The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% ...can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.
Catalyst-free growth of nanocrystalline carbon films on silicon substrates under direct current glow discharge in a mixture of hydrogen and methane was studied by scanning and transmission electron ...microscopy, Raman spectroscopy, as well as X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy (BESSY II, Berlin). The in-time development of the film structure on a carbided silicon substrate includes the formation of diamond-like particles, ultra-thin graphite flakes parallel to the surface, carbon nanowalls nucleated on the stacked flakes and their growth accompanied by a permanent decrease of the structural defect density, and finally nanotube nucleation at the nanowall edges. Based on the observation of the carbon nanotube/nanowall linear size variation in time and using the calculated binding energies and the diffusion thresholds obtained from the literature, we propose that direct attachment of the CH
3 radicals to the carbon nanowall edge is the predominant mechanism and the rate-limiting step of its growth, whereas carbon nanotube growth is controlled by radicals diffusing along its outer surface.
Actinometry of O, N and F atoms Lopaev, D V; Volynets, A V; Zyryanov, S M ...
Journal of physics. D, Applied physics,
02/2017, Letnik:
50, Številka:
7
Journal Article
Recenzirano
The applicability of actinometry for measuring the absolute concentration of O, N and F atoms in discharge plasma was studied. For this purpose, concentrations of these atoms were measured downstream ...of an ICP plasma by means of the actinometry method and of appearance potential mass-spectrometry (APMS). Comparison of the results showed good agreement between the two methods. Since the excitation cross sections of electron states O(3p 3P) and O(3p 5P) applied in actinometry are well tested, this allows using the APMS method for absolute calibration of the theoretical excitation cross sections for N and F atoms. As a result, total excitation cross sections σetotal of the atomic levels N(3p 4Po), F(3p 2Po) and F(3p 4Do) have been obtained for the first time. Since different types of electron energy distribution function (EEDF) were observed (Maxwellian, bi-Maxwellian and Druyvesteyn) the influence of these possible EEDF types on actinometric coefficients CArX (X = O, N, F), that link the ratio of the atom and actinometer intensities IX/IAr with that of their concentrations X/Ar, was also analyzed. It was shown that at the same ionization rate (effective electron temperature) the excitation rate constants keX,Ar are highly sensitive to the shape of EEDF, whereas actinometric coefficients CArX depend on it only slightly. Dependence of actinometric coefficients on electron temperature CArX(Te) is positive if the emitting level of the X-atom is lower than that of the actinometer, and negative if vice versa. The energy difference between the emitting states of O and Ar atoms is maximal (~3 eV), so that CArO(Te) is not constant for a whole range of electron temperatures typical for discharge plasmas (~2-8 eV). For nitrogen atoms CArN(Te) varies considerably with Te only when Te < 4 eV. In the case of fluorine atoms the energy difference of emitting F and Ar states is only ~1 eV and coefficient CArF(Te) is nearly constant in a wide region of Te > 1.5 eV.
N2 dissociation in pure nitrogen plasma has a long history of research. It seems to be a complex process which comprises many reactions involving various electronic and vibrational nitrogen states ...whose contributions can vary depending on conditions. In this paper, we studied N2 dissociation in the stationary N2 discharge both experimentally and theoretically. We used a DC glow discharge in a quartz tube in pure N2 at moderate pressures (5-50 Torr). The degree of dissociation, atomic nitrogen loss rate and gas temperature were measured by applying optical emission spectroscopy (OES) and as a result an 'effective' rate constant for nitrogen dissociation was obtained across a wide range of the reduced field E/N. The analysis of N2 dissociation was carried out using a specially developed 1D radial self-consistent model which takes into account the spatial inhomogeneities of species concentrations, E/N, electron energy distribution function, Tgas etc, together with fairly complete plasma-chemical kinetics and all the cross-sections known to date for electron kinetics. The model was successfully validated through the experimental results obtained for electric field, gas temperature and N atom density. Comprehensive analysis of closely coupled processes in nitrogen plasmas-gas heating, VDF formation and N2 dissociation-was carried out. Simulations reproduced the experimental data on well and allowed us to evaluate the different contributions of the various dissociation channels considered. It was shown that the nitrogen dissociation mechanism in the stationary N2 discharge is provided by direct electron impact via the excitation of the pre-dissociative states from the vibrationally excited nitrogen molecules N2(X, ). The upper limit for the rate constant of the processes N2(A) + N2(14 19) → N + N + N2 was estimated to be 5 · 10−14 cm3 s−1.
To find a high purity flux for low background experiments is one of the most challenging problems. In this work, we report the production process of a highly purified ammonium acetate flux solution ...for low background experiments. A sub-distilled method has been used to purify initial precursors from contamination for the syntheses of final product. As a result, a high purity ammonium acetate solution was synthesized with a minimum content of elements which collectively represent the main source of background radiation (K < 2.3 × 10
–8
g/g, Th < 2.6 × 10
–11
g/g and U < 1 × 10
–11
g/g). An Estimation of the impurity content of the product has been performed with Instrumental neutron activation analysis, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry.
The flux densities and current spectra of plerions and combined supernova remnants (SNRs): 3C58, 3C144, G11.2–0.3, G21.5–0.9, and 3C396 are determined on an artificial moon (AM) flux scale. The radio ...emission variability of the objects on different time scales is studied by multiple measurements using the RT-32 radio telescope at the Svetloe Observatory, Institute of Applied Astronomy, Russian Academy of Sciences and by mutual comparisons of the published measurement data, which have been brought to a common system using the AM flux scale. The radio emission from the SNRs displays both slow evolutionary variations and rapid ones, nonstationary in time. The rapid variability of the SNRs has features that are similar to those observed during solar flares. This fact may testify to the identity of the physical mechanisms underlying the rapid variability of the radio emission from plerions and from the Sun. Field line reconnections are considered as such a common mechanism.
The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in ...order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of μas structures within their cores.
The O(3P) atom loss has been studied in O2 RF plasma in the quartz tube in the intermediate pressure range (10-100 Torr) when the transition from the surface to volume loss is observed. Space- and ...time-resolved actinometry on Ar and Kr atoms was used to study O(3P) atom loss. The research has shown that such a transition actually takes place. However, it was revealed that the gas temperature plays a significant role in this. Gas temperature was measured spectroscopically using the band emission. It was demonstrated that the gas temperature in the plasma volume was rather high (>1200 K) due to the high values of the specific input RF power which in turn led to a significant O(3P) loss rate decrease in the discharge volume. The atomic oxygen loss is limited by the O(3P) surface recombination as well as by the volume recombination in a thin layer near the wall. It leads to a low integral loss rate and provides a high oxygen dissociation degree. Analysis based on measured O(3P)/N, Tgas, O3 spatial profiles and surface loss model including recombination with chemisorbed and physisorbed atoms has revealed the importance of both surface and volume losses. High values of the specific input RF power also lead to increase of the gas temperature near the wall and the temperature of the internal tube surface. As a result, the O atom surface loss rate increases and the volume loss rate near the wall decreases, so overall the contributions of both O(3P) volume and surface recombination are comparable at pressures up to 100 Torr. The O(3P) loss kinetics at intermediate pressures appears to be a rather complex phenomenon and requires at least 1D or even 2D modeling for its correct description. Using global models under similar conditions may lead to dubious results in a detailed study of kinetic mechanisms and processes, but it can be useful for a simple analysis of experimental results.
PDF
