Linear and nonlinear optical properties of KDP crystals with incorporated Al2O3⋅nH2O nanoparticles

Optical and nonlinear optical properties of a novel composite system based on KDP single crystals with embedded nanoparticles of nanostructured oxyhydroxide of aluminum (Al₂O₃·nH₂O, NOA), were studied. KDP crystals with NOA nanoparticles (KDP:NOA) possess high optical quality and homogeneity. Optical spectroscopy showed the presence of an absorption band at 270 nm caused by NOA nanoparticles incorporated in the KDP matrix. There was observed an enhancement of nonlinear refractive index and inversion of its sign in KDP:NOA crystals in comparison with nominally pure KDP crystals under excitation of picosecond laser pulses. The obtained results demonstrate that KDP:NOA is a promising composite material for optoelectronics and nonlinear optics.     

Linear and nonlinear optical properties and luminescence of Dy+3-doped aluminoborate glasses: Judd–Ofelt investigation

The nominal glasses composition ((40-x) % H₃BO₃—30% CaO—30% Al₂O₃—x Dy₂O₃), where x?=?1, 2, 3, 4, 5 and 6) were prepared using the melt quenching technique. The absorption spectra reveal the common normal 13 transition peaks of the Dy₂O₃-doped glasses. The linear and nonlinear optical properties were calculated. The Photoluminescence spectra and the decay lifetime were examined. The Judd–Ofelt parameters trend was Ω₄?>?Ω₂?>?Ω₆. The oscillator strength of the experimental, and calculated electronic dipole absorption transition were estimated. The radiative life-time, the radiative branching ratio, the emission and absorption transition cross section were also calculated. The gain coefficient of the transitions was predicted. All the calculated parameters were compared with the previous work. The results reveal that the current glasses composition is a good candidate as a lasing host material and the glasses are highly efficient composition when using in the optical communication fibers.

     

Electrical and optical properties of single crystalline α-Al2O3 doped with nickel

Nickel, substituting for aluminium in α-Al₂O₃ acts as an acceptor with a level ∼2.46 eV above the conduction band if a large polaron model applies, ≅ 2.57eV−H(μ _h) above the band if a small polaron model applies. It is present as Ni³⁺ at high, and as Ni²⁺ at low, oxygen pressures, the concentration of Ni³⁺ being reduced to one-half of its high value at =1 Pa. Analysis of the data provides proof that the native defect compensating the charge of Ni²⁺ (=ni _al ^′ ) is V _O ^2. , Al _i ^3. being a minority species; H _F,Al−1/2H _s=121 kJ mol⁻¹.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

The effect of Ge implantation dose on the optical properties of Ge nanocrystals in SiO(2)

Ge nanocrystallites (Ge-nc) embedded in a SiO(2) matrix are investigated using Raman spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. The samples were prepared by ion implantation with different implantation doses (0.5, 0.8, 1, 2, 3 and 4) × 10(16)?cm(-2) using 250?keV energy. After implantation, the samples were annealed at 1000?°C in a forming gas atmosphere for 1?h. All samples show a broad Raman spectrum centred at w≈304?cm(-1) with a slight shift depending on the implantation doses. The Raman intensity also depends on the Ge(74+) dose. A maximum photoluminescence intensity is observed for the sample implanted at room temperature with a dose of 2 × 10(16)?cm(-2) at 3.2?eV. Infrared spectroscopy shows that the SiO(2) films moved off stoichiometry due to Ge(74+) ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO(x) at exactly the dose corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304?cm(-1). Finally, the Raman spectra were fitted with a theoretical expression to evaluate the average size, full-width at half-maximum (FWHM) and dispersion of Ge-nc size.     

Microstructural characterisation and mechanical properties of Ni–Ge alloys containing Ni3Ge

Abstract

Six Ni–Ge alloys were prepared and equilibrated at 1000°C. The microstructures, compositions of phases, solubilities in various phases, volume fractions of phases, lattice parameters of Ni₃ Ge, and microhardness values of phases were determined. Two alloys contained Ni₃Ge and α, one alloy was single phase Ni₃Ge, and three alloys contained Ni₃Ge and Ni₅Ge₃. The volume fractions of second phase were 6 and 33%α and 37 and 54%Ni₅Ge₃. The amount of second phase in the third Ni₃Ge–Ni₅Ge₃ alloy was too low to be determined accurately. The two phase alloys containing 6%α, 37%Ni₅Ge₃, or 54%Ni₅Ge₃ were tested in compression. A yield strength maximum was observed in the three alloys. The deformation behaviour of the alloy containing 6%α was similar to that of single phase Ni₃Ge: crack formation along Ni₃Ge grain boundaries and very low plastic strain were revealed. In alloys containing Ni₃Ge and an appreciable percentage of Ni₅Ge₃, crack formation was not observed along Ni₃Ge grain boundaries. Instead, at low temperatures, deformation and crack growth occurred within Ni₅Ge₃ grains and, at high temperatures, decohesion occurred along the Ni₃Ge/Ni₅Ge₃ interphase. The plastic strain in the alloy containing 54%Ni₅Ge₃ increased to about 40%.

MST/1724     

Sonochemical fabrication and catalytic properties of α-Fe2O3 nanoparticles

In this study, α-Fe₂O₃ (hematite) nanoparticles were synthesised by a sonochemical method. The influence of different factors such as chemical composition of the precursors, atmosphere of the reactions and type of the sonicator on the chemical formula, crystallinity, morphology and size of the obtained products were investigated. Powder X-ray diffraction, scanning electron microscopy and IR spectroscopy, were used to characterise the nanostructures. The catalytic tests were performed in the reaction of methyl phenyl sulphide oxidation. The results exhibit the good catalytic performance of the as-prepared α-Fe₂O₃ nanoparticles.     

Morphology-controllable synthesis and gas-sensing properties of α-MoO3

Different morphologies of orthorhombic molybdenum trioxide (MoO₃) were successfully synthesized through a facile hydrothermal method followed by a subsequent heat treatment. We found that the surfactants played a critical role in the formation process and the possible formation mechanism was discussed. Especially when chromic chloride hexahydrate was added as a surfactant, the unique net-like structure was prepared. Furthermore, the gas-sensing properties of the sample were tested towards the reducing ethanol gas. The results indicated that the MoO₃ with a net-like structure shows the largest response than the other structures.     

Structural,optical and electrical properties of Bi2−xMnxTe3 thin films

Journal of Materials Science: Materials in Electronics - Undoped and Mn doped Bi2Te3 (x = 0, 0.05 and 0.10 at%) thin films were prepared via thermal evaporation method from their bulk alloys. X-ray...     

Preparation and optical properties of transparent glass-ceramics containing LiGa5O8∶ Cr3+

Transparent glass-ceramics containing LiGa₅O₈Cr³⁺ crystallites have been prepared by heat treatment of Li₂O-Ga₂O₃-SiO₂-Cr₂O₃ glassy material. Average crystallite size evaluated from the full-width at half-maximum of the X-ray diffraction lines varies from about 3–7 nm as the heat-treatment temperature increases from 650 °C to 800 °C. The ligand field strength of the Cr³⁺ ion estimated from optical absorption measurements increases with an increase in the heat-treatment temperature. The fluorescence spectra of the glass-ceramics resemble that of LiGa₅O₈ Cr³⁺ polycrystal. In particular, for the specimen containing a crystallite of 7 nm, intense emission due to the ²E⁴A₂ transition has been observed. These optical measurements demonstrate that the Cr³⁺ ions are incorporated into LiGa₅O₈ microcrystals in the present glass-ceramics. For the transparent glass-ceramics and LiGa₅O₈Cr³⁺ polycrystal, the temperature dependence of the peak position of the zero-phonon line (R-line) has been analysed assuming that the electronic transition is described by the Raman process and the vibrational density of state is expressed by the Debye model. The Debye temperature of the transparent glass-ceramics is slightly lower than that of LiGa₅O₈ Cr³⁺ polycrystal, indicating that the softening of the phonon occurs in the LiGa₅O₈Cr³⁺ microcrystal precipitated in the transparent glass-ceramics.     

Transport anomalies and magnetic properties of Sn x Eu1.2−x Mo6S8 alloys

We have measured the resistance R, magnetoresistance, and magnetization of sintered samples of the compounds Sn _x Eu_1.2–x Mo₆S₈, where x = 0, 0.12, 0.24, and 0.48. A large resistance anomaly beginning at T ~ 100 K and extending to low temperatures is found in all of the alloys except x = 0.48, which had a high superconducting transition temperature T _c ~ 11.3 K. The resistance anomaly, which appears to be correlated with the depression of T _c, is also correlated with a large negative magnetoresistance at temperatures T 12 K. For all samples except x = 0.48, that part of the magnetoresistance attributed to spin-flip scattering is proportional to the square of the magnetization M ² and is 30–40% of R (0) for some samples. Magnetization measurements are consistent with a spin-7/2 paramagnetic behavior of Eu²⁺ ions when allowance is made for a concentration of 20–30% nonmagnetic (J = 0) Eu³⁺ ions as determined from Mössbauer measurements. The experimental results are inconsistent with predictions of dilute magnetic alloy Kondo models. We speculate that the resistance anomaly and suppression of T _c for x 0.24 are associated with a semiconductor-like behavior.Work performed under the auspices of the U.S. DOE.Work supported by NSF Research Grant DMR 78-2428.     

Electrical and optical properties of µc-SiH films

Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH₄ + H₂ at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofμc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.     

Composition and thickness dependant optical study of a-Pb–Se–Ge–Sn glassy thin films

Thickness and compositional dependence of optical properties of Pb₉Se₇₁Ge_20?xSn_x (8 ≤ x ≤ 12) glass has been studied. Various optical constants such as refractive index, extinction coefficient and optical band gap have been determined by analyzing optical transmittance data in the wavelength range of 200–3,500 nm. Density of localized states and disorder plays a crucial role in deciding the optical properties of amorphous semiconductors. Refractive index and extinction coefficient increase as Sn content increase in material. With the rise in thickness, there may be increase in order of short range order of the film and continuous random network simultaneously, result in reduced band gap. The isoelectronic substitutions of Ge by Sn in the glassy system also contribute to reduction in optical band gap of the material.     

First principles investigation of electronic, optical and transport properties of α- and β-phase of arsenic telluride

Crystalline arsenic telluride exists in two stable phases. The monoclinic α-phase transforms to rhombohedral β-phase under high pressure. The electronic, optical and transport properties of the two phases has been investigated using full potential linear augmented plane wave (LAPW) + local orbitals (lo) scheme, in the framework of DFT with generalized gradient approximation (GGA). We present the energy bands, density of states and optical properties like the complex dielectric functions and absorption coefficients. From the dynamic dielectric constant, the structural anisotropy for the monoclinic α-phase is clearly observed, whereas the longitudinal and transverse components are almost identical for the β-phase. The optical absorption profiles clearly indicate that β-phase has possibility of greater multiple direct and indirect interband transitions in the infrared and visible regions compared to the α-phase. The rhomohedral phase which has the Bi₂Te₃ type structure has the possibility of thermoelectric properties, therefore transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results.     

Hydrothermal synthesis and magnetic properties of α-MnO2 nanowires

In the present study, one-dimensional (1D) α-MnO₂ nanowires with width of 50–60 nm, length about several micrometers have been successfully prepared under hydrothermal conditions in the presence of sodium carboxymethyl cellulose. The samples were characterized by X-ray diffraction, scanning electron microscope, superconducting quantum interference device and N₂ adsorption–desorption experiment. The magnetic measurement reveals that the α-MnO₂ nanowires exhibit a ferromagnetic behavior at 5 K and a paramagnetic behavior at 300 K. The N₂ adsorption–desorption experiment shows that surface area is 160.4 m² g^?1, which is even larger than those of mesoporous nanostructures. At the same time, the possible formation mechanism for the formation of α-MnO₂ nanowires has been proposed according to the experimental results.     

Study on nonlinear optical,dielectric and pyroelectric properties of novel organic–inorganic hybrid material

A novel organic and inorganic hybrid material was prepared from a nonlinear, optically active imidazole derivative, 4-(nitrophenyl)-2,4-bis-(4,4′-[N,N-bis-(2-hydroxyethyl)aminophen-yl])imidazole (NPAH4), and metal alkoxide of Ta(V) via sol–gel process. The second-order nonlinear and pyroelectric properties of the hybrid film were investigated in terms of the second harmonic generation (SHG) and pyroelectric coefficient measurement. The SHG coefficient d₃₃ was found to be 28.6 pm/V at the fundamental wavelength of 1064 nm and the pyroelectric coefficient P was found to be 1.6×10⁻⁶ C/cm² K.     

Electrical properties and phase transition of Ge1−x Sn x Se2.5 thin films

The Ge_1–x Sn _x Se_2.5 system was prepared by melting the correct ratio of high purity elements in quartz evacuated ampoules followed by quenching in ice. It was found that, within the Ge_1–x Sn _x Se_2.5 system, a glassy state can be formed when 0 x 0.4. On increasing x to 0.6 a glassy state could not be obtained, as is confirmed by X-ray diffraction. Differential thermal analysis (DTA) was carried out to study the effect of composition on the stability of amorphous phase. Ge_1–x Sn _x Se_2.5 (where 0 x 0.6) thin films have been prepared by the thermal evaporation technique. The electrical conductivity of the thin films have been studied as a function of composition and film thickness.     

Improvement of structural and mechanical properties of alumina coatings by incorporation of TiO2 and α-Al2O3 nanoadditives

Abstract

Alumina coatings embedded with different nanoadditives were fabricated on aluminium alloy by microarc oxidation (MAO). Incorporation of nanograins into the prepared coatings was accomplished by dispersing nanoadditives into different electrolytes during the MAO process. Our results show that nanograins are successfully embedded in the ceramic coatings, and the embedded coatings are compact and have lower porosity. The mechanical properties of the nanograin embedded coatings such as hardness, adhesion and wear resistance are consequently improved, and the samples prepared in aluminate electrolyte with α-Al₂O₃ nanoadditive have better mechanical properties than those prepared in other electrolytes. Our results also show that the mechanical properties of MAO coatings are closely related to the surface structure. The introduction mechanism of nanograins into the ceramic coatings resulted from the reactions occurring in the microarc discharge channels such as diffusion and electrophoresis, which is believed to improve the structure of the prepared coatings.