Energy of Pair Interaction of Molecular Systems: Excited State – Ground State of Molecules Pentyl – and Pentyloxy – Cyanobiphenyls

Abstract

The energies of pair interaction of molecular systems: first excited state and ground state of molecules pentyl - and pentyloxy - cyanobiphenyls was calculated and equilibrium configuration of these molecular systems was determinate. Pair orientated destabilization energies evaluation is given at the absorbtion and emission processes.     

Development of LuAG-based scintillator crystals – A review

A review of research and development of Lu₃Al₅O₁₂ (LuAG)-based single crystal scintillators is presented. Crystals of this type have been prepared by the micro-pulling down method at the initial stage of material screening and by Czochralski or Bridgman methods to obtain higher quality and larger size single crystals afterward. Several different activators, namely Ce³⁺, Pr³⁺, Yb³⁺ and Sc³⁺ have been reported in the literature and such doped LuAG single crystals have been extensively studied to understand a number of issues, including: the scintillation mechanism, underlying energy transfer and trapping processes including the nature and role of material defects involved in the scintillation process and their relation to manufacturing technology. Significant improvements in the understanding of aluminum garnet scintillators lead to the discovery of multicomponent garnet single crystal scintillators in 2011, which are described. These materials gave rise to new class of ultraefficient complex oxide scintillators, the light yield of which considerably exceeds the values achieved for the best Ce-doped orthosilicate scintillators.     

Multiple solution-doping in optical fibre fabrication I – Aluminium doping

This work is part of a study of solution-doping in Modified Chemical Vapour Deposition, as used in fabrication of specialty silica optical fibres. The present paper concentrates on aluminium solution-doping and the effects of introducing additional heat-treatment stages into the process. The behaviours of the aluminium salt when heat-treated independently and after deposition in the silica soot have been studied by X-ray diffractometry, thermo-gravimetric analysis with mass spectrometry, electron microscopy and microanalysis. It has been shown that a procedure involving multiple cycles of solution-soaking and heat-treatment of the soot layer increases the level of aluminium doping obtainable. Efficiency of aluminium incorporation has been measured in the soaked soot, the sintered glass layer and in the final collapsed preform. An interpretive model of the multiple cycle soak/heat-treatment process is suggested.     

Electrical and sensory properties of zinc oxide – porous silicon nanosystems

Abstract

Zinc oxide nanostructures have been grown by electrochemical deposition on porous silicon–silicon substrate. The photoelectric and sensory properties of the obtained ZnO–porous silicon nanosystems were investigated in both DC and AC regimes. The obtained structures were characterized by photosensitivity in the 400–1100?nm wavelength range and by high sensitivity to moisture. Increase of relative humidity resulted in significant decrease of the electrical resistance and increase of the capacitance of the hybrid structures. To estimate the sensory properties of the ZnO–porous silicon nanostructures their adsorption sensitivity and dynamic characteristics were analyzed. Discovered features of the charge transport processes broaden the prospects of the semiconductor nanosystems application in gas sensors and photodetectors.     

New preparation method of diamond like carbon – the layer-by-layer method

A new method––the layer-by-layer method––is used to prepare diamond like carbon (DLC) films. The layer-by-layer method is a cyclic process for the deposition of DLC by a rf magnetron sputtering using Ar gas and with alternate the atomic hydrogen treatment, which samples are called LL-DLC. A DLC sample without atomic hydrogen treatment and an atomic-hydrogen-treated DLC sample are prepared to compare with LL-DLC. LL-DLC samples are prepared with the substrate temperature from RT to 400 °C. The data of the electrical conductivity including Fermi level E_F, optical energy gap E_O4, X-ray photoelectron spectroscopy, sp³ fraction obtained by Raman spectra, infrared absorption coefficient spectra and atomic force microscope are used to characterize these DLC films. These results are also discussed comparing with amorphous carbon nitride a-CN_X and the layer-by-layer prepared amorphous carbon nitride LLa-CN_X.     

Dielectric investigations on a binary system showing a “filled” SA Phase

A binary system of a double swallow-tailed compound and a substance with a strong polar terminal group shows a pronounced induced S_A phase. Investigations of the static dielectric anisotropy indicated a deviation from the simple mixing rule which was empirically introduced. We derived a better approximation taking into account the different molecular volumes of the substances. An unexpected increasing mobility of the strong polar molecules could be detected by relaxation measurements. This may be connected with a change in the short range order of the strong polar compound which is caused by the repulsive forces of the molecules.     

Neutron Scattering by a Liquid Crystal Substance with a “Cubic” Phase

The applicability of the rotational diffusion model around the long molecular axes in liquid crystalline phases is being questioned.     

First crystal structure of a pentacyclic biomarker: 4,4,6a,12b,14b-Pentamethyl-1,2,3,4,4a,5,6,6a,6b,7, 8,12b,13,14,14a,14b-hexadecahydropicen-3β-ol

The crystal structure of the title compound (1, C₂₇H₄₀O 1/8 H₂O) synthesized via photo-induced electron transfer promoted biomimetic cascade cyclization, is reported. Compound 1 crystallizes in the monoclinic space group C2/c, with cell parameters a = 53.982(4), b = 7.1889(6), c = 11.170(1) Å, = 96.86(1). The structure adopts a fully trans-fused ring junction with all methyl groups axially oriented. The geometrical aspects associated with 1 were discussed and compared with the previously determined X-ray data for structurally analogous compounds.     

α-Li3InF6, a ternary fluoride with a new structure type

Reaction of anhydrous binary fluorides LiF and InF₃ in sealed platinum tube at the temperature gradient 680/670°C yields α-Li₃InF₆. This low-temperature form crystallizes in the space group P2₁/m with the cell dimensions a = 4.797(3) Å, b = 8.679(1) Å, c = 10.366(1) Å and β = 90.90(1)°. The framework is built from InF₆ and LiF₆ octahedra, beside [Li₂F₆] bitetrahedra. The b-axis seems to be the backbone in the structural features. Running along it, zigzag anionic chains , resulting from one—edge shared [Li₂F₁₀] groups and double files of single InF₆ octahedra sharing common corners with [Li₂F₆], create an approximately hexagonally packed framework in the plane (1 0 0). The antiferroelectric behaviour evident from dielectric studies is confirmed by the antiparallel displacements of In and Li atoms from octahedral centres. This structure is mainly featured by the disorder observed in the lightest atoms. These atoms, which exhibit two kinds of environments, have been refined as two partially occupied sites for the tetrahedral one. Within the Li₃MF₆ compounds (M: trivalent or 3d element), this new structure reveals unexpected structural features, inducing its ferroic properties.     

Ammonothermal crystal growth of gallium nitride – A brief discussion of critical issues

The acidic ammonothermal technique is used to develop a technology for production of free-standing gallium nitride (GaN) crystals to match the demand driven by the device technology for the wide-band-gap semiconductor group-III element nitrides. Here we report on advances toward a deeper understanding of parameters that govern mass transport and seeded crystallization of GaN under the conditions of acidic ammonothermal crystal growth with the ultimate goal to improve the process control. Comparison with the basic ammonothermal environment has been made.     

An X – Ray Study of the p-n-Alkoxycinnamic Acids. Part III.1

The effect upon molecular packing of increasing chain length in a homologous series of mesogens has been examined in the case of the p-n-alkoxycinnamic acids by determination of the crystal structures of the four nematogenic acids having two, four, six, and eight carbon atoms in the alkyl chain. The chains have the all-trans extended conformation, and the molecules exist in the crystal as planar hydrogen-bonded dimers. The dimers are arranged in end-to end fashion in parallel rows. Similar side-to-side packing of pairs of dimmers is found in each crystal structure giving a good fit between adjacent aromatic cores, but the amplitudes of thermal vibration of the chain carbon atoms increase markedly with increasing chain length, indicating a low packing efficiency for these moieties.     

Viscoelastic Parameters of a Side-Chain Nematic Polymer: I—Results of a Proton NMR Study

The reorientational behaviour in a static magnetic field of a nematic siloxane side-chain polymer is investigated by proton NMR. At variance with what occurs in main-chain and lyotropic nematic polymers, the return to equilibrium of a tnonodomain whose mean director has been rotated at an angle α to the field, is found to be homogeneous for all angles a between 0 and π/2. The usual nematic order parameter and the static (on the proton NMR time scale) order parameter are deduced from analysis of the equilibrium lineshapes. The twist viscosity γ₁ is deduced from the study of time dependent lineshapes following the rotations α. The temperature dependence of γ₁ is discussed in terms of the Vogel equation γ₁ = B S ^β exp(E _β/R(T - T _o}). It is not possible to discriminate between β = 1 or 2, but in both cases, the freezing temperature of the director T_o is found to be non-zero. A nematic to smectic pretransitional effect on γ₁ is observed. The information concerning the viscoelastic parameters contained in the value of the static order parameter is also discussed.     

Chemical reaction kinetics leading to the first Stober silica nanoparticles – NMR and SAXS investigation

²⁹Si-NMR and ¹³C-NMR were used in methanol and ethanol to monitor the intermediates or hydrolyzed monomers that lead to the formation of the first primary particles as detected by small angle X-ray scattering. This identification was facilitated by using initial NH₃ and H₂O levels at the lower end of those experienced in Stober synthesis to slow the reaction kinetics. We found that [NH₃] and [H₂O] control the balance between hydrolysis of tetraethylorthosilicate (TEOS) and the condensation of its hydrolyzed monomers. Transesterification between methanol and TEOS did occur; however, it was negligible compared to the production of hydrolyzed intermediates. The first nanostructures appear at a hydrolyzed monomer concentration around 0.1 M, indicating that formation of the primary structures is thermodynamically controlled by a supersaturation of the intermediate species. Differences in particle size between methanol and ethanol are attributed to thermodynamic interactions between the solvent and the hydrolyzed intermediates.     

Optical investigations of germanium nanoclusters – Rich SiO2 layers produced by ion beam synthesis

In this work, refractive index and extinction coefficient spectra of germanium nanoclusters – rich SiO₂ layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 250–1000 nm range. The samples were produced by Ge⁺ ion implantation into SiO₂ layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 °C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 °C and spherical Ge nanocrystallites 5–8 nm in diameter are observed in the SiO₂ layers after annealing for 1 h at even higher temperatures of 1000–1100 °C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO₂/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band’s tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E’center in SiO₂. The annealing process results in the emergence of weaker extinction coefficient bands in the 400–600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.     

The structure of 11,12-bis[spiro(cyclopropyl)]-1,4,4a,5,8,8a,9a,10a-octahydro-1,4∶5,8-dimethano-9,10-anthraquinone

In the solid state the 21 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4 in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths.     

Structure of a new crystal modification of the bacterial NAD-dependent formate dehydrogenase with a resolution of 2.1 Å

Formate dehydrogenase (FDG) from methylotrophic bacteria Pseudomonas sp. 101 catalyzes the reaction of oxidation of the formate ion to carbon dioxide, which is accompanied by the reduction of nicotinamid adenine dinucleotide (NAD⁺). The structures of the apo and holo (enzyme-NAD-azide triple complex) forms of the enzyme were determined earlier. In an attempt to prepare a complex of FDG with the product of the enzymatic reaction (NADH), a new crystal modification of FDG is obtained (space group P4₂2₁2, a = b = 93.3 Å, c = 103.05 Å). The FDG structure is solved by the molecular replacement method and refined to R = 20.7%. The asymmetric part of the unit cell contains one FDG molecule. In contrast to the previously studied FDG structures, the biologically active dimer is formed by the crystallographic rotation axis. A comparative structural analysis of the studied form with the apo and holo forms of the enzyme is performed. The influence of the molecular structure on the environment in the crystal is investigated.     

Orientation Relationships and Lattice Misfit between a Nb Matrix and γ-Silicide in a Nb–Si Composite

Crystallography Reports - Orientation relationships {110}Nb||{100}γ and 〈111〉Nb||〈001〉γ between the crystal lattices of the Nb solid solution and particles of...