Research Trends in Contemporary Materials Science

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Authors: M. Radmilović-Radjenović, Z.Lj. Petrović, Željka Nikitović, A. Strinić, V. Stojanović, Aleksandra Nina, B. Radjenović
Abstract: Neutral beam processing has evolved into one of the most promising methods for overcoming plasma process induced damage. Surface treatment by neutrals avoids problems with surface charging effects, frequently encountered when using common ion treatment, especially for low k-materials. In this paper, the influence of various parameters on the neutralization of ion beams in Ar-CF4 mixture based on a Particle in Cell with Monte Carlo collisions (PIC/MCC) simulation is studied. The efficiency of neutralization has been treated by considering both surface neutralization of ions and collisions of ions in the gas.
Authors: B. Radjenović, M. Radmilović-Radjenović, Z.Lj. Petrović
Abstract: A comprehensive simulation of etching profile evolution requires knowledge of the etching rates at all points of the profile surface during the etching process. Electrons do not contribute directly to the material removal, but they are the source, together with positive ions, of the profile charging that has many negative consequences on the final outcome of the process especially in the case of insulating material etching. The ability to simulate feature charging was added to the 3D level set profile evolution simulator described earlier. The ion and electron fluxes were computed along the feature using the Monte Carlo method. The surface potential profiles and electric field for the entire feature were generated by solving the Laplace equation using finite elements method. Calculations were performed in the case of a simplified model of Ar+/CF4 nonequilibrium plasma etching of SiO2.
Authors: D. Peruško, N. Bibić, S. Petrović, M. Popović, M. Novaković, I. Radović, M. Milosavljević
Abstract: The effects of nitrogen pre-implantation of AISI C1045 steel substrates on the properties of deposited TiN coatings were investigated. Nitrogen ion implantations were performed at 40 keV, to the fluences from 5x1016 – 5x1017 ions/cm2. On so prepared substrates we deposited 1.3 μm thick TiN layers by reactive sputtering. Structural characterizations of the samples were performed by grazing incidence X-ray diffraction analysis (GXRD), standard X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM). Microhardness was measured by Vicker’s method. The obtained results indicate the formation of iron-nitrides in the near surface region of the substrates, more pronounced for higher implanted fluences. The structure of the deposited TiN coatings shows a strong dependence on the pre-implantation of the substrates, which is attributed to the changed local structure at the surface. Ion implantation and deposition of hard TiN coatings induce an increase of the microhardness of this low performance steel of more than eight times.
Authors: T. Makabe, T. Yagisawa
Abstract: A self-consistent modeling of two-dimensional and temporal (2D-t) structures of RF magnetron plasma with a metallic (copper) and a dielectric (SiO2) target is performed at 5 mTorr in argon by using plasma hybrid model consisting of a particle-in-cell/Monte Carlo (PIC/MC) simulation for electrons and the relaxation continuum (RCT) model for ions. The erosion profiles of both targets are numerically predicted through the flux velocity distribution of ions incident on the surface. The mechanism of plasma maintenance in a dielectric target is quite different from that in a metallic one. Two major differences exist in an erosion profile between both targets. One is the presence of dual peaks in the erosion profile of the dielectric target. The other is the discrepancy in the position of the maxima between incident ion flux and erosion depth on the dielectric target. These are direct influences of the radially localized structure in an interfacial sheath based on the charge accumulation on a dielectric surface.
Authors: Maxim V. Kuznetsov, Yuri G. Morozov, Ivan P. Parkin
Abstract: The results of a new potentiometric technique for in situ diagnostics of self-propagating high-temperature synthesis (SHS) of different complex oxides are presented. This technique is based on electrochemical processes. The characteristic peaks attributed to the electric responses from cation streams of alkali, alkaline-earth and some elements of group VI are discovered and the respective routes of the corresponding chemical reactions found.
Authors: Rados Gajić, R. Meisels, F. Kuchar, Dj. Jovanović, K. Hingerl
Abstract: Study of the refraction and rightness effects in 2D Archimedean lattice photonic crystals is presented. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Besides the familiar Archimedean lattices like square, triangular, honeycomb and Kagome ones, we consider also, the less known 32,4,3,4 (ladybug) and 3,4,6,4 (honeycombring) structures. This involves the calculations of band structures, band-gap maps, equifrequency contours, FDTD simulations of electromagnetic propagation through the structures, as well as an experimental verification of negative refraction at microwaves.
Authors: I. Popović, M. Zlatanović
Abstract: Matching of pulse plasma generators to various gas discharges for surface treatment of materials depends on plasma processing equipment. In order to investigate the influence of pulse plasma generator and gas discharge parameters on electrical signal waveforms during the process of unipolar pulse plasma nitriding, equivalent electrical circuit was introduced. The influence of parasitic inductance of interconnection lines and vacuum chamber physical properties was also included in the given equivalent circuit. Gas discharge characteristics at different process parameters were investigated. It was found that the gas discharge and pulse plasma generator properties, as well as the electrical characteristics of interconnecting lines determined the system electrical signal response. From the analysis of optical signals emitted by the gas discharge it was found that the optical signal response might be represented by a typical RC integrator circuit response with the time constant higher than that of the equivalent electrical circuit of generator load. The conclusion was drawn that the process of charge particles generation is followed by the process of active species generation responsible for thermo-chemical processes on the cathode surface. Thus, the increase of the pulse plasma frequency is limited by the thermo-chemical process efficiency, and not only by the generator switching characteristics or by gas discharge electrical properties.
Authors: D. Milivojević, Jovan Blanuša, V. Spasojević, V. Kusigerski, B. Babić-Stojić
Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01, 0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors. Thermal treatment procedure was carried out in air at different temperatures in the range 400 - 900°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.
Authors: P.M. Lukić, R.M. Ramović, Rajko M. Šašić
Abstract: The focus of this paper was the investigation and modeling of transport characteristics in a strained SiGe based MOSFET structure, which might be of fundamental importance for the understanding of its operating characteristics. In the investigation, carrier mobility dependence on the lateral and vertical electric field is especially considered. Carrier mobility models for long channel as well as short channel SiGe MOSFETs are also presented. Average effective electric field model is proposed taking into account impact of high electric field effects on the effective channel length. In the final effective carrier mobility model, for the short channel SiGe MOSFETs, serial drain to source resistance is included. At the same time, proposed models are relatively simple. By using the presented model, simulations were performed.
Authors: D. Arsenović, S.B. Vrhovac, Z.M. Jakšić, Lj. Budinski-Petković, A. Belić
Abstract: We study by numerical simulation the compaction dynamics of frictional hard disks in two dimensions, subjected to vertical shaking. Shaking is modeled by a series of vertical expansions of the disk packing, followed by dynamical recompression of the assembly under the action of gravity. The second phase of the shake cycle is based on an efficient event−driven molecular−dynamics algorithm. We analyze the compaction dynamics for various values of friction coefficient and coefficient of normal restitution. We find that the time evolution of the density is described by ρ(t)=ρ∞ − ρEα[−(t/τ)α], where Eα denotes the Mittag−Leffler function of order 0<α<1. The parameter τ is found to decay with tapping intensity Γ according to a power law τ ∝ Γ−γ , where parameter γ is almost independent of the material properties of grains. Also, an expression for the grain mobility during compaction process has been obtained.

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