Nanosecond laser operation by spectroscopical parameters of the oxadiazole derivatives

We have studied the variation of principal spectroscopic parameters (absorption edge, spectral positions of the first three principal bands, oscillator strengths) for three oxadiazoles (pyrazoloquinoline derivatives) with different state dipole moments incorporated into the polymethyl methacrylate (PMMA) polymer matrices in the 3% in weighting units. For investigations we have chosen three derivatives with different values of the state dipole moments. We have found that during illumination by 10 ns Nd-YAG laser beam with pulse duration about 10 ns, frequency repetition about 10 Hz and power density about 0.8–1.3 MW cm⁻² the observed photoinduced changes red shifted for the three principal spectral bands situated at 330–350 nm; 450–500 nm and 525–550 nm. It was established that under influence of the pulsed Nd-YAG laser we observe substantial spectral shifts of the observed spectral maxima. The value of the shift is increased with decreased state dipole moment values.     

Polypyrrole thin films for gas sensors prepared by Matrix-Assisted Pulsed Laser Evaporation technology: Effect of deposition parameters on material properties

Thin films of polypyrrole (PPY) were prepared by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technology from two matrices: water and dimethylsulfoxide (DMSO). The deposition was carried out using a KrF excimer laser (laser fluence F ranged from 0.1 to 0.6 J cm^− 2). This work deals with optimization of two deposition parameters - laser fluence and number of pulses - for both matrices. From the deposition curves, the fluence thresholds, F_th, and maximum growth rates were subsequently determined (water matrix: F_th ~ 0.40-0.45 J cm^− 2, maximum growth rate 0.16 nm pulse^− 1; DMSO matrix: F_th ~ 0.25-0.30 J cm^− 2; maximum growth rate 0.20 nm pulse^− 1). The changes in chemical composition of deposited layers were studied by Attenuated Total Reflection Fourier Transform Infrared spectroscopy. Surface morphology was characterized by Atomic Force Microscopy. A discussion is also presented concerning relationships between laser fluence and chemical composition of deposited layers with respect to their potential application in gas sensors. Finally, the response of a sensor with a MAPLE deposited PPY active layer to air humidity is presented.     

Recovery of Pd from Spent Fuel: 1. Electrochemical Recovery of Palladium from Nitric Acid Solutions

The rate of cathodic deposition of palladium from nitrate solutions at a platinum electrode and the current efficiency of the process were studied as influenced by the concentrations of nitric acid, NaNO₃, U, and other admixtures. In the range of potential E from +0.5 to +0.25 V, the rate of Pd deposition from 1 M HNO₃ solution was 0.7–0.9 mg cm⁻² at current efficiency of about 70%. The degree of palladium recovery by cathodic deposition is more than 99% with the coefficient of separation from α- and β-emitting nuclides of 10²–10³.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 334–338.Original Russian Text Copyright © 2005 by Kirshin, Pokhitonov.     

Density and deposition rate of chemical-vapour-deposited boron nitride

A study is made on the density and deposition rate characteristics of chemical-vapour-deposited boron nitride (CVD-BN) plates synthesized by use of the BCl₃-NH₃-H₂ system at a deposition temperature (T _dep) of 1200 to 2000°C and a total gas pressure (P _tot) of 5 to 60 torr. At aP _tot of 5 torr, all the CVD-BN plates synthesized at eachT _dep above 1300°C had a density greater than 2.O g cm^–3, and thus showed no noticeable dependence onT _dep. Over theP _tot range from 10 to 60 torr. on the other hand, the density of the plates reached the maximum of 2.08g cm^–3 at aT _dep of 2000° C. AsT _dep was lowered, the density decreased down to a minimum of 1.40 g cm^–3 The deposition rate varied with bothT _dep andP _tot and showed a maximum value under a certainP _tot at a givenT _dep. The value ofP _tot where the deposition rate becomes maximum changed depending on theT _dep. The maximum deposition rate was 0.6 mm h^–1 for the CVD-BN plates when the density was less than 2.0 g cm^–3, and 0.4 mm h^–1 when the density was above 2.0 g cm^–3 The effects of deposition conditions on the characteristics of density and deposition rate are discussed in terms of the structure and deposition mechanism.     

MOCVD of p-Cd x Hg1 – x Te/GaAs Heteroepitaxial Structures

Metalorganic chemical vapor deposition from Cd and Te alkyl compounds and Hg vapor is used to grow p-type Cd _x Hg_{1 – x} Te epitaxial layers on semi-insulating GaAs(111)Bsubstrates by the interdiffused multilayer process (alternating CdTe and HgTe layers) at a substrate temperature of 350°C, followed by postgrowth annealing. Layers are obtained with x = 0.2–0.4, 77-K carrier concentrations in the range (1–5) × 10¹⁶ cm^–3, and 77-K carrier mobilities from 200 to 400 cm²/(V s). The rocking curves of the epilayers have a full width at half maximum in the range 2–4 min of arc.     

Structural, optical and photoelectrochemical properties of brush plated CdSe x Te1 − x thin films

CdSe _x Te_{1 – x} films have been deposited by the brush plating technique for the first time, on titanium and conducting glass substrates at room temperature. These films were annealed in argon atmosphere at 475°C for 15 min. Their structural, optical and photoelectrochemical (PEC) properties are presented and discussed. The power conversion efficiency has been found to be 9.0% at 60 mW cm^–2white light illumination. A peak quantum efficiency of 0.7 has been obtained for the films of composition CdSe_0.7Te_0.3. Donor concentration of 10¹⁷cm^–3and electron mobility of 60 cm²V^–1sec^–1were obtained.     

Polyaniline films deposited by anodic polymerization: Properties and applications to chemical sensing

Polyaniline conductive thin films have been used for the detection of a number of important gases and vapors: organic solvents, ammonia, oxygen, hydrogen sulfide, nitrogen and sulfur oxides. The films can be produced by spin coating, thermal evaporation, the Langmuir–Blodgett technique and cyclic voltammetry. This paper presents preliminary results on acidity sensing with electrodeposited polyaniline layers. Polyaniline conductive thin films were prepared by anodic polymerization from an acidic solution of the monomer on two kinds of substrates: gold plated silicon and indium-tin oxide on glass. Ultraviolet-visible (UV-VIS) spectrometry of layers showed a maximum absorption peak around 800 nm for all the samples investigated (independent of preparation conditions) and revealed that the polymeric films were in the emeraldine base form, 18–25% protonated. The room-temperature in-plane d.c. conductivities of the polymer films were found to be between 4×10^–9 S cm^–1 and 9×10^–10 S cm^–1 (deposition rate approximately 4 m h^–1; film thickness 750–1100 nm). Immersion of the polyaniline films in dilute hydrochloric solution resulted in changes in the d.c. conductivity by up to nine orders of magnitude, reaching a value of 4×10^–2 S cm^–1 while immersed in the acidic solution. Humidity tests carried out by exposing polyaniline samples to water vapors changed the d.c. conductivity by one order of magnitude to 1.34×10^–8 S cm^–1.     

Fracture toughness of the fibre-matrix interface in glass-epoxy composites

The failure process arising at a broken fibre end in polymer matrix composite materials has been studied experimentally and analytically using the finite element method. A series of experiments were carried out using S-glass and E-glass single filaments, with different sizings and/or coupling agents, embedded in epoxy matrices with different moduli. A finite element analysis was used to simulate the experiments and calculate the change in strain energy accompanying the observed fracture mode. The strain energy release rate upon arrest of the crack, G _arrest, was then calculated. The measured interface debonding energies varied from G _arrest=57–342 J m^–2, depending primarily on the nature of the fibre sizing and the ratio of moduli of the fibre and matrix. Transverse and shear matrix cracks were characterized by G _arrest values of 58–103 J m^–2. Subtle changes in the constituent properties or fibre surface treatment resulted in a change in the fracture mode. This measurement and analysis technique may suggest reasons for the variability of previous measurements of interfacial adhesion, and provide a standard method for characterizing fracture modes at broken fibre ends.     

Gas permeability of poly(organophosphazenes)

The gas permeability and oxygen-to-nitrogen selectivity were determined for some poly-(organophosphazenes). It was found from the data that the membrane having the highest gas permeability was [NP(NHPrⁿ)(NEt₂)] _n , which had 1.5 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to oxygen or 2.2 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to nitrogen. On the other hand, the membrane having the highest oxygen-to-nitrogen selectivity of about 3 had the formula [NP(OC₆H₄Cl-p)₂] _n Also, the selectivity did not depend on the glass transition temperature of the membranes. The membrane prepared from [NP(OC₆H₄CH₃-p)2] _n had a negative activation energy for oxygen and nitrogen permeability.     

The thermal diffusivity of ice and water between −40 and + 60° C

The thermal diffusivity _s of triply-distilled deionised water, and ^L of single-crystal ice along the c-axis, have been measured by Angström's method. The temperature range covered was –40 to +60° C. The results for water compare well with published data for the thermal conductivity, but for ice there are unexplained discrepancies. The linear relationships _s=(8.43–0.101 T) 10^–3 cm²/sec and _L=(1.35+0.002 T) 10^–3 cm²/sec where T° C is the temperature, fit the data obtained.     

Nanosecond laser-induced thermal evaporation of silicon carbide

Excimer (XeCl) laser pulses, 15 ns in duration and with fluences up to 10 J · cm^–2, have been employed to induce melting and evaporation of 6H-SiC thin layers in vacuum. Sample surface modification in the nanosecond time scale have been tnonitorizedin situ by optical probing. Eventually, the ablation product was collected on silicon single-crystal substrates placed in front of the SiC target. Modeling of the heating and the thermal evaporation processes resulted in estimation of surface temperatures as high as 10,000 K, evaporation rates of the order of 10²⁵ molecules · cm^–2 · s^–1 and recoil pressures of the order of 1 GPa. Comparison with experiments showed that the simple mechanism of purely thermal evaporation is able to describe the process of particle removal from a surface by short laser pulses only in the low-energy density range. Above a certain threshold the model breaks down and other mechanisms have to be considered.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Photosensitivity in GeO2–SiO2 glasses and optical waveguides

Permanent refractive index changes caused by a KrF excimer laser operating at 248 nm in GeO₂–SiO₂ glasses deposited on Si (100) substrates using flame hydrolysis deposition (FHD) are presented. The sample was amorphouslike investigated by X-ray diffraction (XRD), and the ratio of Ge:Si is 14:86 from X-ray photoelectron spectroscopy (XPS) analysis. The 10-min irradiation with a KrF excimer laser (10 Hz, 187 mJ/cm²) induced a positive refractive index change of 0.341% at 1550 nm, which has achieved an international level of this field. An innovative photomask with a Cr-loaded structure coated on a UV quartz glass, was used to fabricate a 50 μm gap with a period of 100 μm waveguide grating under 1460 mJ/cm²/pulse at 6 Hz, and the diffraction patterns were observed clearly. The extinction coefficients of the samples are also measured over the range 250–1600 nm.     

Salt diffusion in brick structures

Salts causes surface damages and efflorescence for masonry walls. This has increased the interest to understand the salt transfer phenomena taking place in porous matrix. There is still however a lack of published transport data in the literature. Especially the diffusion coefficients of salts in different brick structures are lacking. In this work a method for measuring the rate of diffusion of salt in ceramic material is presented and applied to the measurement of diffusivity of NaCl in three different brick materials. Fick's first law of diffusion was applied to calculate the diffusion coefficients in a pseudo stationary state by means of linear regression analysis. The result for the diffusivity of 0.05 molar NaCl in water in new Finnish red brick was (0.499 ± 0.004 ) * 10^–5 cm²/s in the temperature of 25 ± 0.05°C. The corresponding values for the old light brick and old dark brick was (0.453 ± 0.008) * 10^–5 cm²/s and (0.337 ± 0.009) * 10^–5 cm²/s respectively. The diffusion coefficients are given as an effective diffusion coefficients calculated with the porosity value measured to each of the specimen. The concept of salt diffusion and diffusion mechanism inside the porous matrix are also discussed.     

Preparation and characterization of plasticized polymer electrolytes based on the PVdF-HFP copolymer for lithium/sulfur battery

PVdF-TG-LiX polymer electrolytes comprised of polyvinylidene fluoride (PVdF)-hexafluoropropylene (HFP) copolymer, tetra(ethylene glycol) dimethyl ether as plasticizer, LiCF₃SO₃, LiBF₄ and LiPF₆ as lithium salt and acetone as solvent have been prepared by solvent casting of slurry that mixed PVdF-HFP copolymer with acetone and salt using a ball-milling technique, which was performed for 2 and 12 h with a ball-to-material ratio of 400:1, and their electrochemical and thermal properties were studied. The ball-milled PVdF-TG-LiX polymer electrolytes have higher ionic conductivity as well as lower glass transition temperature and melting points than the magnetically stirred one. The PVdF-TG-LiPF₆ polymer electrolytes prepared by ball-milling, for, 12 h, in particular, resulted in a maximum value in the ionic conductivity, which was 4.99×10^–4 S cm^–1 at room temperature. The ball-milled PVdF-TG-LiX polymer electrolytes were introduced into Li/S cells with sulfur as cathode and lithium as the anode. The first specific discharge capacities with discharge rate of 0.14 mA cm^–2 at room temperature were about 575 and 765 mA h g–cathode^–1 for magnetic stirring and 12 h ball milling.     

Some experimental results on thin polypropylene films loaded with finely-dispersed copper

Experiments have shown that small additions of copper to polymer film where both components are deposited from the vapour phase, and the copper content is in the range of 0.1 to 1.0% by weight, can have a profound effect on the electrical conductivity of the polymer films and a special system of boats for the evaporation sources was devised to enable films of controlled composition to be produced. Structural studies using the electron microscope and X-tray photoelectron spectroscopy show that the copper is finely dispersed within the polypropylene matrix with grain size of the order of 10m diameter and that some of the copper has been converted to copper oxide, but the composite film retains its overall amorphous structure. Electrical measurements on polypropylene samples loaded with 0.15% copper by weight show (a) for MIM sandwich structures with typical dielectric thickness of 300 nm, ohnnicV-I characteristics up to approximately 10⁶ V cm^–1 and a space-charge-limited characteristic beyond that and (b) for planar structures with typical effective inter-electrode separation of 0.05 cm, ohmicV-I characterintics up to approximately 2 × 10³V cm^–1 end beyond that a high-field conduction of the Poole-Frenkel type. For both typen of samples a trapping centre at 0.33 to 0.34 eV is estimated. The planar structure shows considerable photosensitivity.     

Photocatalytic membrane for removal of organic contaminants during ultra-purification of water

Experiments were performed using a photocatalytic membrane fabricated by embedding titanium dioxide particles within a polymer matrix. Catalyst particles were activated by ultraviolet illumination of the membrane. Experimental results demonstrated the feasibility of the photocatalytic process for elimination from water of trace organic solute concentrations. A mathematical model is proposed that aided in the estimation of kinetic parameters associated with the process. The process simulation is based upon a mechanism whereby the primary organic solvent is mineralized via a series of reactions that involve not less than two organic solute intermediates. The reaction rate parameter associated with 254-nm illumination is estimated to be directly proportional to light intensity. Where 185-nm light and 254-nm light were used together, their catalytic effects were shown to be comparable, but the oxidative effect of 185-nm illumination had the added benefit of noncatalytic oxidation. Catalyst and support system improvements are indicated to increase the photocatalytic effect.Abbreviations C _i TOC present as solute i within membrane volume, spatially dependent (ppb solute in water) - TOC present as solute i exiting the "downstream" side of the membrane chamber (ppb solute in water) - TOC present as solute i entering the "upstream" side of the membrane chamber (ppb solute in water) - intensity of illumination, frequency specific and spatially dependent (mW cm^–2) - incident intensity of illumination, frequency specific (mW cm^–2) - intensity of 185-nm illumination incident upon the membrane surface (mW cm^–2) - intensity of 254-nm illumination incident upon the membrane surface (mW cm^–2) - overall surface reaction rate constant for solute i, incorporating both illumination intensity and reaction energetics (s^–1) - bulk reaction rate constant for solute i attributed to 185-nm illumination of CSTR volume (cm² mW^–1 s^–1) - surface reaction rate constant for solute i attributed to 185-nm illumination (cm² mW^–1 s^–1) - surface reaction rate constant for solute i attributed to 254-nm illumination (cm² mW^–1 s^–1) - L membrane thickness (cm) - m modified Beer's law exponent - q TOC analyzer consumption volumetric flow rate (cm³ s^–1) - Q recirculation volumetric flow rate (cm³ s^–1) - S membrane diametral area (cm²) - u _x linear velocity of fluid (cm s^–1) - initial reservoir volume (cm³) - V ^b membrane chamber CSTR volume "upstream" of the membrane (cm³) - V ^p membrane pore volume (cm³) - x spatial coordinate across membrane (cm) - modified Beer's law coefficient (cm^–m ) - membrane porosity (cm³ fluid (cm³ total)^–1) - illumination wavelength (nm)     

Rate-dependent fracture toughness of pure polycrystalline ice

A series of three-point bend tests using single edge notched testpieces of pure polycrystalline ice have been performed at three different temperatures (–20°C, –30°C and –40°C). The displacement rate was varied from 1 mm/min to 100 mm/min, producing the crack tip strain rates from about 10^–3 to 10^–1 s^–1. The results show that (a) the fracture toughness of pure polycrystalline ice given by the critical stress intensity factor (K _IC) is much lower than that measured from the J—integral under identical conditions; (b) from the determination of K _IC, the fracture toughness of pure polycrystalline ice decreases with increasing strain rate and there is good power law relationship between them; (c) from the measurement of the J—integral, a different tendency was appeared: when the crack tip strain rate exceeds a critical value of 6 × 10^–3 s^–1, the fracture toughness is almost constant but when the crack tip strain rate is less than this value, the fracture toughness increases with decreasing crack tip strain rate. Re-examination of the mechanisms of rate-dependent fracture toughness of pure polycrystalline ice shows that the effect of strain rate is related not only to the blunting of crack tips due to plasticity, creep and stress relaxation but also to the nucleation and growth of microcracks in the specimen.     

Influence of different process parameters on physical properties of fluorine dopes indium oxide thin films

Fluorine-doped indium oxide films were prepared by the spray pyrolysis technique. The physical properties of these films were investigated with respect to various process parameters, namely variation of dopant concentration (in the solution), deposition temperature (T _s), carrier gas (air) flow rate and the thickness of the film. The best films had a Hall mobility of the order of 28 cm²V^–1 s^–1 and a carrier density of 2.7 × 10²⁰ cm^–3. These films were deposited at T _s=425 °C at an air flow rate of 71 min^–1 for an atomic ratio of fluorine to indium of 72%. The electrical resistivity of these films was of the order of 10^–4 cm and the average transmission in the visible range was found to be 80–90%. The films were polycrystalline, n-type semiconductors with [400] as a preferred orientation. The preferred orientation changes from [400] to [222] depending upon the process parameters.     

High-temperature thermal barrier coating formation by laser alloying of CP-Ti with pre-placed Ni-SiC coating

High-temperature thermal barrier coating was created on CP-Ti using a pre-placed Ni-SiC layer by laser alloying technique. The coating was developed using 80% Ni + 20% SiC, 50% Ni + 50% SiC and 60% Ni + 40% SiC, and the latter two compositions are found to be efficient in producing a uniform layer. The 100% SiC pre-placement was also used. A flaw-less coating of 0.4–0.6 mm thickness was produced at a lower power density of 1.3 to 1.9 × 10⁵ W cm^–2. Very high power density of 2.5–3.0 × 10⁵ W cm^–2 is inefficient to produce uniform coating. The laser alloyed coating consists of dendrites and intermetallic precipitates. The degree of dendrite population depends upon the coating composition and laser processing conditions. The coating hardness was 600–1200 HV, which is three to six times higher than the base titanium. Uniform hardness was obtained for the coatings produced at a laser power density of 1.3 × 10⁵ W cm^–2. The titanium silicide (TiNiSi, Ti₅Si₃, TiSi) and nickelide (NiTi₂) phases formed on the laser-alloyed coating surface was confirmed by X-ray analysis. These intermetallic phases can improve high-temperature properties of titanium and its alloys. The effect of laser power density and coating composition on the alloying depth alloying width, hardness and microstructure are discussed. The present work investigated the microstructure evolution, hardness and compound phases by means of optical and scanning electron microscopy, Vickers hardness testing, EDXRD and SIMS analysis. A 5 kW CW CO₂ laser was used for laser alloying experiments.     

Investigation of Doped Inert Gas Solids for Cryogenic Lasers

Inert gas polycrystalline samples containing about 0.05–0.5% of dopants such as neutral excimers XeF, KrF, NeF, and ionic excimers Rb²⁺F^–, Cs²⁺F^–, Cs²⁺Cl^–, and also molecules CO-Hg, NO, N₂O and ¹³CO₂ are considered as active media for cryogenic lasers emitting in a broad wavelength range from VUV through VIS into far IR. A correlation between the values of the oscillator strength f in the range of 0.4–10^–6, the cross section for stimulated emission between 10^–15–10^–17 cm² and the pump energy density at laser threshold (10^–3–10^–2 J/cm³) confirms the lasing potential of the systems XeF/Ar (B-X, 411 nm) and of those emitting in IR in agreement with experiment. For the deep UV and VUV transitions B-X of alkalihalides in solid Ne (196.5 nm, 220.1 nm, 136 nm) high pumping thresholds are derived despite of high f values because of large line width.