National Institute Of Materials Physics - Romania

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5781 articles found

2641. The integral magneto-refractive effect: A method of probing magneto-resistance

Authors: Vopsaroiu, M; Cain, MG; Kuncser, V

Published: SEP 1 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3631778

We show that the optical infrared magneto-refractive effect can be used to probe magneto-resistance effects in absolute terms. A spin valve sample with synthetic anti-ferromagnet has been studied using non-contact infrared reflection spectroscopy measurements. Direct experimental comparison shows excellent agreement between electrical and optical measurements in both shape of the magneto-resistance curves and absolute values. This opens the possibility of developing fast and efficient tests of magneto-resistive samples and sensors using an in situ, non-contact, non-destructive optical approach, without the need to determine a calibration factor between the electrical and optical measurements. [doi:10.1063/1.3631778]

2642. Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Authors: Papa, F; Negrila, C; Dobrescu, G; Miyazaki, A; Balint, I

Published: SEP 2011, JOURNAL OF NATURAL GAS CHEMISTRY, 20, 542, DOI: 10.1016/S1003-9953(10)60221-6

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

2643. Tailoring the optical properties of Mg (x) Zn1-x O thin films by nitrogen doping

Authors: Epurescu, G; Birjega, R; Galca, AC

Published: SEP 2011, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 104, 893, DOI: 10.1007/s00339-011-6433-x

Thin films of Mg (x) Zn1-x O and Mg (x) Zn1-x O doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm(2) and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped Mg (x) Zn1-x O thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for Mg (x) Zn1-x O thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.

2644. Maple prepared organic heterostructures for photovoltaic applications

Authors: Stanculescu, A; Socol, M; Socol, G; Mihailescu, IN; Girtan, M; Stanculescu, F

Published: SEP 2011, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 104, 928, DOI: 10.1007/s00339-011-6440-y

In this study, we present the deposition of ZnPc, Alq3, and PTCDA thin films using Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. We also report the realisation of multilayer structures, made by the successive application of MAPLE. The films have been characterized by spectroscopic (UV-VIS and Photoluminescence) and microscopic (SEM and AFM) methods, and the effect of different deposition conditions such as fluence, number of pulses, and target concentration on the properties has been analysed. This paper also presents some investigations on the electrical conduction in sandwich type structures ITO or Si/organic layer/Au or Cu and ITO/double organic layer/Cu, emphasising the dominant effect of the height of the energetic barriers at the inorganic/organic and organic/organic interfaces.

2645. On the determination of vortex creep parameters in superconductors using standard magnetization relaxation data

Authors: Ivan, I; Miu, D; Popa, S; Jakob, G; Miu, L

Published: SEP 2011, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 24, DOI: 10.1088/0953-2048/24/9/095005

The relaxation of the irreversible magnetic moment m(t) in YBa(2)Cu(3)O(7) (YBCO) films was investigated as a function of temperature T and the external magnetic field H along the c axis applied in zero-field cooling conditions, for the determination of vortex creep parameters. The data analysis was performed using the T and current density dependence of the normalized vortex creep activation energy, or by the fit of the m(t) data with the well known interpolation formula in the framework of the general vortex creep equation. It was found that (i) even for specimens with strong static pinning the characteristic pinning energy remains small in the low-T range, where the vortex creep appearing in standard magnetization measurements is elastic, (ii) the observed strong increase of the time scale for creep and the decrease of the creep exponent with increasing H beyond the theoretical predictions can be attributed to the crossover elastic-creep-plastic-creep generated by the macroscopic currents induced in the specimen during magnetization measurements, and (iii) the creep parameters extracted with the interpolation formula are highly affected by the m(t) data registered at short t, which may lead to unphysical creep parameter values.

2646. Corrosion Inhibition of Carbon Steel in Hydrochloric Acid Solution Using a Sulfa Drug

Authors: Samide, A; Tutunaru, B; Negrila, C

Published: SEP 2011, CHEMICAL AND BIOCHEMICAL ENGINEERING QUARTERLY, 25, 308, DOI:

The corrosion inhibition of carbon steel in 1.0 mol L(-1) HCl in the presence of an antibacterial sulfa drug Sulfathiazole, IUPAC name 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide (TBSA) was investigated using mass loss and electrochemical measurements such as: potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). For the study of the surface morphology scanning electron spectroscopy (SEM) was used. The results showed that TBSA acts as a corrosion inhibitor in 1.0 mol L(-1) HCl solution by suppressing simultaneously the cathodic and anodic processes via adsorption on the carbon steel surface and that the inhibition efficiency increases with increasing concentration. XPS analysis revealed that the corrosion product consists of an oxyhydroxide/oxide mixture and that the iron oxyhydroxide proportion is higher than the iron oxide proportion.

2647. Structural phase transformations in annealed cubic ZnS nanocrystals

Authors: Ghica, D; Nistor, SV; Nistor, LC; Stefan, M; Mateescu, CD

Published: SEP 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 4335, DOI: 10.1007/s11051-011-0379-y

The structural changes of cubic ZnS (cZnS) nanocrystals (NCs) doped with 0.2 at.% Mn2+ pulse annealed in vacuum and in air, up to 500 A degrees C, were investigated by multifrequency electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples, prepared by a surfactant (Tween20)-assisted liquid-liquid reaction at pH = 6, consist of NCs with a tight size distribution around 3 nm and high crystallinity self-assembled into a stable mesoporous structure. The EPR spectra of the as prepared samples contain only the characteristic lines of the substitutional Mn2+(I) centers. No spectra from Mn2+ ions localized in (hydro)oxidized regions of the NCs surface were observed. The absence of such a surface layer could explain the stability of the cubic (sphalerite) structure observed by XRD and TEM in the investigated cZnS:Mn NCs annealed in vacuum up to 500 A degrees C. The observation of the cubic-hexagonal transformation for the same NCs annealed in air supports the role of such layer in promoting this structural transformation. The narrowing of the EPR spectral lines above 200 A degrees C with the increase in the average size of the cZnS:Mn crystallites was observed. The effect was more pronounced for the sample annealed in air. EPR also revealed the formation of minute amounts of substitutional Mn2+-type centers in a hexagonal ZnO structure at T similar to 300 A degrees C, corresponding to the early stages of the thermally induced oxidation of the cZnS:Mn NCs.

2648. Piezoelectric BNT-BT0.11 thin films processed by sol-gel technique

Authors: Cernea, M; Galca, AC; Cioangher, MC; Dragoi, C; Ioncea, G

Published: SEP 2011, JOURNAL OF MATERIALS SCIENCE, 46, 5627, DOI: 10.1007/s10853-011-5512-x

0.89(Na0.5Bi0.5)TiO3-0.11BaTiO(3), (BNT-BT0.11) thin film was fabricated by sol-gel/spin coating process, on platinized silicon wafer. Perovskite structure with random orientation of crystallites has been obtained at 700 A degrees C. Piezoelectric activity of BNT-BT0.11 thin film was detected using piezoresponse force microscopy (PFM). Effective piezoelectric coefficient d (33eff) of such film, recorded at 5 V applied dc voltage, was similar to 29 pm/V, which is similar to other BNT-BT (x) thin films. The complex refractive index and dielectric function of BNT-BT0.11 thin films were also investigated. The high leakage current density significantly influences the dielectric, ferroelectric, and piezoelectric properties of the BNT-BT0.11 films.

2649. Synthesis of ZnO thin films by 40 ps @ 532 nm laser pulses

Authors: Ristoscu, C; Socol, M; Socol, G; Mihailescu, IN; Jafer, R; Al-Hadeethi, Y; Batani, D

Published: SEP 2011, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 104, 876, DOI: 10.1007/s00339-011-6429-6

The synthesis by pulsed laser deposition of ZnO thin films with a Nd:YAG laser system delivering pulses of 40 ps @ 532 nm is reported. The laser beam irradiated the target placed inside a vacuum chamber evacuated down to 1.33x10(-1) Pa. The incident laser fluence was of 28 J/cm(2) in a spot of 0.1 mm(2). The ablated material was collected onto double face polished (111) Si or quartz wafers placed parallel at a separation distance of 7 mm. The AFM, SEM, UV-Vis, FT-IR and absorption ellipsometry results indicated that we obtained pure ZnO films with a rather uniform surface, having an average roughness of 37 nm. We observed by SEM that particulates are present on ZnO film surface or embedded into bulk. Their density and dimension were intermediary between particulates observed on similar structures deposited with fs or ns laser pulses. We noticed that the density of the particulates is increasing while their average size is decreasing when passing from ns to ps and fs laser pulses. The average transmission in the UV-Vis spectral region was found to be higher than 85%.

2650. Chemically Modified (Nano)Silica as Sensitive Material for Arginine and Lysine

Authors: Tudose, M; Culita, D; Marinescu, G; Ghica, C; Ionita, P

Published: SEP 2011, JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS, 21, 497, DOI: 10.1007/s10904-011-9470-1

Silica has been derivatized with aminopropyl groups which subsequently have been chemically modified with N-methoxy-2,6-dinitroaniline derivatives to yield a solid which changes its color in the presence of arginine or lysine, from yellow to blue. Other amino-acids (such as glycine, valine, cysteine, cystine, alanine, phenylalanine, histidine) do not showed this behavior. The same procedure may be applied to silica nanoparticles. The new materials were characterized by UV-Vis, IR, and TEM.