Structural and electrical properties of Li doped ZnO under Ar/H2 atmosphere

Thin films of ZnO were grown by the sol–gel method using spin-coating technique on (0001) sapphire substrates. The effect of doping under Ar/H₂ atmosphere on the structural and electrical properties of ZnO was investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), I–V characterization, Hall effect and micro-photoluminescence. The films that were annealed at 600 °C in Ar/H₂ (95/5) % atmosphere showed (002) a predominant orientation. The crystalline nature of 2 mol.  % of Li doped films were better when compared to 1 mol.  % of Li doped films. The incorporation of Li in ZnO lattice was confirmed by X-ray photoelectron spectroscopy, and micro-photoluminescence. Hall effect measurements and I–V characterization of the Li doped ZnO thin films exhibited a better p-type behavior.     

Structural and morphological properties of silver nanoparticles–phosphate glass composites

New types of composite materials belonging to the (100 − x) [50P₂O₅ · 30CaO · 20Na₂O]xAg₂O glasses system with 0 ? x ? 0.25 are obtained. Their local structure is analyzed with the help of Raman and infrared spectroscopy and it was found that the glasses structure is built up from predominantly ionic phosphate units. UV–VIS absorption measurements performed on the samples reveal the existence of silver nanoparticles within the soda–calcium-phosphate glass matrix. The electronic absorption spectra and TEM pictures analyses indicate the presence of silver nanoparticles of almost spherical shapes and various sizes inside the glass matrix, depending on the Ag₂O content. By using the experimental UV–VIS data and a theoretical approach important structural and morphological parameters, such as the radius of the silver nanospheres and the volume fraction of the spheres are determined for one of the investigated composites (x = 0.05 mol%).     

Argon solvent effects on optical properties of silver metal clusters

Argon gas at a high pressure (～80 bar) has been expanded using a miniaturized pulsed valve at room temperature, producing a supersonic beam of cold, large argon droplets. Atoms of silver are subsequently embedded into the droplet using the pick-up technique. The resulting Ag(n)Ar(droplet) distribution was analyzed using multiphoton laser ionization time-of-flight mass spectrometry. Besides bare metal clusters, snowballs of silver monomers and dimers encapsulated in up to 50 argon atoms have been observed. The influence of the solvent on the optical absorption of the solute was studied for embedded Ag(8) using resonant two-photon ionization in the ultraviolet. A redshift and broadening of the Ag(8)Ar(droplet) optical spectrum compared to that measured in pure [Federmann et al., Eur. Phys. J. D 1999, 9, 11] and Ar-doped helium droplets [Diederich et al., J. Chem. Phys.2002, 116, 3263] was observed, which is attributed to the interaction with the larger Ar matrix environment.     

Morphology-dependent luminescence properties of poly(benzyl ether) dendrimers

Poly(benzyl ether) dendrimers with o-, m-, and p-isomers of dialkoxybenzene at their focal points [o-, m-, and p-(Gn)₂Ar], having generation numbers (n) of 0–3, were synthesized. ¹H NMR pulse relaxation times (T₁) of the exterior MeO groups of o- and m-(Gn)₂Ar (n = 0–3) all remained in the range of 0.92–1.43 s. In sharp contrast, an exceptionally short T₁ value (0.23 s) was observed for p-(G3)₂Ar. Although their absorption spectral profiles were slightly different from one another, an essential difference was observed for their fluorescence properties. When the generation number was increased, the fluorescence efficiency of o-(Gn)₂Ar increased, but that of p-(Gn)₂Ar decreased, whereas m-(Gn)₂Ar exhibited a relatively small change in the fluorescence efficiency. Fluorescence depolarization studies showed a highly efficient intramolecular energy migration in p-(G3)₂Ar as compared with o-(G3)₂Ar and m-(G3)₂Ar. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3524–3530, 2003     

Structural transformations in silver nanoparticles

A molecular dynamics simulation was performed for silver clusters of 147, 309, and 561 atoms with the initial cuboctahedral habit in the temperature range 0–1000 K with an embedded atom potential for silver. Structural transitions of the silver clusters to complex twins (icosahedral habit) with coherent (111)/(111) boundaries over all edges of icosahedra were found, which started at temperatures of 50 K, 350 K, and 700 K, respectively. To analyze the structural transformations in nanoparticles, an algorithm is proposed based on a simplicial Delaunay decomposition (Delaunay triangulation). It was found that after the transition of silver nanoparticles to complex twins, the atomic motion becomes vibrational; the atoms vibrate around the sites that correspond to the vertices of the regular polyhedra. In the case of the 147-atom silver nanoparticle, the polyhedra are arranged in the following sequence, starting from the center of mass: icosahedron (12 atoms), icosododecahedron (30 atoms), icosahedron (12 atoms), dodecahedron (20 atoms), truncated icosahedron (60 atoms, isostructural with fullerene C₆₀), icosahedron (12 atoms), and one atom at the center of mass.     

Structural properties of silver nanoclusters–phosphate glass composites

The structure of the xAg₂O(100 − x)[50P₂O₅·30CaO·20Na₂O] glasses, with x = 0, 3 and 5 mol%, was investigated by means of Raman and infrared spectroscopy. The structural changes induced by the Ag₂O presence into the soda-calcium–phosphate matrix were evidenced and discussed in terms of the network depolymerization process and distortion of the PO₄ tetrahedra. The existence of silver nanoclusters inside the glass matrix, considered to be mainly responsible for the found structural behavior, was supposed by results obtained from the analysis of the UV–vis absorption spectra and further proved by transmission electron microscopy images.     

Reduction of aryl halides at transition metal cathodes. Conditions for aryl–aryl bond formation: The Ullmann's reaction revisited

The cathodic reduction of some aryl halides ArX (1-naphthyl halides NpI and NpBr, iodo benzene and bromobenzene PhI and PhBr taken as model substrates) was achieved essentially in propylene carbonate (PC) considered for its high dielectric permittivity. Different electrode materials such as copper, silver, palladium, silver palladium alloy and nickel were used. Such conditions permit the activation of the C–X bond by metal (the step featuring similarity with Ullmann's reaction). Electron transfer to organometallic intermediates generated at the metal interface activates the formation of Ar–Ar linkages often in good yields, especially in the case of aryl iodides.     

Charging of water at inert and hydrophobic surfaces. Effect on interfacial properties of silver halides

Isoelectric point of silver halides depends on pH due to charging of interfacial water layer. The isoelectric point of water at inert and hydrophobic surfaces lies at pH≈3 so that water at surfaces is negatively charged in the pH region above 4. Consequently the electroneutrality point of silver halides pAg_eln in aqueous environment, with respect to adsorption of silver and halide ions, does not correspond to the isoelectric point pAg_iep measured at pH≈6, as previously assumed. The effect of assumed value of pAg_iep was examined. The equilibrium constants for adsorption of silver and halide ions on silver chloride and silver bromide were calculated for the range of assumed pAg_iep values ranging from isoelectric points measured at pH=6 to pH=3. The values of pAg_iep obtained at pH=3 was taken as pAg_eln and the corresponding equilibrium constants of interfacial reactions were obtained.     

Synthesis,crystal structure,and fluorescence properties of several schiff-base compounds

Two new Schiff-base compounds, 1,6-bis(4-dimethylaminobenzyl)-2,5-diaza-1,5-hexadiene (bdh), 1,4-bis(4-dimethylaminobenzyl)-2,3-diaza-1,3-butadiene (bdb), and a silver complex of the latter ([Ag₂(bdb)₃(NO₃)₂]·H₂O, 1) have been synthesized and characterized. The crystal structure of complex 1 was determined. 1 is a dinuclear complex, with the silver ions lying in coordination tetrahedra formed by two nitrogen atoms from the bdb ligands and two oxygen atoms from the nitrate anions. The fluorescence properties of bdh and bdb were studied; the fluorescence of bdb was quenched by the addition of silver ions, indicating that it is a potential fluorescent reagent for the analysis of silver.     

Structural effects on the antitumour activity of organotin compounds 2. Further diaryltin dichloride complexes with nitrogen-donor ligands

The synthesis and investigation of the anti-tumour activity of a further series of six new diorganotin dichloride complexes Ar₂SnCl₂.L₂, where Ar = 2-thienyl, 2,4-dimethoxyphenyl, 4-methyoxyphenyl, 4-methylphenyl or 4-trifluoromethylphenyl and L₂ = 2-(2-pyridyl)benzimidazole (PBI) or 2-amino-methylpyridine (AMP), is reported. One of these complexes was found to be active against P388 lymphocytic leukaemia in mice. The results obtained are in general agreement with previously published work. The activity of the diaryltin dichloride complexes is shown to be dependent on the electronic effect of the aromatic group. The use of PBI as a ligand, however, shows no advantage over other ligands used in the series investigated.     

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

An interesting observation was made when studying the S _N Ar reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room temperature after 100 min. With2 having a methoxy-subtituted Ar group.     

Arine als elektrophile Reagentien, 1. Mitt.: Umsetzung mit Alkylen-phosphoranen

Arines, which may be considered as electrophilic reagents, react with Alkylenephosphorances (Ar)₃P-C(R₁)(R₂) attacking principally the nucleophilic C atom. The resulting zwitterion A (Ar)₃P⊕?C(R₁)(R₂)(o-C₆H₄)? form the more stable Benzophospha-cyclobutane-derivative with pentavalent phosphorus. This finally undergoes a rearrangement, in which the phosphorus atom passes over from the pentavalent into the trivalent state. The corresponding phosphine possesses the following general structure, as far as could be observed.

$$(Ar)_2 P---(o--) \cdot C_6 H_4 ---C(R_1 )(R_2 )(Ar).$$     

Structural contribution to the effect of hydrophobic hydration of noble gases

Within the concepts of structurally-thermodynamic characteristics of solvation and pseudo-chemical potential, the sample collection of the most authentic experimental data on solubility of gaseous He, Ne, Ar, Kr, Xe, and Rn in H₂O and D₂O is analysed at ≈0.1 MPa and T = 278–318 K. The conclusion is drawn that at deuteration of water molecules and also with increasing molar mass of noble gas, the relative contribution of effect of its hydrophobic hydration decreases. However in case of pass from lightweight noble gases (He, Ne, Ar) to heavy ones (Kr, Xe, Rn), structural transformations in their aqueous solutions become more expressed as a whole due to strengthening interaction between dissolved substance and solvent.     

Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag₆, linear AgS₂ (in projection drawing), or tetrahedral AgS₃P binding modes, and the sulfur atoms adopt T-shaped SAg₃ and orthogonal SAg₄ modes. An additional T-shaped AgS₃ mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ⁴-S or μ⁴-Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS₃P motif, regardless of whether the parent NC functions as an electron donor or acceptor.     

Effect of the AACVD based synthesis atmosphere on the structural properties of multi-walled carbon nanotubes

The synthesis of multi-walled carbon nanotubes (MWCNT_S) has been the focus of considerable research effort for more than twenty-five years and it continues to receive increasing attention because of its importance to produce carbon nanotubes with suitable parameters for future applications. To the best of our knowledge this study presents for the first time the complex studies concerning the effect of aerosol-assisted chemical vapour deposition (AACVD) process conditions (including temperature (750–1200 °C) and the composition of the carrier gas (N₂, Ar, He, 5% H₂-95% Ar, 3% H₂O-97% Ar)) on the conversion of the carbon source and on the properties of the carbon nanotubes. In addition, it was also found that oxidative or reductive atmosphere applied during the AACVD process have a great impact on the quality and the degree of toluene conversion into the carbon solids obtained during the synthesis. X-ray Diffraction (XRD), Specific Surface Area and Porosity analysis (BET), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Transmission Electron Microscopy (TEM), Raman spectroscopy and Thermo-gravimetric Analysis (TG) were used to characterize the carbon nanotubes.     

Gas-sensitive properties of thin nickel oxide films

The results of a study of the gas-sensitive properties of nickel oxide layers with respect to n-hexane, acetone, ethanol, benzene, o-xylene, toluene and ammonia are presented. NiO layers 100 ± 5 nm thick were obtained by chemical vapor deposition in the systems (EtCp)₂Ni–О₂–Ar and (EtCp)₂Ni–О₃–О₂–Ar. The electrical resistance of the layers changes in the presence of hexane, ethanol, benzene, and ammonia vapors. The electrical resistance of the obtained layers changed in the presence of vapors of hexane, ethanol, benzene and ammonia. Response and recovery time of the sensing element of the gas sensors did not exceed 6 s in the temperature range 500–600 K.     

From mesogens to metallomesogens. Synthesis,characterisation, liquid crystal and luminescent properties

Continuation with our previous investigation which refers to the synthesis of a series of hydrophobic symmetrical azine compounds: 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16 or 18), a series of hydrophobic asymmetrical azine compounds: [1-(4-propyloxy)-2-(4?-(n-alkoxy))benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16 or 18) was synthesised following an efficient and practical method. These compounds were synthesised by the condensation reaction of hydrazine hydrate with 4-propyloxybenzaldehyde and appropriately 4-(n-alkoxy)benzaldehydes in acidic medium and ambient conditions (very simple way with no need of any sophisticated techniques). Moreover, two new series of silver(I) complexes based on symmetrical or asymmetrical azines have been synthesised (linear-binuclear type complexes with the general formula [Ag₂(L)(NO₃)₂] were obtained). The organic compounds and their silver(I) complexes were characterised using different techniques: microelemental analysis and spectral data (FTIR, UV–Vis, ¹HNMR, ¹³C{¹H}NMR, 2D ¹H-¹H-COSY, 2D ¹H-¹³C-HSQC and mass spectra) as well as molar conductivity measurements for silver(I) complexes. Liquid crystal behaviour of the prepared compounds were studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies revealed that all azine compounds and some of silver(I) complexes are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase.     

Synthesis and properties of tellurium(II) compounds: Diaryltelluroesters,ArCOTeAr′

A series of organotellurium(II) derivatives of the general formula ArCOTeAr′ (Ar,Ar′ = phenyl, p-tolyl, p-anisyl, p-bromophenyl, p-trifluoromethylphenyl, 1-naphtyl) have been prepared and characterized chemically and spectroscopically. Various chemical reactions of this class of compounds have been investigated, and the reaction of these compounds with (PhCN)₂PdCl₂ to give the polymeric (Pd(TeAr′)₂)_n derivatives suggests that these organotellurium reagents may be useful precursors of TeAr′^? ligands in reactions with transition-metal substrates.     

Synthetic and Structural Studies on High-Nuclearity Silver Ethynide Cluster Systems

A large family of crystalline organometallic compounds with silver ethynide (R–C≡CAg) as a component has been synthesized and characterized. In most cases the R–C≡C^? species coordinate to 3–5 silver(I) atoms, which may be symbolized as R–C≡C?Ag _n (n = 3, 4, 5; R = alkyl, aryl, heteroaryl) by leaving out the charges. In the present review, emphasis is laid on systematic synthetic and structural studies of high-nuclearity silver ethynide clusters, of which the size and shape can be controlled to a certain extent by the judicious choice of templating anions and auxiliary ligands.     

Electrochemical properties of freestanding TiO2 nanotube membranes annealed in Ar for lithium anode material

Freestanding and highly ordered TiO₂ nanotube membranes were prepared via anodization and annealed at 450, 600, and 800 °C in air and Ar, respectively. Based on the results of XRD and SEM, the membranes annealed in Ar and air possessed different morphology and crystalline phases. Compared with the sample annealed in air, a trace amount of carbon on TiO₂ membrane annealed in Ar was detected by EDS spectrum. Electrochemical measurements showed that TiO₂ membrane annealed in Ar exhibited better discharge capacity and cyclic stability. The noticeably improved electrochemical performances were attributed to the presence of carbon which enhanced the surface electronic conductivity, the crystalline transformation, and the appropriate morphology, such as large pore, thin wall, and well tube structure.