Thermo-physical parameters and characteristics of self-organized nanogratings induced by femtosecond laser

Self-organized nanoripples are induced on bulk metal Cu and Ag by femtosecond laser, and the influence of number of shots on nanostructure formation has been investigated. The AFM images show that obtained grooves on Cu are about 50 nm deep, and have an average spacing of 481.41 nm, which is smaller compared to the incident radiation wavelength (800 nm). Arrays of ablated craters are machined on Cu and Ag surfaces by femtosecond laser in order to determine the optical characteristics of laser irradiated surface. Compared with that of untreated sample, the locations of maximum absorption wavelength of laser treated samples are not shifted, while average absorbance intensities are enhanced both for modified Ag and Cu surfaces. Finally, the effects of thermal conductivity, dielectric function as well as electron–phonon coupling coefficient on nanograting morphology induced by femtosecond laser are discussed qualitatively.     

Powder synthesis and electrical,dielectric spectroscopic characterization of rare earth disilicates (D-Er2Si2O7): Transistor scaling-22 nm or beyond

Rare earth disilicates are now a day's being analyzed as a dielectric layer for transistor scaling for the advanced 22 nm regime or beyond. So to explore these materials, the polymorphic powdered Er₂Si₂O₇ (D phase) is synthesized by solid state double sintering method to study its characteristics. Structural characterization has been performed by X-ray diffraction. SEM and EDX results shows the rods like morphology of particles and composition. The dc electrical properties are evaluated by two probe method as a function of temperature. The dielectric spectroscopic measurements of D-Er₂Si₂O₇ are performed in the temperature range 300–420 K and frequency range 1 kHz to 1 MHz. The dc electrical transport phenomenon is analyzed using Mott’s variable-range hopping approach. The ac conductivity σ_ac(ω) is obtained through the dielectric spectroscopic measurements.     

Fiber laser welding of austenitic steel and commercially pure copper butt joint

The fiber laser welding of austenitic stainless steel and commercially pure copper in butt joint configuration without filler or intermediate material is presented. In order to melt stainless steel directly and melt copper via heat conduction a defocused laser beam was used with an offset to stainless steel. During mechanical tests the weld seam was more durable than heat affected zone of copper so samples without defects could be obtained. Three process variants of offset of the laser beam were applied. The following tests were conducted: tensile test of weldment, intermediate layer microhardness, optical metallography, study of the chemical composition of the intermediate layer, fractography. Measurements of electrical resistivity coefficients of stainless steel, copper and copper–stainless steel weldment were made, which can be interpreted or recalculated as the thermal conductivity coefficient. It shows that electrical resistivity coefficient of cooper–stainless steel weldment higher than that of stainless steel. The width of intermediate layer between stainless steel and commercially pure copper was 41–53 µm, microhardness was 128–170 HV_0.01.     

Thermo-optical properties of polar dielectric laser dye solvents

This work is devoted to study the thermo-optical properties of three important pure polar dielectric laser dye solvents (aniline, pyridine and ethyl ether). Experimental measurements of the refractive index n and its thermo-optic coefficient dn/dT are carried out using dual laser Mach–Zehnder interferometric technique. The determined values of n and dn/dT are used to extract new data concerning the mentioned laser dye solvents. Applying the empirical relationship of Cauchy between the refractive index and the wavelength, the optical dispersion dn/dλ and dn/dT, as a function of wavelength are calculated and represented. Additionally, Cauchy's constants as a function of temperature has been calculated and a comparison between the studied solvents are considered.     

Growth and characterization of Nd:Bi12SiO20 single crystal

A Nd:Bi₁₂SiO₂₀ crystal was grown by the Czochralski method. The thermal properties of the crystal were systematically studied. The thermal expansion coefficient was measured to be α=11.42×10^?6 K^?1 over the temperature range of 295–775 K, and the specific heat and thermal diffusion coefficient were measured to be 0.243 Jg^?1 k^?1 and 0.584 mm²/s, respectively at 302 K. The density was measured to be 9.361 g/cm³ by the buoyancy method. The thermal conductivity of Nd:Bi₁₂SiO₂₀ was calculated to be 1.328 Wm^?1 K^?1 at room temperature (302 K). The refractive index of Nd:Bi₁₂SiO₂₀ was measured at room temperature at eight different wavelengths. The absorption and emission spectra were also measured at room temperature. Continuous-wave (CW) laser output of a Nd:Bi₁₂SiO₂₀ crystal pumped by a laser diode (LD) at 1071.5 nm was achieved with an output power of 65 mW. To our knowledge, this is the first time LD pumped laser output in this crystal has been obtained. These results show that Nd:Bi₁₂SiO₂₀ can serve as a laser crystal.     

Growth of 〈1 0 0〉 directed ADP crystal with slotted ampoule

Good quality ammonium dihydrogen phosphate single crystals have been grown by: (i) Sankaranarayanan–Ramasamy (SR) method and (ii) SR method with slotted ampoule. The grown crystals were subjected to UV–Vis spectroscopy, high-resolution X-ray diffractometer, dielectric, piezoelectric and laser damage threshold studies. Compared to the (1 0 0) plane of the conventional method grown ADP crystal and 〈1 0 0〉 directed SR method grown ADP crystal, the crystal grown by SR method with slotted ampoule has higher growth rate, higher optical transparency, high crystalline perfection, low dielectric loss, high piezoelectric charge coefficient and high laser damage threshold due to diffusion of segregated impurities away from the growing crystal in the slotted ampoule growth.     

Correlation between sintering temperature and properties of ZnO ceramic varistors

The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700–1400 °C. The increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 μm). With increasing sintering temperature up to 1200 °C, the nonlinear region is clearly observed in the I–V characteristics, whereas this region is completely absent only for the sample sintered at 1400 °C. As the sintering temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm, while the nonlinear coefficient is increased in the range of (23.86–47.76). Furthermore, the barrier height decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical band gap is gradually decreased in the range of 3.08–2.70 eV with increasing sintering temperature. These results showed a strong correlation between sintering temperature and the properties of ZnO ceramic varistor.     

Synthesis,growth and characterization of a novel semiorganic nonlinear optical single crystal: l-Asparagine cadmium chloride monohydrate

The semiorganic single crystal of l-asparagine cadmium chloride monohydrate was grown by slow evaporation solution growth technique at room temperature. The presence of various functional groups has been identified by using FT IR spectral analysis ranging between 4000 and 400 cm^?1. Chemical composition of the synthesized material was confirmed by elemental analysis. The crystalline nature of new crystal was confirmed by powder XRD pattern. The UV–vis–NIR spectroscopic study revealed that the grown crystal has good optical transmittance. The dielectric constant has been carried out over a frequency range from 100 Hz to 1 MHz. The mechanical strength was studied using Vicker's microhardness tester.     

Synthesis and growth of sodium bitartrate monohydrate a new organometallic nonlinear optical single crystal

Sodium bitartrate monohydrate (SBTMH) a new organometallic nonlinear optical material, with molecular formula, [C₄H₅NaO₆ · H₂O] has been synthesized at ambient temperature. Spectral, thermal and optical techniques have been employed to characterize the new material. Bulk single crystals of size 13 × 4 × 4 mm³ of SBTMH have been grown by slow cooling method. The unit cell parameters of the grown crystal were determined by single crystal XRD. Functional groups present in the sample were identified by FTIR spectral analysis. Thermal stability of SBTMH was determined using TGA/DTA. The grown crystals exhibit nonlinear properties. The dielectric response of the crystal with varying frequencies was studied. The optical transparency range and the lower cut-off wavelength of the material were identified from the UV–vis–NIR absorption spectrum.     

Optical properties of PMN–PT thin films prepared using pulsed laser deposition

(1 ? x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–PT) thin films have been deposited on quartz substrates using pulsed laser deposition (PLD). Crystalline microstructure of the deposited PMN–PT thin films has been investigated with X-ray diffraction (XRD). Optical transmission spectroscopy and Raman spectroscopy are used to characterize optical properties of the deposited PMN–PT thin films. The results show that the PMN–PT thin films of perovskite structure have been formed, and the crystalline and optical properties of the PMN–PT thin films can be improved as increasing the annealing temperature to 750 °C, but further increasing the annealing temperature to 950 °C may lead to a degradation of the crystallinity and the optical properties of the PMN–PT thin films. In addition, a weak second harmonic intensity (SHG) has been observed for the PMN–PT thin film formed at the optimum annealing temperature of 750 °C according to Maker fringe method. All these suggest that the annealing temperature has significant effect on the structural and optical properties of the PMN–PT thin films.     

Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420–520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338–413 K) and frequency range (200 Hz–5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358–373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (T<363 K) and E=1.09 eV (363 K<T).The frequency dependence of ac conductivity, σ_ac, has been analyzed by Jonscher's universal power law σ(ω)=σ_dc+Aω^s. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound.     

Thermal and electrical conductivities of silver–indium–tin alloys

The variations of thermal conductivity with temperature for the Ag–[x] wt% Sn–20 wt% In alloys (x=8, 15, 35, 55 and 70) were measured using a radial heat flow apparatus. From the graphs of thermal conductivity versus temperature, the thermal conductivities of solid phases at their melting temperature for the Ag–[x] wt% Sn–20 wt% In alloys (x=8, 15, 35, 55 and 70) were found to be 46.9±3.3, 53.8±3.8, 61.2±4.3, 65.1±4.6 and 68.1±4.8 W/Km, respectively. The variations of electrical conductivity of solid phases versus temperature for the same alloys were determined from the Wiedemann–Franz equation using the measured values of thermal conductivity. From the graphs of electrical conductivity versus temperature, the electrical conductivities of the solid phases at their melting temperatures for the Ag–[x] wt% Sn–20 wt% In alloys (x=8, 15, 35, 55 and 70) alloys were obtained to be 0.036, 0.043, 0.045, 0.046 and 0.053 (×10⁸/Ωm), respectively. Dependencies of the thermal and electrical conductivities on the composition of Sn in the Ag–Sn–In alloys were also investigated. According to present experimental results, the thermal and electrical conductivities for the Ag–[x] wt% Sn–20 wt% In alloys linearly decrease with increasing the temperature and increase with increasing the composition of Sn.     

Influence of Zn–Zr ions on physical and magnetic properties of co-precipitated cobalt ferrite nanoparticles

Cobalt ferrite nanoparticles having the chemical formula CoFe_2−2xZr_xZn_xO₄ with x ranging from 0.0 to 0.4 were prepared by chemical co-precipitation method. The powder X-ray diffraction pattern confirms the spinel structure for the prepared compound. The particle size was calculated from the most intense peak (3 1 1) using Scherrer formula. The particle size of the samples was found within the range of 12–23 nm for all the compositions. The magnetic and electrical properties of these materials have been studied as a function of temperature. Activation energy and drift mobility have been calculated from the DC electrical resistivity measurements. Dielectric properties such as dielectric constant and dielectric loss tangent were measured at room temperature in the frequency range 100 Hz–1 MHz.     

Preparation and properties of transparent SnO–P2O5 glasses

Colorless, transparent SnO–P₂O₅ (SP) glasses with 60–70 mol% SnO compositions were prepared by melting at 880–1000 °C in Ar atmosphere using commercial SnO and P₂O₅ powders as raw materials and vitreous carbon crucibles. SP glasses are characterized by glass transition temperature, onset of crystallization, thermal expansion coefficient and weight loss after immersion test. The viscosity of 67SnO–33P₂O₅ glass was measured by a penetration method in the range of 10^7.9–10^10.5 Pa s at 267–290 °C. The results of optical properties show that the transparent SP glasses have high refractive indexes over 1.75 and high transmission over 80% in the visible and IR region of 380 and 2700 nm.     

Unexpected temperature rise in end-pumped Nd3+:YAG composite slab laser

Unexpected temperature rise is observed in end-pumped YAG–Nd³⁺:YAG–YAG slab laser experimentally. The measured optical absorption spectrum of undoped YAG in 780–830 nm indicates an absorption coefficient of 0.015 cm^?1 at 808 nm. The influence of the weak absorption on temperature distribution in end-pumped composite slabs is analyzed numerically and a good agreement with infrared measurement is achieved. The results of finite element analysis show that longer heat sinks and wider slabs bring lower temperature.     

Effect of laser incident energy on the structural,morphological and optical properties of Cu2ZnSnS4 (CZTS) thin films

The polycrystalline Cu₂ZnSnS₄ (CZTS) thin films have been prepared by pulsed laser deposition (PLD) method at room temperature. The laser incident energy was varied from 1.0 at the interval of 0.5–3.0 J/cm². The effect of laser incident energy on the structural, morphological and optical properties of CZTS thin films was studied by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and optical absorption. The studies reveal that an improvement in the structural, morphological and optical properties of CZTS thin films with increasing laser incident energy up to 2.5 J/cm². However, when the laser incident energy was further increased to 3.0 J/cm², leads to degrade the structural, morphological and optical properties of the CZTS thin films.     

The dc and ac properties of potassium trioxalatoferrate (III) trihydrate

The complex potassium trioxalatoferrate (III) trihydrate {K₃(Fe(C₂O₄)₃ · 3H₂O)} was synthesised and characterised by energy dispersion X-ray fluorescence (XRF) and X-ray diffraction (XRD). The electrical and dielectric properties of the complex pellet were studied by ac- and dc-techniques in room temperature and in a temperature range of 293–373 K. The data of the ac conductivity as a function of frequency in a frequency range of 1–100 kHz follow the correlated barrier hopping CBH model and the parameters of the model were determined and connecting them with the optical properties. The temperature dependence of dc conductivity shows that the semiconducting behaviour of conduction phenomenon in the complex is realised by hopping mechanism between localised states and the minimum hopping distance was determined. High relative permittivity of about 30 at 100 kHz was obtained for the complex, which can find technological applications like alternative for the SiO₂ insulator in MOS devices.     

Peculiarities of thermo-optic coefficient under different temperature regimes in optical fibers containing fiber Bragg gratings

Direct experimental measurements of the thermo-optic for fixed temperature intervals (20–200 °C, 200–500 °C, 500–660 °C, 660–780 °C) in fused silica fiber containing fiber Bragg gratings (FBGs) were conducted. The diffraction efficiency of a FBG fluctuated with temperature between 2.01 × 10^? 4 and 0.17 × 10^? 4 while the temperature shift of the Bragg's peak was monitored between 1300 and 1311 nm with sub-Angstrom precision. Numerical simulations were focused on FBG's diffraction efficiency calculations accounting for the temperature drift of the gratings, and found to be in excellent agreement with obtained experimental data.It was found that the first-order thermo-optic coefficient changes between 1.29 and 1.85 × 10^? 5 K^? 1 for the linear fit and at T = 0 °C its value was found to be close to 2.37 × 10^? 5 K^? 1 for the polynomial fit of experimental data. The average thermo-optic coefficient undergoes a minimum in the vicinity of 440 °C. Additional observation indicates a negative sign of the second-order thermo-optic coefficient. The value of thermal expansion coefficient was much less (0.5 × 10^? 6 K^? 1) than that for the average thermo-optic coefficient. Based on the energy dispersive spectroscopy it was determined that thermal erasing of the FBGs at a temperature around 780 °C corresponds to germanium monoxide diffusion out of core in silica-based fibers.     

Structural,dielectric and impedance properties of NaCa2V5O15 ceramics

Polycrystalline sample of NaCa₂V₅O₁₅ (NCV) with tungsten bronze structure was prepared by a mixed oxide method at relatively low temperature (i.e. 630 °C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Microstructural study showed that the grains are uniformly and densely distributed over the surface of the sample. Detailed studies of dielectric properties showed that the compound has dielectric anomaly above the room temperature (i.e. 289 °C), and shows hysteresis in polarization study. The electrical parameters of the compound were studied using complex impedance spectroscopy technique in a wide temperature (23–500 °C) and frequency (10²–10⁶ Hz) ranges. The impedance plots showed only bulk (grain) contributions, and there is a non-Debye type of dielectric dispersion. Complex modulus spectrum confirms the grain contribution only in the compound as observed in the impedance spectrum. The activation energy, calculated from the ac conductivity of the compound, was found to be 0.20–0.30 eV. These values of activation energy suggest that the conduction process is of mixed type (i.e. ionic–polaronic).     

Optoelectronic properties of Ni–GaP diodes with a modified surface

We report the promising results for Ni–GaP Schottky diode structures manufactured on the substrates with chemically-etched nano-scale surface formations that are responsible for a clearly marked luminescence band located at the energy exceeding the band gap of the bulk GaP. The other peculiarity produced by surface patterning concerns a remarkable redshift of material's optical absorption edge. At the room temperature, the height of potential barrier for Ni–GaP structure is 1.8 eV, with the monochromatic sensitivity peaking at 0.35 A/W. The comparative study of diode performance under different light sources exhibited the pronounced linear photocurrent-illumination dependence for about five orders of illumination magnitude, evidencing good optical and electrical quality of Ni–GaP diodes with surface-modified semiconductor substrate.