be solely attributed to clean Si (i.e. Si surrounded only by Si), but also to silicon atoms bounded with carbon. Even with a sum of partial pressures of oxygen and carbon containing molecules in the range of 5 x 10(-10) mbar, the sample is contaminated very quickly, having a (1/e) lifetime of about 76 minutes.

Ultrathin ferromagnetic Fe layers on Si(001) have recently been synthesized using the molecular beam epitaxy (MBE) technique, and their structural and magnetic properties, as well as their interface reactivity have been investigated. The study was undertaken as function of the amount of Fe deposited and of substrate temperature. The interface reactivity was characterized by Auger electron spectroscopy (AES). The surface structure was characterized by low-energy electron diffraction (LEED). The magnetism was investigated by magneto-optical Kerr effect (MOKE). A higher deposition temperature stabilizes a better surface ordering, but it also enhances Fe and Si interdiffusion and it therefore decreases the magnetism. Despite the rapid disappearance of the long range order with Fe deposition at room temperature, the material exhibits a significant uniaxial in-plane magnetic anisotropy. For the Fe deposition performed at high temperature (500 degrees C), a weak ferromagnetism is still observed, with saturation magnetization of about 10 % of the value obtained previously. MOKE studies allowed inferring the main properties of the distinct formed layers.

Pure and europium (Eu3+) doped cerium dioxide (CeO2) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce4+ sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce4+ relative to Ce3+ ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.