Free-running ruby laser annealing of boron implanted silicon

An analytical treatment of the thermal phenomena during free-running ruby laser annealing of boron implanted silicon is presented. The heat equation was solved for a simplified shape of the pulse train consisting of a uniform succession of triangular spikes, identical in energy. During one spike the optical and thermal parameters of the sample were taken constant, but for each new spike, new values of these parameters were calculated taking into account their temperature dependence. Such a model predicts the melting of the top surface before the laser pulse has ended, for energy densities higher than 9×10⁴ J/m². RHEED confirms the presence of recristallization at about the same value of the laser-pulse energy densities.     

Growth and characterization of β-SiC films obtained by fs laser ablation

We achieved the growth of cubic silicon carbide (SiC) films on (1 0 0)Si substrates by pulsed laser deposition (PLD) at moderate temperatures such as 750 °C, from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The morphology of deposited films is dominated by columns nucleated from a thin nanostructured beta silicon carbide (β-SiC) interface layer. The combined effects of columnar growth, tilted facets of the emerging columns and the presence of particulates on the film surface, lead to a rather rough surface of the films.     

Crossed Product Algebras and the Homology of Certain p-Adic and Adélic Dynamical Systems

We identify the Hochschild, cyclic, and periodic cyclic homology groups of dynamical systems algebras arising from the action of Q on the spaces of finite and infinite adéles of Q. In the process, we establish several results on the homology of the space of functions on a locally compact, totally disconnected space and its crossed products. Then we use these results to compute the homology groups of the Bost–Connes algebra.     

A glucose dehydrogenase biosensor as an additional signal amplification step in an enzyme-flow immunoassay

Both the antibody affinity and the detectability of the label are essential in deciding the final characteristics of a heterogeneous immunoassay. This paper describes an approach to obtain a supplementary enhancement of the signal generated by using an enzyme label, e.g., by including the product of the enzymatic reaction in an additional amplification cycle during the detection step performed with an amperometric biosensor based on glucose dehydrogenase (GDH). An immunoassay format with a labelled analyte derivative that competes with the analyte present in the sample for a limited amount of antibody binding sites was employed. The beta-galactosidase label hydrolyses the substrate aminophenyl-beta-galactopyranoside, and the generated aminophenol enters then into a bioelectrocatalytic amplification cycle at the GDH biosensor. The principle was applied for determination of 4-nitrophenol, with the best minimal concentration of 1.5 microM and a midpoint of the calibration of 24 microM. The potentials and limitations of such a system are discussed.     

Direct observation of laser-induced crystallization of a-C:H films

The post-growth modification of diamond-like amorphous hydrogenated carbon a-C:H films by laser treatment has been studied by transmission electron microscopy and Raman spectroscopy. a-C:H films grown on Si substrates by benzene decomposition in a rf glow discharge were irradiated with 15 ns pulses of a KrF-excimer laser with fluences in the range of E=50–700 mJ/cm². At fluences below 100 mJ/cm² an increase in the number of graphitic clusters and in their ordering was evidenced from Raman spectra, while the film structure remained amorphous according to electron microscopy and electron diffraction observations. At higher fluences the appearance of diamond particles of 2–7 nm size, embedded into the lower crystallized graphitic matrix, was observed and simultaneously a progressive growth of graphite nanocrystals with dimensions from 2 nm to 4 nm was deduced from Raman measurements. The maximum thickness of the crystallized surface layer (400 nm) and the degree of laser annealing are limited by the film ablation which starts at E>250 mJ/cm². The laser-treated areas lose their chemical inertness. In particular, chemical etching in chromium acid becomes possible, which may be used for patterning the highly inert carbon films.     

Poly(siloxane‐urethane) crosslinked structures obtained by sol‐gel technique

Poly(siloxane‐urethane) crosslinked structures were prepared from isophorone diisocyanate, α,ω‐bis(hydroxybutyl)oligodimethylsiloxane and a new hybrid diol containing hydrolysable Si? OC₂H₅ groups besides OH groups. The latest was synthesized by the acid‐catalyzed reaction between 1,3‐bis(3‐glycidoxypropyl)tetramethyldisiloxane and 3‐aminopropyltriethoxysilane. The formations of the urethane groups along the polymer backbone as well as the formation of the silica domains were first confirmed by the presence of the specific bands in Fourier transform infrared spectra. The resulted materials were characterized using differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The results of the dynamic mechanical analysis (DMA) performed at various frequencies revealed shape memory capabilities for some of the obtained structures. The silica formed because of the hydrolysis‐condensation reactions proved to have reinforcing effect upon siloxane‐urethane structure also evidenced by DMA and increasing water vapor sorption capacity as was measured by dynamic vapor sorption. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Antibacterial and Photocatalytic Properties of ZnO Nanoparticles Obtained from Chemical versus Saponaria officinalis Extract-Mediated Synthesis

In the present work, the properties of ZnO nanoparticles obtained using an eco-friendly synthesis (biomediated methods in microwave irradiation) were studied. Saponaria officinalis extracts were used as both reducing and capping agents in the green nanochemistry synthesis of ZnO. Inorganic zinc oxide nanopowders were successfully prepared by a modified hydrothermal method and plant extract-mediated method. The influence of microwave irradiation was studied in both cases. The size, composition, crystallinity and morphology of inorganic nanoparticles (NPs) were investigated using dynamic light scattering (DLS), powder X-ray diffraction (XRD), SEM-EDX microscopy. Tunings of the nanochemistry reaction conditions (Zn precursor, structuring agent), ZnO NPs with various shapes were obtained, from quasi-spherical to flower-like. The optical properties and photocatalytic activity (degradation of methylene blue as model compound) were also investigated. ZnO nanopowders’ antibacterial activity was tested against Gram-positive and Gram-negative bacterial strains to evidence the influence of the vegetal extract-mediated synthesis on the biological activity.     

Photoluminescence properties of PVP/Eu(TTA)2(Phen3PO)2NO3 nanocomposites

Thin films (1-10 μm thickness) of nanocomposites (NC) based on organic coordinated compound (OCC) Eu(TTA)₂(Phen₃PO)₂NO₃ (where TTA is thenoyltrifluoroacetonate (C₈H₅F₃O₂S), Phen - 1,10-phenanthroline (C₁₂H₈N₂)) and polymer - polyvinylpyrrolidone ((C₆H₉NO)_n) (PVP)) were obtained by chemical methods. NC were characterized by measurements of optical transmission, and photoluminescence (PL) at different concentrations of Eu(TTA)₂(Phen₃PO)₂NO₃ in NC. Using the optical transmission spectra, the characteristic parameters of NC such as threshold of absorbance and the position of the absorption edge on the concentration of the OOC in NC, etc., were determined. The light displacement of threshold absorption to infrared region was observed with increasing of concentration of coordinated material in NC. It was established that the excitation spectrum at which the photoluminescence in NC take place cover the range of wavelength from 200 to 410 nm. The PL of nanocomposites was detected as specific for internal transitions 4f-4f of the Eu³⁺ ion ⁵D₀ → ⁷F_i (i = 0,1,2,3 and 4) centred at 537, 580, 615, 650 and 702 nm, respectively at T = 300 K. The dominant PL was observed at 615 nm and its halfwidth is less than 10 nm. The intensity of photoluminescence at 615 nm of NC is 2 times higher than the value of intensity of PL of Eu(TTA)₂(Phen₃PO)₂NO₃ powders at equal conditions of excitation.