Morphological characterization of TiO2 thin films

Films prepared by reactive magnetron sputtering always present some structural and morphological heterogeneities.In this work, optical parameters, n(λ), k(λ) and E₀, of TiO₂ thin films were obtained, using only optical transmittance measurements. Films were described according to Abèles's model. Using a mono-oscillator type dispersion curve for the refractive index and a Lorentzian type curve for the absorption coefficient, we were able to demonstrate that the films were optically equivalent to a porous layer, with some dispersion in film thickness.The detailed analysis of the experimental transmittance data, fitted between 330 nm to 2200 nm, also enabled us to correlate the effective refractive index of each film with its deposition conditions.     

Optical constants and crystal chemical parameters of Sc2W3O12

The refractive indices of Sc₂W₃O₁₂, measured at wavelengths of 435.8–643.8 nm, were used to calculate n_a = 1.7331, n_b = 1.7510, n_c = 1.7586 at λ = 589.3 nm and n_∞ values at λ = ∞ from a one-term Sellmeier equation. Mean refractive indices, 〈n_D〉, and mean dispersion values, 〈A〉, are, respectively, 1.7475 and 110 × 10^?16 m². Total electronic polarizabilities, α_obs, were calculated from n_∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 28.415 Å³ and the calculated total polarizability α_T of 26.74 Å³ (Δ = +6.3%) is attributed to (1) a large M–O–W angle, and (2) a high degree of W 5d–O 2p and Sc nd–O 2p hybridization, where n signifies unspecified Sc d orbitals.     

Effect of solidification parameters on the microstructure of Sn-3.7Ag-0.9Zn solder

In this work, Sn–Ag–Zn alloy of eutectic composition (Sn-3.7wt.%Ag-0.9wt.%Zn) was directionally solidified upward at a constant temperature gradient (G = 4.33 K/mm) in a wide range of growth rates (V = 3.38–220.12 μm/s) and a constant growth rate (V = 11.52 μm/s) with different temperature gradients (G = 4.33–12.41 K/mm) using a Bridgman type directional solidification furnace. The microstructure was observed to be a rod Ag₃Sn structure in the matrix of β–Sn from the directionally solidified Sn-3.7wt.%Ag-0.9wt.%Zn samples. The values of eutectic spacing (λ) were measured from transverse section of samples. The dependency of eutectic spacing on the growth rate (V) and temperature gradient (G) were determined with linear regression analysis. The dependency of λ on the values of V and G were found to be λ = 10.42V ^? 0.53 and λ = 0.27G ^? 0.48, respectively. The values of bulk growth were also determined to be λ²V = 86.39 μm³/s by using the measured values of λ and V. The results obtained in present work were compared with the previous similar experimental results obtained for binary and ternary alloys.     

Optical constants of thermally evaporated Se–Sb–Te films using only their transmission spectra

Amorphous Se_82 ? xTe₁₈Sb_x thin films with different compositions (x = 0, 3, 6 and 9 at.%) were deposited onto glass substrates by thermal evaporation. The transmission spectra, T(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. Based on the use of the maxima and minima of the interference fringes, a straightforward analysis proposed by Swanepoel has been applied to derive the optical constants and the film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. Tauc relation for the allowed non-direct transition describes the optical transition in the studied films. With increasing antimony content the refractive index increases while the optical band gap decreases. The optical band gap decreases from 1.62 to 1.26 eV with increasing antimony content from 0 to 9 at.%. The chemical-bond approach has been applied successfully to interpret the decrease of the optical gap with increasing antimony content.     

Effect of growth rate on microstructure parameters and microhardness in directionally solidified Ti–49Al alloy

Intermetallics Ti–49Al (at.%) alloy was directionally solidified with different growth rates (V = 5 μm/s–30 μm/s) at a constant temperature gradient (G = 12.1 K/mm) by using a Bridgman type directional solidification furnace. The primary dendritic spacing (λ), interlamellar spacing (λ_L), and microhardness (HV) were measured. Effect of V on HV, λ and λ_L was experimental investigated. The dependencies of λ, λ_L and HV on the growth rate were determined by using linear regressing analysis. According to the result, the values of λ and λ_L decrease with the increasing of V, and the values of HV increase with the increasing of V and with the decreasing of λ and λ_L. The results were compared with previous similar experimental results for TiAl-based alloys.     

Optical constants and band gap determination of Pb0.95La0.05Zr0.54Ti0.46O3 thin films using spectroscopic ellipsometry and UV–visible spectroscopy

We report the structural evolution and optical properties of lanthanum doped lead zirconate titanate (PLZT) thin films prepared on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition. X-ray diffraction demonstrates the post-deposition annealing induced crystallization for PLZT films annealed in a temperature (T_a) range of 550–750 °C. PLZT films annealed at higher temperature exhibit polycrystalline structure along with larger grain size. Optical band gap (E_g) values determined from UV–visible spectroscopy and spectroscopic ellipsometry (SE) for PLZT films were found to be in the range of 3.5–3.8 eV. E_g decreases with increasing T_a. The optical constants and their dispersion profiles for PLZT films were also determined from SE analyses. PLZT films show an index of refraction in the range of 2.46–2.50 (λ = 632.8 nm) with increase in T_a. The increase in refractive index at higher T_a is attributed to the improved packing density and crystallinity with the temperature.     

Irreversible photobleaching,photorefraction and photoexpansion in GeS2 amorphous film

The photoinduced irreversible effects in thermally evaporated amorphous GeS₂ films were investigated. The magnitude of the photobleaching induced by gap photons was found at around ≈13%. The photoinduced increase in the optical band gap and the increase in the slope of the short wavelength absorption edge are discussed within the Davis–Mott model and within Tauc's model for optical transitions in amorphous solids. Based on the optical measurements and the Atomic Force Microscopy we also observed photoexpansion at around ≈4.8% accompanied by a decrease in the refractive index from n = 2.02 for the virgin film to n = 1.94 for a film illuminated until a nearly steady state.     

Interplay between random laser performance and self-frequency conversions in NdxY1.00−xAl3(BO3)4 nanocrystals powders

Random Laser emission at 1.06 μm, self-second-harmonic generation at 0.53 μm and self-sum-frequency generation at 0.46 μm were investigated in Nd_xY_1.00−xAl₃(BO₃)₄ nanocrystalline powders, for 0.05 ⩽ x ⩽ 1.00, excited by a pulsed laser operating at 808 nm, focusing on the interplay between the RL performance and the second-order nonlinear processes. The RL performance, characterized by a figure-of-merit relating the laser slope efficiency and the excitation pulse energy threshold, improved as x increased up to 1.00 while the efficiency of the self-frequency conversion processes reduced for increasing x because of distortions introduced in the crystalline structure of the grains. The RL wavelength was also dependent on the Nd³⁺ concentration and presented a redshift from 1061.9 nm to 1063.5 nm for increasing values of x.     

Distribution,structures and nonlinear properties of noncentrosymmetric titanates

The difference has been revealed between the statistical distributions of centrosymmetric and noncentrosymmetric titanates over crystal symmetry systems. Space formations of Ti–O polyhedra has been analyzed for 52 noncentrosymmetric titanates. The type of Ti–O polyhedra space formations is dependent on the stoichiometric ratio, SR = n(O)/n(Ti), where n(O) is the number of oxygen and n(Ti) is the number of titanium atoms in formal composition of the compound. Individual (Ti–O) polyhedra are found for SR ≥ 3.5 (SR ≥ 6 for octahedra), chains and layers of the polyhedra exist in the range stoichiometric ratio, SR = 3.5–7.0. Only framework formations are possible at SR ≤ 3.5.     

Synthesis,optical and thermal characterization of novel thiazolyl heterocyclic azo dye

Thiazolyl heterocyclic azo dye and its metal (Ni²⁺, Co²⁺)–azo complexes were synthesized. Their structures were confirmed by elemental analysis, UV–VIS absorption spectra, FT-IR, ¹H NMR and MALDI-MS. The thermal properties of metal complexes were studied by DSC–TGA. The optical constants (complex refractive index N = n + ik) and thickness of the complex thin films on polished single-crystal silicon substrates were investigated on a scanning ellipsometer. Results indicate that thiazolyl metal–azo complexes possess good optical and thermal properties. They would be a promising recording medium candidate for NVD with the Super-resolution near field structure (Super-RENS) technology.     

Crack growth behavior of 7075-T6 under biaxial tension–tension fatigue

Crack growth behavior of aluminum alloy 7075-T6 was investigated under in-plane biaxial tension–tension fatigue with stress ratio of 0.5. Two biaxiality ratios, λ (=1 and 1.5) were used. Cruciform specimens with a center hole, having a notch at 45° to the specimen’s arms, were tested in a biaxial fatigue test machine. Crack initiated and propagated coplanar with the notch for λ = 1 in L–T orientation, while it was non-coplanar for λ = 1.5 between L–T and T–L orientations. Uniaxial fatigue crack growth tests in L–T and T–L orientations were also conducted. Crack growth rate in region II was practically the same for biaxial fatigue with λ = 1 in L–T orientation and for the uniaxial fatigue in L–T or T–L orientations, while it was faster for biaxial fatigue with λ = 1.5 at a given crack driving force. However, fatigue damage mechanisms were quite different in each case. In region I, crack driving force at a given crack growth rate was smallest for biaxial fatigue with λ = 1.5 and for uniaxial fatigue in T–L orientation, followed by biaxial fatigue with λ = 1 and uniaxial fatigue in L–T orientation in ascending order at a given crack growth rate.     

Laser surface melting of a complex high alloy steel

The effect of laser surface melting (LSM) on the microscopic morphology of a complex high alloy steel has been examined in single track experiments. Different combinations of power (1–4 kW) and scan speed (500–1000 mm min⁻¹) were selected in order to obtain a range of depths of melt penetration. An increase in the depth of melt penetration has correlated with rise in the estimated surface temperature induced by laser melting. Within the strongly refined structure of the laser melted alloy, the interdendritic spacing, λ varied from 0.29 μm to 0.97 μm with increase in the depth of melt penetration. The microhardness in the laser surface melted region has been shown to decrease linearly with λ^−0.5.     

Spectroscopic ellipsometry and magneto-transport investigations of Mn-doped ZnO nanocrystalline films deposited by a non-vacuum sol–gel spin-coating method

Nanocrystalline Zn_1?xMn_xO films (x = 0, 0.05, 0.1, 0.15, and 0.2) were deposited onto corning glass substrates by a non-vacuum sol–gel spin coating method. All of the films were annealed at 450 °C for 2 h. The structural, optical and magneto-transport properties were investigated by X-ray diffraction, spectroscopic ellipsometry and a system for the measurement of the physical properties. X-ray diffraction analysis of the films reveals that the Mn-doped ZnO films crystallize in the form of a hexagonal wurtzite-type structure with a crystallite size decreases with an increase of the Mn concentration. It was also found that the microstrain increases with the increase of the Mn content. Evidence of nanocrystalline nature of the films was observed from the investigation of surface morphology using transmission, scanning electron microscopy and atomic force microscopy. The optical constants and film thicknesses of nanocrystalline Zn_1?xMn_xO films were obtained by fitting the spectroscopic ellipsometric data (ψ and Δ) using a three-layer model system in the wavelength range from 300 to 1200 nm. The refractive index was observed to increase with increasing Mn concentration. This increase in the refractive index with increasing Mn content may be attributed to the increase in the polarizability due to the large ionic radius of Mn²⁺ compared to the ionic radius of Zn²⁺. The optical band gap of the nanocrystalline Mn–ZnO films was determined by an analysis of the absorption coefficient. The direct transition of the series of films was observed to have energies increasing linearly from 3.17 eV (x = 0) to 3.55 eV (x = 0.2). Magnetoresistance (MR) was measured from 5 K to 300 K in a magnetic field of up to 6 T. Low-field positive MR and high-field negative MR were detected in Mn-doped ZnO at 5 K. Only negative MR was observed for temperatures above 200 K. The positive MR in Mn-doped ZnO films was observed to decrease drastically when the temperature increased from 5 K to 100 K. The isothermal MR of Zn_1?xMn_xO films with different Mn concentrations at 5 K reveals that the increase of the Mn content induces a giant positive MR above x = 0.05 and reaches up to 55% at an applied field of 30 kOe for x = 0.2.     

Investigation on third order nonlinear optical,electrical and surface properties of organic stilbazolium crystal of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate

The third order nonlinear optical, electric and dielectric properties of an organic stilbazolium derivative of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate (DSMOS) crystal are reported. The nonlinear refractive index (n₂), two photon absorption coefficient (β) and third order optical susceptibility χ⁽³⁾ have been measured by Z-scan technique using Gaussian beam from the Nd:YAG laser at 1064 nm. The results show a large negative nonlinear refractive index (n₂ = −1.122 × 10−9 cm²/W) with a molecular two photon absorption coefficient β value of 3.625 × 10⁻⁶ cm/W. The low dielectric constant observed in the high frequency region indicates the suitability of the sample for electro-optic applications. The surface features are also investigated by atomic force microscopy (AFM).     

Influence of annealing on the optical properties of 5,10,15,20-tetraphenyl-21H, 23H-porphine iron (III) chloride thin films

Optical constants (refractive index, n, and absorption index, k) of the as-deposited and annealed films of 5,10,15,20-tetraphenyl-21H, 23H-porphine iron (III) chloride (FeTPPCl) have been obtained in the wavelength range 190–2500 nm by using spectrophotometric measurements. The obtained optical constants were used to estimate the type of transition for the as-deposited and annealed films. We present a single oscillator model that describes the dispersion of refractive index. Drude model of free carriers absorption have been described for the analysis the dispersion of refractive index dispersion before and after annealing.     

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (0001) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 μm were grown in the temperature range 700–720 °C. The growth rate of ZnO films was estimated to be 0.3 μm h^− 1. Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films.     

Achieving a weak basal texture in a Mg–6Al–3Sn alloy by wave-shaped die rolling

An innovative rolling approach was proposed to achieve weak basal texture in rolled Mg alloy sheets, by laying a wave-shaped die during rolling. It was shown that, Mg–6Al–3Sn (AT63) alloy sheets processed by this wave-shaped die rolling (labeled as WDR) exhibited basal textures with low intensity and tilted basal peak. A substantial basal texture weakening was found to occur during WDR after a single pass. Moreover, the WDRed alloy sheets exhibited basal texture gradients through the center to the surface, reflecting the asymmetric deformation mode of the sheets during rolling. In addition, WDR was effective to refine the grain size of AT63 alloy, from ~ 35 μm to ~ 10.3–11.5 μm. Tensile tests revealed that, the WDRed AT63 sheets presented much enhanced strain hardening ability (n = 0.295) and high elongation to failure (ε_f = 22.5%), as compared with the equivalent AT63 sheet rolled without wave-shaped die.     

Temperature-dependent Sellmeier equations of nonlinear optical crystal Na3La9O3(BO3)8

The principal refractive indices of Na₃La₉O₃(BO₃)₈ (NLBO) crystal in the wavelength range of 0.363–2.325 μm were accurately measured by using the minimum deviation method within the temperature range from 23.5 °C to 160 °C. We derived the expressions of thermal refractive index coefficient as a function of wavelength that could be used to calculate the principal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also derived and used to calculate the phase-matching (PM) angles for a frequency conversion device based on NLBO crystal at different temperatures. We found that the thermal refractive index coefficients of NLBO crystal changed from positive to negative values with the increase of wavelength. In addition, the phase matching conditions for third harmonic generation (THG) at different temperatures were also investigated.     

Thickness dependence of optical parameters for Ge–Se–Te thin films

The present work deals with thickness dependent study of the thin films of Ge₁₀Se_90 − xTe_x (x = 0, 10) chalcogenide glasses. Bulk samples of Ge₁₀Se₉₀ and Ge₁₀Se₈₀Te₁₀ have been prepared by melt quenching technique. Thin films (thickness d = 800 nm and 1100 nm) of the prepared samples have been deposited on glass substrate using vacuum evaporation technique. The optical parameters i.e. optical band gap (E_g^opt), absorption coefficient (α), refractive index (n) and extinction coefficient (k) are calculated from the transmission spectrum in the range 400–1500 nm. The optical band gap decreases with the increase of thickness from 1.87 ± 0.01 eV (d = 800 nm) to 1.80 ± 0.01 eV (d = 1100 nm) for Ge₁₀Se₉₀ and from 1.62 ± 0.01 eV (d = 800 nm) to 1.48 ± 0.01 eV (d = 1100 nm) for Ge₁₀Se₈₀Te₁₀ thin films.     

Non-isothermal flow of a power law fluid past a rectangular obstacle (of aspect ratio 1 × 2) in a channel: Drag and heat transfer

A two-dimensional numerical study has been carried out to investigate the drag and Nusselt number characteristics under forced convection conditions between a streaming power law liquid and a rectangle (with its longer side aligned with the direction of flow) placed symmetrically between two solid walls. In particular, the values of the individual and total drag coefficients, and of the Nusselt number are obtained as functions of the flow behaviour index (1.4 ⩾ n ⩾ 0.5), of Reynolds number (5 ⩽ Re ⩽ 40) and of the Peclet number (5 ⩽ Pe ⩽ 400) for a fixed value of the blockage ratio (1/8). Within these ranges of kinematic and rheological conditions, the drag and Nusselt number show only fair to moderate deviation from the corresponding Newtonian values at the same values of the Reynolds and Peclet numbers. Qualitatively speaking, the shear-thinning behaviour (n < 1) augments the drag and heat transfer while the shear-thickening behaviour (n > 1) causes both the drag and heat transfer to drop below the corresponding Newtonian values. The power-law fluid behaviour does not seem to alter the streamline, isovorticity and isotherm plots in a significant manner, except for the fact that the shear-thinning behaviour not only delays the formation of a visible wake but the resulting wake is also somewhat shorter than that in a Newtonian fluid. The shear thickening, on the other hand, has exactly the opposite influence on wake formation.