Thermotropic and optical properties of chiral nematic polymers

The thermotropic and optical properties of methacrylate copolymers and chemically modified poly(-benzyl L-glutamate) were investigated as part of our effort to explore the optical applications of these materials. It was found that besides the commonly cited comonomer ratio, physical blending and annealing followed by quenching represent a new and more flexible means to tune the selective reflection wavelength. In the chemically modified poly(-benzyl L-glutamate) system with Tg as low as — 25 °C, it appears that the relatively high-melt viscosity is capable of sustaining the cholesteric mesophase, generated by annealing and quenching, while subjected to heating up to 100°C.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Structural and optical properties of microcrystalline silicon films deposited by plasma enhanced chemical vapour deposition

Hydrogenated microcrystalline (c) silicon films were prepared by plasma enhanced chemical vapour deposition using an Ar-diluted SiH₄ gas at various deposition conditions. The substrate temperature and RF power were varied from 150 to 400 C and from 10 to 120 W, respectively. Structure and microstructure were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Hydrogen bonding and optical properties were investigated by FTIR spectra and UV transmission spectra. The crystal fraction of the films increased as the deposition temperature decreased and RF power increased. More definite columnar morphology was developed with increasing crystal fraction. The existence of c-Si above a critical RF power (>30 W) suggests that SiH₂ radical in plasma plays an important role for the formation of columnar morphology and c-Si. IR absorption analysis showed that the SiH₂/SiH bonding ratio in the silicon films increased as the crystal fraction increased. The UV absorption coefficient of the films became smaller as the deposition temperature and RF power increased.     

Structural and optical properties of GaGeTe thin films

Smooth and pinhole-free thin films of Ga₅Ge₁₉Te₇₆ have been obtained by vacuum evaporation. The as-deposited films are amorphous. Thermal annealing at 222°C leads to an amorphous-to-crystalline transition. A maximum contrast of 30% in reflectivity (measured at 1 µm) has been obtained on phase transition from amorphous to crystalline state. The optical constants and the bandgap are reported.     

Databank on thermodynamic and optical properties of plasma

Methods of evaluation of thermodynamic and optical properties of multicomponent gases within a wide range of conditions are discussed. A databank on component composition, thermodynamic functions, spectral and group absorption coefficients, and Planck and Rosseland mean free paths of radiation for plasmas of air, water, silicon dioxide, and the Martian atmosphere (0.965 CO₂+0.035 N₂) is composed based on calculations.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 2, pp. 291–305, March–April, 1995.     

Structural and optical properties of plasma-deposited boron nitride films

The plasma-enhanced chemical vapor deposition of boron nitride films in a low pressure, parallel plate reactor incorporating an electromagnet was investigated. Films were deposited from gas mixtures of diborane, hydrogen and ammonia. The ratio of boron to nitrogen was approximately 1.7 when an ammonia-to-diborane ratio of 4 was used. The films had the following optical properties: a band gap in the range 5.6–5.8 eV, an absorption coefficient (at 6.0 eV) of about 1×10⁵ cm⁻¹ and an index of refraction of 1.7. In general the optical properties were identical, with or without the application of a low intensity magnetic field.     

Structural and optical properties of nitrogen doped ZnO films

Zinc oxide is getting an enormous attention due to its potential applications in a variety of fields such as optoelectronics, spintronics and sensors. The renewed interest in this wide band gap oxide semiconductor relies on its direct high energy gap (E_g ∼ 3.437 eV at low temperatures) and large exciton binding energy. However to reach the stage of device production the difficulty to produce in a reproducible way p-type doping must be overcome.In this study we discuss the structural and optical properties of ZnO films doped with nitrogen, a potential p-type dopant. The films were deposited by magnetron sputtering using different conditions and substrates. The composition and structural properties of the films were studied combining X-ray diffraction (XRD), Rutherford backscattering (RBS), and heavy ion elastic recoil detection analysis (HI-ERDA). The results show an improvement of the quality of the films deposited on sapphire with increasing radio-frequency (RF) power with a preferentially growth along the c-axis. The ERDA analysis reveals the presence of H in the films and a homogeneous composition over the entire thickness. The photoluminescence of annealed samples evidences an improvement on the optical quality as identified by the well structured near band edge recombination.     

Structural and optical properties of GaN-based nanocrystalline thin films

We study the effect of annealing on structure, morphology and optical properties of nanocrystalline films of GaN, GaN:O and GaN:Mn prepared by ion assisted deposition on silicon, quartz and glassy carbon substrates. Blisters and holes having diameters proportional with the thickness of the film were observed in GaN:O deposited on silicon and glassy carbon. The Mn excess in GaN:Mn turns through annealing into Mn_xN_y islands. The degree of short- and intermediate-range order in the films was investigated by micro-Raman spectroscopy, extending to about 3 nm for gallium oxynitride films annealed to 973 K and to more than 10 nm in GaN samples. A diminished oxygen content following the annealing procedures on GaN:O samples is noticed from the reduced intensity of the oxygen mode at 1000 cm^− 1 in the Raman spectra. This observation is supported with X-ray photoemission spectroscopy measurements. The presence of oxygen at concentrations above 15at.% in the films leads to an abrupt nanocrystalline-amorphous transition.     

Structural and optical properties of tin oxide branched nanostructures

Branched nanostructures of tin oxide (SnO2) have been synthesized by Vapor-Liquid-Solid (VLS) mechanism using a gold catalyst in the temperature range of 800-850 degrees C under an ambient gas flow of 200 sccm. The microstructural and the optical properties of the as prepared products have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-Raman, and photoluminescence (PL) studies. SnO2 branches with a rutile phase are found to have a preferential orientation along (101). Typical lengths of these branches are found to be approximately 3-5 microm and diameters in the range of 50-100 nm. Selected area electron diffraction (SAED) pattern shows that the SnO2 branches have a tetragonal cross section with [101] crystal direction. A Raman line at 631 cm(-1) (Sn-O bond) is obtained in the micro Raman spectra. Low temperature PL spectrum shows a strong green emission band near 506 nm.     

HMDSO plasma polymerization and thin film optical properties

Thin films were deposited from hexamethyldisiloxane (HMDSO) in a glow discharge supplied with radiofrequency (rf) power. Actino-metric optical emission spectroscopy was used to follow trends in the plasma concentrations of the species SiH (414.2 nm), CH (431.4 nm), CO (520.0 nm), and H (656.3 nm) as a function of the applied rf power (range 5 to 35 W). Transmission infrared spectroscopy (IRS) was employed to characterize the molecular structure of the polymer, showing the presence of Si-H, Si-O-Si, Si-O-C and C-H groups. The deposition rate, determined by optical interferometry, ranged from 60 to 130 nm/min. Optical properties were determined from transmission ultra violet-visible spectroscopy (UVS) data. The absorption coefficient , the refractive index n, and the optical gap E₀₄ of the polymer films were calculated as a function of the applied power. The refractive index at a photon energy of 1 eV varied from 1.45 to 1.55, depending on the rf power used for the deposition. The absorption coefficient showed an absorption edge similar to other non-crystalline materials, amorphous hydrogenated carbon, and semiconductors. For our samples, we define as an optical gap, the photon energy E₀₄ corresponding to the energy at an absorption of 10⁴ cm⁻¹. The values of E₀₄ decreased from 5.3 to 4.6 as the rf power was increased from 5 to 35 W.     

Synthesis and the third-order non-linear optical properties of new azobenzene-containing side-chain polymers

A new series of aromatic azobenzol compounds containing vinyl have been designed as monomers. The azobenzene-containing side-chain polymers containing azo NLO chromophore in each side chain have been synthesized via free radical polymerization. FT-IR, elemental analysis and ¹H NMR were performed to characterize the azo monomers. The molecular weight of the polymers and their distribution were determined by gel permeation chromatography (GPC). The third-order NLO coefficient of azo monomers and their polymers were measured by degenerated four wave mixing (DFWM) technique. As a result, the enhancement of the molecular conjugation and the increase of the NLO chromophore concentration in the molecular chain contribute much to heightening the third-order NLO effect. The electronic effect of substituent on the azobenzol group and the push–pull electronic structure contributes much to enhancing the NLO property.     

Structural and optical properties of electrodeposited indium selenide thin films

Journal of Materials Science Letters -     

Structural,optical and photoconducting properties of sprayed CdSe films

CdSe films were grown by the pyrolytic decomposition of a mixture of aqueous solutions of selenourea (NH₂CSeNH₂) and CdCl₂·5H₂O. The effect of changes in the selenium-to-cadmium ion ratio on the photoconductivity was examined. The as-grown films had low resistance and showed poor photoconductivity gain. When the films were annealed in air the resistance as well as the gain increased appreciably. These changes have been attributed to chemisorption of oxygen. The samples with one part CdCl₂·5H₂O and one part NH₂CSeNH₂ were found to be the most photosensitive, the ratio of dark resistance to light resistance being of the order of 10⁵. The spectral response of the resistance of these films shows a dip in the region of 690 nm, which is in close agreement with the band gap determined from optical absorption measurements.     

Structural and optical properties of single-crystalline ultraviolet-emitting needle-shaped ZnO nanowires

Well-crystallized with excellent optical properties, needle-shaped ZnO nanowires have been synthesized on silicon substrate in a high density via the thermal evaporation of metallic zinc powder without the use of catalysts or additives. Extensive structural analysis showed that the grown nanowires are highly crystalline with the wurtzite hexagonal phase, grown along the [0001] in the c-axis direction. The presence of an optical-phonon E₂ mode in Raman spectrum at 437 cm^{− 1} and sharp and strong UV emission at 379 nm with no green emission in the room-temperature photoluminescence (PL) spectrum confirms good crystallinity with the excellent optical properties for the deposited nanowires.     

Synthesis and the third-order non-linear optical properties of new azobenzene-containing side-chain polymers

A new series of aromatic azobenzol compounds containing vinyl have been designed as monomers. The azobenzene-containing side-chain polymers containing azo NLO chromophore in each side chain have been synthesized via free radical polymerization. FT-IR, elemental analysis and ¹H NMR were performed to characterize the azo monomers. The molecular weight of the polymers and their distribution were determined by gel permeation chromatography (GPC). The third-order NLO coefficient of azo monomers and their polymers were measured by degenerated four wave mixing (DFWM) technique. As a result, the enhancement of the molecular conjugation and the increase of the NLO chromophore concentration in the molecular chain contribute much to heightening the third-order NLO effect. The electronic effect of substituent on the azobenzol group and the push–pull electronic structure contributes much to enhancing the NLO property.     

Structural,optical and magnetic properties of cobalt-doped CdSe nanoparticles

Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe₂) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.     

Structural,optical and electrical properties of CdZnS thin films

The thin films of Cd_1-x Zn _x S (x?=?0, 0.2, 0.4, 0.6, 0.8 and 1) have been prepared by the vacuum evaporation method using a mechanically alloyed mixture of CdS and ZnS. The structural, optical and electrical properties have been investigated through the X-ray diffractometer, spectrophotometer and Keithley electrometer. The X-ray diffraction patterns of these films show that films are polycrystalline in nature having preferential orientation along the (002) plane. In the absorption spectra of these films, absorption edge shifts towards lower wavelength with the increase of Zn concentration. The energy band gap has been determined using these spectra. It is found that the energy band gap increases with increasing Zn concentration. The electrical conductivity of so prepared thin films has been determined using a I–V characteristic curve for these films. The result indicates that the electrical conductivity decreases with increasing Zn content and increases with temperature. An effort has also been made to obtain activation energy of these films which increases with increasing Zn concentration in CdS.     

Structural and optical properties of yttria-stabilized-zirconia films grown by MOCVD

The morphology of yttria doped zirconia thin films deposited by metal organic chemical vapour deposition (MOCVD) in two different substrate materials, glassy quartz and sapphire single crystals has been examined. The Y₂O₃ doping concentration has been varied from 3 to 12 mol percent. Structural characterization has been realized by X-ray diffraction, raman spectroscopy and scanning electron microscopy. The structure of the films corresponds to that of bulk crystals of the same composition. Refractive index has been determined by the optical transmission method. Refractive index close to those of bulk crystals are obtained for epitaxially grown zirconia on sapphire substrates, whereas low refractive index values, related with low packing densities, are obtained for thin films in the glassy substrate.