Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 10 nm and cluster density was 10¹⁰ cm⁻². A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.     

Local plasmon excitations in one-dimensional array of metal nanowires for sensor applications

Optical properties of a one-dimensional periodic array of subwavelength metal nanowires in the regime of local plasmon excitation are investigated experimentally and theoretically. Both gas and liquid sensing by one-dimensional gold nanowires on a glass substrate produced by holographic lithography are demonstrated experimentally. The obtained spectral sensitivity of a local plasmon sensor to the refractive index of the environment is found comparable to that of a surface plasmon polariton sensor based on the grating coupler effect. The influence of nanowire shape on spectral sensitivity is studied theoretically in a differential formalism framework using a curvilinear coordinate transformation for triangular, trapezoidal, and rectangular cross sections of the nanowires. For nanowires with trapezoidal cross section, theoretical calculations for the spectral sensitivity to variation of the refractive index of the environment agree well with experimental data.     

Quantized field-electron emission at 300 K in self-assembled arrays of silicon nanowires

Dense ensembles of silicon nanowires were prepared by metal-catalyzed chemical vapor deposition on silicon substrates. Some of these ensembles were doped with phosphorous during growth. The nanowires were characterized using scanning electron microscopy, X-ray diffraction, and mass spectroscopy. Field emission of electrons from these structures was studied at room temperatures in ultra-high vacuum. The measurements were carried out using a parallel-plate diode cell. At high-applied fields, the current–voltage characteristics deviate from the Fowler–Nordheim law and exhibit a step-wise increase in the current with the increasing voltage at 300 K. Possible mechanisms of the observed quantized field emission are discussed.     

Multifractal parameterization of space forms on surfaces of Zn x Cd1 − x Te-Si(111) heterocompositions and its relationship to the conditions of layer synthesis

Multifractal (MF) analysis of space forms on the surfaces of thin layers of Zn _x Cd_{1 ? x} Te solid solution precipitated onto a Si(111) substrate via the hot wall approach is performed. AFM images of film surfaces are used for MF analysis. The parameters of MF spectra are determined for the film surfaces of the above system. It is shown that the MF functions of system correspond to their canonical forms, and the resulting computational procedure can be applied to describe and analyze the state of spatial fractal structures that form on a layer’s surface. The quantitative relationships between the parameters of the MF spectrum of a film’s surface and its conditions of precipitation are revealed.     

Magnetic properties and surface morphology of layered In2Se3 crystals intercalated with cobalt

The magnetic properties of layered Co _x In₂Se₃ crystals electrochemically intercalated with cobalt in an external magnetic field and without a magnetic field and the morphology of the van der Waals surfaces of layers of these crystals have been investigated. It has been found that the ferromagnetic ordering at room temperature is observed only for Co _x In₂Se₃ crystals intercalated in an external magnetic field. These crystals are nanocomposite materials that consist of a layered matrix and arrays of nanorings and nanowires formed from Co nanocrystals on the van der Waals surfaces of the In₂Se₃ layers. Cobalt nanocrystals in Co _x In₂Se₃ crystals have a pyramidal equilibrium shape, which is characteristic of the face-centered cubic crystal structure, and their geometrical sizes are of the order of a few nanometers. The specific features of self-organization of cobalt magnetic nanostructures on the van der Waals surfaces of layered semiconductor crystals during their electrolytic intercalation in a magnetic field and the magnetic properties of these structures have been considered.     

4-(4-Acethylphenyl)-3-hydroxycoumarin in the Synthesis of Nitrogen-containing Heterocycles with a Neoflavonoid Moiety

Russian Journal of Organic Chemistry - 4-(4-Acetylphenyl)-3-hydroxy-2H-chromen-2-one has been prepared by the reaction of (4-acetylbenzene)diazonium chloride with 3-hydroxy-2H-chromen-2-one under...     

Synthesis and reactions of 5-aryl-2-thiophenecarbaldehydes

The reaction of 2-thiophenecarbaldehyde with arene diazonium chlorides in the presence of CuCl₂ catalyst gave 5-aryl-2-thiophenecarbaldehydes. Use of 4-nitrobenzene diazonium chloride in the reaction also gave the isomeric 3-(4-nitrophenyl)-2-thiophenecarbaldehyde. Condensation products of the 5-aryl-2-thiophenecarbaldehydes with cyanoacetic acid esters, cyanoacetamide, and with barbituric and dimethylbarbituric acids were prepared. Communication 16 in the series “Synthesis of heterocycles based on the products of arylation of unsaturated compounds”. For Communication 15 see [1]. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1166–1171, August, 2008.     

Synthesis,nature of electronic transitions,and absorption spectra of the dye based on 4-(methyl-1-{2-[4-(1-methyl-2-oxo-1,2-dihydroquinolin-3-yl)phenyl]-2-oxoethyl}pyridinium bromide

The reaction of 3-(4-bromoacetylphenyl)-1-methylquinolin-2(1Н)-one with pyridine and 4-methylpyridine has afforded the corresponding pyridinium salts. Condensation of 4-methyl-1-{2-[4-(1-methyl-2-oxo-1,2-dihydroquinolin-3-yl)phenyl]-2-oxoethyl}pyridinium bromide with 4-dimethylaminobenzaldehyde has given a new biscyanine dye, 1-{1-[4-(1,2-dihydro-1-methyl-2-oxo-3-quinolinyl)benzoyl]-2-[4-(dimethylamino)-phenyl]ethynyl}-4-{2-[4-(dimethylamino)phenyl]ethynyl}pyridinium bromide. Its electronic spectrum has been analyzed, and quantum-chemical simulation of spatial and electronic structure of its possible isomers has been performed.     

Electrolytic molybdenum oxides in lithium batteries

Nonstoichiometric molybdenum oxides (e-Mo_xO_y) were synthesized by cathodic reduction of aqueous ammonium and sodium molybdate solutions. Surface morphology of electrolytic (e) deposits, the chemical composition, crystal lattice structure, and the characteristics of electrochemical Li⁺ intercalation for such synthesized oxides were determined by the cation composition of molybdate solution and the conditions of deposit annealing. The electrochemical intercalation of Li⁺ ions in these Mo-oxides was investigated in thin-layer ballast-free electrodes, as a pasted mposite cathode in lithium batteries, and as an anode in lithium-ion batteries, with liquid organic and polymer electrolytes. The reversible discharge capacity of e-Mo₄O₁₁ synthesized from ammonium molybdate electrolyte in thin-layer ballast-free electrodes can exceed 225 mAh g^–1 for more than 170 cycles.     

Composition and elastic stresses in multilayer structures with Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript> nanoislands

The composition and mechanical stresses in Si_1?xGe_x nanoislands involved in multilayer and single-layer structures grown under the same conditions are determined using Raman spectroscopy. It is demonstrated that an increase in the content of silicon in the nanoislands contained in a multilayer structure does not enhance their relaxation (as compared to that in a single layer) due to the absence of a free surface. The experimental scattering spectrum of folded acoustic phonons contains bands with sufficiently small half-widths, which indicates high quality of the grown superlattices with nanoislands.