Structure in carbon/carbon fibre composites as studied by microscopy and etching with chromic acid

Structure of the matrix carbon in two industrially prepared carbon/carbon fibre composites and in four composites prepared in the laboratory was studied using optical microscopy and SEM examination of surface topography after oxidation in chromic acid solution. In the industrial composites and in the laboratory composites prepared with PAN fibres, the orientation of the basal planes of the matrix carbon is parallel to the fibre length within ～ 5μm of the fibre. The fibre-matrix interface is an area of weakness. Use of CVD coated carbon fibres, however, prevented this alignment; here the basal planes of the matrix carbon are randomly aligned relative to the surfaces of the fibres.     

Structural changes of milk components during acid-induced coagulation kinetics as studied by synchronous fluorescence and mid-infrared spectroscopy

Dynamic oscillatory experiments and front-face synchronous fluorescence spectroscopy and mid-infrared (mid-IR) spectroscopy have been used to investigate structure evolution, at the macroscopic and molecular levels, during milk acidification kinetics. The studies were performed using skim milk, at two different temperatures (30 °C and 40 °C), to which was added glucono-δ-lactone (GDL) to generate different structural changes in casein micelles and gels. Synchronous fluorescence spectra were recorded in the 250-500 nm excitation wavelength range using an offset of 80 nm between the excitation and emission monochromators for each system during the 300 min acidification kinetics. The change in the fluorescence intensity at 281 nm reflects the pH-induced physicochemical changes of casein micelles and, in particular, structural changes in the micelles in the pH range 5.5-5.0. Regarding mid-infrared spectroscopy, the region located between 1700 and 1500 cm(-1), corresponding to the amide I and II bands, and the 1500-900 cm(-1) region, called the fingerprint region, were considered for the characterization of milk coagulation kinetics. Changes in the absorbance at 1063 cm(-1) as a function of pH for kinetics recorded at 30 °C and 40 °C reflected pH-induced phosphate dissolution in the pH range 5.5-5.0. Compared to rheometry, which reveals microstructure changes only in the gel state, spectroscopic methods make it possible to monitor molecular structure changes in micelles throughout the acidification processes.     

Poly-l -lactic acid modified by etching and grafting with gold nanoparticles

This work is focused on characterization of plasma treated and consequently etched and grafted biocompatible polymer poly(l-lactide acid) (PLLA). The interaction of biodegradable polymers with cold plasma is of a great importance in a tissue engineering and surface science. Cold plasma exposure, grafting with gold nanoparticles and etching processes were successfully applied to biopolymer substrate. A method for biopolymer nanostructuring as combination of cold plasma treatment and Au nanoparticle grafting for biocompatibility improvement is introduced. Surface roughness, morphology and surface chemistry was determined. The plasma modification leads to significant increase in surface roughness of PLLA and appearance of sharp spikes and ridges on the PLLA surface. Modification by grafting and etching leads to significant changes in PLLA surface morphology and chemistry. The surface ablation of PLLA has been proved to be significant. In etching of plasma-modified PLLA, methanol proves to be stronger etching agent than water. The grafting of PLLA with gold nanoparticles improved mouse embryonic fibroblasts (NIH 3T3) adhesion and proliferation significantly.     

Miniature tapered photonic crystal fiber interferometer with enhanced sensitivity by acid microdroplets etching

We fabricate a miniature tapered photonic crystal fiber (PCF) interferometer with enhanced sensitivity by acid microdroplets etching. This method is very simple and cost effective, avoiding elongating the PCF, moving and refixing the device during etching, and measuring. The refractive index sensing properties with different PCF diameters are investigated both theoretically and experimentally. The tapering velocity can be controlled by the microdroplet size and position. The sensitivity greatly increases (five times, 750?nm/RIU) and the size decreases after slightly tapering the PCF. The device keeps low temperature dependence before and after tapering. More uniformly and thinly tapered PCFs can be realized with higher sensitivity (～100 times) by optimizing the etching process.     

Structural and optical characteristics of porous GaN generated by electroless chemical etching

This article reports the structural and optical properties of porous GaN prepared by Pt assisted electroless chemical etching. The images of scanning electron microscopy revealed that the density of the pores increased with etching duration, however, the etching duration has no significant effect on the size and shape of the pores. The atomic force microscopy measurements exhibited that the surface roughness was increased with etching durations; however, for long etching duration, the increase of the surface roughness became insignificant. Raman spectra showed that the absence of two forbidden modes i.e. A₁(TO) and E₁(TO) in the as-grown sample was observed in some porous samples. Optical transmission measurements revealed that the increase of pore density would lead to the reduction of light transmission. The studies showed that the structural and optical properties of the GaN could be influenced by the porosity.     

Chemical etching of berlinite in sulphuric acid solutions

The aim of this work is to chemically etch AT wafers of berlinite AIPO₄ in sulphuric acid solutions in order to reach a thickness previously chosen (manufacturing of high frequency plate resonators). The kinetics of etching is studied: the decrease of thickness is followed by frequency measurement. The influence of temperature and acid concentration is measured and the evolution of surface texture is checked both by roughness measurements, resonance frequency and scanning electron microscopy methods.     

Structural features of the L-argininamide-binding DNA aptamer studied with ESI-FTMS

The 24-mer DNA aptamer of Harada and Frankel (Harada, K.; Frankel, A. D. EMBO J. 1995, 14, 5798-5811) that binds L-argininamide (L-Arm) was studied by electrospray ionization Fourier transform mass spectrometry (ESI-FTMS). This DNA folds into a stem and loop such that the loop is able to engulf L-Arm. As controls, two derivatives of the same base composition, one with the same stem but a scrambled loop and the other with no ability to form a secondary structure, were studied. The two DNAs that could fold into stem-loop structures showed a more negatively charged distribution of ions than the linear control. This tendency was preserved in the presence of ligand; complexes expected to have more secondary structure had ions with more negative charges. Distinct species corresponding to no, one, and two bound L-Arm molecules were observed for each DNA. The fractional peak intensities were fit to a straightforward binding model and binding constants were obtained. Thus, ESI-FTMS can provide both qualitative and quantitative data regarding the structure of DNA and its interactions with noncovalent ligands.     

Structural influence on charge-carrier lifetimes in TiO2 powders studied by microwave absorption

A set-up for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized. These measurements have been used as a tool for the investigation of excess charge-carrier lifetimes in TiO₂ (anatase and rutile) powders. The influence of laser wavelength and intensity on TRMC decay shows the importance of the fast-recombination processes. The presence of a long time tail in the TRMC signals of the anatase modification of TiO₂ is attributed to quenching of this recombination by hole-trapping at the surface. The influence of surface treatment by ethanol and water on TRMC decay evidences that dominant effects are bulk recombination in rutile and surface trapping in anatase. The influence of doping in rutile shows that increasing the doping rate accelerates the decay whatever the doping type is. The doping element acts as an impurity favoring recombination by creation of structural defects. The influence of thermal treatment in anatase shows that increasing the thermal treatment temperature increases the lifetimes. High crystalline quality leads to long charge-carrier lifetimes. The results are discussed in view of their relevance for photocatalysis.     

Enlargement of diatom frustules pores by hydrofluoric acid etching at room temperature

Based on the fact that SiO₂ can dissolve in HF solution, three kinds of diatom frustules were treated with 1% HF solution at room temperature. Given the proper reaction times (0–2 h for the diatoms Coscinodiscus and Navicula, and 0–3 h for the diatom Melosira), the size of the pores on the frustules gradually increased and the structures of the frustules remained. While HF treatment does not affect the composition, chemical bonds, or photoluminescence signature of the diatom frustules, the treatment reduces their surface areas. This method may be beneficial to diatom studies, diatom nanotechnology, and diatom device applications that make use of diatom pores.     

Helium implantedAlHf as studied by181Ta TDPAC

Time differential perturbed angular correlation (TDPAC) measurement onAlHf reference sample has shown that a fraction 0.88 of probe nuclei are defect free and are occupying the substitutional sites in fcc Al matrix, and the remaining are associated with Hf solute clusters. Measurements on helium implanted sample indicate the binding of helium associated defects by Hf solute clusters. Isochronal annealing measurements indicate the dissociation of the helium implantation induced defects from Hf solute clusters for annealing treatments beyond 650 K. On comparison of the present results with that reported inCuHf subjected to identical helium implantation, it is inferred that the Hf solute clusters inAlHf bind less strongly the helium associated defects than inCuHf.     

Improvement of multicrystalline silicon wafer solar cells by post-fabrication wet-chemical etching in phosphoric acid

In this study, we have improved electrical characteristics such as the efficiency (η) and the fill factor (FF) of finished multicrystalline silicon (mc-Si) solar cells by using a new chemical treatment with a hot phosphoric (H₃PO₄) acidic solution. These mc-Si solar cells were made by a standard industrial process with screen-printed contacts and a silicon nitride (SiN) antireflection coating. We have deposited SiN thin layer (80 nm) on p-type mc-Si substrate by the mean of plasma enhanced chemical vapour deposition (PECVD) technique. The reactive gases used as precursors inside PECVD chamber are a mixture of silane (SiH₄) and ammonia (NH₃) at a temperature of 380°C. The developed H₃PO₄ chemical surface treatment has improved η from 5·4 to 7·7% and FF from 50·4 to 70·8%, this means a relative increase of up to 40% from the initial values of η and FF. In order to explain these improvements, physical (AFM, EDX), chemical (FTIR) and optical (spectrophotometer) analyses were done.     

Reactions of manganese oxides with sulfuric acid solutions studied by kinetic and electrochemical methods

Reactions of manganese oxides of various compositions with sulfuric acid solutions have been studied by kinetic and electrochemical methods. The surface composition of the manganese oxides has been shown to vary during the dissolution process. We present mathematical dependences of the dissolution rate on kinetic parameters of the electrolyte solution for the oxides of various compositions and interpret the behavior of the manganese oxide with various compositions during dissolution in sulfuric acid solutions of various concentrations.     

Mission success with components not as good as new

It is shown how the probability of mission success can be determined for cases of components which are not as good as new at the beginning of a mission and are not repaired during the mission. After a short definition of the appropriate conditional distribution functions of components lives, a few typical examples of plausible missions for redundant systems are discussed. Among these are such that are time-critical or—concerning flights—space-critical. Since only (advanced) probabilistic reasoning is used, there are no limitations as to the types of life distributions.     

Characteristics of the etching of undoped silica in MCVD-fabricated optical fibers with buffered hydrofluoric acid

The etching reaction between the undoped silica cladding in MCVD-fabricated fibers and buffered hydrofluoric acid (BHF) has been studied by examining the outer diameter decrease of the fibers in a given etching time. The study has revealed that the etching reaction is not diffusion limited. The etch rate is determined and compared with values published for SiO₂ - films. We have also determined the activation energy of the process, which agrees well with values reported for SiO₂ - films.     

Wet chemical etching of silicate glasses in hydrofluoric acid based solutions

The etching of silicate glasses in aqueous hydrofluoric acid solutions is applied in many technological fields. In this review most of the aspects of the wet chemical etching process of silicate glasses are discussed. The mechanism of the dissolution reaction is governed by the adsorption of the two reactive species: HF and HF ₂ ^- and the catalytic action of H⁺ ions, resulting in the breakage of the siloxane bonds in the silicate network. The etch rate is determined by the composition of the etchant as well as by the glass, although the mechanism of dissolution is not influenced. In the second part of this review, diverse applications of etching glass objects in technology are described. Etching of SiO₂ and doped SiO₂ thin films, studied extensively for integrated circuit technology, is discussed separately.