Layered magnetic heterostructures are very promising candidates in spintronics in which the influences of interfaces, surfaces and defects play a crucial role. X-ray photoelectron spectroscopy (XPS) study has been performed for studying in detail the chemical state and electronic structure of Co2FeAl (CFA) Heusler alloy interfaced with Si substrates. XPS survey scan spectra have clearly shown the presence of Fe, Co and Al signal along with the signal due to Si. The presence of Co, Fe and Al signal confirms the formation of CFA alloy phase. Our XPS results support our previous study  on CFA/Si structure in determining the magnetic and transport properties across the interface.
Tomasz Kotwica, Jaroslaw Domaradzki, Damian Wojcieszak, Andrzej Sikora, Malgorzata Kot and Dieter Schmeisser
The paper presents results of investigations on surface properties of transparent semiconducting thin films based on (Ti-Cu)oxide system prepared using multi-magnetron sputtering system. The thin films were prepared using two programmed profiles of pulse width modulation coefficient, so called V- and U-shape profiles. The applied powering profiles allowed fabrication of thin films with gradient distribution of Ti and Cu elements over the thickness of deposited layers. Optical investigations allowed determination of transparency of prepared films that reached up to 60 % in the visible part of optical radiation, which makes them attractive for the transparent electronics domain. Surface properties investigations showed that the surface of mixed (Ti-Cu)oxides was sensitive to adsorption, in particular to carbon dioxide and water vapor. Soft etching with argon ions resulted in surface cleaning from residuals, however, deoxidation of Cu-oxide components was also observed.
Reşit Özmenteş, Cabir Temirci, Abdullah Özkartal, Kadir Ejderha and Nezir Yildirim
Copper(II) oxide (CuO) in powder form was evaporated thermally on the front surface of an n-Si (1 0 0) single crystal using a vacuum coating unit. Structural investigation of the deposited CuO film was made using X-ray difraction (XRD) and energy dispersive X-ray analysis (EDX) techniques. It was determined from the obtained results that the copper oxide films exhibited single-phase CuO properties in a monoclinic crystal structure. Transmittance measurement of the CuO film was performed by a UV-Vis spectrophotometer. Band gap energy of the film was determined as 1.74 eV under indirect band gap assumption. Current-voltage (I-V) measurements of the CuO/n-Si heterojunctions were performed under illumination and in the dark to reveal the photovoltaic and electrical properties of the produced samples. From the I-V measurements, it was revealed that the CuO/n-Si heterojunctions produced by thermal evaporation exibit excellent rectifying properties in dark and photovoltaic properties under illumination. Conversion efficiencies of the CuO/n-Si solar cells are comparable to those of CuO/n-Si produced by other methods described in the literature.
The effect of MgB2 addition on the Eu1Ba2Cu3O7 (EBCO) ceramics was systematically studied. Series of Eu1Ba2Cu3O7 + x(MgB2) samples (x = 0 wt.%, 0.05 wt.%, 0.1 wt.%, 1 wt.%, 3 wt.%) were prepared using traditional solid state method. X-ray powder diffraction measurements were used for phase identification. The lattice parameters and orthorombicity decreased with MgB2 addition. A standard four point measurement method was used to determine transition temperatures Tc of superconducting samples. Tc values of the samples were decreasing with MgB2 concentration. TGA results indicate thermal stability of doped samples.
Tadeusz Groń, Magdalena Piątkowska, Elżbieta Tomaszewicz, Bogdan Sawicki, Piotr Urbanowicz and Henryk Duda
Polycrystalline samples of new scheelite-type tungstates, Pb1−3x xPr2xWO4 with 0.0098 ⩽ x ⩽ 0.20, where denotes cationic vacancies have been successfully prepared by a high-temperature solid-state reaction method using Pr2(WO4)3 and PbWO4 as the starting reactants. The influence of the Pr3+ substitution in the scheelite framework on the structure and optical properties of prepared new ceramic materials has been examined using powder X-ray diffraction method (XRD) and UV-Vis-NIR spectroscopy. The results of dielectric studies of Pb1−3x xPr2xWO4 samples showed both low values of dielectric constant (below 14) and loss tangent (below 0.2). The electrical conductivity and thermoelectric power measurements revealed a low conductivity (∼2 × 10−9 S/m) and the sign change of thermoelectric power around the temperature of 366 K suggesting the p-n transition. These results are discussed in the context of vacancy, acceptor and donor levels as well as the Maxwell-Wagner model.
K. Ramarao, B. Rajesh Babu, B. Kishore Babu, V. Veeraiah, K. Rajasekhar, B. Ranjith Kumar and B. Swarna Latha
In this work, Ni substituted magnesium spinel ferrites having general formula Mg1−xNixFe2O4 (where x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3) were synthesized by standard solid state reaction method. All the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), DC resistivity measurements. X-ray diffraction analysis confirmed the single spinel phase. The lattice constant decreased with increasing Ni content due to the difference in the ionic radii of Mg2+ and Ni2+ ions. The FT-IR spectra reveled two prominent frequency bands in the wave number range of 400 cm−1 to 600 cm−1, which confirmed the cubic spinel structure of obtained compound and completion of chemical reaction. Magnetic studies revealed that the saturation magnetization increased with the substitution of Ni. The increase in magnetization was explained on the basis of distribution of magnetic and non-magnetic cations among A and B sites of the spinel lattice. A significant influence of cation distribution on DC electrical resistivity and activation energy was observed.
Dye sensitized solar cells are photoelectrochemical cells mimicking photosynthesis. They represent a new generation of solar cells which is intensively studied nowadays. This cell was fabricated using TiO2 nanoparticles coated on FTO glass, organic dyes as photosensitizer, PEDOT:PSS as counter electrode and iodide-triiodide as electrolyte. The present work aims at the use of low cost new organic dyes viz. biebrich scarlet, alizarine cyanine green and evans blue for DSSC as an alternative to metallic dyes. In the present work, I-V characteristics, energy or power conversion efficiencies of the dyes have been studied in different solvents. The photoelectrochemical properties of the dyes were observed under 1.5 AM condition.
Phu Tran Tin, Tran Hoang Quang Minh, Nguyen Huu Khanh Nhan, Hsiao-Yi Lee and Tran Thanh Trang
In the last decades, new solutions for improving lighting properties of white LED lamps (WLEDs) have been the main research direction in optoelectronics. In this paper, a modern approach for enhancing luminous flux and color quality of white LED lamps was presented. By mixing green-emitting CaF2:Ce3+,Tb3+ phosphor with yellow-emitting YAG:Ce phosphor compound, the luminous flux and color quality of white LED lamps with conformal phosphor geometry (CPG) increased significantly. From the obtained results it follows that, the luminous flux increased more than 1.5 times, and the correlated color temperature deviation decreased more than 4 times in comparison with the non-green-emitting CaF2:Ce3+,Tb3+ phosphor. The presented research shows that the green-emitting CaF2:Ce3+,Tb3+ phosphor could become a good candidate for enhancing luminous flux and color quality of white LED lamps.
It is important to grow and characterize new bimetallic thiocyanate single crystals as they are expected to exhibit useful optical and electrical properties. In the present study, calcium cadmium thiocyanate CaCd(SCN)4 single crystals were grown by slow evaporation of solvent and were characterized chemically, structurally, thermally, optically and electrically. X-ray diffraction analysis indicates that the grown crystal belongs to the tetragonal crystal system with lattice parameters: a = b = 12.2491(7) Å and c = 15.1012(5) Å. EDAX spectral analysis confirms the expected chemical composition. Thermogravimetric (TG/DTA) measurement implies good thermal stability. Optical (UV-Vis-NIR absorption spectral and SHG efficiency) measurements suggest good optical absorption in the UV and blue regions and the SHG efficiency of 6.13 (in urea unit). The dielectric measurements carried out in the temperature range of 40 °C to 150 °C at five different frequencies, viz. 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz indicate a normal dielectric behavior.
Bismuth niobate (BiNbO4) has attracted attention as a low-fired ceramics with promising microwave application potential. BiNbO4 ceramics was fabricated by mixed oxide method and sintered at temperature T<1000°C. As the sintering aids a small amount of CuO oxide was used. The crystalline structure of the ceramic samples was examined by X-ray diffraction method at room temperature. The Rietveld refinement method was used for analysis of diffraction data. As a result an influence of dopants on crystal structure of bismuth niobate (BiNbO4) ceramics was revealed. It was found that fabricated BiNbO4 ceramics adopted the orthorhombic symmetry (α-BiNbO4 phase, Pnna (52) space group). Small differences in elementary cell parameters were found.