Au–Cu nanoparticles produced by laser ablation of mixtures of Au and Cu microparticles

In this study we investigate the possibility of producing alloy nanoparticles (NP) from mixtures of elemental microparticle (MP) powders using the laser ablation of microparticle (LAM) process. Mixtures of Au and Cu particles with a diameter of 1.5–2.0 m were fed in aerosol form into a laser ablation cell and ablated using a pulsed laser. The resulting NP were collected electrostatically and characterized using TEM. The NP were spherical and crystalline with a size that depended on the collection location but ranged from 2 to 15 nm. Using TEM/SAD, it was determined that the NP had a face-centered cubic (fcc) crystal structure and, with EDS, it was found that individual NP consisted of both Au and Cu. These experimental results confirm previous numerical models that suggested that it might be possible to form alloy NP from mixtures of elemental MP using the LAM process.     

A rationale on the role of intermediate Au(III)–vitamin C complexation in the production of gold nanoparticles

Preparation of gold nanoparticles, particularly gold nanorods, by wet chemistry processes involves gold seeds, an Au(III) salt, structure directing surfactants, and metal ion additives in the growth solution into which a weak reducing agent is added. The most commonly employed weak reducing agent is l-ascorbic acid (vitamin C) which is known to reduce many metal ions in the solution phase and form complexes with relatively low stability constants. A purple-gray gold–ascorbate compound, obtained from the reaction of sodium tetrachloroaurate(III) with sodium ascorbate, is now reported. The compound possesses the expected structural features of vitamin C–metal complexes as verified by its ¹³C CP-MAS NMR spectrum. A discussion is also presented on the possibility of gold–ascorbate complexation operating in gold nanoparticle formation.     

Tunability of electronic and optical properties of the Ba–Zr–S system via dimensional reduction

Transition metal sulfide perovskites offer lower band gaps and greater tunability than oxides, along with other desirable properties for applications. Here, we explore dimensional reduction as a tuning strategy using the Ruddlesden–Popper phases in the Ba–Zr–S system as a model. The three-dimensional perovskite BaZrS₃ is a direct gap semiconductor, with a band gap of 1.5 eV suitable for solar photovoltaic application. However, the three known members of the Ruddlesden–Popper series, are all indirect gap materials, and additionally have lower fundamental band gaps. This is accompanied in the case of Ba₂ZrS₄ by a band structure that is more favorable for carrier transport for oriented samples. The layered Ruddlesden–Popper compounds show significantly anisotropic optical properties, as may be expected. The optical spectra show tails at low energy, which may complicate experimental characterization of these materials.     

Study of the structure and electronic state of thiolate-protected gold clusters by means of 197Au Mössbauer spectroscopy

We have investigated the structures and electronic states of a series of glutathionate-protected Au clusters, Au _n (SG) _m with n = 10 ? ～55, using ¹⁹⁷Au Mössbauer spectroscopy, which allows us to probe the local environment of the constituent Au atoms via isomer shift (IS) and quadrupole splitting (QS). The spectral profile abruptly changes on going from Au₂₂(SG)₁₇ to Au₂₅(SG)₁₈, then it smoothly changes to that of Au～₅₅(SG)_m. However, the spectral profile dramatically changes on going from Au～₅₅(SG)_m to the dodecanethiolate-protected Au cluster with average diameter of 2 nm. The ¹⁹⁷Au Mössbauer spectra of glutathionate-protected Au clusters and dodecanethiolate-protected Au clusters were successfully analyzed on the basis of the structure and electronic state of Au₂₅(SG)₁₈.     

Study on the Cofluorescence Effect of Europium (III)–Yttrium (III)–Balofloxacin–Sodium Dodecyl Sulfate System and Its Analytical Application

A new fluorescence enhancement phenomenon in the europium(III)–balofloxacin–sodium dodecyl sulfate system was observed when yttrium(III) was added. Based on this, a sensitive cofluorescence assay for the estimation of balofloxacin was established. Under the optimized conditions, the enhanced fluorescence signal was linear over the concentration of balofloxacin ranging from 3.0 × 10^?9 to 7.0 × 10^?6 mol L^?1 with a correlation coefficient of 0.9993. The detection limit (3 σ) was determined as 8.3 × 10^?10 mol L^?1. The presented method was successfully applied to determination of balofloxacin in pharmaceutical preparations, human serum, and urine. The possible fluorescence enhancement mechanism was also discussed.     

Effect of copper concentration on atomic site occupation by Fe ions and magnetic properties of (PrDy)–(FeCo)–B alloys

The effect of small copper additions (to ～6 at %) on the distribution of iron ions in six crystallographic sites of the unit cell of the main magnetic phase (PrDy)₂(FeCo)₁₄B has been detected. An increase in the copper concentration leads to a decrease in the 8j₁ site occupation by iron ions. Independently of the presence of copper, the temperature dependences of the saturation magnetization of all samples have a minimum which can correspond to the presence of a low-temperature phase or a compensation point in grain boundary regions of the (PrDy)₂(FeCo)₁₄B main magnetic phase. The alloys under study are not additive sets of all phases in their composition, but behave as new materials with the mutual influence of phases on each other.     

LEED surface crystallography,R-factors and the structure of the (110) surfaces of III–V semiconductors

Investigation of InSb(110) is presented which is used as the basis for a study of the way in which R-factors are used in LEED methods. These are general comments on the nature of R-factors and the methodology of LEED appropriate to many of the complex surfaces such as the zincblende (110) surface now being studied.     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Estimation of higher-order magnetic spin interactions of Fe(III) and Gd(III) ions doped in α-alumina powder with multifrequency EPR

Fe(III) and Gd(III) ions in α-alumina (A1₂O₃) exhibit spin states ofS = 5/2 andS = 7/2 respectively. The magnitude of the zero-field interaction (ZFI) (D = 0.10?0.15 cm^?1) gives rise to an inter Kramers doublet splitting in the same order of magnitude as the X-band electron paramagnetic resonance (EPR) quantum (0.3 cm^?1). It is demonstrated that through a careful step-by-step analysis and spectral simulation of EPR spectra taken at D-band (130 GHz), Q-band (35 GHz), and X-band (9 GHz) at room temperature, the (relative) sign and magnitude of the ZFI parameters, b ₂ ⁰ , b ₄ ⁰ , and b ₄ ³ , can be reliably estimated.     

Spectroscopic and Theoretical Study of Cyanidin–Aluminum (III) Complexes

Complexation of aluminum (III) with cyanidin, a natural anthocyanidin molecule, has been investigated in methanol and buffered solutions of pH 3.0 and 4.0. Electronic absorption spectroscopy was performed to characterize the stoichiometry and stability of the complexes formed. In investigated solvents, aluminum bonded moderately to cyanidin requiring large mole ratios of the components (up to 200) for the access of complexation. Molar ratio plots showed the formation of only one complex with stoichiometry aluminum (III):cyanidin of 1∶1 in both investigated media. Semiempirical calculations, performed in the Austin Model 1 parameterization, enabled the determination of the structural features of free compounds as well as complex structural modifications caused by chelation of Al(III).     

Electronic structure of β-RbNd(MoO4)2 by XPS and XES

β-RbNd(MoO₄)₂ microplates have been prepared by the multistage solid state synthesis method. The phase composition and micromorphology of the final product have been evaluated by XRD and SEM methods. The electronic structure of β-RbNd(MoO₄)₂ molybdate has been studied employing the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). For the molybdate, the XPS core-level and valence-band spectra, as well as XES bands representing energy distribution of the Mo 4d- and O 2p-like states, have been measured. It has been established that the O 2p-like states contribute mainly to the upper portion of the valence band with also significant contributions throughout the whole valence-band region. The Mo 4d-like states contribute mainly to a lower valence band portion.     

Structural feature of calf thymus deoxyribonucleic acid–ruthenium(III) interaction in aqueous solution by difference Fourier transformed infrared spectroscopy

Here is the report on the interaction of ruthenium(III) species with DNA in aqueous solution at pH 7.42 by Fourier transformed infrared difference spectroscopy. Under the physiological pH and molar ratio [Ruthenium]/[DNA]?=?1/80–1/20 direct binding to guanine-N7, adenine-N7, and surprising binding to exocyclic thymine-O2 was found. At low metal concentration no significant shift of the absorption bands was observed, only nonspecific electrostatic binding of ruthenium(III) with negatively charged phosphate groups occurred. The increase of ruthenium(III) concentration caused DNA double helix destabilization and direct binding of the metal cation to guanine-N7 and thymine-O2. At higher ruthenium(III) concentrations denaturation of the DNA helix is evident with no apparent binding of ruthenium(III) to adenine and cytosine. Helix opening allows migration of ruthenium(III) ions from phosphate to available nucleobases (guanine and thymine). No alteration of the sugar phosphate geometry was observed thus confirming that DNA remains in B conformation.     

A study of the nonlinear refractive index in amorphous Ge–As–S layers and nanocomposites with gold nanoparticles

Nonlinear refractive indices of simple and composite chalcogenide glasses with gold nanoparticles are measured by the Z-scan method using a femtosecond Ti:sapphire laser with a central wavelength of 800 nm and a pulse duration of 40 fs. It is shown that introduction of nanoparticles into thin layers of amorphous GeS₂, As₃₀Ge₂₀S₅₀, and As₃Ge₃₅S₆₂ leads to a decrease in the total nonlinear refractive index due to additional absorption of femtosecond laser radiation without efficient excitation of localized plasmons outside the resonance region. For example, the nonlinear refractive index decreases with addition of gold nanoparticles from 16.1 × 10^–12 to 13.0 × 10^–12 cm²/W for GeS₂, from 3.9 × 10^–12 to 3.2 × 10^–12 cm²/W for As₃₀Ge₂₀S₅₀, and from 5.8 × 10^–12 to 4.7 × 10^–12 cm²/W for As₃Ge₃₅S₆₂.     

Growth and characterization of Au,Ni and Au–Ni nanoclusters on 6H-SiC(0001) carbon nanomesh

The nucleation and thermal stability of Au, Ni, and Au–Ni nanoclusters on 6H-SiC(0001) carbon nanomesh as well as the interaction between Au–Ni bimetallic clusters and reactive gases have been studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Both Au and Ni atoms grow as three-dimensional (3D) clusters. Annealing the Au/carbon nanomesh surface up to 1150 °C leads to complete desorption of the Au clusters, while interfacial reaction occurs between Ni clusters and the substrate surface when the Ni clusters are subjected to the same annealing process. The nucleation of Au–Ni clusters depends critically on the deposition sequence. Au atoms preferentially nucleate on the existing Ni clusters, leading to the formation of bimetallic clusters with Au enriched on the surface. If the deposition sequence is reversed, a part of Ni atoms nucleate between the Au clusters. The thermal stability of the Au–Ni clusters resembles that of the Ni/carbon nanomesh surface, irrespective of the deposition sequence. XPS characterization reveals that Ni atoms in Au–Ni bimetallic clusters are oxidized upon exposure to 5.0 × 10^? 7 mbar O₂ for 5 min at room temperature while negligible structure change can be detected when the bimetallic clusters are exposed to CO gas under the similar conditions.     

Effect of the donor–acceptor properties of ligands on the spectroscopic and electrochemical properties of mixed-ligand complexes of Pt(II) and Ir(III) with cyclometalated 2-phenylbenzothiazole

The results of the spectroscopic NMR (¹H, ¹³C, and ¹⁹⁵Pt), infrared, optical, and voltammetric characteristics of the mixed-ligand complexes of Pt(II) and Ir(III) with metalated 2-phenylbenzothiazole and tert-butylisocyanide (tBuNC), acetonitrile (AN), ethylenediamine (En), O-ethyldithiocarbamate (Exn^–), and diethyldithiocarbamate (Dtc–) ions are presented. It is demonstrated that the change in donor–acceptor interaction of ligands tBuNC, AN, En, Exn^–, and Dtc^– with metal leads to an increase in the energy of the highest occupied molecular orbital of the complexes and is accompanied by a shift of the cathode potential of the metal-centered oxidation, a bathochromic shift of the spin-allowed and spin-forbidden metal-tocyclometalated ligand optical charge transfer transitions, and an increase the degree of mixing of the ¹MLCT and triplet intraligand states, responsible for the phosphorescence of the complexes.     

Structural,electronic and magnetic properties of gold cluster doped with calcium: Au n Ca (n = 1–8)

The geometrical structures, relative stabilities, electronic and magnetic properties of calcium-doped gold clusters Au _n Ca (n?=?1–8) have been systematically investigated by employing density functional method at the BP86 level. The optimised geometries show that the ground-state structures are planar structures for Au _n Ca (n?=?3–8) clusters. Ca-substituted Au _{n +1} clusters, as well as Au-capped Au _{n ?1}Ca clusters, are dominant growth patterns for the Au _n Ca clusters. The relative stabilities of Au _n Ca clusters for the ground-state structures are analysed based on the averaged binding energies, fragmentation energies and second-order difference of energies. The calculated results reveal that the Au₂Ca isomer is the most stable structure for small size Au _n Ca (n?=?1–8) clusters. The HOMO-LUMO energy gaps as a function of the cluster size exhibit a pronounced even–odd alternation phenomenon. Subsequently, charge transfers and magnetic moment of Au _n Ca (n?=?1–8) clusters have been analysed further.     

Nanometer-microscopy of the electron transmission through an ultrathin (3–22 nm) Au film and of the Au-Si schottky barrier height

Direct imaging with nanometer scale resolution of the Schottky barrier height and of the ballistic transmission of electrons through an ultrathin metal film is demonstrated for the first time. The images are obtained by applying a new pixel-by-pixel evaluation method to the ballistic electron emission spectroscopy (BEES). We find a laterally uniform Schottky barrier height _B=0.88 eV for ultrathin (3–22 nm) Au films evaporated on Si. The transmission coefficient is strongly correlated with the island structure of the Au film. A transmission decay length =14 nm is determined by a statistical analysis of the transmission coefficient with variation of the film thickness.     

A highly luminescent complexes of Eu(III) and Tb(III) with norfloxacin and gatifloxacin doped in sol–gel matrix: A comparable approach of using silica doped Tb(III) and Eu(III) as optical sensor

Highly luminescent complexes of Eu and Tb ions with norfloxacin (NFLX) and gatifloxacin (GFLX) were prepared in sol–gel matrix. The red and green emissions of Eu and Tb ions were obtained by the energy transfer from the triplet state of (NFLX) and (GFLX) to the excited emitting states (⁵D₀ and ⁵D₄) of Eu and Tb, respectively. The intensity of the electric field emission bands (⁵D₀→⁷F₂, 617 nm and ⁵D₄→⁷F₅, 545 nm) of Eu and Tb ions were proportional to the concentration of (NFLX at pH 6.0) and (GFLX at pH 3.5) in acetonitrile with excitation wavelengths (λ_ex) (340 and 395) and (370 and 350 nm) for Eu and Tb ions, respectively. The monitored luminescence intensity of the system showed a good linear relationship with the concentration of NFLX within a range of 5×10^?9–5.8×10^?6 and 5×10^?8–1.0×10^?6 mol L^?1 with a correlation coefficient of 0.990, and for GFLX within a range of 2.4×10^?9–3.2×10^?5 and 5×10^?8–8.0×10^?6 mol L^?1 with a correlation coefficient of 0.995. The detection limit (LOD) was determined as 3.0×10^?9 and 1.0×10^?8 mol L^?1 for NFLX and 1.6×10^?10 and 2.0×10^?8mol L^?1 for GFLX. The limit of quantification (LOQ) is 9×10^?9 and 3.0×10^?8 and 4.8×10^?10 and 6.0×10^?8 in case of Eu and Tb, respectively.