STEM study of Li4 Ti5 O12 anode material modified with Ag nanoparticles.

Comprehensive scanning transmission electron microscopy (STEM) analysis of Li4 Ti5 O12 (LTO) powder modified by deposited Ag nanoparticles was performed. Nanocomposite powders with Ag content of 1 wt.%, 4 wt.%, 10 wt.% were fabricated in a chemical process from suspensions of Ag and LTO. Apart from the STEM results, the presence of pure silver on the surface of the ceramic powder was confirmed by XRD and XPS analyses. The silver particles deposited on the LTO particles were characterized using the EDS mapping technique. The quantified results of the EDS mapping showed a relatively homogenous distribution of silver nanoparticles on the powder surface for every metal content. The mean diameter of the nanoparticles deposited on the LTO powder was about 4 nm in all cases. An increase in the Ag content during chemical surface modification did not cause changes in the microstructure. Focusing on an analysis of the metallic nanoparticles on the ceramic powder, electron tomography was used as an investigative technique. A very precise analysis of three-dimensional nanostructures is desirable for a comprehensive analysis of complex materials. The quantified analysis of the Ag nanoparticles visualized using electron tomography confirmed the results of the size measurements taken from the two-dimensional EDS maps.

High order kinoforms as a broadband achromatic diffractive optics for terahertz beams.

We discuss thin optical structures that allow chromatic aberrations to be avoided in the THz domain. The paper contains the theoretical considerations, computer modeling and experimental evaluation of the high order kinoform diffractive elements in the THz range. According to the obtained results application of the high order kinoforms enables broadband operation in the THz range.

Thin layer spectroelectrochemical (RVC-OTTLE) studies of pertechnetate reduction in acidic media.

The electroreduction of the pertechnetate ions has been examined in sulfuric acid solutions (0.5-4 M) using optically transparent thin layer spectroelectrochemical (RVC-OTTLE) cell. Soluble Tc(III), TcO2+ and [Tc(µ-O)2Tc]3+/4+ species with absorption bands at 420-450, 400, and 502 nm, respectively, were found to be formed during the reduction of TcO4- ions. The strongly acidic medium was found to stabilize technetium ionic forms with lower oxidation states. Spectroelectrochemical measurements performed in 4 M H2SO4 show different stability of dimeric structure of Tc(III, IV) and simple TcO2+ ions. The monooxotechnetium(IV) ions can be electrooxidized at potentials lower than 0.6 V versus Ag,AgCl(sat.) while dimeric structures of Tc, [Tc(µ-O)2Tc]3+/4+, are electrooxidized to pertechnetate ions at potentials higher than 0.8 V versus Ag,AgCl(sat.).

Modeling of the optical system illuminated by quasi-monochromatic spatially incoherent light: new numerical approach.

This Letter presents a new method for modeling of complex optical setups illuminated by quasi monochromatic spatially incoherent light. The algorithm provides better performance and quality than other modeling methods both for isoplanatic and nonisoplanatic systems. The algorithm maintains energy relations, image orientation, and magnification of the system. Computer modeling and experimental results are presented.

Depth measurements of etch-pits in GaN with shape reconstruction from SEM images.

The method, which allows shape reconstruction by reading the intensity from the scanning electron microscopy image, is presented and discussed in details. The method is applied to read the morphology of etch-pits, which were formed on the GaN surface by etching in molten KOH-NaOH eutectic mixture to delineate dislocations. The etch-pit depth distributions are obtained and used to determine densities of pits related to screw, mixed or edge-type dislocations. The results are compared with atomic force microscopy.

Dependence of cathodoluminescence on layer resistance applied for measurement of thin-layer sheet resistance.

The dependence of spatially and spectrally resolved cathodoluminescence in a scanning electron microscope on resistances in semiconductor structures, especially on the layer resistance, is reported. This previously unstudied dependence is utilized for thin-layer sheet-resistance measurement. The method is illustrated by an assessment of lateral confinements in semiconductor-laser heterostructures.

Identification of electron beam vibration sources by separation of magnetic distortion from electric distortion on scanning electron microscope imaging.

Different types of distortions in scanning electron microscopy require different methods of their elimination, and therefore influence of these types on particular elements of the SEM system should be known. The proposed method allows for separation of the direct influence of the magnetic field on the electron beam in the SEM chamber from its influence in the SEM column and from the distortions generated in the SEM scanning block. For this purpose, a series of distorted images is registered for several working distances (between the final aperture of the electron column and the specimen) and for several energies of the electrons. Magnitudes of the distortions are measured on these images. For each applied electron energy, the dependence of the results versus the working distance is approximated with the second-order polynomial function. The analysis of the polynomial coefficients allows for the separation of the above-mentioned kinds of distortions. The presented method enables a selection of the most efficient solution to the distortions reduction. It utilizes the SEM itself and does not need any additional equipment.

Transmission electron microscopy characterization of Au/Pt/Ti/Pt/GaAs ohmic contacts for high power GaAs/InGaAs semiconductor lasers.

We report on transmission electron microscopy studies of Au/Pt/Ti/Pt(10-30 nm) contact structures for high power GaAs/InGaAs semiconductor lasers. The studies showed that annealing at 450 degrees C of contact structures causes the reaction of whole Pt with substrate components (Ga and As) and the formation of Pt-GaAs interlayers with smooth interfaces as required for such structures. Annealing of the structures at 470 and 490 degrees C unfavourably affects the contact structure. At this condition, the strong downward diffusion of Au and Pt from the top layers causes a formation of Au-Pt pits, which break the Ti barrier. Transmission electron microscopy observation revealed that Au/Pt/Ti/Pt(10-30 nm) system annealed at 450 degrees C is appropriate for practical applications. The EDS technique used to identify the phase composition in the Pt(30 nm)/GaAs structure (specially produced for the EDS analysis) annealed at 450 degrees C showed that two layers were formed as a result of the reaction of the whole Pt layer with GaAs, and they consist of Ga, Pt and As. The top layer has the highest concentration of Ga. However, the bottom layer, which is close to the substrate, has the highest concentration of As.

Transmission electron microscopy study of erbium silicide formation from Ti/Er stack for Schottky contact applications.

In this paper, we present results of transmission electron microscopy studies on erbium silicide structures fabricated under various thermal conditions. A titanium cap has been used as a protective layer against oxidation during rapid thermal annealing of an erbium layer in a temperature range of 300-700 degrees C. Both layers (200 nm Ti and 25 nm Er) were deposited by electron-beam sputtering. The investigations have shown that the transformation of the 25-nm-thick erbium into erbium silicide is completed after annealing at 500 degrees C. At higher temperatures, the formation of a titanium silicide layer above erbium silicide is observed. The lowest Schottky barrier has been measured in the sample annealed at 700 degrees C.

New approach to cathodoluminescence studies in application to InGaN/GaN laser diode degradation.

Cathodoluminescence (CL) studies are widely applied in semi-conductor science and technology. However, for structures with a p-n junction the CL spatial distribution can be strongly affected by internal current flows of the electron beam induced current generated within the structure. This influence is the investigated in application to CL studies of degradation in aged laser diodes with InGaN multiquantum wells.

The investigation on the mechanism of electrochemical hydrogen storage in sandwich nickel foam/palladium/carbon nanofibers electrodes.

The kinetics of the process of reversible hydrogen sorption occurring in/on the nickel foam/palladium/carbon nanofibers (Ni/Pd/CNFs) electrodes is examined. It was shown that the hydrogen sorption/desorption properties for palladium can be altered after Pd layer is sandwiched between nickel foam and carbon nanofibers (CNF) layers. The layered Ni/Pd/CNFs electrodes were prepared by a two-step method consisting of chemical deposition of a very thin palladium layer on the Ni foam surface to form Ni/Pd electrodes followed by coating the Pd surface with the CNF layer by the CVD method. The process of hydrogen sorption/desorption into/from Ni/Pd as well as Ni/Pd/CNF electrodes was examined in alkaline electrolyte using the cyclic voltammetry method. The presence of CNF layer on the Pd surface exerts a great influence on the mechanism of the anodic desorption of hydrogen. A new anodic peak of hydrogen desorption revealed for Ni/Pd/CNF electrodes is ascribed to hydrogen storage in CNF phase. The CV measurements showed distinct differences between the rate of hydrogen release from the palladium and carbon phase.

Selective etching of dislocations in GaN and quantitative SEM analysis with shape-reconstruction method.

Due to the differences in etch-pit morphologies, chemical etching offers a possibility to determine densities of dislocations in respect to their type. In the present paper we propose a method, which implements a simple shape-from-shading procedure, i.e. with results derived from image brightness dependence on surface slope. It allows estimation of etch-pit depth distributions from scanning electron microscopy micrographs. This method is used to obtain depth distributions from GaN surface after etching in molten KOH-NaOH eutectic mixture. Depth distributions are used to estimate densities of etch-pits related to a given dislocation type. The distributions are compared with dislocation densities determined with transmission electron microscopy.

Elimination of scanning electron microscopy image periodic distortions with digital signal-processing methods.

Electromagnetic interference is one of the main distortion sources in scanning electron microscopy. Electromagnetic interference-generated scanning electron microscopy image distortions are usually visible as edge blur (at low scan rates) or vibration (at high scan rates). Hardware solutions to this problem, e.g. electrostatic and magnetic shielding, are expensive and, in some cases, difficult to implement. The current investigations led to a significant decrease in the periodic distortions by a novel adaptation of software-based digital signal processing to scanning electron microscopy problems, without any hardware modification.

In situ electron beam induced current measurements of the local thickness in semiconductor devices.

A quantitative electron beam induced current method is shown, applicable in situ for electron beam current measurement on a semiconductor sample without the need for a Faraday cup. As a validation technique, the measurement of top overlayer thickness in the semiconductor structure was chosen for two reasons. First, the measured thickness is easily verified using the same electron microscope in the secondary electron mode by measuring the layer thickness at the layer edges. Second, the measurement of a layer thickness and its local variations constitute an important issue in semiconductor processing and characterization. The proposed method is used in the planar view of the sample, and also for locations far from the layer edges. Quasi-three-dimensional maps of the thickness spatial distribution are presented.

Facile preparation of disulfide-bridged peptides using the polymer-supported oxidant CLEAR-OX.

Formation of disulfide bonds in synthetic peptides is one of the more challenging transformations to achieve in peptide chemistry, in view of the possible formation of oligomeric by-products and other side reactions, as well as occasional solubility problems in aqueous oxidizing media. It was shown previously that 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB identical with Ellman's reagent), when attached to polyethylene glycol-polystyrene (PEG-PS), controlled-pore glass (CPG), or modified Sephadex supports, was an effective oxidizing agent that promoted disulfide formation under mild conditions. More recently, this work was extended to Cross-Linked Ethoxylate Acrylate Resin (CLEAR) supports, because of their compatibility with both organic and aqueous solvent mixtures. The resultant new tool, termed CLEAR-OX, was used to conveniently produce several model cyclic disulfides with improved purities and yields, when compared with solution oxidations. A particularly striking example was the gram-scale oxidation of a urotensin II antagonist peptide containing a hindered penicillamine unit.

Assessment of adherence with multiple informants in pre-adolescents with spina bifida: initial development of a multidimensional, multitask parent-report questionnaire.

Adherence to medical regimens was assessed in 67 pre-adolescents with spina bifida (8- and 9-year-olds; 37 boys, 30 girls), with mother, father, teacher, and health professional report. The Parent-Report of Medical Adherence in Spina Bifida Scale (PROMASB) was developed and includes multidimensional scales for the following tasks: catheterization, bowel care, skin care, medication, and ambulation. With few exceptions, the PROMASB has adequate psychometric properties. However, findings revealed modest to low correlations between respondents. Mothers and fathers reported significantly more noncompliance than teachers and health professionals. For the most part, all informants reported that most children were compliant across all tasks. Additional analyses based on qualitative data suggest that parents attribute compliance difficulties to motivational as well as attentional-memory factors.

Identification of the structural elements of amphotericin B and other polyene macrolide antibiotics of the hepteane group influencing the ionic selectivity of the permeability pathways formed in the red cell membrane.

The selectivity of the transmembrane permeability induced by polyene antibiotics was studied in human erythrocytes and related to the hemolytic potency of the drugs. The selectivity induced was differently, dependent on the antibiotic structure in aromatic (vacidin A, gedamycin) and nonaromatic heptaenes (amphotericin B, candidin). Aromatic heptaenes were more effective than nonaromatic in inducing permeability to K+. For both groups of antibiotics, permeability to K+ was not affected by substitution at the carboxyl group but important differences in the induction of permeability to H+, OH- and Cl- were found. The strongly hemolytic aromatic heptaenes vacidin A and gedamycin exhibited much higher protonophoric activity than the nonaromatic ones: amphotericin B, and candidin. The protonophoric properties of aromatic heptaenes were related to the presence of a free carboxyl group in the antibiotic molecule. Indeed the esterification or amidation of the carboxyl group of vacidin A or gedamycin eliminated the ability of the antibiotic to increase H+ conductance and consequently diminished their hemolytic activity to an important extent. Both groups of antibiotics differed also in the efficiency of anion permeability induction. Only unsubstituted aromatic heptaenes, at high concentration, induced Cl-/OH- exchange and conductive flux of Cl- in a concentration-dependent manner. Substitution at the carboxyl group of vacidin A or gedamycin eliminated this property. Amphotericin B as well as its carboxyl-substituted derivatives formed a pathway characterized by low K+ over Cl- selectivity, whatever the concentration. The hemolytic activity, related to K+ permeability increased by heptaenes was dependent on simultaneous increase of the permeability to anions, and net KCl influx. Carboxyl-substituted derivatives of aromatic heptaenes presenting a remarkably high selectivity for K+, had consequently a very poor hemolytic activity.

Molecular models of small phosphorylated chromatin peptides. Structure-function relationship and regulatory activity on in vitro transcription and on cell growth and differentiation.

We previously reported the isolation of low molecular weight phosphorylated peptides from the chromatin of several tissues. The chromatin peptides show a regulatory activity on DNA in vitro transcription and on cell growth and differentiation. In this paper, we report a molecular model of the native peptides designed according to the structural information obtained by means of biochemical and mass spectrometry analysis: pyroGlu-Ala-Gly-Glu-Asp-Ser(P)-Asp-Glu-Glu-Asn. This or very similar sequences are present in many transcription factors; on the basis of the structural model we presented and of related protein sequences, we have synthesized the peptide pyroGlu-Asp-Asp-Ser-Asp-Glu-Glu-Asn. This peptide affects transcription rate in reconstituted systems in vitro and in isolated nuclei; moreover, it inhibits the growth of HL60 cells with a parallel stimulus of differentiation.

Polyene macrolide antibiotics: indirect stimulation of the Na+/H+ exchanger of BALB/c B lymphoid cell line, A20.

The fluorescent pH probe, 2'-7'-bis (carboxyethyl) 5-carboxyfluorescein, was used to follow changes in internal pH (pHi) induced by aromatic polyene antibiotics in the BALB/c lymphoid cell line A20. The antibiotics studied were vacidin, which contains a free carboxylic group in the position C18 of the macrolide ring, and vacidin glycyl methyl ester and perimycin, which are without free carboxylic groups. Although all of them induced transmembrane Na+ and K+ movements, only vacidin had protonophoric activity, as previously demonstrated for red blood cells [Cybulska B et al., Biochem Pharmacol 38: 1755-1762, 1989]. However, with all three antibiotics, pHi changes were observed in A20 cells. It was demonstrated that the transmembrane H+ movements resulted to different degrees, principally in the case of perimycin and vacidin glycyl methyl ester, or partially in the case of vacidin, from the stimulation of the Na+/H+ exchanger by the induced Na+ permeability. The non-aromatic polyene antibiotic amphotericin B had a low ability to increase proton permeability.