I.A. Perezhogin

Polytypes and twins in the diamond-lonsdaleite system formed by high-pressure and high-temperature treatment of graphite.

As a result of the high-temperature and high-pressure treatment of graphite we obtained a powder containing diamond and lonsdaleite. The structure and properties of the powder were studied by transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). It was found that the synthesized material contains not only diamond nanoparticles, but also some relatively large (up to several nanometers) fragments of lonsdaleite. 4H and 6H polytypes were found in some of the diamond particles. Incoherent twin boundaries were observed in the diamond particle containing fragments of lonsdaleite.

Polarization rotation due to femtosecond filamentation in an atomic gas

The linear-to-elliptical transformation of a 400 nm femtosecond-probe pulse in the birefringent filament in argon of an 800 nm linearly polarized femtosecond-pump pulse is studied numerically and experimentally. The rotation of the probe elliptical polarization is the largest in the high-intensity filament core. With propagation, the rotated radiation diffracts outward by the pump-produced plasma. The transmission of the analyzer crossing the probes polarization is maximum at the pump-probe angle of 45 degrees and gives equal values for each pair of angles symmetrically situated at both sides of the maximum.

Specific features of the self-action of elliptically polarized light pulses and the formation of vector solitons in an isotropic medium with the anomalous frequency dispersion and the spatial dispersion of cubic nonlinearity

Numerical methods are used to study the effect of local and nonlocal nonlinear optical susceptibilities on the parameters of a soliton whose degree of ellipticity depends on time and that is formed at a distance of several dispersion lengths in a medium with the anomalous frequency dispersion. The rotation angle of the major axis of the polarization ellipse does not depend on time and linearly increases with an increasing propagation coordinate. If the tensor components of the local nonlinear susceptibility have opposite signs, the incident elliptically polarized pulse can propagate in the regime that involves the pulse splitting into components for which the absolute values of the electric-field degrees of ellipticity are close to unity. In this case, the electric-field vector at the center of the pulse rotates in the opposite direction with respect to the rotation at the edges.

Longer Carbon Nanotubes by Controlled Catalytic Growth in the Presence of Water Vapor

One of the most important problems in the synthesis of carbon nanotubes is the problem of controlling their morphology, namely, length, aspect ratio, alignment and so forth. Catalytic synthesis of carbon nanotubes in a suspended bed reactor allowed for the study of the possibilities of controlling the growth of nanotubes by introducing a certain amount of water vapor and carbon-containing materials in the reaction zone. The synthesized long carbon nanotubes were studied by Raman spectroscopy, transmission and scanning electron microscopy. We found that water concentration influences both yield and structure of nanotubes. It is shown that the yield of centimeter-long nanotubes can be maximized at an optimum H2O/C ratio, while deviations dramatically change morphology and thickness of the nanotubes.

C60 three-dimensional polymerization by impulse heating effect

Impulse laser heating combined with a quick sample cooling in a diamond anvil cell provides unique conditions for the 3D polymerization reaction of C60. The reaction proceeds under the 8–10 GPa pressure and 2700 K temperature in the case of heating-cooling cycle time around 0.1 μs. Such a short heating time permits to increase the maximal temperature of the fullerite sample by 1700 K on conditions that C60 are still surviving. As a result, the pressure of the phase transition to 3D polymerized fullerite phase with 519 GPa bulk modulus was essentially decreased. Furthermore, the transition has proceeded at quasi-hydrostatic conditions without activation by applying a plastic deformation.

Formation of the lines of circular polarization in a second harmonic beam generated from the surface of an isotropic medium with nonlocal nonlinear response in the case of normal incidence

For the first time we have obtained the analytical expressions describing the spatial distribution of the polarization of a second harmonic beams light field reflected from the surface of an isotropic gyrotropic medium in the case when a normally incident fundamental beam contains a polarization singularity of an arbitrary type. The contribution of bulk and surface responses of the nonlinear medium in the formation of the lines of circular polarization in the second harmonic beam were analyzed. The relation between topological characteristics and polarization states of the singularities in the incident and reflected beams was established.

Graphite-to-diamond (13C) direct transition in a diamond anvil high-pressure cell

13C-graphite treated in a diamond anvil high-pressure cell was studied by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and electron energy loss spectroscopy. It was found that 13C-diamond and lonsdaleite originate after the treatment under high pressure and shear deformation.

Toward the Ultra-incompressible Carbon Materials. Computational Simulation and Experimental Observation

The common opinion that diamond is the stiffest material is disproved by a number of experimental studies where the fabrication of carbon materials based on polymerized fullerenes with outstanding mechanical stiffness was reported. Here we investigated the nature of this unusual effect. We present a model constituted of compressed polymerized fullerite clusters implemented in a diamond matrix with bulk modulus B0 much higher than that of diamond. The calculated B0 value depends on the sizes of both fullerite grain and diamond environment and shows close correspondence with measured data. Additionally, we provide results of experimental study of atomic structure and mechanical properties of ultrahard carbon material supported the presented model.

Ultrashort elliptically polarized laser pulse interaction with helical photonic metamaterial

Using the finite-difference time-domain (FDTD) method we have numerically investigated the transmission and reflection of both long and ultrashort elliptically polarized light pulses in periodic metamaterial made of polymer. In the first time we have analyzed the polarization evolution in the hodograph of the transmitted long pulses, and we demonstrated the behavior of the electric field in transmitted ultrashort pulses. The mechanisms of light-matter interaction in terms of the electromagnetic energy oscillation in polymeric metamaterial are shown. We studied the influence of all the parameters of metamaterial unit cell (a helix) on the transmission and reflection. Particularly, the increase of the amount of the helix cycles broadens the polarization-selective frequency range for the transmitted light.

Decomposition of Fe5C2 catalyst particles in carbon nanofibers during TEM observation

Abstract The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe3C). However, for Hägg carbide nanoparticles (χ-Fe5C2), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.