In this work we report on modification of electrical and optical properties of extended thin films of single-wall carbon nanotubes induced by iodination from gaseous phase. High resolution ...transmission electron microscopy and Raman data have revealed formation of different types of polyiodide species or one-dimensional iodine crystals (depending on pristine nanotube geometry) inside nanotubes. UV–vis–NIR optical absorption spectra of iodinated nanotubes demonstrated a clear suppression of the optical absorption band corresponding to the first electron transition for semiconducting nanotubes (with the factor determined by the nanotube geometry). It was interpreted as a result of charge transfer from nanotubes to polyiodide species formed inside them. Because of this effect the Fermi level shifted down into the valence band, and the nanotube conductivity type was changed. For filled nanotube films the metallic type of temperature-dependent electrical resistance behavior was observed at elevated temperatures. A reduction of the electrical resistance of pristine films by an order of magnitude (from 1550Ohm/sq to 270Ohm/sq; from 865Ohm/sq to 150Ohm/sq; from 700Ohm/sq to 70Ohm/sq at 300K) has been observed. The obtained sheet resistances are comparable with those for the most popular today material for transparent conductive electrodes – indium tin oxide.
Oxygen-glucose deprivation (OGD) leads to depression of evoked synaptic transmission, for which the mechanisms remain unclear. We hypothesized that increased presynaptic Ca2+i during transient OGD ...contributes to the depression of evoked field excitatory postsynaptic potentials (fEPSPs). Additionally, we hypothesized that increased buffering of intracellular calcium would shorten electrophysiological recovery after transient ischemia. Mouse hippocampal slices were exposed to 2 to 8 min of OGD. fEPSPs evoked by Schaffer collateral stimulation were recorded in the stratum radiatum, and whole cell current or voltage clamp recordings were performed in CA1 neurons. Transient ischemia led to increased presynaptic Ca2+i, (shown by calcium imaging), increased spontaneous miniature EPSP/Cs, and depressed evoked fEPSPs, partially mediated by adenosine. Buffering of intracellular Ca2+ during OGD by membrane-permeant chelators (BAPTA-AM or EGTA-AM) partially prevented fEPSP depression and promoted faster electrophysiological recovery when the OGD challenge was stopped. The blocker of BK channels, charybdotoxin (ChTX), also prevented fEPSP depression, but did not accelerate post-ischemic recovery. These results suggest that OGD leads to elevated presynaptic Ca2+i, which reduces evoked transmitter release; this effect can be reversed by increased intracellular Ca2+ buffering which also speeds recovery.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ratings are widely used in stock analysis, as they increase information transparency, simplify the assessment and investment decision-making in the stock markets, and increase their effectiveness. ...However, the use of ratings is constrained by subjective factors, which necessitates replacing expert assessments with objective characteristics. The aim of the study is to develop a stock valuation rating model, which allows obtaining additional information about the qualitative characteristics of shares in relation to existing rating methods, ensuring the transparency of the rating methodology and limiting the influence of subjectivity, affiliation and bias of an expert analyst. On the basis of the method of dynamic standard, a rating score is constructed, which expresses the measure of the proximity of the normative and actual order of the growth rates of indicators characterizing the investment attractiveness of stocks. When choosing current indicators for inclusion in the rating, the principle of their dynamic co-subordination (normative ordering by growth rates) proposed by I.M. Syroezhin and successfully used in the analysis of economic situations has been applied. The authors have built a share valuation rating model, which is a system of inequalities for the growth rates of six indicators (reference aggregated indicator — benchmark): the market price of a share, the size of the dividend per share, the company’s net profit, revenue, equity and the number of shares in circulation. One of the advantages of the developed model is its universality: it is applicable to any industry, any market, and any accounting system. The model will make it possible to address the problems of expert subjectivism, the use of projected values and the availability of initial information (indicators of official reporting). The authors note the limitation of the model — it is not applicable to the valuation of early-stage companies. The model has been tested by compiling ratings of common stocks from the MICEX index10 for one-year and five-year periods. A comparative analysis of the ratings showed that a higher rating of stocks is observed in the long term. This also determines the applicability of the developed model as a stock analysis tool for long-term fundamental investments.
Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to a large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and to close-packed ...surfaces of fcc-Ni(111) and hcp-Co(0001). Epitaxial deposition of h-BN on ferromagnetic metals is aimed at small interface scattering of charge and spin carriers. We report on the controlled growth of h-BN/Ni(111) by means of molecular beam epitaxy (MBE). Structural and electronic properties of this system are investigated using cross-section transmission electron microscopy (TEM) and electron spectroscopies which confirm good agreement with the properties of bulk h-BN. The latter are also corroborated by density functional theory (DFT) calculations, revealing that the first h-BN layer at the interface to Ni is metallic. Our investigations demonstrate that MBE is a promising, versatile alternative to both the exfoliation approach and chemical vapour deposition of h-BN.
Electrical transport mechanisms of 2D carbon nanotube networks are presently under intensive studies. The related experimental data are ambiguous and controversial. We report on terahertz-infrared ...spectra of optical conductivity and dielectric permittivity of thin transparent films composed of pristine and CuCl- or iodine-doped single-walled carbon nanotubes (SWCNTs) measured in the frequency range from 7 to 25 000 cm−1 and at temperatures from 5 to 300 K. Controversially to the existing results, we have not observed a clear signature of the so-called terahertz conductivity peak. Instead, a typical metallic-like frequency- and temperature-dependent behavior of the conductivity and permittivity has been discovered. It was attributed to the high quality interconnected SWCNT network providing the almost free pathways for charge carriers. Applying Drude conductivity model, we have determined the temperature and doping dependences of effective parameters of the carriers in the films: plasma frequency, scattering rate, mobility, mean-free path. The obtained results demonstrate a great potential of the material in the field of electromagnetic applications at frequencies up to few terahertz.
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We report on the synthesis of a novel optoelectronic material, Sn-rich Ge1–x Sn x nanocrystals in a Ge matrix. The nanocrystals have been formed after annealing of a metastable Ge-rich Ge1–y Sn y ...film, which was embedded in the Ge matrix. Electron microscopy investigations have revealed that these nanocrystals possess two lattice types: (i) a diamondlike cubic structure with a high Sn fraction (x > 0.5) and (ii) an ordered zincblende structure (x = 0.5).
We report on novel defect-free SiSn/Si heterostructures grown pseudomorphically on Si(001) substrates using temperature-modulated molecular beam epitaxy. This approach results in a sustainable ...epitaxial growth for SiSn/Si multilayers. Transmission electron microscopy and electron diffraction manifest that SiSn layers possess a diamond lattice structure. X-ray diffraction reveals up to 9.5 at% Sn in the crystal lattice of SiSn layers.
•Novel promising thermoelectric material: cubic-phase SiSn/Si multilayers.•Pseudomorphic metastable SnSi thin alloys are epitaxially grown on Si(001).•Temperature-modulated molecular beam epitaxy is applied.
A criterion for the growth of Stranski–Krastanov islands mediated by surfactants is obtained. It involves that surfactants decrease the island nucleation barrier. Thereby, at a low coverage (θ ≪ 1 ...mono layer) surfactants facilitate islands formation. At a high coverage (θ ≈ 1 mono layer) the islands growth might be still facilitated, but also hampered under special conditions. The latter is caused by the reduction of the ad‐atom surface diffusion. We report on a non‐monotonic dependence of Ge/Si(100) island array density on the Sb coverage and discuss it in the frame of the obtained criterion.
We present results on the charge-induced transformation of linear 1D-iodine structures encapsulated inside single-walled carbon nanotubes (SWCNTs) with a diameter of about 1 nm. A supercapacitor-type ...electrochemical cell was developed for the controlled charging of iodide-filled nanotube electrodes. In situ Raman study confirms the change of anion types that are composed of the one-dimensional iodine structures formed inside the SWCNTs. Electronic doping of the iodine@SWCNT system leads to rapid growth of the Raman mode of I 3 – anions and suppression of the mode of the lower-charged I 5 – anions. On the other hand, doping with holes leads to a gradual suppression of the I 3 – mode and then the I 5 – mode. UV–visible in situ measurements confirm iodine@SWCNT doping.
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