Generation of phase nuclei by solitons of the new “undulator” type in martensitic phase transitions of crystalline materials

The microdynamics of large-amplitude nonlinear lattice vibrations of plutonium and uranium materials has been investigated at high reactor temperatures in the ranges of martensitic phase transitions. Topologically new large-amplitude solitons of the “undulator” type have been revealed. Transverse and longitudinal “undulator” solitons in crystals with hexagonal and cubic symmetry, depending on the direction of motion, have different kinematic and amplitude characteristics, which differ from the characteristics of the previously known solitons. The transverse “undulator” solitons, like electrons in undulators, are observed with periodic atomic displacements orthogonal to the direction of soliton propagation. The longitudinal “undulator” solitons with displacements of atoms in the direction of soliton propagation are characterized by periodic delays with two-step velocities on the trajectory in a certain analogy with two-period engineering undulator devices. It has been shown that, at high energies, such “undulator” solitons of two types generate nuclei of a new phase in early stages of structural phase transitions.     

Interlayer tunneling spectroscopy of graphite at high magnetic field oriented parallel to the layers

Interlayer tunneling in graphite mesa-type structures is studied at a strong in-plane magnetic field H up to 55 T and low temperature T = 1.4 K. The tunneling spectrum dI/dV vs. V has a pronounced peak at a finite voltage V ₀. The peak position V ₀ increases linearly with H. To explain the experiment, we develop a theoretical model of graphite in the crossed electric E and magnetic H fields. When the fields satisfy the resonant condition E = vH, where V is the velocity of the two-dimensional Dirac electrons in graphene, the wave functions delocalize and give rise to the peak in the tunneling spectrum observed in the experiment.     

Orbital quantization in a system of edge Dirac fermions in nanoperforated graphene

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level E _F, which is varied by the gate voltage V _g, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO₂ substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(V _g) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of E _F through an equidistant set of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.     

Bending vibrations of semiconductor wafers with local heat sources

Experimental and theoretical analysis of temperature fields generated by the pulsed current heating of metallization paths on a semiconductor wafer surface is performed. It is shown that any step change in the heating power causes bending vibrations of the wafer. Within the safety margins for semiconductor device operation, the vibration amplitude is proportional to the step amplitude. The damping factor for the entire wave packet is found (Γ=1103 s^?1), and frequency components of acoustic radiation excited in a 300-µm-thick silicon wafer are determined.     

Heterogeneous reduction of potassium heptafluorotantalate

The results obtained in the study of the influence of heterogeneous reduction conditions on the characteristics of the tantalum powder obtained are presented. A new technique for heterogeneous reduction of potassium heptafluorotantalate with dosium is described. The technique allows production of powders with characteristics corresponding to those obtained in a large-scale experiment, with small amounts of reactants.     

Nickel-catalyzed addition of benzenethiol to alkynes: Formation of carbon-sulfur and carbon-carbon bonds

Nickel-catalyzed addition of benzenethiol to alkynes leads to alkenyl and dienyl sulfides; the direction of the process can be controlled by varying the PhSH/alkyne ratio. An advanced procedure, which ensures higher yields of 2-phenylsulfanylalkenes, includes gradual addition of alkyne to the other reactants. The structures of conjugated dienyl sulfides formed in the reaction were determined by 2D NMR spectroscopy. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2030–2034, November, 2006.     

Anomalies in the concentration quenching of luminescence in doped Y2SiO5:Pr3+ nanocrystals

In Y₂SiO₅:Pr³⁺ nanocrystals, an ordered phase is observed in the ¹ D ₂ luminescence decay curves of Pr³⁺ ions at their anomalously low concentration (0.5 at %). This effect is caused by the predominant accumulation of activator ions near the nanocrystal surface, which provides relaxation of the elastic strains arising as a result of the misfit between the ionic radii of Pr³⁺ and Y³⁺. The concentration quenching of Pr³⁺ luminescence is due to cooperative cross relaxation.