Detecting electronic states at stacking faults in magnetic thin films by tunneling spectroscopy

Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated with the stacking fault are visualized by tunneling spectroscopy, and its origin is identified by band structure calculations.     

Detailed insight into the hydrogen bonding interactions in acetone-methanol mixtures. A molecular dynamics simulation and Voronoi polyhedra analysis study

Voronoi polyhedra (VP) analysis of mixtures of acetone and methanol is reported on the basis of molecular dynamics computer simulations, performed at 300 K and 1 bar. The composition of the systems investigated covers the entire range from neat acetone to neat methanol. Distribution of the volume, reciprocal volume and asphericity parameter of the VP as well as that of the area of the individual VP faces and of the radius of the empty voids located between the molecules are calculated. To investigate the tendency of the like molecules to self-associate the analyses are repeated by disregarding one of the two components. The self-aggregates of the disregarded component thus turn into large empty voids, which are easily detectable in VP analysis. The obtained results reveal that both molecules show self-association, but this behavior is considerably stronger among the acetone than among the methanol molecules. The strongest self-association of the acetone and methanol molecules is found in their mole fraction ranges of 02-0.5 and 0.5-0.6, respectively. The caging effect around the methanol molecules is found to be stronger than around acetones. Finally, the local environment of the acetone molecules turns out to be more spherical than that of the methanols, not only in the respective neat liquids, but also in their mixtures.     

Recent trends in ultra‐fast HPLC: New generation superficially porous silica columns

New generation columns, i.e. packed with superficially porous silica particles are available as trade names with following manufacturers: Halo, Ascentis Express, Proshell 120, Kinetex, Accucore, Sunshell, and Nucleoshell. These provide ultra‐fast HPLC separations for a variety of compounds with moderate sample loading capacity and low back pressure. Chemistries of these columns are C₈, C₁₈, RP‐Amide, hydrophilic interaction liquid chromatography, penta fluorophenyl (PFP), F5, and RP‐aqua. Normally, the silica gel particles are of 2.7 and 1.7 μm as total and inner solid core diameters, respectively, with 0.5‐μm‐thick of outer porous layer having 90 Å pore sizes and 150 m²/g surface area. This article describes these new generation columns with special emphasis on their textures and chemistries, separations, optimization, and comparison (inter and intra stationary phases). Besides, future perspectives have also been discussed.     

Diffusion of dextran within poly(methacrylic acid) hydrogels

We describe an investigation of fluorescence correlation spectroscopy into the diffusion of fluorescein‐tagged dextran (FDEX) in a poly(methacrylic acid) (PMAA) hydrogel. The temperature dependence of FDEX diffusion is shown to follow Zimm behavior in pure water, and the decrease in the diffusion coefficient when in the PMAA hydrogel has been modeled. The addition of acid and alkali (HCl and NaOH, respectively) not only control the swelling and collapse of the hydrogel but also reveal a strong pH dependence of the dextran diffusion coefficient, which shows a (nonmonatonic) increase with pH. The addition of NaCl and CaCl₂ salts similarly showed evidence of network swelling, most notably at low salt concentration, but also that the diffusion coefficient within the gel at these low concentrations is larger than that in the equivalent solution without the hydrogel, indicating that the combination of hydrogel and salt works to increase the diffusion coefficient above that in pure water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Probing the mechanisms of ambient ionization by laser‐induced fluorescence spectroscopy

The ionization mechanisms of several atmospheric pressure ion sources based on desorption and ionization of samples deposited on a surface were studied. Home‐built desorption electrospray ionization (DESI), laserspray ionization (LSI), and atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI) sources were characterized using low‐molecular‐weight compounds, in particular fluorescent dyes. Detection of the desorbed and ionized species was performed by laser‐induced fluorescence and ion cyclotron resonance mass spectrometry. The dependences of the signal intensities on various experimental parameters were studied. The data obtained reveals common features, such as formation of solvated species and clusters in the ionization processes, in all of the techniques considered. Copyright © 2012 John Wiley & Sons, Ltd.     

Microemulsion method for producing hydroxyapatite

Hydroxyapatite nanoparticles were obtained in the course of reaction in microemulsion system stabilized by surfactant (sodium bis-2-ethylhexylsulfosuccinate). By the methods of X-ray phase analysis, IR spectroscopy, elemental analysis, and electron microscopy the presence of crystals in the samples of hydroxyapatite as the main phase, and detected the formation of additional calcium phosphate compounds was demonstrated.     

Protecting TERS probes from degradation: extending mechanical and chemical stability

The detailed surface chemistry of aluminum oxide protected silver films for use specifically in surface enhanced Raman spectroscopy and tip enhanced Raman spectroscopy (TERS) was investigated. We have demonstrated that increased storage and scanning use lifetimes for silver plasmonic structures are directly connected with the elimination of chemical degradation at the plasmonic structure surface. X‐ray photoelectron spectroscopy of the metal films confirmed that a 2–3 nm thick coating of aluminum oxide prevented chemical attack of the underlying silver film for three months of storage in a desiccator, significantly increasing the storage lifetime of current probes. The scanning lifetime of a TERS probe when used to image a hard patterned silicon substrate was doubled with the addition of this protective coating. These measurements were performed without laser illumination in order to separate laser‐induced heating degradation from pure mechanical degradation of the metallized probe currently encountered during TERS data collection. Copyright © 2013 John Wiley & Sons, Ltd.     

Functionalized nanoparticles based solid‐phase membrane micro‐tip extraction and high‐performance liquid chromatography analyses of vitamin B complex in human plasma

Iron nanoparticles were prepared by a green method following functionalization using 1‐butyl‐3‐methylimidazolium bromide. 1‐Butyl‐3‐methylimidazole iron nanoparticles were characterized using FTIR spectroscopy, energy dispersive X‐ray fluorescence, X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. The nanoparticles were used in solid‐phase membrane micro‐tip extraction to separate vitamin B complex from plasma before high‐performance liquid chromatography. The optimum conditions obtained were sorbent (15 mg), agitation time (30 min), pH (9.0), desorbing solvent [water (5 mL) + methanol (5 mL) + sodium hydroxide (0.1 N) + acetic acid (d = 1.05 kg/L, pH 5.5), desorbing volume (10 mL) and desorption time (30 min). The percentage recoveries of all the eight vitamin B complex were from 60 to 83%. A high‐performance liquid chromatography method was developed using a PhE column (250 × 4.6 mm, 5.0 μm) and water/acetonitrile (95:5, v/v; pH 4.0 with 0.1% formic acid) mobile phase. The flow rate was 1.0 mL/min with detection at 270 and 210 nm. The values of the capacity, separation and resolution factor were 0.57–39.47, 1.12–6.00 and 1.84–26.26, respectively. The developed sample preparation and chromatographic methods were fast, selective, inexpensive, economic and reproducible. The developed method can be applied for analyzing these drugs in biological and environmental matrices.