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Filimonov Alexey V., Rudskoj Andrey I., Naberezhnov Alexander A., Vakhrushev Sergey B., Fotiadi Alexander E., Koroleva Ekaterina Yu., Golosovsky Igor V., Kumzerov YuriA., Nacke Bernhard

Nanocomposite materials on the base of dielectric porous matrices

Published in category «International Collaboration Reports»

The correlations between physical properties and structure of various types of nanocomposite magnetic and ferroelectric materials on the basis of natural and artificial porous have been studied by different experimental methods. The temperature evolution of the structure, order parameter and dielectric response are studied as functions of characteristic size of nanoparticles. It is shown the existence of crossover of phase transition (PT) from the first order to the second one for ultra-small ferroelectric and magnetic particles.

Views: 1741 Comments: 0

Wagner Friedrich, Sergeev Vladimir Yu., Goncharov Pavel R.

The research laboratory of the Physics of Advanced Tokamaks of the St. Petersburg State Polytechnical University

Published in category «International Collaboration Reports»

Within the research laboratory of the Physics of advanced Tokamaks, which has been founded in 2011on the basis of a MEGA-Grant, the two groups from the university and the Ioffe Institute cooperate on the three tokamaks, Globus-m, Tuman-3m and fT-2. The research of both partners benefitted from the means of the MEGA-Grant. The laboratory has given itself a transparent governing structure and its annual outcome is assessed by an international advisory committee. a graduate school has been founded to ensureproper education. The laboratory could serve as a model for integrated research and education centre in Russian thermonuclear program. The urgent need to modernize the Russian fusion devices has become obvious.

Views: 1280 Comments: 0

Louksha Oleg I., Sominski Gennadiy G., Arkhipov Alexander V., Dvoretskaya Nataliya V., Samsonov Dmitry B., Syomin Sergey V., Wagner Friedrich

Gyrotron research at the St. Petersburg State Polytechnical University

Published in category «International Collaboration Reports»

This paper presents the results of investigations performed by the researchers of the department of Physical electronics in the laboratory headed by Prof. F. Wagner and supported by the ministry of education and science of the Russian Federation on the basis of MEGA-Grant. Methods for the improvement of helical electron beam quality and for enhancement of gyrotron efficiency, new gyrotron electron beam diagnostics are discussed.

Views: 1382 Comments: 0

Artamonov Dmitry N., Korzhova Victoria V., Vlasova Olga L., Bezprozvanny Ilya B.

Optogenetic approach allows controlling morphological parameters of dendritic spines in cortico-striatal co-culture

Published in category «International Collaboration Reports»

Optogenetics is a unique technique that allows controlling the physiological condition within single cellor specific cell population, including controlling individual neuron activity. In the present work optogenetics has been applied to control the morphology and density of synaptic connections between striatal and cortical neurons in mixed cortico-striatal co-culture system. Different methods for visualization of medium spiny neurons dendritic spines have been compared. Studying synaptic dysfunction is necessary for understanding both normal physiology of brain and pathological mechanisms in different neurodegenerative diseases. The described approach could be utilized in a numerous biomedical applications.

Views: 1286 Comments: 0

Gerchikov Leonid G.

Electron-ion scattering and plasmon damping in metallic clusters

Published in category «Condensed matter physics»

Processes of electron scattering on fine ionic structure leading to the decay of dipole plasmon oscillations in alkali metal clusters are investigated. The study is based on separation of the collective plasmon oscillations and single particle excitations. Coupling between these two types of electronic motions caused by electron-ion scattering leads to the plasmon damping. The relative contributions of elastic and inelastic electron-ion scattering to plasmon linewidth are considered. The results are compared with experimental data on cluster photoabsorption for sodium clusters of different size.

Views: 781 Comments: 0

Gerchikov Leonid G., Mamaev Yuri A., Yashin Yuri P., Kuz’michev Vitaly V., Aulenbacher Kurt, Riehn Erich

Electronic transport in strained AlInGaAs/AlGaAs superlattices

Published in category «Condensed matter physics»

Transport of spin polarized electrons in semiconductor alingaas/algaas superlattices (sl) with strained quantum wells used for photoemitter application is studied. The experimental study is based on the time resolved measurements of electron emission from the cathode after its photoexcitation by fs laser pulse. We report the variation of the sl response time with the number of superlattice periods. We have also performed theoretical calculations of photocathode pulse response and compared the obtained results with experimental data. Our analysis testifies the presence of partial electron localization in sl. We demonstrate that electron localization suppresses electronic transport and strongly limits the cathode quantum efficiency.

Views: 781 Comments: 0

Zakharkin Maxim V., Okuneva Nina M., Vergentev Tikhon Yu., Banshchikov Alexander G., Koroleva Ekaterina Yu., Sokolov Nikolai S.

In-plane conductivity of thin films and heterostuctures based on LaF3-SrF2

Published in category «Condensed matter physics»

The in-plane conductivity of solid solution la1-xsrxf3-x (x = 0 ÷ 0.24) films with thicknesses from 40 to 260 nm grown on glass-ceramics based on sio2, al2o3, caf2 (111) and mgo (100) substrates, and laf3-srf2 heterostructures grown on mgo (100) substrates were studied by impedance spectroscopy at temperature range from room temperature to 300 °c and at frequencies from 10-1 to 106 hz.

It was found that there was a maximum of ionic conductivity for la1-xsrxf3-x (x = 0 ÷ 0.24) solid solution films at x ≈ 0.05. The conductivity of la0.95sr0.05f2.95 films is by 2 - 4 orders of magnitude higher than that of pure lanthanum fluoride films on the substrates of magnesium oxide, sapphire and glass-ceramics. It was also shown that there was a maximum of in-plane conductivity of laf3-srf2 heterostructures for the thickness of each layer ~ 20 nm. The activation energy was evaluated from the temperature dependencies of the dc-conductivity of the films according to Arrhenius - Frenkel law. It was 400 - 800 mev for all measured samples.

Views: 1151 Comments: 0

Lukianov Sergey O., Andreeva Nataliya V., Vakhrushev Sergey B., Filimonov Alexey V., Wurz Mark C., Rissing Lutz

Surface polar nanoregions structure of potassium tantalate doped with lithium obtained at cryogenic temperatures using piezoresponse force microscopy technique

Published in category «Condensed matter physics»

In the present work we have used a piezoresponse force microscopy (Pfm) technique for the studyof the polar surface structure of potassium tantalate single crystal doped with li+ ions (KlT-3 %) at low temperatures. The results of our measurements confirmed the existence of polar nanoregions in the temperature range of 10 - 80 K. We obtained a temperature evolution of the nanoregions and estimated theirdimensions. Resolving polar nanoregions structure of KlT-3% crystal in zero-field heating after zero-field cooling regime could indicate the existence of ferroelectric phase transition in this material.

Views: 1252 Comments: 0

Lushin Evgeny N., Castro Arata Rene Alejandro

Determination of the glass transition temperature in polymer composites and systems

Published in category «Condensed matter physics»

The results of the study of the frequency dependence of the dielectric constant in a wide range of tem-perature in tetrazole polymers are presented. It has been found that the temperature at which the dielectric constant changes sharply in all systems is the glass transition temperature.

Views: 900 Comments: 0

Ilinskiy Alexander V., Castro Arata Rene Alejandro, Nabiullina Lilia A., Pashkevich Marina E., Shadrin Evgeniy B.

Dielectric spectroscopy as means of diagnostics of electronic states of sillenites

Published in category «Condensed matter physics»

The physical parameters of impurity centers of Bi[12]SiO[20] crystals have been determined by the dielectric spectroscopy method.

Views: 1226 Comments: 0

Stepanova Tamara P., Anan’eva Tatiana D., Karpenko Elena D., Kapralova Victoria M.

A dipole moment and conformations of poly-N-vinylpyrrolidone and of its complex with C[60] fullerene in aqueous solutions

Published in category «Condensed matter physics»

The study of temperature dependences of dipole moments and conformational properties of poly-n-vinylpyrrolidone (PVP) and polymer complex of PVP with c60 fullerene (PVP + fc60) was carried out in dilute aqueous solutions at 293-313 K. It was shown that dipole moment values for PVP and PVP + fc60 were 24-32 d and 18 d, correspondingly. The presence of the molecular group -n-c=o in each monomer unit near the macromolecule backbone promotes the formation of helical blocks in macromolecular coils. In external electric field, the non-alternating projections on the direction of this field and on the vectors connecting the neighboring segments of the macromolecule appear. It was demonstrated that the changes in the characteristics of the dielectric polarization could be explained by structuring in the coils of PVP and PVP + fc60 in aqueous solutions.

Views: 1222 Comments: 0

Vorobjev Leonid E., Firsov Dmitry A., Panevin Vadim Yu., Sofronov Anton N., Balagula Roman M., Makhov Ivan S.

Near- and far-infrared emission from GaAs/AlGaAs quantum wells under interband optical excitation

Published in category «Condensed matter physics»

The results of experimental studies of low-temperature impurity-assisted photoluminescence of n-dopedGaas/alGaas quantum well structures both in near- and far-infrared (terahertz) spectral ranges under interband optical excitation are presented. In the near-infrared photoluminescence spectra the opticalelectron transitions from the donor ground state to the hole subband are revealed. The depopulation of the impurity ground states due to these transitions allowed us to observe photoluminescence in terahertz spectralrange related to electron transitions from the first electron subband to the donor state as well as to intracenteroptical transitions. Experimental results in near- and far-infrared spectral ranges are well-consistent with the results on terahertz photoconductivity and theoretical calculations.

Views: 1372 Comments: 0

Shubina Ekaterina N., Karaseov Platon A., Mishin Maxim V., Protopopova Vera S., Vinogradov Andrei Ya., Karaseov Nikita N., Arkhipov Alexander V., Shahmin Alexander L., Podsvirov Oleg A., Titov Andrey I.

Effect of temperature on properties of DLC films and DLC-Ni:C sandwich growth

Published in category «Condensed matter physics»

A possibility of formation of sandwich structures comprising of both DLC and nano-crystalline Ni-Carbon films on silicon substrate is presented. The influence of DLC film exposition to high temperature during preparation of Ni:C layers on its properties has been investigated by means of isochronal thermal annealing in carrying gas used. All structures obtained were examined by atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. It has been established that annealing leads to decrease of the internal residual stress in the DLC films as well as causes swelling of samples with temperature rise.The fraction of sp{3} hybridized bonds increases and the sp{2} fraction symmetrically decreases with increase of annealing temperature. The different sequences of growth processes to obtain DLC-Ni:c-DLC sandwich structure were investigated. The best way to get good structure quality is to grow initial DLC film at 200 V and 100 W and Ni:C layer at 500 °c.

Views: 1641 Comments: 0

Arkhipov Alexander V., Krel Stanislav I., Mishin Maxim V., Uvarov Andrey A.

Сorrelations in field electron emission current from local spots at nanoporous carbon films

Published in category «Physical electronics»

Heterogeneous nanocarbon materials including both diamond and graphite phase domains demonstrate enhanced efficiency of electron emission that often remains unexplained by theory. Characteristic features of the actual mechanism of facilitated emission were searched for via position-resolved investigation of emission current fluctuations. The reported studies were performed with nanoporous carbon chemically derived fromsic. Partially ordered and spatially correlated character of fluctuations observed in the experiment allows to presume involvement of self-sustaining non-stationary electric field as a possible factor of emission enhancement.

Views: 1241 Comments: 0

Golovitski Alexander P.

Electron energy relaxation length in connection with the problem of electron energy distribution locality in glow discharge plasma in a xenon-chlorine mixture

Published in category «Physical electronics»

The analytic calculations of relaxation length of electron energy based on a probabilistic approachand numerical calculations of nonlocality effect on the plasma-chemical processes rates have been carriedout for plasma of an electronegative glow discharge in a mixture of xenon and chlorine. It is shown, that for total pressure higher than 6 Torr and with amount of chlorine more than 1/25 the effect of electronenergy distribution nonlocality is negligibly small and the local approach can be used for modeling such discharges.

Views: 1110 Comments: 0

Sominski Gennadiy G., Sezonov Vyacheslav E., Taradaev Evgeniy P., Tumareva Tatiana A., Givargizov Evgeny I., Stepanova Alla N.

Cold field emitters for electron devices operating in technical vacuum

Published in category «Physical electronics»

The paper describes the field emitters of a new type: multi-tip cathodes with special protective coatings and layered cathodes prepared from the nano-layers of the materials with different work function values.The article presents data on the technology of emitter creation and their operation at technical vacuum conditions.

Views: 1184 Comments: 0

Kniazkov Anatoly V.

The polarization-optical method for spectral analysis of light

Published in category «Physical optics»

An analysis of passing the light emission that has Gaussian spectrum through the polarization-optical scheme (POS) with half-wave phase plate has been performed. The results of theoretical calculations of the coherence length of the radiation as a function of the contrast of POS output intensities are obtained for the different widths ∆λ of the Gaussian emission spectrum. The research results of the contrast of POS with λ/2 phase plate are obtained for the following case: high-power leds radiation of red, green and blue spectrum; semiconductor laser red wavelengths; a second harmonic ND-laser (green wavelength range).

Views: 950 Comments: 0

Privalov Vadim E., Seteikin Alexey Yu., Fotiadi Alexander E.

Simulation of laser radiation propagation in inhomogeneous media with complex geometry

Published in category «Physical optics»

A mathematical model has been developed. It makes possible to analyze the process of the three-dimensional propagation of laser radiation in inhomogeneous media with a complex geometry using the proposed modification of the Monte Carlo method. The model also allows to carry out the calculation of the distribution of the absorbed laser energy density in multilayered materials with complex geometry and can be used in solving problems of analysis of thermal fields visualization. Those problems arise in irradiated tissues.

Views: 1036 Comments: 0

Ipatov Andrey N., Ivanov Vadim K., Polozkov Roman G.

On stability of nanoscale electron-positron droplets

Published in category «Theoretical physics»

This paper presents the results of the total energy calculation for electroneutral electron-positron clusters with closed shells. The calculations were performed within the random Phase approximation with exchange to take into account many-particle correlations that allowed us to reduce the energy per one electron-positron pair below the energy per one pair of dipositronium molecule. The most stable electron-positron clusters are found for the cluster sizes in the interval from 20 to 40 pairs.

Views: 1209 Comments: 0

Novikov Evgeny A.

A second-order method for additive stiff problem

Published in category «Theoretical physics»

A second-order accuracy method for additive stiff systems of ordinary differential equations is developed. Inequalities for accuracy control are obtained. Numerical results are presented.

Views: 1061 Comments: 0