Surface emitting lasers

In this paper we review the recent progress and basic technology of vertical cavity surface emitting lasers (SEL). First, the concept of surface emitting lasers is introduced, and then device technologies will be presented. We will feature some important issues, such as multi-layer structures and 2-dimensional arrays. Lastly, the future prospects of SELs are discussed.     

Theory of adiabatic variation of critical temperature of the Bose-Einstein condensation of an ideal gas in optical lattice

We calculate the critical temperature of the Bose-Einstein condensation of an ideal Bosegas in the presence of an external periodic potential in one, two, or three directions. A number of assumed approximations enables us to show that the only parameter determining the critical temperature of condensation is the width of the lower energy band with the direct proportionality to the one-third power of this width for each direction of periodicity of the external potential. This also proves the result, obtained earlier by means of numerical calculation, that deepening of the periodic potential (which is known to lead to narrowing of energy bands) leads to lowering of the critical temperature. The fundamental role of quantum tunneling in establishing this regularity is emphasized.     

XPS study of fluorinated carbon multi-walled nanotubes

Arc-produced carbon multi-walled nanotubes (MWNTs) were fluorinated at 420 °C in a flow of diluted F₂ gas containing small admixture of HF gas. Fluorinated materials (F-MWNTs) with 10–55 wt.% fluorine content were studied by XPS. It was shown that fluorination begins at the external layers of nanotubes and the reaction front propagates inside the multi-layer particles in concert with structural deterioration of graphene layers. The C₂F stoichiometry still allows MWNT wall integrity, similar to known for SWNTs. The fluorine contents in the product can noticeably exceed this higher fluorine limit for tube stability. The position of the F 1s line at 688.2 eV does not depend on the fluorine concentration. Nearly covalent C–F bonds dominate the F-MWNT samples, with a small quantity (2–9%) of ionic bonds also present. Fluorinated carbon tends to spatially separate from non-fluorinated carbon.     

Spatial modulation of X-rays in the presence of external acoustic field

The two-crystal X-ray diffraction from (111?1) reflecting atomic planes of quartz single crystal with AT-cut was experimentally considered in the Laue geometry, when both the crystals are simultaneously in the field of bulk acoustic waves. It is shown that as a result of spatial modulation of reflected beam an odd number of parallel X-ray beams is obtained.     

The Stevens rearrangement of propargyl-containing ammonium salts

The Stevens rearrangement of ammonium salts with two propargyl group at the ammonium nitrogen results in the formation of amines containing acetylene-acetylene and acetylene-allene fragments.     

Influence of a flat wall on the motion of an aerosol particle in an inhomogeneous temperature field

The method of successive approximation is used to investigate the influence of a flat wall on the thermophoretic force acting on an aerosol particle of radius R at distance1 from the wall and moving in the direction normal to it. The problem is solved in the first approximation in R/1 1.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 185–188, September–October, 1980.We are grateful to Yu. I. Yalamov for suggesting the problem, for discussing the results, and for constant interest in the work.     

Approximate solution of the Schrödinger equation for an atom in the field of a standing wave

We present an approximate method of calculation of energy spectrum and wave functions of translational motion of a two-level atom in the field of a standing wave at zero value of the quasimomentum. Wave functions in the momentum representation are expressed in terms of confluent hypergeometric functions in case of continuous spectrum and in terms of Hermitian polynomials in case of discrete spectrum. The energy spectrum exhibits infinite compaction at transition from discrete part to continuous, as it is the case for, e.g., Coulombian potential.     

Determination of radiation reflection and transmission operators in a slab

In the framework of a discrete radiative transfer model, a method is proposed for finding the reflection and transmission operators in the conservative case.     

Synthesis of graphene-like materials by graphite oxide reduction

Graphene-like materials were produced by the reduction of graphite oxide with a series of chemical reagents and high-temperature treatment. Hydrazine hydrate, hydroxylamine hydro-chloride, sodium borohydride, and sodium sulfite were used as reducing agents. The obtained materials were studied by elemental and thermal gravimetric analyses, scanning electron microscopy, X-ray diffraction, and IR and Raman spectroscopy. Depending on the used reducing agents, the graphene-like materials contained different amounts of residual oxygen.