Emission and excitation photoluminescence spectra of porous silicon thin layers have been investigated at natural oxidation. The shift of both types of spectra to high-energy region with time has ...been shown. Analysis of excitation spectra points out the indirect behavior of electron transitions responsible for visible photoluminescence, which remains unaltered at natural oxidation. The value of optical bandgap is estimated in each case. It is shown that the optical bandgap broadens during oxidation due to size reduction of silicon nanocrystallites.
► Porous silicon emission and excitation spectra blue shifted at natural oxidation. ► Excitation spectra points out the indirect behavior of electron transitions. ► Optical bandgap broadens during oxidation due to Si nanoparticles size reduction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The photoluminescence excitation and emission spectra of n-type stain etched porous silicon layers were investigated. From these spectra the average values of optical bandgap and photoluminescence ...peak position were determined. Based on these experimental data, the photoluminescence emission spectra of porous silicon were analyzed by the phenomenological theory and the fitting parameters of the theory were defined. The size and bandgap distributions of silicon nanoparticles were determined and their mean values were calculated. It was found that the investigated PS samples are the ensemble of nanoparticles with size between 1.5nm and 2.8nm and a bandgap from 2eV to 3.2eV distributed with different probabilities depending on the formation time of porous silicon. It is shown that with increasing formation time, the average size of nanocrystals is slightly increasing, while the average bandgap is slightly narrowing.
•Stain etched n-type porous silicon layers were formed in modified solution.•Joint theoretical analysis of excitation and emission spectra was performed.•Size and bandgap distributions of nanocrystals were determined.•Mean values of nanocrystal size and bandgap were determined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The structures of phenol-formaldehyde oligomers functionalized by benzylamine were studied. The mechanisms of the synthesis and transformations of initial oligomers with various molar ratios of the ...nitrogen-containing modifier were discussed. The optical densities of the main bonds were obtained by the IR spectroscopy method, the regularities of their changes were reported and substantiated.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at sNN=2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon's transverse momentum (pT) and rapidity (yCM) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are 〈PΛ〉(%)=6.8±1.3(stat.)±2.1(syst.) for Au+Au and 〈PΛ〉(%)=6.2±0.4(stat.)±0.6(syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The influence of composition of various solutions, applied for final treatment of Si wafers before stain‐etched porous silicon (PS) formation, on the incubation period and antireflective properties ...has been investigated. PS layers were obtained by chemical etching in HF:HNO3:CH3COOH modified solution at oxidant insufficiency. It is shown that the minimum incubation period and the reflectivity correspond to the final treatment of wafers in undiluted HF. Studies of reflection spectra have shown the possibility of smooth adjustment of the minimum in the reflection spectra, which is of interest for the formation of antireflection coating for solar cells.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Employing the Bonn–Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5 GeV)+p→pK+Λ. This reaction might contain information about the kaonic cluster ...“ppK−” (with quantum numbers JP=0− and total isospin I=1/2) via its decay into pΛ. Due to interference effects in our coherent description of the data, a hypothetical K‾NN (or, specifically “ppK−”) cluster signal need not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectrum like pΛ. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a K‾NN cluster. At a confidence level of CLs=95% such a cluster cannot contribute more than 2–12% to the total cross section with a pK+Λ final state, which translates into a production cross-section between 0.7 μb and 4.2 μb, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The synthesis of nitrogen-containing alkyl(C8–C12)phenol formaldehyde oligomers grafted with vegetable oils was investigated with the aim of creating new materials with the properties of protective ...coatings. Soybean and linseed oils were used as the vegetable oils. The interaction between phenol formaldehyde oligomers and vegetable oils probably occurs through the functional groups formed as a result of oxidative processes at the carbon atoms in the a-position to double bonds. The probable structure was established using infrared and nuclear magnetic resonance spectroscopy, and the physicochemical properties of the synthesised products were studied.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Bi12TiO20 (BTO) single crystal was grown by Czochralski method and investigated mechanically by nanoindentation measurements. X-ray diffraction pattern of the crystal presented one intensive peak ...around 37.95° associated with (330) plane of cubic crystalline structure. Nanoindentation experiments were performed at various loads between 5 and 100 mN. Hardness and Young's modulus of the crystal were determined by Oliver-Pharr method. The hardness-load dependency exhibited behavior of indentation size effect. True hardness value of BTO crystal was revealed as 4.4 GPa. Young's modulus decreased with increase of load and load-independent Young's modulus was found around 93 GPa at high loads. The load-dependent elastic and plastic deformation components were calculated and it was observed that the dominant component in BTO single crystal is plastic deformation at the applied loads. The present paper reports for the first time the mechanical characteristics of the BTO single crystal by carrying out nanoindentation experiments.
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•Bi12TiO20 (BTO) single crystal was grown by Czochralski method.•The mechanical properties were investigated by nanoindentation measurements.•Nanoindentation experiments were performed at various loads between 5 and 100 mN.•True hardness value of BTO crystal was found as 4.4 GPa.•Load-independent Young's modulus was found around 93 GPa at high loads.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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