S. C. Katyal

Determination of optical parameters of a-(As2Se3)90Ge10 thin film

A thin film of the ternary chalcogenide glassy alloy (As2Se3)90Ge10 has been deposited on a glass substrate by the thermal evaporation technique under vacuum. The optical parameters, refractive index (n) and extinction coefficient (k), have been calculated in the wavelength range 400–1500 nm by analysing the transmission spectrum. The dispersion of the refractive index is described in terms of a Wemple–DiDomenico single oscillator model. The value of the static refractive index has been found to be 2.518. The optical absorption edge is described using a non-direct transition model proposed by Tauc and the optical band gap calculated by Taucs extrapolation is 1.58 ± 0.01 eV. The dielectric properties and optical conductivity has also been calculated.

Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique

Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473K at higher frequency range of 9–19MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108Ωcm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773K).

Linear and nonlinear refractive index of As–Se–Ge and Bi doped As–Se–Ge thin films

The present work reports the linear and nonlinear refractive index for (As2Se3)90Ge10 and [(As2Se3)90Ge10]95Bi5 thin films. The formulation proposed by Fournier and Snitzer has been used to predict the nonlinear behavior of refractive index. The linear refractive index and Wemple–DiDomenico parameters were used for the determination of nonlinear refractive index in the wavelength region 0.4 to 1.5 μm. Linear refractive index has been determined using the well known Swanepoel method. This is observed that nonlinear refractive index increases linearly with increasing linear refractive index. With Bi addition this has been found that nonlinear refractive index increases by 2.4 times, while on comparing with pure and doped silica glasses results are 2–3 orders higher. Density and molar volume has also been calculated. The obtained results may lead to yield more sensitive optical limiting devices and these glasses may be used as an optical material for high speed communication fibers.

Effect of antimony addition on the optical behaviour of germanium selenide thin films

This paper reports the influence of antimony (Sb) addition on the optical properties (optical energy gap and refractive index) of thin solid films of the chalcogenide glassy Ge0.17Se0.83?xSbx(x = 0, 0.03, 0.09, 0.12, 0.15) system. This has been done by analysing the transmittance (T) and reflectance (R) spectra in the spectral region 400?2000?nm. It was found that the optical energy gap decreases with increasing Sb content from 1.92 to 1.63?eV with an uncertainty of ? 0.01?eV. The results were interpreted in terms of bond energies and on the basis of the concept of electronegativity. The refractive index has been found to increase with increasing Sb content. The increase in the refractive index has been explained on the basis of polarizability. Dispersion of refractive index has been analysed using the Wemple?DiDomenico single oscillator model. The static refractive index increased from 2.45 to 2.91 for the studied compositions. An estimate of the energy gap has also been taken theoretically and it has been found that both the optical energy gap (measured from T and R spectra) and the theoretical energy gap follow similar trends.

CdS nanofilms: Effect of film thickness on morphology and optical band gap

CdS nanofilms of varying thickness (t) deposited by chemical bath deposition technique have been studied for structural changes using x-ray diffractometer (XRD) and transmission electron microscope (TEM). XRD analysis shows polycrystalline nature in deposited films with preferred orientation along (002) reflection plane also confirmed by selected area diffraction pattern of TEM. Uniform and smooth surface morphology observed using field emission scanning electron microscope. The surface topography has been studied using atomic force microscope. The optical constants have been calculated from the analysis of %T and %R spectra in the wavelength range 300 nm-900 nm. CdS nanofilms show a direct transition with red shift. The optical band gap decreases while the refractive index increases with increase in thickness of nanofilms.

Effect of Te on linear and non-linear optical properties of new quaternary Ge-Se-Sb-Te chalcogenide glasses

We report linear and non-linear optical properties of a new quaternary chalcogenide glass series Ge19-ySe63.8Sb17.2Tey (y = 0, 2, 4, 6, 8, 10). In linear optical properties; refractive index, extinction coefficient and the Tauc gap are reported and their variation with Te content has been discussed. In non-linear properties; third order nonlinear susceptibility and non-linear refractive index has been discussed. The variation of non-linear refractive index has also been reported with normalized photon energy. A correlation between the Tauc gap and nonlinear refractive index has been discussed. Results indicate that these materials may find applications in modern optical devices.

Room temperature ferromagnetic ordering in indium substituted nano-nickel-zinc ferrite

Nano-nickel-zinc-indium ferrite (NZIFO)(Ni0.58Zn0.42InxFe2−xO4) with varied quantities of indium (x=0,0.1,0.2) have been synthesized via reverse micelle technique. X-ray diffraction and transmission electron microscopy confirmed the size, structure, and morphology of the nanoferrites. The addition of indium in nickel-zinc ferrite (NZFO) has been shown to play a crucial role in enhancing the magnetic properties. Room temperature Mossbauer spectra revealed that the nano-NZFO ferrite exhibit collective magnetic excitations, while indium doped NZFO samples have the ferromagnetic phase. The dependence of Mossbauer parameters, viz. isomer shift, quadrupole splitting, linewidth, and hyperfine magnetic field, on In3+ concentration has been studied. Mossbauer study on these nanosystems shows that the cation distribution not only depends on the particle size but also on the preparation route. Mossbauer results are also supported by magnetization data. Well defined sextets and appearance of hysteresis at room temper...

Physical and optical properties of binary amorphous selenium-antimony thin films

Amorphous thin films with compositions Se1−xSbx (x=0, 0.025, 0.05, 0.075, and 0.10 at. %) have been deposited by thermal evaporation (at ∼10−4 Pa) from bulk samples. The compositional dependence of their optical properties, refractive index, extinction coefficient, absorption coefficient, and optical band gap with increasing Sb content is investigated using transmission spectra in the range of 400–1200 nm. The refractive-index dispersion has been analyzed on the basis of the Wemple–DiDomenico single-oscillator approach. It has been found that the refractive index increases with increasing Sb content. The behavior of the optical band gap, when the composition of the material is varied, shows, as expected, just the opposite trends. The optical band gap decreases from 2.025 to 1.753 eV with ±0.001 eV uncertainty. Band gap calculated theoretically also shows a decrease with the increase in Sb content. The optical behavior is supported by physical properties, i.e., decrease in optical band gap is supported by ...

Substitution driven structural and magnetic transformation in Ca-doped BiFeO3 nanoparticles

Bi1−xCaxFeO3; (x = 0–0.20) nanoparticles were synthesized by tartaric acid based sol–gel route. X-ray diffraction and electron microscopy studies reveal the phase purity and nanocrystalline nature (45–90 nm) of Bi1−xCaxFeO3 samples. The Ca ion substitution driven structural transition from rhombohedral (space group R3c) to orthorhombic (Pnma) symmetry leads to enhancement in saturation magnetization due to the distorted cycloid spin structure (as also suggested by Mossbauer studies) and uncompensated surface spins which is accorded with electron paramagnetic resonance (EPR) studies as well. The ferromagnetic ordering contribution increases up to x = 0.15 samples with maximum saturation magnetization of 0.09 emu g−1 for x = 0.15 sample. The presence of high content orthorhombic phase for x = 0.20 sample results in the sharp decrease in the ferromagnetic component due to appearance of collinear antiferromagnetic ordering in agreement with EPR results. X-ray photoelectron spectroscopy confirmed the dominancy of Fe3+ oxidation states along with the shifting of the binding energy of Bi 4f orbital indicating the substitution of Ca2+ at Bi-site. Systematic change of Mossbauer parameters of nanoparticulate samples with Ca concentration are obtained by Mossbauer spectroscopy. The results of both one- and two-sextet fittings of the Mossbauer spectra provide evidence for destruction of the spin cycloid in Ca-doped BiFeO3 nanoparticles.

Superparamagnetic La doped Mn–Zn nano ferrites: dependence on dopant content and crystallite size

Magnetic nanoparticles are found to exhibit exciting and substantially distinct magnetic properties due to high surface-to-volume ratio and several crystal structures in comparison to those discovered in their bulk counterparts. The properties of nanoparticles also largely depend on the route of their synthesis. In the present work, we report the synthesis of superparamagnetic nanoparticles of Mn0.5Zn0.5La x Fe2−x O4 (x = 0, 0.025, 0.050, 0.075, 0.1) ferrites by co-precipitation method. Structural, morphological and elemental study has been performed using x-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), FESEM and EDS. Different structural parameters (crystallite size, interplanar spacing and lattice constant) have been calculated from XRD. Formation of cubical spinel structure has been confirmed from XRD and FTIR. Cation distribution for all the samples has been proposed and used for calculation of various theoretical parameters. Magnetic properties have been investigated using vibrating sample magnetometer at room temperature and show transition between paramagnetic and superparamagnetic behavior. Maximum saturation magnetization and magnetic moment have been obtained at x = 0.050. The results are attributed to the solubility of La in Mn–Zn ferrite and the size of nanoparticles. The samples have also been analyzed for dielectric, electric and optical properties. For x ≤ 0.050, a blue shift in absorbance and photoluminescence measurements has been observed due to quantum confinement.