Effect of thermal treatment on the nonlinear optical response and stability of hybrid inorganic-organic films

Hybrid inorganic-organic second-order nonlinear optical (NLO) materials have been obtained through hydrolysis and co-condensation between tetraethyl silicate (TEOS), Vinyltriethoxysilane (VTES) and an alkoxysilane dye (ICTES-DR1). The hybrid materials showed a thermal stability up to 306 °C in thermogravimetric analysis (TGA) thermograms and no visible glass transition temperature (T_g) was observed in the range 50-200 °C in differential scanning calorimetry (DSC) thermograms. The poling profiles of the hybrid films were investigated by using the in situ second harmonic generation (SHG) measurement. The thermal stability of the second order NLO properties of the poled films were also investigated by the in situ SHG intensity probing. It has been shown that the NLO response and its thermal stability were strongly dependent on the thermal pretreatment of the films.     

Thermal, mechanical, and electronic properties of glycine-sodium nitrate crystal

Glycine-sodium nitrate, C₂H₅N₂NaO₅ (GSN), crystals were grown from aqueous solutions by slow cooling with a temperature lowering rate of 1 °C/day in the range of 40-22 °C. These crystals were analyzed by differential thermal and thermogravimetric analysis (DTA-TGA) and mechanical hardness tester in order to obtain their thermal and mechanical properties. Mechanical characterization was done by studying the variation of microhardness with applied load. The dielectric properties of GSN were calculated by using the CASTEP code within the framework of the generalized gradient approximation (GGA). For better understanding of the optical properties of GSN, the second derivative of ε₂(E) was evaluated. DTA-TGA analysis showed that the material has a thermal stability up to 198 °C. The microhardness test was carried out for several faces of GSN crystals, and the tests revealed a load dependence to hardness. Analysis of the second derivative of ε₂(E) allowed to obtain better resolution of the electronic transitions involving the energy bands. Besides, a theoretical representation of the orbitals’ energy diagram was obtained. A discussion about the relation of structure-properties and molecular character of GSN is presented here.     

Nickel ion—A structural probe in BaO-Al2O3-P2O5 glass system by means of dielectric, spectroscopic and magnetic studies

BaO-Al₂O₃-P₂O₅ glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant ε′, loss tan δ, AC conductivity σ_AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiO?0.6 mol%.     

Planar quarter wave stacks prepared from chalcogenide Ge-Se and polymer polystyrene thin films

Planar quarter wave stacks based on amorphous chalcogenide Ge-Se alternating with polymer polystyrene (PS) thin films are reported as Bragg reflectors for near-infrared region. Chalcogenide films were prepared using a thermal evaporation (TE) while polymer films were deposited using a spin-coating technique. The film thicknesses, d∼165 nm for Ge₂₅Se₇₅ (n=2.35) and d∼250 nm for polymer film (n=1.53), were calculated to center the reflection band round 1550 nm, whose wavelengths are used in telecommunication. Optical properties of prepared multilayer stacks were determined in the range 400-2200 nm using spectral ellipsometry, optical transmission and reflection measurements. Total reflection for normal incidence of unpolarized light was observed from 1530 to 1740 nm for 8 Ge-Se+7 PS thin film stacks prepared on silicon wafer. In addition to total reflection of light with normal incidence, the omnidirectional total reflection of TE-polarized light from 8 Ge-Se+7 PS thin film stacks was observed. Reflection band maxima shifted with varying incident angles, i.e., 1420-1680 nm for 45° deflection from the normal and 1300-1630 nm for 70° deflection from the normal.     

Investigation on substituent effect in novel azo-naphthol dyes containing polymethacrylates for nonlinear optical studies

A novel structurally isomeric and free-radically polymerizable methacrylates bearing azo-naphthol group in the side chain spaced away from the backbone by a hexamethylene spacer and substituted in 4-position with electron-withdrawing and donating substituent were synthesized for NLO applications. These polymers were characterized by UV, IR, ¹H-NMR and ¹³C-NMR spectroscopy. The photoisomerization properties of all the polymers were studied. The glass transition temperature and thermal stability of the polymers were investigated by DSC and TGA, respectively. The third-order nonlinear optical properties of the polymer film were measured by the Z-scan technique using Ar-ion laser and exhibits negative optical nonlinearity. The results revealed that these polymers possess potential applications in nonlinear optics.     

Synthesis, growth and characterization of novel second harmonic nonlinear chalcone crystal

Nonlinear optical (NLO) materials are useful in many of the industrial applications. New NLO chalcone derivative (2E)-3-[4-(methylsulfanyl)phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (4N4MSP) crystals have been grown by slow evaporation technique at ambient temperature. The grown crystals were subjected to single crystal X-ray diffraction study. The crystal has noncentrosymmetric structure in the orthorhombic system with space group Aba2 and unit cell parameters a=14.0647(15) Å, b=33.738(4) Å and c=6.0039(6) Å. To confirm the presence of various functional groups in the compound, FT-IR spectrum was recorded. The crystal was subjected to TGA/DTA analysis to find its thermal stability. The grown crystals were characterized for their optical transmission and mechanical hardness. The second harmonic generation (SHG) efficiency of the crystal is obtained by classical powdered technique using Nd:YAG laser and its value is 28.57 times that of urea. The laser damage threshold for 4N4MSP crystal was determined using Q-switched Nd:YAG laser. The refractive index values for green and red wavelengths were measured by Brewster angle technique. The dielectric and electrical measurements were carried out to study the different polarization mechanism and conductivity of the crystal. Good thermal, mechanical, transmission and SHG response make it desirable for the NLO applications.     

Mechanical and Thermal Properties of Poly(Tetrahydrofurfuryl Methacrylate) Nano-Composites

To obviate the brittleness and improve the mechanical properties of poly(tetrahydrofurfuryl methacrylate) (PTHFMA), clay mineral nano-composites of PTHFMA with two different montmorillonites (MMT), Cloisite® 20A and Cloisite® 30B, were prepared. The mechanical properties were investigated by dynamic mechanical analysis (DMA) and nanoindentation. The thermal properties of the nano-composites were studied using thermogravimetric analysis (TGA). According to the DMA results, tanδ was increased by addition of the clay, leading to the improvement in the mechanical properties which was also confirmed by the nanoindentation results. TGA thermograms showed better thermal stability for the nano-composites compared to that of the homopolymer. Considering all results, the clay mineral polymer nano-composites (CPN) with Cloisite® 20A exhibited better properties compared to those with Cloisite® 30B. Transmission electron microscopy (TEM) micrographs, and X-ray diffraction (XRD) patterns validated intercalation-exfoliation of the clay mineral layers for the Cloisite 20A and intercalation of the Cloisite 30B in the polymer matrix.     

Nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer

The nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer were investigated. The single beam Z-scan measurement showed the polymer film possessed a value of nonlinear refractive index n₂ = −1.07 × 10⁻⁹ cm²/W under a picosecond 532 nm excitation. Photoinduced anisotropy in the polymer was studied through dichroism and photoinduced birefringence. A photoinduced birefringence value Δn ∼ 10⁻² was achieved in the polymer film. The mechanism for the nonlinear optical response and the physical process of photoinduced anisotropy in the polymer were discussed.     

Highly thermal stable transparent conducting SnO2:Sb epitaxial films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Antimony-doped tin oxide (SnO₂:Sb) single crystalline films have been prepared on α-Al₂O₃ (0 0 0 1) substrates by metal organic chemical vapor deposition (MOCVD). The antimony doping was varied from 2% to 7% (atomic ratio). Post-deposition annealing of the SnO₂:Sb films was carried out at 700-1100 °C for 30 min in atmosphere ambient. The effect of annealing on the structural, electrical and optical properties of the films was investigated in detail. All the SnO₂:Sb films had good thermal stability under 900 °C, and the 5% Sb-doped SnO₂ film exhibited the best opto-electrical properties. Annealed above 900 °C, the 7% Sb-doped SnO₂ film still kept high thermal stability and showed good electrical and optical properties even at 1100 °C.     

Nonlinear optical susceptibilities χ of nitridosilicate powders

Nitridosilicates are of interest as novel nonlinear materials due to their extraordinary chemical and thermal stability. Unfortunately, large nitridosilicate single crystals are presently not available for the investigation of their nonlinear optical properties. The first experiments are presented in which an averaged nonlinear susceptibility χ⁽²⁾ for several nitridosilicates is studied by using two different powder techniques, the Kurtz Perry method and the SHEW method (Second Harmonic Wave generated by an Evanescent Wave). We observe nonlinearities of the new materials which are comparable to those of LiIO₃. The highest averaged M_eff=(χ_eff⁽²⁾)²/4n_2ωn_ω² values found are ∼0.9 pm²/V². The refractive indices of the materials are determined to be between n=2 and 3.     

Optical and photoluminescent properties of plasma polymer films used in electroluminescent display structures

The optical and photoluminescent properties of plasma polymer layers synthesized from hexamethyldisiloxane are examined. The value of the polymer layer transparence is in the limits from 55% at 400 nm to 88% at 800 nm. Photoluminescence is stimulated by using the spectral line λ=365 nm emitted by a Hg spectral lamp.The organosilicon plasma polymers are included as protective and capsulating layers in electroluminescent (EL) structures. The structure obtained is characterized by a significant increase in emission brightness, compared to inorganic protective layers. For EL structures with a chalcogenide protective layer the increase is more than 6 times and for structures with heterogeneous matrix on the base of TiO₂ it is more than 20 times. As a stable covering the organosilicon plasma polymer increases the lifetime of the EL structures too.     

Optical and electronic properties of nano-Cd1−xMnxTe alloy

Cd_1−xMn_xTe thin films were fabricated by thermal interdiffusion of multilayers of sputtered compound semiconductors as well as thermally evaporated elements. Electron microscopy revealed their nanostructures. The alloys have been investigated for evaluation of optical and electronic parameters. Spectrophotometry helped to find out the bandgap and composition; photoluminescence was used for observing relative transition probabilities at room temperature. Photoresponse showed the light dependence of the resistance of the alloy films. Hall measurements and four-probe tests indicated the influence of manganese on the room-temperature electronic properties of the alloy.     

Identification of optical nonlinearities of dye-doped nematic and polymer-dispersed liquid crystals using Z-scan technique

This study investigates the nonlinear optical properties of azo-dye-doped nematic and polymer-dispersed liquid crystal (ADDPDLC) films with nano-sized LC droplets using the Z-scan technique, which is a simple but powerful technique for measuring the optical Kerr constants of materials. The results indicate that the optical Kerr constant (n₂) of the azo-dye-doped nematic LC (ADDLC) film is large because of the photoisomerization effect and the thermal effect. Therefore, the optical Kerr constant of this material can be modulated by varying the temperature of the sample and the direction of polarization of incident laser. The range of n₂ modulated is from −5.26 × 10⁻³ to 1.62 × 10⁻³ cm²/W. The optical Kerr constants of ADDPDLC films at various temperatures are also measured. The experimental results reveal that liquid crystals in the ADDPDLC film strengthen the nonlinearity. The n₂ of the ADDPDLC film is maximal at ∼35 °C, because of the decrease in the clearing temperature of the ADDPDLC films. The clearing temperatures of the liquid crystals (E7), and the ADDPDLC film used in this work were found to be 61 °C and 43 °C, respectively.     

More studies on the sulfonated poly(phenylene oxide)+imidazole Brønsted acid-base polymer electrolyte membrane

In this article, we report the synthesis of a serious of proton-conducting polymer electrolytes made of sulfonated poly(phenylene oxide) (SPPO) and imidazole (Im) by tuning the mixing ratios. The samples were labeled by their mole composition as SPPO-xIm, where x is the molar ratio of Im to SPPO repeat unit. These membranes were studied by means of Thermogravimetric-differential thermal analysis (TG-DTA) and scanning electronic microscope (SEM) and investigation of activation energies of the SPPO-xIm at different relative humidity was also performed. TG-DTA curves reveal these SPPO-xIm composite materials had the high thermal stability. The proton conductivity of SPPO-xIm composite material increased with the temperature, and the highest proton conductivity of SPPO-xIm composite materials was found to be 6.92×10⁻³ S/cm at 200 °C under 33% relative humidity (RH) with a “mixing rate” where x=2.     

Structural-electronic aspects related to the near-infrared light emission of Fe-doped silicon films

The need of efficient (fast and low consumption) optoelectronic devices has always been the driving force behind the investigation of materials with new or improved properties. To be commercially attractive, however, these materials should be compatible with our current micro-electronics industry and/or telecommunications system. Silicon-based compounds, with their matured processing technology and natural abundance, partially comply with such requirements—as long as they emit light. Motivated by these issues, this work reports on the optical properties of amorphous Si films doped with Fe. The films were prepared by sputtering a Si +Fe target and were investigated by different spectroscopic techniques. According to the experimental results, both the Fe concentration and the thermal annealing of the samples induce changes in their atomic structure and optical-electronic properties. In fact, after thermal annealing at ∼750 °C, the samples partially crystallize with the development of Si and/or β- FeSi₂ crystallites. In such a case, certain samples present light emission at ∼1500 nm that depends on the presence of β- FeSi₂ crystallites and is very sensitive to the annealing conditions. The most likely reasons for the light emission (or absence of it) in the considered Fe-doped Si samples are presented and discussed in view of their main structural-electronic characteristics.     

Magnetic and transport properties of SmCoAsO1−xFx

A series of SmCoAsO_1−xF_x (with x=0, 0.05, 0.1, and 0.2) samples have been prepared by solid state reactions. X-ray powder diffraction proved that all samples can be indexed as a tetragonal ZrCuSiAs-type structure. A clear shrinkage of the lattice constants a and c with increasing F content indicated that F has been doped into the lattice. The magnetic and transport properties of the samples have been investigated. Parent SmCoAsO compound exhibited complicated magnetism including antiferromagnetism, ferromagnetism, and ferrimagnetism. For the fluorine doped samples, the antiferromagnetic Néel temperatures were almost independent of the F content and metamagnetic transitions were observed below antiferromagnetic Néel temperatures. With increasing F content, high temperature (below 142 K) ferrimagnetic state gradually changed to ferromagnetic state. In the resistivity result, metallic conduction in the region of 2-300 K and Fermi liquid behavior at low temperatures were shown in all samples. Transport properties at applied magnetic fields showed anomalies at low temperatures.     

Compositional dependence of the optical properties of amorphous semiconducting glass Ge10AsxSe(90−x) thin films

Optical properties of ternary chalcognide amorphous Ge₁₀As_xSe_(90−x) (with 10?x?25 at%) thin films prepared by thermal evaporation have been measured in visible and near-infrared spectral region. The straightforward analysis proposed by Swanepoel has been successfully employed, and it has allowed us to determine the average thickness , and the refractive index, n, of the films, with high accuracy. The refractive index, n and the average thickness has been determined from the upper and lower envelopes of the transmission spectra measured at normal incidence, in the spectral range 400-2500 nm. The absorption coefficient α, and therefore extinction coefficient k, have been determined from the transmission spectra in the strong-absorption region. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple-DiDomenico model, and the optical absorption edge is described using the ‘nondirect transition’ model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc's extrapolation. The relationship between the optical gap and chemical composition in Ge₁₀As_xSe_(90−x) amorphous system is discussed in terms of the average heat of atomization H_s and average coordination number N_c. Finally, the chemical bond approach has been also applied successfully to interpret the decrease of the glass optical gap with increasing As content.     

Controlled growth and field emission properties of zinc oxide nanopyramid arrays

Single-crystalline, pyramidal zinc oxide nanorods have been synthesized in a large quantity on p-Si substrate via catalyst-free thermal chemical vapor deposition at low temperature. SEM investigations showed that the nanorods were vertically aligned on the substrate, with diameters ranging from 60 to 80 nm and lengths about 1.5 μm. A self-catalysis VLS growth mechanism was proposed for the formation of the ZnO nanorods. The field emission properties of the ZnO nanopyramid arrays were investigated. A turn-on field about 3.8 V/μm was obtained at a current density of 10 μA/cm², and the field emission data was analyzed by applying the Fowler-Nordheim theory. The stability of emission current density under a high voltage was also tested, indicating that the ZnO nanostructures are promising for an application such as field emission sources.     

Characterization of PbSe1−xTex thin films

The lead salts and their alloys are extremely interesting semiconductors due to their technological importance. The fabrication of devices with alloys of these compounds possessing detecting and lasing capabilities has been an important recent technological development. The high quality polycrystalline thin films of PbSe_1−xTe_x with variable composition (0≤x≤1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. As deposited films were annealed in vacuum at 350 K. The optical, electrical and structural properties of PbSe_1−xTe_x thin films have been examined. The optical constants (absorption coefficient and bandgap) of the films were determined by absorbance measurements in the wavelength range 2500-5000 nm using Fourier transform infrared spectrophotometer. The dc conductivity and activation energy of the films were measured in the temperature range 300-380 K. The X-ray diffraction patterns were used to determine the sample quality, crystal structure and lattice parameter of the films.     

Compositional dependence of the optical properties of novel Ge-Ga-Te-CsI far infrared transmitting chalcohalide glasses system

A systematic series of (Ge₁₅Ga₁₀Te₇₅)_1−x(CsI)_x (x=0, 5, 10, 15 at%) far infrared transmitting chalcohalide glasses were prepared by the traditional melt-quenching method. The physical, thermal and optical properties were determined. The allowed direct transition and indirect transition of samples were calculated according to the Tauc equation. The results show that glass transition temperatures (T_g) were in the range 133-175 °C, with ΔT values between 81 and 130 °C. The highest values of metallization criterion (0.244) and energy gap (1.191 eV) were obtained for (Ge₁₅Ga₁₀Te₇₅)₈₅(CsI)₁₅. When the dissolved amount of CsI increased from 0 to 15 at%, the direct optical band gap and indirect optical band gap were in the ranges 0.629-1.075 eV and 0.438-0.524 eV, respectively. The Ge-Ga-Te-CsI glasses have an effective transmission window between 1.7 and 25 μm, encompassing the region of interest for bio-sensing applications.