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Veis Alexander N.

The energy spectrum and some properties of lead sulphide implanted with oxygen

Published in category «Condensed matter physics»

Spectral dependencies of optical reflection and absorption coefficients in lead sulfide implanted with oxygen ions and annealed in vacuum have been investigated at T = 300 K. It was found that the average value of hole concentration within the sample space area where properties were modified by ion implantation and vacuum annealing was equal to (3.25 ± 0.30)•1018 cm–3. The depth of the space in question was estimated and its quantity was shown to make the tenths of micrometers. It was demonstrated that because of annealing process oxygen ions occupied places in the chalcogen sublattice healing anion vacancies. It was also found that vacuum annealing of lead sulfide with implanted oxygen did not cause elimination of all anion vacancies. Moreover, the concentration of sulfur vacancies increased considerably in comparison with its value in the initial samples non-subjected to ion implantation. This fact testifies that oxygen in lead sulfide possesses acceptor action which is compensated by chalcogen vacancies. It was established that in the lead sulfide, the only quasi-local energy level, being located in the valence band at the energy distance of 0.16 eV from its top, was connected with oxygen impurity. No other energy levels which one could connect with oxygen or with the complexes containing oxygen in lead sulfide was revealed. The storage stability of properties of investigated material was demonstrated.

Views: 813 Comments: 0

Koroleva Ekaterina Yu., Stukova Elena V., Baryshnikov Sergey V., Milinskiy Alexey Yu.

Dielectric investigation of composites based on thiourea

Published in category «Condensed matter physics»

The composites of thiourea with lithium niobate (a), with lead titanate (b) and with barium titanate (c) (in all cases thiourea part was 0.90) have been investigated close to structural phase transitions in thiourea using dielectric spectroscopy. The hysteresis increase and temperature decrease of the ferroelectric phase transition from phase I to phase II for all investigated compounds as compared with similar properties of the polycrystalline thiourea were found. The most decrease in the transition temperature was observed for the (c) composite. The results were analyzed in the framework of the Landau-Ginzburg theory.

Views: 822 Comments: 0

Lashkova Natalia A., Permiakov Nikita V., Maximov Alexander I., Spivak Yulia M., Moshnikov Vyacheslav A.

Local analysis of semiconductor nanoobjects by scanning tunneling atomic force microscopy

Published in category «Condensed matter physics»

The features of the I-V measurements in local regions of semiconductor nanostructures by conductive AFM are discussed. The standard procedure of I-V measurements in conductive AFM leads not infrequently to the thermomechanical stresses in the sample and, as a consequence, non-reproducibility and unreliability of measurements. The technique of obtaining reproducible current-voltage (I-V) characteristics is proposed. According to the technique, a series of measurements of the selected scanning area in the mode of conducting AFM should be taken, each at the certain value of the potential. According to a series of scans I-V curve at a particular point (for any point of the scan) was plotted. The program is realized in the LabVIEW software. The proposed method extends the capabilities of scanning probe microscopy in the diagnosis of nanostructured semiconductor materials.

Views: 780 Comments: 0

Karov Dmitry D., Puro Alfred E.

Tensor tomography of stresses in cubic single crystals

Published in category «Condensed matter physics»

The possibility of optical tomography applying to investigation of a two-dimensional and a three-dimensional stressed states in single cubic crystals has been studied. Stresses are determined within the framework of the Maxwell piezo-optic law (linear dependence of the permittivity tensor on stresses) and weak optical anisotropy. It is shown that a complete reconstruction of stresses in a sample is impossible both by translucence it in the parallel planes system and by using of the elasticity theory equations. For overcoming these difficulties, it is offered to use a method of magnetophotoelasticity.

Views: 643 Comments: 0

Aladov Andrei V., Valjukhov Vladimir P., Demin Sergey V., Zakgeim Alexander L., Tsatsulnikov Andrey F.

The wireless network of controlled energy-effective LED lighting sources

Published in category «Experimental technique and devices»

This article is the result of works on the treatment and the practical realization of a branching WPAN of the LED controlled energy-efficient light sources having the architecture of the EEEI 802.15.4 Standard (MAC and PHY layers).Either of the two layers provide a means for rendering the data and the management services for the transmission and the reception of the PHY protocol data units. This WPAN comprises an five-color emitting module with a control processor, power drivers, and a controlling part with appropriate software and a short-range 2.4 GHz radio-frequency channel for information exchange with an emitting module. Star is used as the basis for the network formation. As a coordinator PAN would allow the option of using either PC or the remotely controlled desk. Such a PAN configuration provides to conduct a test mode, installation, a control and micro-program store in the desk or LED light sources. In a round-daily energy-saving mode the PAN operates under a program with the desk. A software development which consists of six programs for all transfer types in the PAN was made.

Views: 789 Comments: 0

Ermak Sergey V., Semenov Vladimir V., Piatyshev Evgenii N., Kazakin Aleksey N., Komarevtcev Ivan M., Velichko Elena N., Davydov Vadim V., Petrenko Mikhail V.

Microfabricated cells for chip-scale atomic clock based on coherent population trapping: fabrication and investigation

Published in category «Experimental technique and devices»

The article is devoted to investigation of the coherent population trapping (CPT) signals in the microfabricated alkali metal vapor cell. At the first step the experimental technological setup for MEMS manufacture was assembled. The microfabricated cell was designed to realize two optical pumping schemes: the conventional one where the cell is just placed under the laser beam, and another one with double reflection of the laser beam to increase the beam path in narrow cell space). The inflation of the cell with alkali metal (87Rb), buffer gas type and gas pressure were calculated preliminary. The miniature cells with alkali metal were manufactured using laser activation. To measure the CPT signals the experimental setup was used, and characteristics of CPT resonance signals were obtained. The resonance line width of 2 – 3 kHz and signal-to-noise ratio of 1500 in 1 Hz band width were found. These parameters of the CPT resonance line can provide the frequency non-stability of the small-scale atomic clock at the level of 10–11 for 100 s of measuring time. The results obtained suggested several leads for future research.

Views: 917 Comments: 0

Golovitski Alexander P.

Estimating the parameters of a positive column of the halogen-containing glow discharge at moderate pressures

Published in category «Physical electronics»

The methodical recommendations for estimating the plasma parameters of an electronegative glow discharge containing halogens at moderate pressures (up to 40 Torr) with the use of simple analytic formulae and without numerical modeling are given. The initial data are easily measureable discharge parameters such as a discharge current, a voltage and a gas mixture pressure and composition as well. It is shown how one can easily consider such important plasma features as non-Maxwellian electron energy distribution function and halogen molecules dissociation by electron impact. As a result, such plasma parameters as the absolute degree of electronegativity, the value of border coordinate between ion-ion and electron-ion plasmas, and the forms of transversal profiles of electron and negative ion concentrations can be evaluated. The comparison of the results with the ones given by a global numerical model shows the suitability of said analytic approach to estimating plasma parameters of real discharges.

Views: 643 Comments: 0

Arkhipov Alexander V., Gabdullin Pavel G., Gnuchev Nikolay M., Davydov Sergey N., Krel Stanislav I., Loginov Boris A.

Field-induced electron emission from nanoporous carbons of various types

Published in category «Physical electronics»

Influence of fabrication technology on field electron emission properties of nanoporous carbon (NPC) has been investigated. Samples of NPC derived from different carbides via chlorination at different temperatures demonstrated similar low-field emission ability with threshold electric field 2 – 3 V/µm. This property correlated with the presence of nanopores with characteristic size 0.5 – 1.2 nm determining high values of specific surface area (> 800 m2/g) of the material. In most cases, current characteristics of emission were approximately linear in Fowler-Nordheim (FN) coordinates (excluding a low-current part near emission threshold), but the plots’ slope angles were in notable disagreement with known material morphology and electronic properties, unexplainable within the frames of FN emission theory. We suggest that the actual emission mechanism for NPC involves hot electrons generated at internal boundaries, and that emission centres may be associated with relatively large (20 – 100 nm) onion-like particles observed in many microscopy images.

Views: 816 Comments: 0

Krasnova Nadezhda K.

Genesis of potential structures for electron spectrography

Published in category «Physical electronics»

The article focuses on studies of spectrographic structures being useful for energy analysis of charged particles. These structures are electrostatic fields which possess a main feature of spatial separation of a secondary charged particles flow being analyzed, into some monoenergetic beams. The availability of similar charged particle trajectories in electrostatic fields is a necessary condition for realization of spectrographic mode. Such flow separation is typical not only for electrostatic fields with potentials being homogeneous functions in Euler sense, but also for other structures. A class of general homogeneous functions with logarithmical singularity has been considered. In these fields a similarity concept is obeyed approximately. A general analytical expression for the potential structures is given, and an evaluation criterion for breaking similar tracks is formulated. A technique for creating potential structures is presented; it allows building effective electrostatic spectrographs. The surfaces of equal potentials of some concrete realizations are presented. An outlook for the spectrographs use is discussed.

Views: 663 Comments: 0

Arkhipov Alexander V., Gabdullin Pavel G., Mishin Maxim V.

Orbitron-type vacuum gauge with nanocarbon field cathode

Published in category «Physical electronics»

A novel electron-optical scheme (EOS) of ionization-type vacuum gauge is proposed that allows the use of field-emission nanocarbon cathodes. The developed gauge satisfies the requirements imposed by possible utilization in on-board satellite equipment: low mass, size and energy consumption, low turn-on time, etc. High efficiency and sensitivity of the sensor are achieved by the use of an electrostatic trap for accumulation of electrons ionizing the gas molecules. Magnetic field was not used for mass economy reason and to avoid possible influence onto other on-board equipment. The main problem solved in the work originated from the intrinsic contradiction between the aims of achieving long-term confinement of electrons in the trap and focusing of the applied electric field at the cathode, the latter being necessary to utilize the phenomenon of field-induced emission. Experimental tests were performed with two prototype devices realizing different versions the EOS design, viability of both developed schemes has been confirmed.

Views: 913 Comments: 0

Arkhipov Alexander V., Mishin Maxim V., Sominski Gennadiy G.

Analyzer of high-load electron beams with resolution in two energy components, space and time

Published in category «Physical electronics»

The new apparatus is developed for experimental determination of electron energy and spatial distributions in dense medium-energy long-pulsed magnetically confined beams – typically, 10 A/cm2, 60 keV, 100 µs, 0.1 T. To provide most detailed and unambiguous information, direct electrostatic cut-off method is used for electron energy analysis. In combination with variation of the magnetic field in the analysis area, this method allows to determine both (axial and transverse) components of electron energy. Test experiments confirmed ~1% energy resolution being predicted from calculations, accounting for electrode shapes, space-charge effects and nonadiabatic energy transfer effects in varied magnetic field. Space and time resolution of the apparatus are determined by the input aperture size (~1 mm) and cut-off electric field pulse-length (~5-10 µs) respectively.

Views: 834 Comments: 0

Krasnova Nadezhda K., Pavlov Vladimir V., Solovyev Konstantin V.

On a class of ideal focusing systems for energy analysis

Published in category «Physical electronics»

A method of physical analogies, when field lines of two line charges are associated with the trajectories of some two-dimensional mechanical system and equipotentials of the field are associated with the system action, is discussed. Both action and its arbitrary function are orthogonal to particle trajectories simultaneously. This fact can be used to regularize result two-dimensional potential function and to optimize three-dimensional charged particle motion. The method is applied to create charged particle energy analyzer with an ideal focusing in the symmetry plane. The system useful property is that its energy dispersion tends to infinity when the angle between direction to detector and initial velocity tends to π. Also, through some simple examples it was shown that together with the ideal focusing in a plane of symmetry the system has transversal first order focusing for some initial angles.

Views: 702 Comments: 0

Mkrtychev Oleg V., Privalov Vadim E., Fotiadi Alexander E., Shemanin Valery G.

Nanocomposites laser ablation studies

Published in category «Physical electronics»

The first experimental measurements of the threshold energy density values for the laser ablation of glass nanocomposites with nanodimensional coatings have been carried out under the action of the YAG-Nd laser power pulse radiation. The coatings in question were of different composition and had been created by the sol-gel technology. The procedure for determination of the laser ablation threshold energy density values was worked out on the base of the breakdown probability level of 0.5. The statistical processing of measurement data over all the samples allowed to obtain the relationship of the ablation destruction threshold energy parameters to the coatings physical and chemical properties such as a pulse duration of laser radiation, the sample transmission in visible region of the spectrum, a coating thickness and a chemical composition of film-forming solution.

Views: 715 Comments: 0

Atkarskaya Alla B., Evtushenko Evgeny I., Nartsev Vladimir M., Privalov Vadim E., Fotiadi Alexander E., Shemanin Valery G.

Optical properties of the glass composites with nanofilms: the relationship to the dispersed phase of sol

Published in category «Physical electronics»

It has been found that the particles size, volume fraction of the film-forming sol disperse phase, the pack-density of the particles in the layer, effect on the optical properties of nanodimensional films and composites consisting of a glass substrate coated with the surface film. The threshold energy density of the laser ablation destruction of the films being components of the composites also depends largely on the state of the sol dispersed phase. This value needed for the ablation under the laser radiation with nanosecond pulse duration was found to increase with the dispersed phase particles pack-density in the layer. Moreover, this value increased with the particle size and decreased as the fraction by volume of that phase and particles pack-density rose when using microsecond pulse duration. These relationships are due to low thickness and density of the nanofilm, and as a result the laser beam interacted practically with the dense glass substrate.

Views: 775 Comments: 0

Stepanova Tamara P., Nosova Galina I., Solovskaya Nina A., Kapralova Victoria M., Yakimansky Alexander V.

The constant electric field effect on the dipole moment of a comb-like polymer with chromophore groups in side chains

Published in category «Physics of molecules»

The study of conformational properties and tendency to association for chromophorecontaining comb-like copolymer of β-(3,4-dicyanophenylazobenzenethyazole) methacrylate (A) and amylmethacrylate (B) (1:1) has been carried out. The copolymer AB is of particular interest because of nonlinear optical properties of its films. Dielectric permittivity and dipole moment temperature dependences in dilute cyclohexanone solutions in the temperature range from 20 to 70 °С, in the electric field E ≤ 104 V/cm were investigated by means of static dielectric polarization. It was shown that temperature and concentration dependences of dielectric permittivity for the solvent, copolymer AB, monomer A and polymer B were linear indicating low molecular interactions at temperatures and fields used. The invariable stoichiometry of components in solution for concentration lower than 10–3 mol/mol was proved. The values of dielectric permittivity were extrapolated to infinite dilution and increments α = (∆ε12/∆x2)x2=0 were calculated. The solvent dipole moments were calculated in terms of the Onsager theory whereas dipole moments of AB, A and B were calculated in terms of the Backingham statistical theory of dielectric polarization. Intramacromolecular conformational transition was found to be at ∼40 °C. Dipole moment of A was shown to increase with both temperature and electric field strength. Copolymer side chains trans-location takes place due to intramacromolecular association resulting in the compensation of dipole moments and Kirkwood factor g ≈ 0.6. The association of A units increases in the electric field reducing the dipole moment per monomer unit significantly and g values approximately twice.

Views: 688 Comments: 0

Gavricova Tatiyana A., Zykov Valery A., Ilyin Vladimir I.

The results of the 16-th All-Russian Youth Conference on Semiconductor and Nanostructure Physics and Semiconductor Opto- and Nanoelectronics

Published in category «Chronicle»

The paper briefly summarizes the results of the 16th All-Russian Youth Conference of Semiconductor and Nanostructure Physics and Semiconductor Opto- and Nanoelectronics (St.Petersburg, on November 24 – 28, 2014). The titles of students’ and post-graduate students’ reports diplomaed and awarded by prizes are presented.

Views: 668 Comments: 0