Z-scan determination of the third-order optical nonlinearity of a triphenylmethane dye using 633 nm He–Ne laser

The third-order nonlinear optical response of a triphenylmethane dye (Acid blue 7) was studied using the Z-scan technique with a continuous-wave He–Ne laser radiation at 633 nm. The magnitude and sign of the third-order nonlinear refractive index n₂ of aqueous solution of Acid blue 7 dye were determined; the negative sign indicates a self-defocusing optical nonlinearity in the sample studied. The negative nonlinear refractive index n₂ and nonlinear absorption coefficient β were estimated to be −1.88 × 10⁻⁷ cm²/W and −3.08 × 10⁻³ cm/W, respectively, corresponding to Re(χ⁽³⁾) = −8.35 × 10⁻⁶ esu, and Im(χ⁽³⁾) = −6.88 × 10⁻⁷ esu. The experimental results show that Acid blue 7 dye have potential applications in nonlinear optics.     

Transport properties of SrCe0.95Y0.05O3−δ and its application for hydrogen separation

Transport properties of SrCe_0.95Y_0.05O_3−δ were studied by impedance spectroscopy and by measuring open-cell voltage (OCV) and gas permeation. Ionic transference numbers were determined by measuring the OCV of concentration cells and water vapor evolution of an O₂/H₂ fuel cell. We observed interfacial polarization on the basis of the I–V curves obtained by discharging a hydrogen concentration cell or an O₂/H₂ fuel cell. The observed high protonic conductivity (high proton and low oxide ion transference numbers) makes SrCe_0.95Y_0.05O_3−δ a potential material for hydrogen separation. From proton conductivity measurements, under a given hydrogen partial pressure difference of 4%/0.488%, the hydrogen permeation rate (of a dense membrane with 0.11 cm in thickness) was calculated to be ≈0.072 cm³ (STP) cm⁻² min⁻¹ at 800°C, whereas the permeation rate calculated from short-circuit current measurements was ≈0.023 cm³ (STP) cm⁻² min⁻¹ at 800°C. The difference between calculated and observed permeation rates is probably due to interfacial polarization.     

Characterization of optical and nonlinear optical properties of silver nanoparticles prepared by laser ablation in various liquids

The optical, structural, and nonlinear optical properties of silver nanoparticles prepared by laser ablation in various liquids were investigated at 397.5, 532, and 795 nm. The TEM and spectral measurements have shown temporal dynamics of size distribution of Ag nanoparticles in solutions. The thermal-induced self-defocusing dominated in the case of high pulse repetition rate as well as in the case of nanosecond pulses. In the case of low pulse repetition rate, the self-focusing (γ = 3 × 10⁻¹³ cm² W⁻¹) and saturated absorption (β = −1.5 × 10⁻⁹ cm W⁻¹) of picosecond and femtosecond radiation were observed in these colloidal solutions. The nonlinear susceptibility of Ag nanoparticles ablated in water was measured to be 5 × 10⁻⁸ esu (at λ = 397.5 nm).     

Preparation of high purity spherical γ-alumina using a reduction-magnetic separation process

A purified alumina hydrosol has been prepared by removing metal impurities using a new reduction-magnetic separation process. The amount of iron in the alumina hydrosol was reduced by over 78% from 0.0094% to 0.0020%. As a result of co-crystallization, the copper content was simultaneously reduced from 0.0003% to 0.0001%. Spherical γ-alumina granules were prepared by the oil-drop method using the purified alumina hydrosol as starting material. The γ-alumina granules had a bulk density of about 0.50 g cm⁻³, crush strength of around 90N per granule, specific surface area of about 200 m² g⁻¹ and pore volume of about 0.75 cm³ g⁻¹. The purification process employed during the preparation of the alumina hydrosol had no effect on the physical properties, pore structure and crystal structure of the final spherical alumina granules.     

Ion-pair and triple-ion studies of some tetraalkylammonium halides in pure 1,3-dioxolane at 298.15 K

Conductivities of some tetraalkylammonium halides, viz. tetramethylammonium iodide (Me₄NI), tetraethylammonium bromide (Et₄NBr), tetraethylammonium iodide (Et₄NI), tetra-n-propylammonium bromide (Pr₄NBr), tetra-n-butylammonium bromide (Bu₄NBr), tetra-n-butylammonium iodide (Bu₄NI) and tetra-n-heptylammonium bromide (Hp₄NBr) were measured at 298.15 K in 1,3-dioxolane which has a low permittivity (ε = 7.13). A minima in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed for concentrations which were dependant upon both the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M⁺ + X⁻ ↔ MX, K_P) and triple-ions (2M⁺ + X⁻ ↔ M₂X⁺; M⁺ + 2X⁻ ↔ MX₂⁻, K_T). A linear relationship between the triple-ion formation constants [log (K_T/K_P)] and the salt concentrations at the minimum conductivity (log C_min) was given for all the salts in 1,3-dioxolane. The formation of triple-ions might be attributed to the ion sizes in solutions in which Coulombic interactions and non-Coulombic interactions act as the main forces between the ions (R₄N⁺…..X⁻).     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Population lensing effect in Cr:LiSAF probed by Z-scan technique

An experiment has been performed for measuring a nonlinear refractive index that is due to the polarizability difference Δ_P between excited (⁴T₂) and ground (⁴A₂) states in a Cr³⁺:LiSAF crystal at λ = 647 nm. The latter one is responsible for a population lensing effect which has been monitored by using the eclipsing Z-scan technique. We have performed a data analysis that allows to distinguish between thermal and population contributions to the lensing effect. We have found Δ_P = 4.6 × 10⁻²⁵ cm³ which is in a good agreement with our previous measurements with a different technique.     

The third-order optical nonlinearity of The pyrochlore phase 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 thin film on quartz

The xPb(Mg_1/3Nb_2/3)O₃–(1−x)PbTiO₃ (PMNT) (with x=0.7) thin film is prepared on quartz substrates prepared using a sol–gel process. The PMNT thin film has a well-crystallized pyrochlore phase structure. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refraction index coefficient γ, the nonlinear absorption coefficient β of the thin film are 1.37×10⁻¹² cm²/W and −6.73×10⁻⁸ m/W, respectively. The real and imaginary part of the third-order nonlinear susceptibility of the film are 1.06×10⁻¹⁷ and −1.65×10⁻¹⁹ m²/V², respectively. The results suggested that the nonlinearity is dominated by the refractive for the film.     

Structural and electrical properties of crystalline (1−x)Ta2O5−xTiO2 thin films fabricated by metalorganic decomposition

Polycrystalline (1−x)Ta₂O₅−xTiO₂ thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO₂ layer was formed at the (1−x)Ta₂O₅−xTiO₂/Si interface. Thin films with 0.92Ta₂O₅–0.08TiO₂ composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×10¹¹ cm⁻² eV⁻¹, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm² was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10⁻⁹ A/cm² up to an applied electric field of 6 MV/cm.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Deuterium conductivity, diffusion and implantation in Sr-doped LaYO3

A study of deuterium conductivity and diffusion in the oxide perovskite La_0.9Sr_0.1YO_3−δ is presented in this work. Deuterium ions were implanted into La_0.9Sr_0.1YO_3−δ (50 keV, 1×10¹⁶ atoms/cm²) and the corresponding deuterium depth profile was determined by SIMS and compared with a Monte Carlo simulation (TRIM96). This implant was used as a standard for the determination of deuterium concentration in a La_0.9Sr_0.1YO_3−δ sample pre-treated in D₂O atmosphere. In this way, it was fully confirmed that La_0.9Sr_0.1YO_3−δ incorporates water at high temperatures. The conductivity of La_0.9Sr_0.1YO_3−δ was measured in D₂O atmosphere and compared with other proton (deuteron) conductors. Concentration and conductivity data were used in conjunction to estimate the deuterium diffusivity and the constant of reaction of (heavy) water incorporation into LaYO₃. Some comments on the catalytic activity of this oxide are made.     

Z-scan study of third-order optical nonlinearities in bismuth-based glasses

The third-order optical nonlinearity was measured in bismuth-based glasses by Z-scan technique using femto-second laser pulses. Re(χ⁽³⁾) = 4.9 × 10⁻¹¹ esu at 748 nm was obtained in the glass containing 65.5 mol% of Bi₂O₃. Although, the wavelength dependence of Re(χ⁽³⁾) shows resonant effect significantly, relatively small nonlinear absorption coefficient β = 0.8 cm/GW at 769 nm was estimated. Bismuth-based glass exhibits the largest third-order optical nonlinearity in oxide glasses, indicating they are promising materials used for nonlinear optical devices.     

Structural and compositional analysis of InBixAsySb(1−x−y) films grown on GaAs(0 0 1) substrates by liquid phase epitaxy

The growth of epitaxial InBi_xAs_ySb_(1−x−y) layers on highly lattice mis-matched semi-insulating GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Orientation and single crystalline nature of the film have been confirmed by X-ray diffraction. Scanning electron micrograph shows abrupt interface at micrometer resolution. Surface composition of Bi(x) and As(y) in the InBi_xAs_ySb_(1−x−y) film was measured using energy dispersive X-ray analysis and found to be 2.5 and 10.5 at.%, respectively, and was further confirmed with X-ray photoelectron spectroscopy. Variation of the composition with depth of the film was studied by removing the layers with low current (20 μA) Ar⁺ etching. It was observed that with successive Ar⁺ etching, In/Sb ratio remained the same, while the As/Sb and Bi/Sb ratios changed slightly with etching time. However after about 5 min etching the As/Sb and Bi/Sb ratios reached constant values. The room temperature band gap of InBi_0.025As_0.105Sb_0.870 was found to be in the range of 0.113–0.120 eV. The measured values of mobility and carrier density at room temperature are 3.1×10⁴ cm² V⁻¹ s⁻¹ and 8.07×10¹⁶ cm⁻³, respectively.     

Methane mobility in carbon nanotubes

Quasi-elastic neutron scattering has been used to characterize the diffusivity of CH₄ molecules condensed in single-wall carbon nanotubes. It is shown that the two sites of adsorption, previously observed by adsorption volumetry and calorimetry measurements, correspond to a solid-like phase for the more strongly bound site at T<120 K and to a liquid-like component for the more weakly bound site at 70<T<120 K. The diffusion coefficients of the mobile molecules range between 3×10⁻⁷ to 15×10⁻⁷ cm² s⁻¹. The fraction of this viscous liquid diminishes as the temperature is decreased; the adsorbate is fully solidified at 50 K and below.     

Optical constants of Tl4Ga3InSe8 layered single crystals

The optical properties of Tl₄Ga₃InSe₈ layered single crystals have been studied by means of transmission and reflection measurements in the wavelength range of 500–1100 nm. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.94 and 2.20 eV, respectively. Transmission measurements carried out in the temperature range of 10–300 K revealed that the rate of change of the indirect band gap with temperature is γ=−4.1×10⁻⁴ eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0)=2.03 eV. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index were found to be 4.10 eV, 23.17 eV, 6.21×10¹³ m⁻² and 2.58, respectively. From X-ray powder diffraction study, the parameters of monoclinic unit cell were determined.     

Davydov splitting and two-photon excitation of cadmium tungstate (CdWO4) single crystal phosphorescence

Phosphorescence characteristics of CdWO₄ excited by one-photon (λ = 308 nm) and two-photon (λ = 570–590 nm) processes were measured. A Davydov splitting of 120 ± 20 cm⁻¹ was obtained in the phosphorescence spectra, suggesting a diffusion coefficient of about 1.2 × 10⁻² cm² s⁻¹, and a diffusion length of about 3.1 × 10⁻⁴ cm for the room temperature measured lifetime of 8μs. The phosphorescence quantum efficiency was less than 2% at low temperatures (only 0.25% at room temperature), indicating that the dominant decay mechanism was radiationless. The radiative lifetime was thus estimated as 1–2 ms. The two-photon phosphorescence excitation is characterized by an absorption cross-section of the order of 10⁻⁴⁹cm⁴s.     

Electrode contact study for SiGe thin film operated at high temperature

A study on the electrode contact of the sputtered SiGe thin film is reported for application of devices working at high temperature. Surface morphological characterization with optical microscope and AFM (atomic force microscope) together with the electrical characterization by TLM measurements (transmission line method) were performed before and after aging at 500 °C for 24 h using various sputtered multilayer electrodes, Ti/Au/Ti, Ta/Pt/Ta and Ti/Pt/Ti, on 300-nm B-doped SiGe thin film deposited by magnetron sputtering and furnace crystallisation at high temperature. After aging at 500 °C for 24 h, the Ti/Au/Ti multilayer electrodes seriously degraded to be non-ohmic contact, showing rough surface morphology. The Ti/Pt/Ti metal layers showed the lowest specific contact, resistivity before and after aging, 1.46 × 10⁻³ Ω cm² and 1.68 × 10² Ω cm² respectively.     

MBE grown type-II MWIR and LWIR superlattice photodiodes

We report on the status of GaSb/InAs type-II superlattice diodes grown and fabricated at the Jet Propulsion Laboratory designed for infrared absorption 2–5 μm and 8–12 μm bands. Recent LWIR devices have produced detectivities as high as 8 × 10¹⁰ Jones with a differential resistance–area product greater than 6 Ohm cm² at 80 K with a long wavelength cutoff of approximately 12 μm. The measured internal quantum efficiency of these front-side illuminated devices is close to 30% in the 10–11 μm range. MWIR devices have produced detectivities as high as 8 × 10¹³ Jones with a differential resistance–area product greater than 3 × 10⁷ Ohm cm² at 80 K with a long wavelength cutoff of approximately 3.7 μm. The measured internal quantum efficiency of these front-side illuminated MWIR devices is close to 40% in the 2–3 μm range at low temperature and increases to over 60% near room temperature.     

EPR study of erbium-impurity complexes in silicon

Electron paramagnetic resonance (EPR) measurements have been used to characterise Er complexes formed in FZ silicon by the implantation of erbium together with either oxygen or fluorine. The samples have a 2 μm thick layer containing 10¹⁹ Er/cm³ alone or in addition 3×10¹⁹ O/cm³, 10²⁰ O/cm³ or 10²⁰ F/cm³. Various post-implantation anneals were carried out. Several different erbium centres, which have either C_1h monoclinic or trigonal symmetry, are observed and the way in which the type of centre depends on the implantation and annealing conditions is reported.     

Optical second-harmonic investigations of the isothermal desorption of SiO from the Si(100) and Si(111) surfaces

The isothermal desorption of SiO from the Si(100) and Si(111) surfaces was investigated by means of optical second-harmonic generation (SHG). Due to the high adsorbate sensitivity of this method, desorption rates could be measured over a wide range from 10⁻¹ to 10⁻⁶ ML s⁻¹. From their temperature dependence between 780 and 1000 K, activation energies of E_A=3.4±0.2 eV and E_A=4.0±0.3 eV and pre-exponential factors of ν₀=10^16±1 s⁻¹ and ν₀=10^20±1 s⁻¹ for SiO desorption were obtained for Si(100) and Si(111), respectively. In the case of the Si(100) surface, a pronounced decrease of the first-order rate constants was observed upon increasing the initial coverage from 0.02 to 0.6 ML. The results are interpreted in terms of coverage-dependent oxygen-binding configurations, which influence the stability of the oxide layer.