acta physica slovaca

Acta Physica Slovaca 53(2003)
  • Š. Barta
    Spin-dependent scattering on the interface layers in magnetic multi-layers
    Acta Physica Slovaca 53, 81 (2003)

    Abstract: We present a calculation of the transmission coefficients $T^{\uparrow(\downarrow)}$. The idea of the calculation of $T^{\uparrow(\downarrow)}$ is the following: Starting from the exchange Hamiltonian of the Heisenberg type which describes the exchange energy of the ${\it d}$-electrons in the ferromagnetic layers and the exchange interaction energy between ${\it d}$ and ${\it s}$ electrons, we statistically averaged the exchange interaction energy according to the distribution function of ${\it d}$-electrons at the given temperature and magnetic field. The average energy represents the potential discontinuities at the interface between paramagnetic and ferromagnetic layers. The scattering of the ${\it s}$-electrons on the potential discontinuities represents the microscopic origin of the coefficients $T^{\uparrow(\downarrow)}$. It was shown that these coefficients are angular and spin-dependent.

  • D. Franta,I. Ohlídal,P. Klapetek,A. Montaigne-Ramil, A. Bonanni,D. Stifter,H. Sitter
    Optimal constant of ZnTe and ZnSe epitaxial thin films
    Acta Physica Slovaca 53, 95 (2003)

    Abstract: In this paper the spectral dependences of the optical constants, \ie refractive index and extinction coefficient, are presented within the spectral region 220--850 nm. For determining these spectral dependences a multi-sample modification of the combined optical method based on a simultaneous interpretation of experimental data corresponding to variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry is used. Further, physical models and an iterative procedure enabling us to determine the spectral dependences of the optical constants of both the epitaxial films are described in detail. The spectral dependences of the optical constants are introduced in the forms of curves and tables.

  • K. Gmucová,D. Barancok, J. Cirák, P. Tomcík
    Sensitivity enhancement of carbon fibre microelectrode modified by LB layers of polythiophene to trace metals and hydrogen in aqueous solutions
    Acta Physica Slovaca 53, 105 (2003)

    Abstract: The detection of trace metals in aqueous solutions is of great importance in relation to the environmental protection. A significant sensitivity enhancement in the double-step voltcoulometry was reached by using a chemically modified carbon fibre microelectrode. The sensitivity to the method used for cleaning of the microelectrode surface before being coated by the Langmuir-Blodgett polythiophene film was demonstrated. The changes in kinetics of redox reactions, taking place on the microelectrode surface, were described.

  • J. Müllerová,S. Jurecka, A. Kucerová
    Extraction of optical parameters of thin films from spectral measurements for design and optical performance of multilayer structures
    Acta Physica Slovaca 53, 111 (2003)

    Abstract: Optical parameters of a-Si:H and indium tin oxide (ITO) thin films deposited on glass substrates are determined from spectral measurements of reflectance and/or transmittance. It is shown how important the exact knowledge of optical parameters as well as thicknesses of the layers for the design and the optical performance of multilayer structures is. The model of the ~p-i-n-based a:Si-H solar cell with ITO as transparent conductive oxide layer is used for illustrating. The modelling of the solar cell integral reflectance in the spectral region of (650--830) nm is used as a criterion to reverse engineering of a multilayer structure with suppressed reflectance losses. The reflectance of a~solar cell is modelled and the simulation of the varying optical parameters of individual layers including their thicknesses is discussed. Besides this, the advantage of using an antireflective layer under ITO is discussed.

  • K. Olejnik, J. Zemek, J. Stejskal
    Surface coverage of polyaniline-coated silica gels
    Acta Physica Slovaca 53, 121 (2003)

    Abstract: Silica gels of 15\,$\mu $m and 130\,$\mu $m mean sizes were covered by polyaniline hydrochloride (PANI) nanofilms during polymerisation under different conditions. A surface coverage of the silica gel was determined from the C 1s or N 1s photoelectron spectra by two methods. The first one, the line shape analysis carried out by QUASES-Tougaard software, enables us to recognise also the surface morphology of the samples. The second method accounts for the C 1s or N 1s peak area ratios originating from the PANI-coated silica gels and from the PANI standard. The results indicate that silica gel surfaces are not fully covered by the PANI film. The coverage values are consistent mutually, correlate well with polymerisation conditions and are in good agreement with a PANI content determined independently by burning the PANI-coated silica gel samples.

  • J. Osvald
    C-V measurment of a doping profile of -doped GaAs and its spatial resolution - numerical study
    Acta Physica Slovaca 53, 129 (2003)

    Abstract: We have studied numerically the ability of C-V profiling method to describe precisely \mbox{$\delta$-doped} concentration in the semiconductor. %C-V doping profiles were modelled for special input values of doping simulations of %C-V curves within a drift-diffusion approximation. C-V doping profiles were modelled for a special input value of doping concentration using C-V curves calculated within a drift-diffusion approximation. The calculated free carrier concentrations for applied votages were used to simulate C-V behaviour and a capacitance doping concentration profile of the sample. The maximum apparent doping concentration extracted from the simulation process is slightly lower than the $\delta $-doping concentration input. Certainly $\delta $-peak in concentration could not be reproduced with an absolute fidelity. The width of the calculated concentration peak at its bottom is several semiconductor Debye lengths. The concentration peak is shifted very slightly to the bulk of the semiconductor. The shape of the calculated concentration profile was practically not influenced by the position of the layer in the depletion region.

  • S. De Wolf,G. Agostinelli, H.F.W. Dekkers, J. Szlufcik
    Rear-surface pasivation and design for thin p-type multicrystalline silicon solar cells
    Acta Physica Slovaca 53, 135 (2003)

    Abstract: Recently, an important trend within crystalline silicon solar cell processing is the assignment of a more prominent role to thin ($ \le $150$\mu $m) substrates. This considerably reduces dominant material costs, albeit at the expense of giving up well-established solar cell processing steps, such as the screenprinted aluminium back-surface-field (BSF) and contact formation, due to excessive warping of the cells. Next to this, thinner wafers evidently increase the need for excellent rear-surface passivation-schemes. Finally, it is generally accepted that when using multicrystalline Si (mc-Si) substrates, dedicated processing-steps are essential to upgrade the average minority charge carrier lifetime in the bulk, \textit{$\tau $}$_{bulk}$. Generally, this is done by applying gettering and/or hydrogenation-steps, both being relatively high temperature steps. Futhermore, for such thin solar cells, to be sufficiently efficient, the minority charge carrier diffusion length in the bulk, $L_{bulk}$, should exceed twice the waferthickness.\\ This paper describes a solar cell processing route potentially overcoming all three constraints as pointed out on thin $p$-type mc-Si silicon substrates. It will be shown that the use of POCl$_{3}$-diffusion is rather essential to increase \textit{$\tau $}$_{bulk}$. For the rear side, it is then shown that direct Plasma Enhanced Chemical Vapour Deposited (PECVD) a-Si:H layers can yield surface recombination velocities with values below 1.5m.s$^{-1}$. This is achieved throughout a broad excess minority charge carrier density, \textit{$\Delta $n}, range of about 5x10$^{18}$ to 5x10$^{22}$m$^{-3}$, for 20nm thick intrinsic PECVD a-Si layers on top of 1.0x10$^{-2}\Omega $.m $p$-type Float Zone (FZ) silicon wafers. Finally, results are given of subsequent POCl$_{3}$ gettering and PECVD a-Si:H surface passivation throughout a complete cast mc-Si Polix 1.0x10$^{-2}\Omega $.m $p$-type ingot by means of $L_{eff}$ extraction.

  • J. Douari
    Multi-species anyons supersymmetry on two-dimensional lattice
    Acta Physica Slovaca 53, 143 (2003)

    Abstract: The algebra of multi-species anyons characterized by different statistical parameters $\nu_{ij}=e_{i}e_{j}\Phi_{i}\Phi_{j}/(2\pi)$, $i,j=1,...,n$ is redefined by basing on fermions and $k_{i}$-fermions ($k_{i}\in\bf{N}\rm /\{0,1\}$ with $i\in\bf{N}\rm $) and its superalgebra is constructed. The so-called fractional supersymmetry of multi-species anyons is realized on 2d lattice.

  • S. B. Faruque
    Circular orbits of a particle in Kerr field: A study using effective one-body approach
    Acta Physica Slovaca 53, 157 (2003)

    Abstract: Constraint Hamiltonian dynamics is used in an effective one-body approach to study relativistic gravitational two-body system with spin-orbit interaction. Radii of circular orbits and approximate location of innermost stable circular orbit (ISCO) of a non-spinning body around a slowly spinning body whose gravitational field is described by the Kerr metric are derived.

  • A. Likar, T. Vidmar
    Optimal functions for peak search methods based on spectrum convolution
    Acta Physica Slovaca 53, 165 (2003)

    Abstract: Any peak search method for high resolution gamma-ray spectroscopy based on convoluted spectra is faced with the choice of the convolution functions. We derive the optimal convolution functions for extraction of the most important parameters of a peak -- the area of the peak, its position and the width. It is shown that such functions strongly depend on the signal-to-background ratio. For small peaks on high background the functions are well approximated by derivatives of the peak shape itself. For peaks on low background the optimal convolution functions are very simple, approaching in the limit of vanishing background the linear or quadratic shape.

  • S. W. Harun,N. Tamchek, P. Poopalan, H. Ahmad
    Effect of injection of C-band amplified spontaneous emision on two stage L-band erbium-doped fibre amplifier
    Acta Physica Slovaca 53, 173 (2003)

    Abstract: An effect of injection of conventional-band amplified spontaneous emission (C-band ASE) on a two-stage long wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated. It uses two circulators and a broadband fiber Bragg grating (FBG) to route unused C-band backward ASE from the second stage back to the input end of the first stage of the amplifier. The amplifier gain is clamped at 15.5 dB and the saturation power increases from $-13$ dBm to $-8$ dBm with injection of the C-band ASE. The gain level can be controlled to be in the range from 15.5 to 16.8 dB by varying the variable optical attenuator (VOA) loss from 0 to 20 dB without much variation in noise figure. These results show that the injection of C-band ASE can be used to clamp the L-band gain in a two-stage L-band EDFA, which has higher gain compared to a single stage.

  • J. K. Baria
    A local pseudopotential in the study of metallic properties of rhodium and iridium
    Acta Physica Slovaca 53, 177 (2003)

    Abstract: A local pseudopotential has been proposed in this paper. This potential is used to calculate total energy, phonon dispersion curves (q-space and r-space), phonon density of states, Mode Gr\"{u}neisen parameters, dynamic elastic constants, bulk modulus, maximum phonon frequency, mean phonon frequency, fundamental frequency (second moment of phonon frequency) and propagation velocities of elastic waves of rhodium and iridium. The contribution of d-like electron is taken into account by introducing repulsive short-range Born-Mayer term. A unique technique is suggested for the determination of the potential parameter which is independent of any fitting procedure and a new criterion for the selection of the exchange and correlation effects is also searched out by considering the minimization of total energy. A good agreement between theoretical investigations and experimental findings has confirmed our formulation.

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