Deep trench etching in macroporous silicon

We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. It also enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics. The limits of this new process are simulated using electrostatic models and are verified experimentally. PACS 82.45.Yz; 81.16.-c     

Non-integrability of some Painlevé VI-equations and dilogarithms

The paper studies the Painlevé VI^e equations from the point of view of Hamiltonian nonintegrability. For certain infinite number of points in the parameter space we prove that the equations are not integrable. Our approach uses recent advance in Hamiltonian integrability reducing the problem to higher differential Galois groups as well as the monodromy of dilogarithic functions.      

Optical and photoelectric properties of pure and cadmium-and lead-doped neodymium sesquisulfide thin films

A technique for preparing γ-Nd₂S₃ crystalline thin films through discrete vacuum thermal evaporation of a presynthesized bulk material is developed. The films deposited are doped with cadmium and lead. The reflectance and transmittance spectra of the films are measured in the photon energy range 0.2–3.0 eV at a temperature of 300 K. The frequency analysis of the absorption coefficient demonstrates that the γ-Nd₂S₃ films are characterized by an exponential absorption edge. The photoconductivity spectra and temperature dependences of the photoconductivity for the γ-Nd₂S₃ films doped with cadmium and lead are measured in the photon energy range 0.2–3.3 eV at temperatures varying from 115 to 380 K. The experimental data obtained are interpreted under the assumption that the acceptor levels formed by vacancies in the cation sublattice and compensated for by cadmium and lead donor dopants play a crucial role in the photoconduction. The ionization energy at the lead donor level is determined.     

Hydrophobicity and thermal stability of fluorinated pentaerythritol esters

Wetting angles and limits of thermal stability of esters derived from pentaerythritol and perfluoro-, ω-chloropolyfluoro-, and perfluoropolyethercarboxylic acids were studied.     

Thickness dependence of the magnetic anisotropy of Fe layers separated by Al

Magnetic multilayers of ⁵⁷Fe with nominal thickness, T _nom, between 0.4 and 1.0 nm separated by 3.0 nm Al spacer layers were prepared by alternate deposition of the constituents in high vacuum. The samples were investigated at 4.2 K in external magnetic field. A fraction of Fe atoms corresponding to about 0.3 nm equivalent Fe-thickness was found to mix into the Al spacer. The extremely strong magnetic anisotropy observed for T _nom < 0.8 nm is attributed to Fe layers of approximately two atomic planes thick. The anisotropy decreases considerably after the building up of the third Fe atomic layer starts at T _nom = 0.8 nm, but full saturation was not achieved even for T _nom = 1 nm and 3 T magnetic field applied perpendicularly to the sample plane.     

The preparation and properties of low molar mass liquid crystals possessing lateral alkyl chains

The first twelve members of three new mesogenic homologous series have been characterized, each of which are composed of molecules possessing lateral alkyl chains. The n-alkyl 2,5-bis-(4-n-hexyloxy-benzoyloxy)-benzoates are purely nematic whereas both nematic and smectic behaviour is observed for the 4-cyano-4'-biphenylyl 3'-n-alkyloxybenzoates and the 4-cyano-4'-biphenylyl 3',4'-n-alkyloxybenzoates. The transitional properties of these series are similar to those of the analogous conventional mesogens and hence, can be rationalized without making any special assumptions concerning the conformational distribution of the lateral alkyl chain.     

On universal spaces and absorbing sets related to a transfinite extension of covering dimension

R. Pol has shown that for every countable ordinal number α there exists a universal space for separable metrizable spaces X with trindX?α. W. Olszewski has shown that for every countable limit ordinal number λ there is no universal space for separable metrizable space with trIndX?λ. T. Radul and M. Zarichnyi have proved that for every countable limit ordinal number there is no universal space for separable metrizable spaces with dimWX?α where dimW is a transfinite extension of covering dimension introduced by P. Borst. We prove the same result for another transfinite extension dimC of the covering dimension.As an application, we show that there is no absorbing sets (in the sense of Bestvina and Mogilski) for the classes of spaces X with dimCX?α belonging to some absolute Borel class.     

Stereochemistry of seven-membered heterocycles: XLV. Highly diastereoselective addition of dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate to 2-substituted 1,3-dithiacyclohept-5-enes

Conformationally heterogeneous 2-substituted 1,3-dithiacyclohept-5-enes (R = Ph, Me, t-Bu), which exist in solution as chair and boat conformers, react with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate with high exo-diastereoselectivity: only the chair conformer is involved. The steric structure of 4-methyl-3,5-dithia-9,10-diazabicyclo[5.4.0]undeca-7,10-diene was determined by X-ray analysis. Its crystal packing and supramolecular structure were also analyzed.