Structural characteristics of single crystalline GaN films grown on (111) diamond with AlN buffer

Hexagonal GaN films with the [0001] direction parallel to the surface normal were grown on (111) oriented single crystalline diamond substrates by plasma-assisted molecular beam epitaxy. Pre-treatments of the diamond surface with the nitrogen plasma beam, prior the nucleation of a thin AlN layer, eliminated the inversion domains and reduced the density of threading dislocations in the GaN epilayers. The films have an in-plane epitaxial relationship [1010]GaN//[110]diamond. Thus GaN (0001) thin films of single epitaxial relationship and of single polarity were realised on diamond with AlN buffer.     

Theoretical investigation on the interaction of nitrogen with dislocations in single crystal CVD diamond

In recent experimental studies, evidence for an atmosphere of nitrogen around the cores of dislocations was found in irradiated single crystal CVD diamond. In this paper, we present a first-principles study on the interaction of nitrogen with dislocations in single crystal CVD diamond, where dislocations are observed as mixed-type 45° and 90° edge-type dislocations lying along <100>. We find a strong binding of nitrogen to the dislocation core for both types of dislocations and show that our results are in consistency with the experiment.     

Study of boron doping in MPCVD grown homoepitaxial diamond layers based on cathodoluminescence spectroscopy, secondary ion mass spectroscopy and capacitance-voltage measurements

Boron incorporation from the gas phase was achieved in MPCVD grown (100)-oriented homoepitaxial diamond layers, either with or without a small fraction of oxygen in the gas phase, in addition to hydrogen, methane and diborane. From secondary Ion Mass Spectroscopy (SIMS), it is shown that the 0.25% of oxygen decreases the Boron concentration [B] by two orders of magnitude. In this way, we demonstrate that it becomes possible to control [B] with low levels of compensation and passivation down to the 10¹⁵ cm^− 3 range. Cathodoluminescence spectroscopy is systematically performed in seventeen samples under a 10 kV acceleration voltage at 5 K and the exciton bound to boron (BE_TO) intensity to the free exciton (FE_TO) intensity ratio is evaluated (I_BETO/I_FETO). A linear relationship between I_BETO/I_FETO and [B] with a coefficient of 3.5 × 10¹⁶ cm^− 3 is demonstrated for [B] < 3 × 10¹⁷ cm^− 3 in single crystalline diamond, irrespective of the gas phase composition during growth.     

AlN films grown on diamond and silicon carbide

Structural changes in surface layers of CVD AlN films were studied by the reflection high-energy electron diffraction technique. Film thickness was varied from 0.2 to 20 μm. Single crystals of diamond, silicon carbide and also bilayered structures of natural diamond/CVD diamond films were used as substrates. On the (111) surfaces of natural diamond, (111) CVD diamond films and (00.1) 6H-SiC at AlN thickness up to 1 μm one can observe the epitaxial correspondence between the growing film and the substrate: (00.1) [11.0] AlN//(111) [110] C_α or (00.1) [10.0] AlN//(00.1) [10.0] 6H-SiC. At larger film thickness the epitaxial growth was replaced gradually by the formation of one of axial textures for which the planes (00.1), (10.3) or (11.4) of wurtzite-like aluminum nitride were parallel to the substrate. During the epitaxial growth the twinning structures with the twinning planes of types (10.1) and (11.1) were observed.     

CuI and H2O2 Inactivate and FeII Inhibits [Fe]‐Hydrogenase at Very Low Concentrations

[Fe]‐Hydrogenase (Hmd) catalyzes reversible hydride transfer from H₂. It harbors an iron‐guanylylpyridinol as a cofactor with an Fe^II that is ligated to one thiolate, two COs, one acyl‐C, one pyridinol‐N, and solvent. Here, we report that Cu^I and H₂O₂ inactivate Hmd (half‐maximal rates at 1 μM Cu^I and 20 μM H₂O₂) and that Fe^II inhibits the enzyme with very high affinity (K_i=40 nM ). Infrared and EPR studies together with competitive inhibition studies with isocyanide indicated that Cu^I exerts its inhibitory effect most probably by binding to the active site iron‐thiolate ligand. Using the same methods, it was found that H₂O₂ binds to the active‐site iron at the solvent‐binding site and oxidizes Fe^II to Fe^III. Also it was shown that Fe^II reversibly binds away from the active site iron, with binding being competitive to the organic hydride acceptor; this inhibition is specific for Fe^II and is reminiscent of that for the [FeFe]‐hydrogenase second iron, which specifically interacts with H₂.     

Anion-responsive luminescent Eu3+ complexes with ring-like rigid quinoline–amide ligands

Two novel ring-like rigid quinoline–amide ligands, 2-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-N-benzylacetamide (L^I) and 3-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-1,1-diphenylpropan-2-one (L^II), were designed to assemble the anion-responsive luminescent europium complexes. Crystallographic studies of the EuL^I(NO₃)₃ and EuL^II(NO₃)₃ revealed that the tetradentate ligands L^I and L^II cooperatively coordinated with Eu³⁺ ion and some available sites around central europium ions for guest anions were reserved in the complexes. The luminescent properties of the Eu(III) nitrate complexes in acetonitrile solutions were investigated. And the lowest triplet state energy levels of the ligands are well placed to allow energy transfer to the resonance level of Eu(III). At the same time, the luminescence titration experiments and the Job's plot analysis demonstrated the formation of 1:1 complexes in the solutions. The luminescence intensities at 616 nm were enhanced by addition of NO₃^? or Cl^? anion to the mixed acetonitrile solutions of Eu(CF₃SO₃)₃ and the ligands.     

Molecular Containers Bind Drugs of Abuse in Vitro and Reverse the Hyperlocomotive Effect of Methamphetamine in Rats

We measured the affinity of five molecular container compounds (calabadions 1 and 2 , CB[7], sulfocalix[4]arene, and HP‐β‐CD) toward seven drugs of abuse in homogenous aqueous solution at physiological pH by various methods (¹H NMR, UV/Vis, isothermal titration calorimetry [ITC]) and found binding constants (K_a values) spanning from <10² to >10⁸ m ^?1. We also report X‐ray crystal structures of CB[7] ? methamphetamine and 1? methamphetamine. We found that 2 , but not CB[7], was able to ameliorate the hyperlocomotive activity of rats treated with methamphetamine. The bioavailability of the calabadions and their convergent building block synthesis suggest potential for further structural optimization as reversal agents for intoxication with nonopioid drugs of abuse for which no treatments are currently available.     

Large-scale AlN nanowires synthesized by direct sublimation method

Hexagonal aluminum nitride (AlN) nanowires were fabricated by direct sublimation method without a catalyst layer. The obtained nanowires have diameters of about 30–100 nm and length up to tens of micrometers. TEM observation indicates that these nanowires are single-crystalline and grow along [0 0 0 1] direction. It is thought that vapor–solid (VS) mechanism should be responsible for the growth of AlN nanowires. In addition, room temperature Raman scattering and photoluminescence spectra from AlN nanowires were studied. Photoluminence spectrum of the AlN nanowires shows a wide emission band centered of 517 and 590 nm, which is related to N vacancies and the transition from the level of V_N⁺ to ground state of the deep level of [V_Al^3? + 3O_N⁺] defects, respectively.     

Molecular dynamics simulation of AlN thin films under nanoindentation

A large-scale molecular dynamics (MD) simulation of nanoindentation was performed to study the structural deformation on wurtzite aluminum nitride (B4-AlN). The nanoindentation induced B4-B1 phase-transition, amorphization and dislocation glide in AlN (0001) thin films were found. It shows that the B4-B1 phase-transition path includes two processes: an anti-parallel vertical movement of N and Al atoms along the [0001] axis, followed by horizontal rearrangements of the two types of atoms. Indentation force-depth (P-h) curve shows minor and major pop-in events. Detailed analysis of the results shows that the first three minor load drops in the P-h curve are related to the nucleation of amorphous structure, whereas the subsequent major load drop is related to the dislocation nucleation and expansion. The dislocations in AlN thin film involve perfect dislocations and Shockley partial dislocations, the latter is associated with the formation of intrinsic stacking faults (SFs) type I₂ during the expansion of dislocation loops.     

An analysis of excluded-volume effects in a polystyrene-cyclohexane system

An attempt was made to analyse Miyaki's data for the radius of gyration <s²> and the intrinsic viscosity [η] of very high molecular weight samples of polystyrene in cyclohexane. The excluded-volume variable z was estimated by adopting the temperature dependence of the excluded-volume integral as predicted by Eichinger. It was found that the volume expansion as given by the ratio of <s²> to <s²>₀ under the unperturned state was a function of z only, as required by two-parameter theories. These data were in good agreement with the Domb-Barrett and the Suzuki equations. On the other hand, the ratio of [η] to [η] ₀ under the unperturbed state also gave a single composite curve when plotted against z. However, it was found that the observed hydrodynamic behaviour was not satisfactorily explained by two-parameter theories of [η]. A brief comment was made on the validity of two-parameter theories from the experimental point of view.     

Two novel self-interpenetrating 3D iron(II) coordination frameworks: Synthesis,spectroscopic and structural characterizations with magnetic properties

Two novel self-interpenetrating 3D Fe(II) coordination frameworks namely {Fe(4,4′-bpy)[Ag₂(CN)₃]₂}_n (I) and {Fe(4,4′-bpy)[Ag(CN)₂]₂[AgCN]₂}_n (II) have been synthesized and fully characterized. The 3D architectures and degree of interpenetration of these coordination frameworks were significantly affected by silver(I) cyanide species. The crystal structure of I presents 4-fold interpenetrating 3D framework with 4,4′-bpy and [Ag₂(CN)₃]⁻ species. While, that of II constructed by 4,4′-bpy and two different silver(I) cyanide species, AgCN and [Ag(CN)₂]⁻ resulting to 2-fold interpenetrating 3D framework. The stability and rigidity of both coordination frameworks are mainly supported dominantly by Ag^I ⋯ Ag^I interactions. Their magnetic properties exhibit high spin behavior.     

Glycine Surfactants Derived from Dodecenyl Succinic Anhydride

We report the synthesis and properties of two surfactants with a novel head group based on glycine. A monocarboxylic surfactant N-glycine methyl ester (2-dodecen-1-yl succinamic acid) (I) was prepared by ring opening of an n-alkyl succinic anhydride. Hydrolysis of the ester functionality yields a dicarboxylic acid II. The sodium salts of I and II were effective surfactants at neutral pH giving a low minimum surface tension (<30 mN m⁻¹ at 20 °C). At high pH (~12) the surface activity of both surfactants is reduced compared to neutral pH, indicating that at neutral pH an ‘acid soap’ is formed. The pK _a of the acid form of the surfactants was determined. Addition of calcium ions reduced the CMC of II but did not reduce the surface tension above the CMC. The resistance of II to calcium ion precipitation was measured at pH 7.     

Tribological behaviour of <100> and <111> fibre textured CVD diamond films under dry planar sliding contact

<100> and <111> fibre textured diamond films are grown on SSiC sliding rings by hot filament CVD and are tribologically tested in dry planar contact under ambient air.The wear of the self-mated textured diamond coating takes place initially at protruding grains of the as-deposited micro rough diamond surface. After 10 km of dry sliding against <100> textured diamond the respective counterparts with <100> and <111> textures exhibit smoothly polished diamond faces without visible surface failures. After dry sliding against <111> textured diamond as static counterpart {100} diamond faces of isolated grains show Hertzian cone cracks and propagation of cracks preferred along {111} easy cleavage planes whereas {111} diamond faces reveal no crack propagation in substrate direction.The results are visualised in a tribo map in which the linear wear of the dynamic diamond face is plotted against the mean coefficient of friction. The best tribological behaviour in terms of low friction and little diamond wear is achieved for sliding couples with <100> fibre texture on the rotating sliding ring and <111> fibre texture on the static ring as mating diamond faces.     

Characterization of capacitance–voltage features of Ni/diamond Schottky diodes on oxidized boron-doped homoepitaxial diamond film

The electrical properties of Ni/diamond Schottky diodes fabricated on oxidized boron-doped homoepitaxial diamond film have been studied in order to investigate the electrical behavior of diamond-based electronic devices. The current–voltage (I–V) characteristics of the Ni–Schottky contacts to the boron-doped homoepitaxial diamond film show excellent rectification properties. The capacitance–voltage (C–V) features of the Ni/diamond Schottky diodes were characterized in the frequency range from 10⁻³ to 2×10⁵ Hz. The C–V measurements indicate that the space charge density (N_I) and built-in potential (V_d) values are approximately 6.0×10¹⁶ cm⁻³ and 1.25 V, respectively, and show weak frequency dependence in the range from 10⁻³ to 10⁴ Hz. Capacitance–frequency measurement at zero bias indicated that the degrading capacitance at high frequency (>10⁴ Hz) is primarily due to the high series resistance of the homoepitaxial diamond film.     

High quality heteroepitaxial diamond films on silicon: recent progresses

This paper reports the progresses made recently on the nucleation and growth of high-quality, [001]-oriented diamond films and discusses the problems to be resolved. The interface structure of diamond on silicon has further been investigated by transmission electron microscopy (TEM). Heteroepitaxial diamond films with increased lateral grain size and reduced grain boundary density were prepared in both microwave plasma chemical vapour deposition (MW-CVD) and hot filament chemical vapour deposition (HF-CVD) processes. Using a growth process combining a bias-assisted H⁺ etching and a [001]-textured growth smooth diamond films with large lateral grain size up to 10 μm can be obtained at a film thickness of approximately 10 μm. By controlling the [001]-textured growth process thick diamond films with a lateral grain size up to 30 μm has been achieved in HF-CVD.     

Kinetics of methanol oxidation on poly(Ni-tetramethyldibenzotetraaza[14] annulene)-modified electrodes

The oxidation of methanol at poly(Ni^II-tetramethyldibenzotetraaza[14] annulene) [Ni^II-(tmdbta)]-modified glassy carbon electrodes prepared by cyclic voltammetry are investigated by thin-film-electrode poly([Ni^II-(tmdbta)]) measurements. The poly([Ni^II-(tmdbta)])-modified electrode shows higher activity towards methanol oxidation in the Ni^III(tmdbta) state. The poly([Ni^II-(tmdbta)])-modified electrode is measured by cyclic voltammetry polarization curves and 8.5 h polarizations. The mechanisms of methanol oxidation are studied by cyclic voltammetry and polarization curves, and a reaction mechanism is proposed. The rate-determining steps are experimentally identified and the rate equation of methanol oxidation is obtained. The poly([Ni^II-(tmdbta)])-modified electrode remains stable during anodic polarization at 0.45 V for 8.5 h in 0.1 M NaOH solution with or without 0.1 M methanol.     

Living tandem free radical polymerization of a liquid crystalline monomer

Treatment of 1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane (I) (an AB₂ monomer) with dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) leads to a hyperbranched material, poly[1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane] (II). I has been prepared by a Pd catalyzed Heck reaction between 4-bromo-acetophenone and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The structure of the soluble hyperbranched material (II) has been determined by ¹H, ¹³C and ²⁹Si NMR, as well as by IR and UV spectroscopy. It has also been characterized by GPC, TGA, DSC and elemental analysis. Polymerization occurs by Ru catalyzed addition of the aromatic C−H bonds which are ortho to the activating acetyl group of I across the C−C double bond of the terminal Si-vinyl group in an anti-Markovnikov manner. Received: 8 September 1997/Revised version: 19 October 1997/Accepted: 20 November 1997     

Oxidase Reactivity of CuII Bound to N-Truncated Aβ Peptides Promoted by Dopamine

The redox chemistry of copper(II) is strongly modulated by the coordination to amyloid-β peptides and by the stability of the resulting complexes. Amino-terminal copper and nickel binding motifs (ATCUN) identified in truncated Aβ sequences starting with Phe4 show very high affinity for copper(II) ions. Herein, we study the oxidase activity of [Cu–Aβ_4−x] and [Cu–Aβ_1−x] complexes toward dopamine and other catechols. The results show that the Cu^II–ATCUN site is not redox-inert; the reduction of the metal is induced by coordination of catechol to the metal and occurs through an inner sphere reaction. The generation of a ternary [Cu^II–Aβ–catechol] species determines the efficiency of the oxidation, although the reaction rate is ruled by reoxidation of the Cu^I complex. In addition to the N-terminal coordination site, the two vicinal histidines, His13 and His14, provide a second Cu-binding motif. Catechol oxidation studies together with structural insight from the mixed dinuclear complexes Ni/Cu–Aβ_4−x reveal that the His-tandem is able to bind Cu^II ions independently of the ATCUN site, but the N-terminal metal complexation reduces the conformational mobility of the peptide chain, preventing the binding and oxidative reactivity toward catechol of Cu^II bound to the secondary site.     

Synthesis,crystal structures and spectral characterization of trans-bisaquabis(o-vanillinato)copper(II), cis-aquabis(o-vanillinato)copper(II) and aqua[bis(o-vanillinato)-1,2-ethylenediimin]copper(II)

trans-Bisaquabis(o-vanillinato)copper(II) (I), cis-aquabis(o-vanillinato)copper(II) (II) and aqua[bis(o-vanillinato)-1,2-ethylenediimin]copper(II) (III) complexes were synthesized and characterized by means of elemental analysis, IR and UV–vis spectroscopy, thermal analysis and X-ray diffraction techniques. The coordination geometry around Cu(II) is a octahedral with coordination number of six for I and is a square-pyramidal with coordination number of five for both II and III. In all three compounds, a three-dimensional structure is formed via C–H⋯O hydrogen-bond interactions and intermolecular π–π and π-ring interactions. The compounds I and III have two-dimensional hydrogen-bonded step-chain structure in xz-plane, while compound II has a zigzag chain structure in xy-plane. On the basis of the first DTA_max of the anhydrous complexes of I and II, the thermal stability sequence is trans-isomer > cis-isomer. This fact should be related with the binding of the ligand.     

Adsorption and selective recognition of 17?-estradiol by molecularly imprinted polymers

The 17?-estradiol-imprinted polymers using non-covalent approach with methacrylic acid as the functional monomer was prepared and characterized. The effect of porogenic solvents on the adsorption capacity and thermal stability of the molecularly imprinted polymers (MIPs) were examined. Scanning electron microscopic images showed that the synthesized MIPs were bulk porous materials. The surface areas of MIPs increased from 151?C188 to 239?C292?m²?g^-1 when templates were removed by methanol using Soxhlet extraction. In addition, the MIPs prepared in chloroform had a higher adsorption capacity towards 17?-estradiol (1,212???g?g^-1) than that in acetonitrile (769???g?g^-1), indicating that less polar porogenic solvent is suitable for synthesis of non-covalent MIPs. FTIR showed that the carbonyl group is the major functional group in MIPs to form monomer-template complex via H-bond. In addition, only a slight decrease (< 5?%) in adsorption capacity of the MIPs was observed when incubated at 80?°C for 5?h. Analysis of the capacity factor values (??_imp??) for MIPs indicated that the rebinding ability from selective recognition sites of MIPs decreased in the order 17?-estradiol?>?testosterone?>?benzo[a]pyrene?>?progesterone?>?phenol, and the ??_imp?? values decreased from 2.68 to 0.63, indicating the excellent selectivity of MIPs among closely related compounds. Results obtained in this study clearly indicate that the imprinted polymer is specific for recognizing 17?-estradiol. The excellent selectivity and high adsorption capacity of 17?-estradiol-imprinted polymers open the door to develop MIPs for effective separation and adsorption of estrogenic compounds.