Optical absorption of tetraphenylporphyrin thin films in UV-vis-NIR region

The optical absorption of thermally evaporated tetraphenylporphyrin (TPP) in the UV-vis-NIR region have been studied. The absorption spectra recorded in the UV-vis region for the as deposited and annealed films showed different absorption bands, namely the Soret(B) at region 360-490nm, Q-band region consist of four bands in the region 500-720nm and two other bands labeled N and M in UV region. The Soret band always shows its characteristic effect splitting in all the TPP thin films and the effect of annealing on the intensities of these components have been observed. The spectra of the infrared absorption allow characterization of vibrational modes for the powder, as deposited and annealed thin films. Some of the optical absorption parameters, namely molar extinction coefficient, varepsilon, half band width, Deltalambda, electronic dipole strength, q(2) and oscillator strength, f, of the principle optical transitions have also been evaluated.     

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Fourier-transform infrared and optical absorption spectra of 4-tricyanovinyl-N,N-diethylaniline thin films

Thin films of 4-tricyanovinyl-N,N-diethylaniline (TCVA) were prepared for the first time using thermal evaporation technique. The molecular structure and electronic transitions of TCVA films were investigated by Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectra. The observed vibrational wavenumbers in FTIR spectra were analysed and assigned to different normal modes of the molecule. UV-vis electronic absorption spectral measurements of TCVA films were analysed to obtain the electronic transitions and optical band gap (E(g)). Other important optical parameters such as molar extinction coefficient (varepsilon(molar)), the oscillator strength (f), and the electric dipole strength (q(2)) were also reported.     

Optical Properties of Nano 5,10,15,20-Tetraphenyl-21H,23H-Prophyrin Nickel (II) Thin Films

Optical properties of the as-deposited and annealed films of 5, 10, 15, 20-Tetraphenyl-21H, 23H-Porphyrin nickel (II), (NiTPP) were investigated using spectrophotometric measurements of both transmittance and reflectance at normal incidence of light in the wavelength range, 200–1100 nm. The obtained data of refractive index, and absorption index, were used to estimate the type of transition and both optical and fundamental gaps. The normal dispersion (λ > 600 nm) of refractive index is discussed in terms of single oscillator model of Wemple-Didomenico, while the anomalous dispersion (λ < 600 nm) is discussed according to multi oscillator. The dispersion parameters; oscillator energy, dispersion energy, optical dielectric constant at higher frequency, lattice dielectric constant, and the ratio of carrier concentration to the effective mass N/m* were determined. The real part of the dielectric constant, the imaginary part of the dielectric constant, the loss factor, the volume and the surface energy loss functions were estimated and discussed.     

AC conductivity and dielectric behavior of bulk Furfurylidenemalononitrile

AC conductivity and dielectric behavior for bulk Furfurylidenemalononitrile have been studied over a temperature range (293–333 K) and frequency range (50–5×10⁶ Hz). The frequency dependence of ac conductivity, σ_ac, has been investigated by the universal power law, σ_ac(ω)=Aω^s. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms, and it was found that the correlated barrier hopping (CBH) model is the predominant conduction mechanism. The temperature dependence of σ_ac(ω) showed a linear increase with the increase in temperature at different frequencies. The ac activation energy was determined at different frequencies. Dielectric data were analyzed using complex permittivity and complex electric modulus for bulk Furfurylidenemalononitrile at various temperatures.     

Nonlinear compression of optical solitons

In this paper, we consider nonlinear Schrödinger (NLS) equations, both in the anomalous and normal dispersive regimes, which govern the propagation of a single field in a fiber medium with phase modulation and fibre gain (or loss). The integrability conditions are arrived from linear eigen value problem. The variable transformations which connect the integrable form of modified NLS equations are presented. We succeed in Hirota bilinearzing the equations and on solving, exact bright and dark soliton solutions are obtained. From the results, we show that the soliton is alive, i.e. pulse area can be conserved by the inclusion of gain (or loss) and phase modulation effects.     

Optical properties of CdIn2Se4 thin films

The optical constants (the refractive index n, the absorption index k, and the absorption coefficient ) of CdIn₂Se₄ thin films were determined in the spectral range of 500–2000 nm. Graphical representation of log() as a function of log(1/) shows two distinct, linear parts indicating the existance of both direct and indirect optical transitions. The corresponding forbidden energy gaps E _g ^d and E _g ^Emphasis>d were determined. The effect of both annealing temperature as well as the substrate temperature on the optical constants of CdIn₂Se₄ thin films was also investigated.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.