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1
Content available remote

Structural and optical properties of layers of pentacene formed by PLD method

100%
Potera P., Sagan P., Virt I., Kuzma M., Wisz G., Rudyj I., Frugynski M.
Open Physics
|
2008
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vol. 6
|
issue 4
765-770
EN
Organic films fabrication offers the possibility of producing electronic devices of low weight, mechanical flexibility and low cost. One suitable material for organic film fabrigation which is the subject of the great interest is pentacene, because it is characterized by the large carrier mobility (∼1 cm2/Vs). In this work, the growth of pentacene layers using pulse laser deposition (PLD) on different substrates (glass/ITO, Si) is described and various processing parameters are investigated. Two pulsed YAG:Nd3+ laser wavelengths were used for the ablation of the PLD target: the first harmonic at 1064 nm aGn:dNdth3+e second at 532 nm. The structure of the layers formed was examined using SEM and RHEED methods. The results were compared with results of optical spectroscopy studies. It will be shown that layers deposed using second harmonics have a higher quality than those for first harmonic. The other PLD parametersalso have a strong influence on the structure quality of layers.
2
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Ferromagnetic Resonance in CdTe:Cr Single Crystals Containing Dopant-Related Macrodefects

100%
Popovych V. D., Kuzma M., Skop N., Stefaniuk I., Cieniek B.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
34-38
EN
We study CdTe:Cr single crystals grown by the physical vapor transport method from pre-synthesized (Cd,Cr)Te alloys with 5 at.% of chromium nominal content. Macrodefects in the form of (111)-oriented thin platelets of dopant-related second phases were detected by scanning electron microscopy patterning of the chemically treated surfaces of the crystals. Magnetic properties of the crystals were investigated by ferromagnetic resonance using X-band Bruker spectrometer (9.43 GHz). Their ferromagnetic resonance spectra show several broad lines, which position depends on the orientation of the sample in relation to the external magnetic field in spectrometer. The angular dependences of ferromagnetic resonance spectra are interpreted in the frame of shape anisotropy of ferromagnetic resonance of the planar defects embedded in a weak magnetic CdTe matrix.
3
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Analytical approximate solutions for two-dimensional viscous flow through expanding or contracting gaps with permeable walls

84%
Dinarvand S., Rashidi M., Doosthoseini A.
Open Physics
|
2009
|
vol. 7
|
issue 4
791-799
EN
In this paper, the problem of laminar, isothermal, incompressible and viscous flow in a rectangular domain bounded by two moving porous walls, which enable the fluid to enter or exit during successive expansions or contractions is solved analytically by using the homotopy analysis method (HAM). Graphical results are presented to investigate the influence of the nondimensional wall dilation rate α and permeation Reynolds number Re on the velocity, normal pressure distribution and wall shear stress. The obtained solutions, in comparison with the numerical solutions, demonstrate remarkable accuracy. The present problem for slowly expanding or contracting walls with weak permeability is a simple model for the transport of biological fluids through contracting or expanding vessels.
4
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Pulsed laser treatment of gold and black gold thin films fabricated by thermal evaporation

84%
Novotný M., Fitl P. e., Sytchkova A., Bulíř J. Ã., Lanaok J., Pokorna P., Najdek D., Boan J.
Open Physics
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2009
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vol. 7
|
issue 2
327-331
EN
The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm−2 to 250 mJ·cm−2 was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm−2 and 3.5 mJ·cm−2 for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser treatment.
5
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Composition of Surface Layers Prepared by Ion Beam Assisted Deposition of Catalytic Metals from Pulsed Arc-Discharge Plasma onto Carbon Paper Substrates

84%
Poplavsky V., Luhin V., Koltunowicz T.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
295-298
EN
The layers were prepared by ion beam assisted deposition of iridium and platinum onto AVCarb® Carbon Fiber Paper P50 electrocatalyst supports for the production of diffusion layers of the membrane-electrode assemblies of low temperature fuel cells with polymer electrolyte membrane. Formation of the layers in the ion beam assisted deposition mode, by means of the deposition of metal and mixing of precipitating layer with the substrate by the accelerated (U=10 kV) ions of the same metal, was performed. In this process neutral fraction of metal vapour and ionized plasma of vacuum pulsed electric arc discharge were used. The investigations of morphology and composition of layers were carried out by the scanning electron microscopy, energy dispersive X-ray microanalysis, wave dispersive X-ray fluorescence analysis, and the Rutherford backscattering spectrometry methods. It was established that the obtained catalytic layers contain atoms of the deposited metals and substrate material as well as impurity oxygen atoms. The surfaces contain also metal inclusions of several micrometer size which arise from the precipitation of deposited metal droplets from the arc discharge of an ion source. The content of iridium and platinum atoms in the layers is ≈2×10¹⁶ cm¯²; the concentration of the deposited metals equals about several atomic percent.
6
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Structural and dielectric studies of lead-free ceramics: Na1/2Y1/2TiO3

84%
Barik S., Choudhary R., Mahapatra P.
Open Physics
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2008
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vol. 6
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issue 4
849-852
EN
The polycrystalline samples of Na1/2Y1/2TiO3 were prepared by the mixed-oxide method. A preliminary X-ray structural analysis was shown to exhibit the formation of a single-phase compound with an orthorhombic structure. Microstructural analysis by scanning electron microscopy (SEM) exhibits well defined grains distributed uniformly through out the sample suggesting the compactness and homogeneity of the sample. Detailed studies of dielectric properties of Na1/2Y1/2TiO3 in a wide frequency range (102–106 Hz) at different temperatures (31–500°C) show a dielectric anomaly at 105°C, which may be related to a ferroelectricparaelectric phase transition as suggested by hysteresis loop at room temperature. An ac conductivity (σ ac) of the material is mainly governed by the polaron hopping mechanism, which is also influenced by both frequency and temperature. The activation energy was obtained from the plot of temperature with a.c. conductivity.
7
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Crystal Structure and Chemical Characterization of La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_{x}O₃ (0 ≤ x ≤ 0.15) Compounds

84%
Troyanchuk I., Bushinsky M., Tereshko N., Fedotova V., Partyka J.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
240-244
EN
Neutron powder diffraction and magnetization measurements have been performed for La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_xO₃ (0 ≤ x ≤ 0.15) stoichiometric compounds. Increase of the Al³⁺ content enlarges the Mn⁴⁺ ions fraction from 0% (x=0) up to around 20% (x=0.15). The x=0 composition around 150 K exhibits a structural transition from the rhombohedral phase to the orthorhombic one whereas the crystal structure of the compounds with x=0.1 and 0.15 remains to be rhombohedral down to 2 K. The substitution of Ti⁴⁺ by Al³⁺ ions is accompanied by a gradual increase in the bond angle Mn-O-Mn and decrease in the Mn-O bond length which lead to enhancement of the covalent component of the chemical bond. All these compounds exhibit ferromagnetic components below 100 K. Magnetic moments estimated per manganese from the neutron powder diffraction data are found to be around 1.3 μ_{B} (x=0) and 1.7 μ_{B} (x=0.1 and 0.15) at 2 K. It is suggested that ferromagnetism is originated predominantly from the Mn³⁺-O-Mn³⁺ and Mn³⁺-O-Mn⁴⁺ superexchange interactions whereas bond angles fluctuation leads to magnetic frustrations. Enhancement of covalence slightly increases ferromagnetism.
8
Content available remote

Fractal surface analysis of Zircaloy-4 SEM micrographs using the time-series method

84%
Paun V.
Open Physics
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2009
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vol. 7
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issue 2
264-269
EN
The SEM microfractographies of Zircaloy-4 are studied by the time-series method. We first develop a computer application which associates a time series to each SEM micrograph. Furthermore, we will apply the phase space embedding technique to reconstruct the attractor and to compute the autocorrelation dimension. Using the fractal analysis technique, the SEM microfractographies of the fracture surface of the Zircaloy-4 samples have been analyzed.
9
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Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

68%
Durak K., Wiertel M., Surowiec Z., Miaskowski A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1593-1597
EN
Nanosized iron oxide powders are materials considered with regard to its application in medical therapy called hyperthermia. Magnetite nanopowders with crystallite size varying from 6.6 to 11.8 nm have been prepared by the co-precipitation method. In this study a change of a crystallite size is driven mainly by varying of initial pH of water ammonia solution in which a process of magnetite precipitation runs. Crystallographic structures and phase composition obtained samples and the size of magnetite nanoparticles were determined by X-ray diffraction method. Positron lifetime spectroscopy has been used to assess defectiveness of microstructure. Experimental positron annihilation spectra were successfully resolved into three lifetime components. It appears that from point of view of microstructure the defects concentrations in studied nanopowder samples are very high which causes a saturation of positron trapping.
10
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Ion Beam Formation of Electrocatalysts for Direct Methanol and Ethanol Fuel Cells on the Basis of Carbon Catalyst Supports

61%
Poplavsky V., Dorozhko A., Luhin V., Matys V., Zukowski P., Czarnacka K.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
278-282
EN
Ion-beam modification of materials whose service properties are mainly controlled by the surface composition is of especial interest, in particular, for electrocatalysts, namely electrodes of fuel cells - perspective chemical current sources. A catalyst is needed for effective operation of fuel cell. In this paper active layers of the electrocatalysts were prepared by ion beam assisted deposition of catalytic (platinum) and activating (cerium) metals onto carbon (AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T) catalyst supports. Formation of layers by ion beam assisted deposition by means of the deposition of metal and mixing of precipitating layer with the substrate by accelerated ions of the same metal, was carried out. Metal deposition and mixing between the precipitable layer and surface of the substrate by accelerated (U=10 kV) ions of the same metal were conducted from a neutral vapor fraction and plasma of vacuum arc discharge of a pulsed electric arc ion source. Study of the morphology and composition of layers was carried out by the scanning electron microscopy, energy dispersive X-ray microanalysis, X-ray fluorescence analysis, and the Rutherford backscattering spectrometry methods. According to the investigations with the use of cyclic voltammetry, the electrocatalysts with the prepared layers exhibited catalytic activity in the reactions of electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature direct methanol and direct ethanol fuel cells.
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