Publications

New sensors based on single wall carbon nanotubes (SWCNTs) and porphyrins have been tested for sensitivity to NO(2) gas. SWCNTs embedded in barium stearate multilayers were deposited with the help of Langmuir-Blodgett technique. It was demonstrated a sensitive effect of the sensor for NO(2) gas. The coverage of the sensor with metalloporphyrin (Mn) leads to strong enhancing of the sensitive effect to NO(2), besides, the selectivity was preserved both around room temperature and at larger operating temperature (up to 200 degrees C). No sensitivity to CO and CH(4) was evidenced. The NO(2) sensitivity strongly increased at 100 degrees C but at high operation temperatures (150-200 degrees C) a different behaviour is observed, probably due to the structural change of porphyrin or porphyrin-SWCNT interaction. The reversibility of the sensor resistivity is reasonably good at the optimum operating temperature (100 degrees C).

Phase change memory materials are promising for the next-generation of non-volatile flash memory that will serve in new mobile computing, entertainment and other handheld electronics. Among them are chalcogenide glasses Ge-Sb-Te (GST) which can exist in two separates structural states - amorphous and cristalline. Switching of the material from one to another state can be done by heating applying an electrical pulse or by exposure to intense laser beam. We report the changes of optical parameters of amorphous Ge1Sb2Te4 films under heat treatment and light exposure.

We obtained a new system containing nematic liquid crystal doped with nanostructured copolymer-clay particles. The clay (Cloisite-type) was modified by copolymerization of maleic anhydride and divinyl benzene and the nanocomposite has intercalated structure. Current-voltage characteristics of the liquid crystal/copolymer-clay systems were analyzed and the electro-optical response at heating -cooling cycles for different applied electric fields is discussed. Dielectric spectroscopy measurements in the low frequency domain have shown different regimes of its temperature dependence as function of the sample nature and the applied voltage. Comparison is made with the bulk liquid crystal. Changes of the phase transition temperature are thus revealed.

Effect of an antibacterial drug, sulfacetamide, IUPAC name N-[(4-aminophenyl) sulfonyl] acetamide (APSA) on the corrosion of carbon steel in 1.0 M HCl solution has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and XPS analysis. The electrochemical measurements indicated that the presence of APSA in 1.0 M HCl solution decreases the corrosion current (i(corr)) and increases the polarization rezistance (R-p). XPS surface analysis showed at this stage, in the absence of APSA, that the main product of corrosion is a non-stoichiometric Fe3+ oxide/oxide-hydroxide, consisting of a mixture of Fe2O3 and FeO(OH), where FeO(OH) is the main phase. Moreover, in presence of inhibitor the surface layer consists of FeO(OH) rather than pure oxide, adsorbed molecules of sulfacetamide and inorganic compounds such as: sulfides, carbonates, sulphates, nitrates, which were obtained by electrochemical degradation of APSA. UV-Vis spectrophotometry and HPLC technique were performed to determine the medium composition before and after corrosion. The results showed a decrease of the inhibitor concentration in 1.0 M HCl solution after carbon steel corrosion, indicating an adsorption process between organic compound molecules from aqueous phase and the electrode surface and/or the electrochemical degradation of APSA.

Replacing the graphite with carbides in the mixture with Fe powder may be an alternative technological process, by the fact that as carbides decompose when heated, the carbon is set free and diffuses into the Fe network ensuring chemical and structural homogeneity corresponding to sintered steels. Using cementite nanopowder mix with Fe powder is to ensure a better compaction by pressing, less time to decompose and C diffusion into the Fe network in a remarkably chemical homogeneity. The obtaining procedure for Fe3C consists in direct carburation of Fe powder in a special chamber.

The optical band gaps of the nanocomposite TiO2-Ge thin films deposited by reactive co-sputtering method onto quartz and silicon substrates at different oxygen partial pressures have been investigated by the optical characterization method. Using 2%, 4% and 6% oxygen dilution in argon, an atomic content of 3%, 22% and 35% germanium in the TiO2 oxide matrix was obtained. Structural characterization of layers was performed by X-ray diffraction and the result revealed that no crystallization phenomena have occurred after the annealing at 700 degrees C. When increasing the annealing temperature, at 750 degrees C the TiO2 anatase phase crystallizes and subsequently it partially convert to the rutile polymorph (at 800 degrees C). The optical band gaps were analyzed using Tauc plot formula for direct and indirect transitions gap. Intermediate energy levels appear in the TiO2 energy gap and a slight increasing of the indirect transitions gap with germanium content was noticed.

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.