Magnetic nanoparticles embedded into semiconductors have current perspectives for use in semiconducting spintronics. In this work, 40 keV Fe+ ions were implanted in high fluences of (0.5 ÷ 1.5) × ...1017 ion/cm2 into an oxide semiconductor and single-crystalline TiO2 plates of rutile structure with (100) or (001) face orientations. Microstructure, elemental-phase composition, and magnetic properties of the Fe-ion-implanted TiO2 were studied by scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies, as well as vibrating-sample magnetometry (VSM). The high-fluence ion implantation results in the formation of magnetic nanoparticles of metallic iron beneath the irradiated surface of rutile. The induced ferromagnetism and observed two- or four-fold magnetic anisotropy are associated with the endotaxial growth of Fe nanoparticles oriented along the crystallographic axes of TiO2.
Abstract
Insights into the fundamental properties of graphene’s Dirac-Weyl fermions have emerged from studies of electron tunnelling transistors in which an atomically thin layer of hexagonal boron ...nitride (hBN) is sandwiched between two layers of high purity graphene. Here, we show that when a single defect is present within the hBN tunnel barrier, it can inject electrons into the graphene layers and its sharply defined energy level acts as a high resolution spectroscopic probe of electron-electron interactions in graphene. We report a magnetic field dependent suppression of the tunnel current flowing through a single defect below temperatures of ~2 K. This is attributed to the formation of a magnetically-induced Coulomb gap in the spectral density of electrons tunnelling into graphene due to electron-electron interactions.
Different growth stages and surface morphology of the epitaxial 3C-SiC/Si(100) structures were studied. Heterocompositions were grown in vacuum from hydric compounds at a lower temperature. The ...composition, surface morphology and crystal structure of the 3C-SiC films were tested using X-ray diffraction, second ion mass spectrometry, scanning ion and electron microscopy, photo- and cathode luminescence. It was demonstrated that the fine crystal structure of the 3C-SiC islands was formed by the close-packed nanometer-size grains and precipitated on the underlying solid carbonized Si layer. Luminescence spectral lines of the solid carbonized Si layer, separated island and solid textured 3C-SiC layer were shifted toward the high ultraviolet range. The spectra measured by different methods were compared and the nature of the revealed lines was considered. This article discusses a quantum confinement effect observation in the 3C-SiC nanostructures and a perspective for the use of nanotextured island 3C-SiC layers as a two-dimensional surface quantum superlattice for high-frequency applications. The conductivity anisotropy and current-voltage characteristics of the two-dimensional superlattices with a non-additive electron dispersion law in the presence of a strong electric field were studied theoretically. Main efforts were focused on a search of the mechanisms allowing realization of the high-frequency negative dynamical conductivity for the structures having a positive static differential conductivity.
Magnetic nanoparticles embedded into semiconductors have current perspectives for use in semiconducting spintronics. In this work, 40 keV Fesup.+ ions were implanted in high fluences of (0.5 ÷ 1.5) × ...10sup.17 ion/cmsup.2 into an oxide semiconductor and single-crystalline TiOsub.2 plates of rutile structure with (100) or (001) face orientations. Microstructure, elemental-phase composition, and magnetic properties of the Fe-ion-implanted TiOsub.2 were studied by scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies, as well as vibrating-sample magnetometry (VSM). The high-fluence ion implantation results in the formation of magnetic nanoparticles of metallic iron beneath the irradiated surface of rutile. The induced ferromagnetism and observed two- or four-fold magnetic anisotropy are associated with the endotaxial growth of Fe nanoparticles oriented along the crystallographic axes of TiOsub.2.
We report an original method of GaN/AlN quantum dots (QDs) formation with low density by ammonia MBE on the (0001)AlN surface using a decomposition process of GaN thin layer. The QDs formation has ...been investigated in situ by reflection high-energy electron diffraction technique. Low density of quantum dots has been obtained in the range 10
7
–10
9
cm
−2
. Single quantum dots photoluminescence lines corresponding to exciton and biexiton transitions were observed in micro-photoluminescence spectra. A lattice gas model was developed for correct description of the GaN QDs statistical ensemble on the surface. Effective interaction between QDs results in the discontinuous phase transitions (first-order phase transitions) from low density of QDs (gas branch) to condensed phase of QDs. The GaN QDs formation has been confirmed by high-resolution transmission electron microscopy and micro-photoluminescence of single quantum dots.
We propose a discrete time dynamical system (a map) as a phenomenological model of excitable and spiking-bursting neurons. The model is a discontinuous two-dimensional map. We find conditions under ...which this map has an invariant region on the phase plane, containing a chaotic attractor. This attractor creates chaotic spiking-bursting oscillations of the model. We also show various regimes of other neural activities (subthreshold oscillations, phasic spiking, etc.) derived from the proposed model.
The paper presents a technology for preparing the silicon Si(111) substrates surface for the III-nitride compounds epitaxial growth by molecular beam epitaxy technique. The technology includes the ...following stages: chemical surface pretreatment by the Shiraki method, bakeout in the preliminary annealing chamber, the substrates heating in the growth chamber in order to obtain an atomically clean and ordered silicon surface, the samples cooling with subsequent registration of the (7x7) superstructure. The search for surface preparation conditions was carried out using (1) high-energy electron diffraction, which in situ revealed carbon contamination in the form of silicon carbide compounds formed during high-temperature heating of silicon, and (2) high-resolution optical microscopy, which recorded dislocation slip lines caused by a temperature gradient in sample heating process. For uniform heating/cooling of the substrate and suppression of the process of generation and slip of dislocations that appear at the edges of the substrate, the substrate mounting arrangement was modified. It has been demonstrated that the surface of Si(111) substrates prepared using the proposed technology is suitable for the epitaxial growth of III-nitride structures.
Searching for New Sites for THz Observations in Eurasia Bubnov, Grigoriy M.; Abashin, Evgeniy B.; Balega, Yuriy Yu ...
IEEE transactions on terahertz science and technology,
2015-Jan., 2015-1-00, Volume:
5, Issue:
1
Journal Article
Peer reviewed
This paper deals with the preliminary results of the astroclimate monitoring in the short millimeter-wave band in the territory of the CIS countries. The optical depths for the 3-mm and 2-mm-band ...windows have been determined with the atmospheric dip method. The preliminary results of single measurements taken at Mus-Khaya Mountain (2,000 m/6,560 ft, Eastern Yakutia) and in Central Russia are presented. The paper also deals with the results of the observations of the first half of 2014 done within the regular monitoring of the astroclimate conditions combined with the meteorological observations at the site of the BTA telescope in the North Caucasus (2,000 m/6,560 ft) and on the Suffa Plateau (2,400 m/7,870 ft, Uzbekistan). The collected statistical data yield the mean number of cloudless days per year. In addition, the seasonal variations of the precipitable water vapour (PWV) have been approximately calculated for each site explored. Knowing the PWV, the total absorption can be predicted for different atmospheric windows, including the terahertz band (2.0 mm, 1.3 mm, and 0.87 mm). Using available data on the measurements of the absorption, the PWV, height, etc., suitability of the site can be evaluated for potential stationing of a millimeter or a submillimeter wave range observatory. The ultimate goal of this research is to find a suitable location for the radio astronomic observatory designed for the ground support of the future submillimeter wave VLBI space mission ("Millimetron"), as well as for the terahertz satellite telecommunication and CMB observations.
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