Volume 70, Number 4, 2018
 
THEORETICAL, MATHEMATICAL, AND COMPUTATIONAL PHYSICS
 
Diffusion problems in composite media with interfacial flux jump
R. BUNOIU, C. TIMOFTE
Rom. Rep. Phys. 70, 116 (2018)
Abstract. We study the homogenization of a thermal diffusion problem in a highly heterogeneous composite medium formed by two constituents, separated by an imperfect interface, where both the temperature and the flux exhibit jumps. Two geometrical settings are considered, in terms of the connectivity of the two constituents. The presence of the flux jump leads to some modified stationary Barenblatt models.
Article no. 116: PDF 
 
ATOMIC, MOLECULAR, AND NUCLEAR PHYSICS
 
Atomic clocks and time keeping in Romania
CIPRIANA TOMESCU, LIVIU GIURGIU
Rom. Rep. Phys. 70, 205 (2018)
Abstract. The paper is a review of the results obtained during the last 5 decades in Romania, and in cooperation with laboratories in France, Switzerland and Germany, in studies of fields such as quantum optics and quantum engineering, towards the realization of ultra-precise atomic clocks. Current and future scientific interests are also presented, in an attempt to highlight the expertise that exists at national level in one of the hottest topics of modern quantum physics.
Article no. 205: PDF 
 
CONDENSED AND SOFT MATTER PHYSICS
 
Specific and selective SERS active sites generation on silver nanoparticles by cationic and anionic adatoms
ANDREI STEFANCU, STEFANIA D. IANCU, VLAD MOISOIU, NICOLAE LEOPOLD
Rom. Rep. Phys. 70, 509 (2018)
Abstract. The here proposed specific adatom approach for surface-enhanced Raman scattering (SERS) highlights the fact that the Raman enhancement originates from the electronic coupling of the analyte with the metal surface, mediated by specific ions that form SERS active sites on the surface of the nanoparticles. The spectra of anionic and cationic analytes can be recorded specifically by generating specific SERS active sites, obtained by adsorbed ions (adions) such as Ca2+ and Cl-, respectively. Thus, the SERS spectrum of anionic and cationic species is turned on by the electronic coupling of the analyte with the metal surface at such SERS active sites. Moreover, the selective SERS turn on of anions, like citrate and Cl- from their mixture is determined by their competitive adsorption to the metal surface. Furthermore, a proportional dependence of the SERS intensity with the number of SERS active sites was observed. The sequential detection of the three analytes, citrate, chloride and Nile Blue in the same solution can't be explained by a model based on the aggregation of the nanoparticles. In the adatom approach, the aggregation of the nanoparticles is an unnecessary step that rather contributes to the low reproducibility of SERS spectra. We strongly believe that the proposed specific adatom approach will lead to a better understanding and control in SERS spectroscopy, thus improving the predictability of the method.
Article no. 509: PDF 
Influence of high pressure on the crystal and magnetic structure of La0.5Ba0.5CoO3
A.V. RUTKAUSKAS, D.P. KOZLENKO, I.O. TROYANCHUK, S.E. KICHANOV, E.V. LUKIN, B.N. SAVENKO
Rom. Rep. Phys. 70, 510 (2018)
Abstract. The crystal and magnetic structures of cobaltite La0.5Ba0.5CoO3 have been investigated by the neutron diffraction method at high pressure up to 4.6 GPa in the temperature range from 10 to 290 K. Under normal pressure, the crystal structure of this compound has a cubic symmetry with the spatial group Pm3m which is kept throughout the investigated pressure range. Ferromagnetic ordering is observed when the temperature is reduced to T = Tc = 178 K. This magnetic ordering and Curie temperature do not change at high pressure up to 4.6 GPa. It is assumed that the stability of the ferromagnetic phase for La0.5Ba0.5CoO3 is provided by preservation of the Co3+ ions concentration in the intermediate-spin state in the total investigated range of the pressure.
Article no. 510: PDF 
Structural and compositional specifications on biogenic ferrihydrite nanoparticles production by Klebsiella oxytoca
S. KICHANOV, A. PANTELICA, D. PANTELICA, S. STOLYAR, R. ISKHAKOV, D. ARANGHEL, P. IONESCU, R. VLADOIU, M. BALASOIU
Rom. Rep. Phys. 70, 511 (2018)
Abstract. Investigations of biogenic ferrihydrite nanoparticles produced by bacteria Klebsiella oxytoca by applying methods of synchrotron radiation powder diffraction, particle-induced X-ray emission (PIXE), proton induced gamma-emission (PIGE) and proton Rutherford backscattering (RBS) are reported and discussed.
Article no. 511: PDF 
The effect of annealing on the structural and optical properties of ZnSe thin films
N. TIGAU, S. CONDURACHE-BOTA
Rom. Rep. Phys. 70, 512 (2018)
Abstract. Zinc selenide (ZnSe) thin films were deposited onto glass substrates by vacuum evaporation and then were annealed at 500 K for 1h, in open atmosphere. The morpho-structural analysis of both the as-deposited and of the annealed films was performed, by using the XRD and SEM techniques. Also, by recording the transmittance and reflectance spectra, relevant optical parameters could be computed, such as the absorption coefficient, the refractive index and the optical energy bandgap. It was found that the annealing process improved the crystallinity of the films, decreased the absorption coefficient and increased the energy bandgap from 2.64 to 2.83 eV.
Article no. 512: PDF 
TiO2 nanoparticles influence on rhodamine 6G droplet emission
M. BONI, ANGELA STAICU, I.R. ANDREI, ADRIANA SMARANDACHE, V. NASTASA, Z. SAPONJIC, M.L. PASCU
Rom. Rep. Phys. 70, 513 (2018)
Abstract. This work aims to investigate the effect of TiO2 nanoparticles addition on the fluorescence emission of solutions of Rhodamine 6G excited in micro-volumetric droplets. In this paper are presented the similarities and the differences of the emission spectra by modifying parameters such as TiO2 concentration, solutions pH and laser fluence. The pumping laser source used was the second harmonic beam emitted by a pulsed ns Nd:YAG laser at 532 nm. Lasing emission is observed and it is favorised by the solution acidity and laser beam intensity.
Article no. 513: PDF 
New directions in developing of planar potentiometric ceramic multilayered oxygen sensor type λ
ROVENA PASCU, GEORGE EPURESCU
Rom. Rep. Phys. 70, 514 (2018)
Abstract. A new generation of lambda potentiometric compact lambda sensor operating at low intermediated temperature (400 - 800 ℃) for real-time control of the residual oxygen concentration of exhaust gases from internal combustion engines will deposited by Pulsed Laser Deposition technique (ArF excimer laser, λ = 193 nm). These electro-ceramic devices are based on a high-k solid electrolyte 8YSZ (Yttria Stabilized Zirconia) with oxygen ionic conductivity and two solid state electrodes with a differential catalytic activity between the sensing La0.5Sr0.5Co0.8Fe0.2O3-δ (LSCF) and reference electrodes (40% Ni-8YSZ). To improve time of operation, an interface of approximately 10 nm thickness of Gd0.1Ce0.9O1.95 thin film will be deposed between LSCF and 8YSZ to block the interdiffusion. Methods of structural, optical and electrical characterizations will influenced technological development of new performant lambda oxygen sensor with stabilized measurements into a defined field of lambda variation avoiding frequent errors specific in classical configuration. The new sensor will have a fast response time by placing then to the exhaust zone with a good withstand at high temperatures (400 - 800 ℃) for a long time; sensor output must be insensitive to the moisture content.
Article no. 514: PDF 
TiO2 2D nanopatterns obtained by high power impulse magnetron sputtering depositions with colloidal masks
ALEXANDRA DEMETER, VASILE TIRON, LUCEL SIRGHI
Rom. Rep. Phys. 70, 515 (2018)
Abstract. Colloidal lithography was used to fabricate periodic 2D nanopatterns of TiO2 on silicon substrate by two methods: a) reactive high power impulse magnetron sputtering (HiPIMS) deposition of TiO2 on substrates with colloidal masks and mask lift-off; b) HiPIMS deposition of titanium on substrates with colloidal masks, mask lift-off and thermal oxidation. For the reactive deposition it was used multipulse HiPIMS (a single HiPIMS pulse was decomposed into a sequence of three shorter micropulses) of a pure Ti target in Ar and O2 gas mixture. For the physical deposition of titanium, it was used HiPIMS of the same titanium target at the same power (100 W) in pure Ar gas. The Ti 2D patterns obtained by the latter method were thermally oxidized in oxygen atmosphere at 900 ℃ for 2 h. The morphology of the fabricated TiO2 patterns was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The photocatalityc activity in visible light towards degradation of methylene blue dye molecules in aqueous solutions and UV light induced hydrophilicity of the fabricated 2D nanopatterned surfaces were investigated.
Article no. 515: PDF 
Deposition of fluorinated polymer films onto track-etched membrane surface
L.I. KRAVETS, V.A. ALTYNOV, A.B. GILMAN, M.YU. YABLOKOV, V. SATULU, B. MITU, G. DINESCU
Rom. Rep. Phys. 70, 516 (2018)
Abstract. The synthesis and characterization of polymer composite membranes with hydrophobic top layer were studied. To prepare the composite membranes the fluorinated polymer films have been deposited on one side of the poly(ethylene terephthalate) and polypropylene track-etched membranes. RF-magnetron and electron-beam sputter deposition of polytetrafluoroethylene were used as synthesis techniques to obtain polymer films onto membrane surface. It was found that polymer deposition on the membrane surface results in the creation of composite membranes that possess asymmetric conductivity in electrolyte solutions (diode- like effect), which manifests itself at various orientations of the electric field in respect to the membrane. It has been shown that the resulting effect of conductivity asymmetry is due to not only a significant decrease of the pore diameter and a change in their geometry in the deposited polytetrafluoroethylene layer, but also the existence of an interface in the pores between the initial membranes and the hydrophobic polymer layer.
Article no. 516: PDF 
 
ENVIRONMENTAL AND EARTH PHYSICS
 
Relationships between PM10 mass concentrations and aerosol optical parameters over Magurele, Romania
S. VOINEA, G. MANOLACHE, G. IORGA. S. STEFAN
Rom. Rep. Phys. 70, 705 (2018)
Abstract. This study is focused on relationship between ground-level Particulate Matter (PM10) and columnar AOD (aerosol optical depth) and AE (Angstrom exponent) at Magurele, Romania. A two years data set (2014-2015) of measurements was used. The annual means of PM10 were about 25 μg m-3 (2014) and about 28 μg m-3 (2015) with highest level attained in cold season (about 29 μg m-3). Seasonal variations of PM10 mass concentrations and AOD show PM10 has a seasonal pattern with a main maximum in winter (DJF), while AOD reached maximum values in summer (JJA). We obtained single peak frequency distributions for both AOD and AE, with mode values around 0.15 (for AOD) and 1.6 (for AE). Fine mode aerosols dominate the PM10 mass concentrations during the entire period. Best correlation coefficients between PM10 and AOD and between PM10 and AE were found during warm season and for the days when the columnar optical parameters were obtained from measurements with observation time for more than 10 hours a day.
Article no. 705: PDF 
 
APPLIED AND INTERDISCIPLINARY PHYSICS
Special features of the nothing on insulator transistor simulated with diamond lateral islands
C. RAVARIU
Rom. Rep. Phys. 70, 801 (2018)
Abstract. A diamond on insulator structure based on the tunneling conduction thru a vacuum gap between source and drain is proposed as a continuity of previous studies. The Nothing On Insulator (NOI) cavity represents the main device body of this kind of transistors. The simulations reveal the diamond device work principle and extract the static characteristics accompanied by specific parameters accordingly to the diamond properties. The simulations establish a gate leakage current of 8 nA for the diamond NOI device versus 10 μA in the silicon case, at the same biases. Nonuniform diamond surfaces with nano-grains or pipes are considered as some real technological aspects.
Article no. 801: PDF 
Integrated methodology for the non-destructive characterization of cultural heritage artifacts
I. FIERASCU, R.C. FIERASCU, A. ORTAN, D.A. MIREA, C. MORARESCU
Rom. Rep. Phys. 70, 802 (2018)
Abstract. Data available in the literature often presents micro-area results from a few points selected on the artifact, or bulk results referring to the whole studied material. The present study aims at an integrated approach, started with an optical microscopy evaluation to the complex bulk and micro-area characterization of selected metallic artifacts.
Article no. 802: PDF 

This is an electronic version of Volume 70 Number 4 2018
 
   
 
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