Influence of the thicknesses of transition layers on the excitation efficiency of a thin-film x-ray waveguide

Theoretical analysis of the resonant excitation of waveguide modes in the conducting channel of a thin-film x-ray waveguide has been performed within the plane-wave approximation with consideration of the interface diffusion due to the interdiffusion processes and irregularities.     

Spin Crossover in a Family of Iron(II) Complexes with Hexadentate ligands: Ligand Strain as a Factor Determining the Transition Temperature

This paper reports the synthesis of a family of mononuclear complexes [Fe(L)]X₂ (X=BF₄, PF₆, ClO₄) with hexadentate ligands L=Hpy-DAPP ({bis[N-(2-pyridylmethyl)-3-aminopropyl](2-pyridylmethyl)amine}), Hpy-EPPA ({[N-(2-pyridylmethyl)-3-aminopropyl][N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}) and Hpy-DEPA ({bis[N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}). The systematic change of the length of amino-aliphatic chains in these ligands results in chelate rings of different size: two six-membered rings for Hpy-DAPP, one five- and one six-membered rings for Hpy-EPPA, and two five-membered rings for Hpy-DEPA. The X-ray analysis of three low-spin complexes [Fe(L)](BF₄)₂ revealed similarities in their molecular and crystal structures. The magnetic measurements have shown that all synthesized complexes display spin-crossover behavior. The spin-transition temperature increases upon the change from six-membered to five-membered chelate rings, clearly demonstrating the role of the ligand strain. This effect does not depend on the nature of the counter ion. We discuss the structural features accountable for the strain effect on the spin-transition temperature.     

Diffraction-induced spatially confined laser pulse splitting in photonic crystals

It is shown theoretically that the effect of diffraction-induced optical pulse splitting in a linear photonic crystal under the conditions of the Laue transmission geometric scheme of Bragg diffraction can be realized for a spatially confined laser pulse in a hundred-period multilayer structure.     

Change in the spatial coherence function at Bragg reflection of an X-ray beam

The influence of coherent properties of an X-ray source (X-ray tube, synchrotron radiation source, free-electron X-ray laser) on the spatial field distribution and the spatial coherence function of this field has been theoretically considered for Bragg reflection from a single crystal.     

Excitation of promising nuclear fusion reactions in picosecond laser plasmas

The results of experiments devoted to studying the excitation of the promising nuclear fusion reactions ⁶Li(d, α)⁴He, ³He(d, p)⁴He, ¹¹B(p, 3α), and ⁷Li(p, α)⁴He, along with the standard reaction D(d, n)³He, in picosecond laser plasmas are presented. For the first time, it was shown that these reactions may proceed at a moderate laser-radiation intensity of 2 × 10¹⁸ W/cm², the respective yield being 2 × 10³ to 10⁵ per laser pulse. A brief survey of the main processes responsible for the generation of fast electrons and fast ions (protons) at the front surface of the target and for the excitation of nuclear fusion reactions is given. The calculated and experimental results on the yield from nuclear fusion reactions in picosecond laser plasmas are compared. The possibilities for optimizing the yield from the promising fusion reactions excited in femto- and picosecond laser plasmas are discussed.     

Reconstruction of the surface layer density profile by the X-ray reflectometry method

The method for reconstructing the profile of the material density distribution arbitrarily varying over the depth of the subsurface layer of the specimen from X-ray reflectometry data is suggested. For the first time, the recurrent relationships for the derivatives of the specular reflection coefficient with respect to the parameters of the subsurface layer are obtained, which reduce the volume of the necessary computations by one to two orders of magnitude. The class of functions for which such density-profile reconstruction can be made within a 5% error is characterized. The method is tested on thin tungsten and carbon films on silicon substrates and thin films of porous silicon films with p ⁺-type conductivity.     

Characterization of the structure of porous germanium layers by high-resolution X-ray diffractometry

The surface morphology and the structure of porous germanium layers obtained by chemical etching of n-type single-crystal Ge(111) substrates with their subsequent annealing in hydrogen atmosphere are studied by high-resolution X-ray diffractometry. It is established that upon etching a 1.5 to 2.0-μm-thick porous germanium layer is formed, which contains quasi-ordered microinhomogeneities in the form of elongated pits with characteristic dimensions of 1 μm and an average distance between them of 3–4 μm. The layer bulk has pores with radii ranging within 25–30 nm and nanocrystallites with an average size of 10 nm, with the average porosity being 56%.     

Thermal decomposition features of calcium and rare-earth oxalates

Thermal decomposition of Ln₂(C₂O₄)₃ · 9H₂O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC₂O₄ · H₂O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374°C in the absence of calcium oxalate gives rise to the solid solution of CeO₂-based rare-earth oxides. Calcite CaCO₃ is formed in the presence of calcium oxalate at annealing temperatures above 442°C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La₂O₃, CeO₂, Pr₆O₁₁, and Nd₂O₃ phases. An increase in temperature above 736°C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO₂-based lanthanide oxide solid solution.     

Emissivity of a multibeam electron gun with a glassy carbon field-emission cathode

A multibeam triode electron gun with a glassy carbon field-emission cathode that is intended for an O-type microwave amplifier is studied. The electric field strength and the current density at the microtips versus the distance to the center of a cell of the cathode–grid unit are calculated. Calculation data are compared with experimental results. It is shown that about 70% of the cathode current in each cell is accounted for by microtips arranged in a circumferential ring no wider than 20 μm. The field-emission current density inside the ring exceeds 40 A/cm², and the current per microtip equals 43.1 μA.