Influence of the thermo-field electron emission from the cathode with a thin insulating film on the film emission efficiency and ignition voltage of the townsend gas discharge
A model of the thermo-field electron emission from the metal cathode with a thin insulating surface film at
temperatures of 200–400 K is developed. An expression for the film emission efficiency in the gas discharge is
obtained. The efficiency is equal to the fraction of electrons emitted into the film from the metal substrate,
which enter the discharge volume and increase the effective secondary-electron emission yield of the cathode.
It is shown that the thermo-field mechanism of electron emission influences noticeably the ignition voltage of
the low-current discharge with such cathode at rather low temperatures exceeding the room temperature by
less than 100 K.
The heat transfer process is simulated in a nano-sized cone-shaped cathode. A model of heat transfer is constructed using the phase field system and the Nottingham effect. We consider influence of the free boundary curvature and the Nottingham effect on the heat balance in the cathode.
This book is the proceedings of the IX International Conference for Professionals & Young Scientists “LOW TEMPERATURE PHYSICS” ICPYS LTP 2018 dedicated to the 100th anniversary of the National Academy of Sciences of Ukraine, and contains 150 peer-reviewed abstracts. These materials present and discuss the studies of modern aspects of experimental and theoretical physics at low and ultralow temperatures, including electronic properties of conducting and superconducting systems, magnetism and magnetic materials, optics, photonics and optical spectroscopy, quantum liquids and quantum crystals, cryocrystals, nanophysics and nanotechnologies, biophysics and physics of macromolecules, materials science, theory of condensed matter physics, technological peculiarities of the instrumentation for physical experiments, and other related fields.
The factors affecting the thermal degradation of a single silicon field-emission pointed cathode during the take-off of the emission current are described experimentally. The results of the numerical modeling of the temperature dynamics of the field-emission cathode in conditions of the presence of a free interface between the liquid and solid phases allowing for the surface tension are described.
A model of field electron emission from the metal cathode with a thin insulating film under the strong electric field, generated in the film by ions bombarding its surface in gas discharge, is developed. It takes into account tunneling of electrons from the electrode metal substrate into the insulating film, their motion in the film and going out of it into the discharge volume. An analytical solution of the onedimensional kinetic equation for the energy distribution function of emitted electrons in the film conduction band is found and an expression for the film emission efficiency equal to the fraction of emitted electrons, which escapes from the film and increases the cathode effective secondary electron emission yield, is obtained. It is demonstrated that calculated dependence of the emission efficiency on the electric field strength in the aluminum oxide film is in an agreement with experimental data for metal-insulatormetal tunneling cathodes. The proposed model can be used for investigation of an influence of the field electron emission from the cathode with a thin insulating film on its emission characteristics in gas discharge devices.
In this work, a model describing the field emission of electrons from the electrode metal substrate into the insulating film, their motion in the film and going out of it into the dischargevolume is formulated. An analytical expression for the film emission efficiency is obtained and its dependence on the film parameters is studied.
The materials of The International Scientific – Practical Conference is presented below.
The Conference reflects the modern state of innovation in education, science, industry and social-economic sphere, from the standpoint of introducing new information technologies.
It is interesting for a wide range of researchers, teachers, graduate students and professionals in the field of innovation and information technologies.
We studied the structure, IR absorption spectra, the spectral characteristics of photoluminescence and morphology of cerium- and terbium-doped orthoborates of gadolinium and yttrium obtained by hydrothermal synthesis at 200°C, as well as solid solutions of orthoborates on the basis of yttrium, gadolinium, and lutetium with composition RECe0.01Tb0.1BO3 (RE = Lu0.5Gd0.39, Lu0.5Y0.39, and Y0.5Gd0.39). The X-ray diffraction spectrum of yttrium orthoborate Y1 – x – yCexTbyBO3 is described by a hexagonal lattice with space group P63/m, which, after annealing at 970°C, transforms into a monoclinic lattice with space group C2/c. High-temperature annealing of the studied orthoborates leads to a multiple, more than two orders of magnitude, increase in the luminescence intensity of Tb3+ ions when the samples are excited in the absorption band of cerium ions. This effect is the result of a significant increase in the concentration of Ce3+ ions in the orthoborates at high temperatures. It is shown that the luminescence of terbium ions is due to energy transfer from Ce3+ to Tb3+, which proceeds with high efficiency (∼85%) by the mechanism of dipole-dipole interaction between cerium and terbium.
The specific features of the structure in a polycrystalline anion-deficient strontium ferrite SrFeO3 – δ have been studied at different oxygen contents by the Mössbauer spectroscopy, X-ray diffraction, and scanning electron microscopy. Three compounds with different compositions have been prepared in the dependence on the condition of heat treatment. Within each of the structures, there are several nonequivalent positions of Fe corresponding to different valence states of Fe and different local oxygen environments, the relation and the degree of distortion of which are changed in the dependence on the oxygen content. Based on the Mössbauer data, the oxygen content in each of the structures is estimated. Yet another ideal Sr16Fe16O45 composition of the SrFeO3 – δ compound is proposed for an intermediate composition in addition to those available in the literature.
Charge-discharge processes of supercapacitor with carbon black KJEC 600/Li in non-aqueous electrolyte: 1 M LiPF6 in a mixture of ethylene carbonate (1/3), diethyl carbonate (1/3), dimethyl carbonate (1/3) are investigated. Galvanostatic cycling was carried out in the range from 1 to 4 V with currents from 100 to 5000 mA/g of carbon black. The maximum discharge capacity of 196 F/g has been reached. The porous structure and hydrophilic-hydrophobic properties of carbon black KJEC 600 were investigated by the standard contact porosimetry method (MSCP). The following values were obtained: total specific surface area of 2500 m2/g, total porosity of 7.8 cm3/g, hydrophilic porosity of 4.9 cm3/g, hydrophobic porosity of 2.9 cm3/g. The obtained experimental dependence of the energy efficiency has a maximum (80%) at a current of 250 mA/g. Mathematical modeling of charge-discharge processes of the supercapacitor is developed with taking into account the charging of the double electric layer (EDL) and adsorption of lithium ions according to the Butler-Volmer equation and the Frumkin isotherm for the carbon electrode are taken into account. From the comparison of the calculated and measured charge-discharge curves it follows that these curves are satisfactorily consistent with each other, which indicates the correctness of the model. The density of the exchange current and the specific capacitance of the EDL refereed to the true surface found by the fitting are equal to i0,ad = 2.8 × 10−29A/сm2 and Cdl = 3.5 μF/сm2 respectively.
On the basis of the developed model for different specific currents the energy efficiency dependences on the exchange current density of the adsorption reaction were calculated. Interestingly, these dependencies have a minimum. Based on the model, the profiles of the potential the surface coverage of lithium ions were also calculated.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.