Showing papers by "Jitendra Kumar published in 2006"

On the sol–gel synthesis and thermal, structural, and magnetic studies of transition metal (Ni, Co, Mn) containing ZnO powders

Abstract: Transition metal containing ZnO powders (Zn1−xMxO, 0≤x≤0.30; M = Ni, Mn, Co) have been synthesized by a sol–gel process using zinc acetate dihydrate, respective acetate and oxalic acid as precursors with ethanol as a solvent. The process essentially involves gel formation, drying at 80 °C for 24 h to provide the oxalate, and calcination at 500 °C for 2 h to undergo an exothermic reaction and yield Zn1−xMxO powder. Their XRD patterns correspond to a wurtzite hcp structure similar to that of pure ZnO, but with the lattice parameters varying slightly with type and extent of doping. It is shown that the dissolution of nickel and cobalt in ZnO is less than 10 at.%, whereas that of manganese lies between 10 and 15 at.%. Other phases that emerge include NiO (hexagonal, a = 2.954 A, c = 7.236 A), ZnCo2O4 (cubic, a = 8.094 A) and ZnMnO3 (cubic, a = 8.35 A) in the Ni, Co and Mn containing ZnO systems, respectively. Observations of hysteresis loops both at 10 and 320 K and the nature of ESR spectra provide evidence for the ferromagnetic state in nickel containing ZnO powder. Besides, the deviation occurs in the magnetization versus temperature curves in zero field cooled (ZFC) and field cooled (FC) conditions (blocking temperature TB being 32 K for 5 at.% Ni). The magnetic behaviour of manganese and cobalt doped zinc oxide is, however, different, namely, (i) no hysteresis loops, (ii) decrease in magnetization with increase of Mn or Co content, and (iii) identical M–T curves under ZFC and FC conditions. The inverse susceptibility versus temperature curves of Zn1−xMnxO compounds reveal ferrimagnetism with Neel temperature TN of 4 K for x = 0.02, but antiferromagnetism for x = 0.15 and 0.25 with Curie–Weiss temperature of −43 and −30 K, respectively.

Optical and structural characterisation of zinc oxide thin films prepared by sol‐gel process

Abstract: Zinc oxide thin films have been prepared on different substrates by the sol-gel method using 2-methoxyethanol solution of zinc acetate dihydrate stabilized by monoethanolamine. The photoluminescence spectra of the films show the band-edge and sub-band transitions. The intensity of the band edge emission peak increases, while the intensity of the deep level emission peak decreases in the films coated on sapphire substrate. Transmittance spectra show that the films are transparent beyond 400 nm. The structural property of the films has been evaluated using X-ray diffraction. The X-ray peak intensity of the film (002) grown on sapphire substrate is higher than the films grown on glass and quartz substrates. The AFM images show improvement in the surface of the annealed films as compared to the as-grown ZnO films coated on sapphire substrates. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of Bis Thiourea Zinc Acetate (BTZA)

Abstract: Single crystals of BTZA have been grown by low temperature solution growth method using slow cooling process at an optimized pH of 3.5. The grown crystals have been examined under an optical microscope to study its surface morphology. The morphological studies show that the growth takes place by spreading of growth layers. Formation of rectangular shaped etch pit on the as-grown crystal has been explained in relation to the growth conditions. Single crystal X-ray diffraction analysis has been carried out to confirm the monoclinic system. Transmission spectrum reveals that the crystal has a low UV cut off of 434.5 nm and has a transmittance of 100%. Dependence of micro hardness on load has been studied. Powder X-ray Diffraction and FT-IR have been carried out to characterize the grown crystals. BTZA forms metal – sulfur bond and has good optical transmission in the entire visible region, which is the essential requirement for a non-linear crystal. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on photoluminescence from tris-(8-hydroxyquinoline)aluminum thin films and influence of light

Abstract: Tris-(8-hydroxyquinoline)aluminum (Alq3), which is the most widely used material in organic electroluminescent devices, has been synthesized. Alq3 thin films have been deposited on glass and silicon substrates. The influence of light exposure on the optical properties of Alq3 thin films has been studied. It is confirmed that the photoluminescence (PL) of Alq3 thin film originates from its two geometrical isomers, namely, facial and meridional, which result from PL decay analysis (biexponential fit). It is also confirmed that the PL from both the isomers decreases for increasing light exposure time leading to the creation of luminescent quencher in Alq3 thin film.

Theoretical investigation of the effect of asymmetry on optical anisotropy and electronic structure of Stranski-Krastanov quantum dots

Abstract: The effect of size and shape anisotropy on the optical properties of Stranski-Krastanov quantum dots QDs is theoretically investigated. The QD is modeled using anisotropic parabolic confinement potential. The complex structure of the valence band is described by Luttinger Hamiltonian. The energy spectra and eigenfunctions of hole states are calculated by numerical diagonalization of the Hamiltonian. The dipole matrix elements are obtained for the interband transitions and hence the degree of linear polarization is calculated. The formulation is applied to self-assembled CdSe quantum dots for numerical analysis. The variation of energy eigenvalues with the QD shape anisotropy parameter is studied and the effect of valence subband mixing is clearly identified. The crossings and anticrossings of the valence subbands have been explained in terms of the symmetries of the corresponding eigenstates. It is worthy to note that these symmetry properties of the energy states are responsible for the specific types of dipole selection rules for the anisotropic QDs. The degree of linear polarization is found to increase almost linearly with anisotropy parameter for the transitions from heavy-hole ground states. On the contrary, for the excited hole states, the change is nonmonotonic due to strong anisotropy-dependent mixing effects.

Investigations on the vibrational spectroscopy and on the thermal behaviour of bis-thiourea zinc acetate—BTZA

Abstract: Single crystals of bis-thiourea zinc acetate (BTZA) for use as a non-linear material have been grown using solution growth technique under optimized growth conditions Investigations have been carried out to assign the vibrational frequencies of the grown crystals FTIR and Raman spectra were taken and compared to evaluate the molecular vibrational properties of the grown crystals Thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) have been carried out to understand the effect of temperature-influenced weight loss and on the endothermic and exothermic characteristics of thermo-gravimetric analysis (TGA)

Effect of swift heavy ions of silver and oxygen on GaN

Abstract: Gallium nitride semiconductors are in the focus of current research. Investigative studies have been carried out to understand the effect of swift heavy ions on metal organic chemical vapour deposition (MOCVD) grown GaN epilayers. Silver (Ag8+) and oxygen (O7+) ions at energy of 100 MeV and fluence of 1 × 1013 ions cm−2 were used in this study. Irradiated samples were characterized by atomic force microscopy (AFM), photoluminescence (PL) and UV–Visible optical absorption. Surface defects were observed from AFM images, which indicate increase in defects after Ag8+ ion irradiation when compared to as-grown GaN. However, with O7+ ion irradiation there is decrease in the surface defects and smoothening of the surface. The PL studies show that O7+ ion irradiation gives rise to red shift and the optical absorption studies provide evidence for the change in the band gap after ion irradiation.

Structural, optical and electrical properties of high energy irradiated Cl-VPE grown gallium nitride

Abstract: The effect of 80 MeV Si (fluences of 1011, 1012, 1013 and 1014 cm−2) on the structural and optical properties of chloride vapour phase epitaxy (Cl-VPE) grown unintentionally doped n-type gallium nitride (GaN) epitaxial layers have been studied by Raman scattering, high-resolution XRD, photoluminescence (PL), UV absorption and Hall measurement techniques. The behaviour of Raman shift for E2(high) and A1(LO) modes of GaN layers have been discussed. New peaks have been observed at the fluences 1013 and 1014 cm−2. Band tailing effect has been observed in the optical absorption spectra of GaN samples. Broadening of the PL emission peak were observed with increasing fluence concentration, which could be attributed to the band tailing effect which plays an important role in determining the optical properties of Si irradiated GaN layers. It is found that the irradiation induces lattice-disordering, decrease in the electron mobility and carrier concentration compared to as-grown samples.

Morphology, surface topography and optical studies on electron beam evaporated MgO thin films

Abstract: Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol-gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh like morphology. The bar regions are believed to be of magnesium hydroxide formed due to absorption of moisture. Their AFM images exhibit columnar/pyramidal/truncated cone structure, providing support to the 3D Stranski-Krastanov model for film growth. Further, they are shown to have high transmittance (∼90%) in the wavelength range 400–600 nm, but absorb radiation below 350 nm substantially giving signature of a band transition.

Controlled Release of Carbofuran in Water from some Polymeric Matrices

Abstract: Controlled release formulations of insecticide-nematicide carbofuran obtained through its monolithic dispersion/incorporation in sodium carboxy methyl cellulose, rosin-yellow, rosin-black, ethyl cellulose, polyvinyl acetate, cellulose acetate, poly vinyl alcohol, polyvinyl chloride, polystyrene, thermokol, bentonite, kaolinite, fullers’ earth, matrices released carbofuran in water beyond 63.0 days. The release of carbofuran was faster from biodegradable than synthetic matrices. Incorporation of clay in polymers slowed down the release. The release was diffusion controlled with a half release time of 7.5–60.3 days in water from different matrices. The period of optimum availability (maximum feasible concentration) of carbofuraa in water from controlled released formulations ranged from 9.0–67.5 days.

Field appraisal of stable neem pesticide tetrahydroazadirachtin-A against mustard aphid (Lipaphiserysiml)

Abstract: In a field evaluation on mustard crop (Brassicajullcea), Thermo and photostabie tetrahydroazadirachtin-A provided superior control of mustard aphid (Lipaphis erysirni Kalt.) as compared to azadirachtin. Oxydemeton-methyl, providing 88.73 % reduction in aphid population was the most effective followed by tetrahydroazadirachtin that provided 64.02 % reduction over untreated control. NeenlAzal® and neem oil EC (25 per cent) were the least effective, recording 17.1 and 7.28 % reduction in aphid population respectively over untreated control. The coccinellid beetle (Coccinella septelJlpunctata) population was the maxinlum in tetrahydroazadirachtin treatment followed closely by azadirachtin and Inininlum in oxydenleton-methyl, neem oil EC and NeenlAzal. Besides being effective against the mustard aphid, high safety 111argin to the predator was exhibited by aza-A and THA .

Field appraisal of controlled release formulations of carbofuran against the rice leaf-folder (Cnaphalocrocis medillalis

Abstract: An experiment was conducted during 2004 to study the bioefficacy of controlled release formulations of carbofuran against the rice leaf-folder (Cnaphalocrocis medinalis Guenee). Controlled release formulations of carbofuran [2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate] were prepared employing polyvinyl chloride, carboxymethyl cellulose and carboxymethyl cellulose- kaolinite. These released carbofuran beyond 45 days as compared to 14 days from its commercial 3G. Carboxymethyl cellulose-based formulation provided a superior control (3.44 %) of rice leaf folder in field grown rice (Oryza sativa L.) at half the dose (375 g ai /ha) in comparison to carbofuran 3 G (4.53 %) at 52 days after treatment. The residue of carbofuran was detected below maximum residue limit of 0.1 mg/ kg in grain 72 days after application.

Structural, thermal, dielectric studies on sol-gel derived MgO from non-alkoxide route

Abstract: Mg oxide powder has been synthesised by sol–gel process via a novel non-alkoxide route. The precursor Mg oxalate gel was characterised by morphology, pore size distribution and differential thermal analysis, Fourier transformation infrared, TEM, SEM and X-ray diffraction analysis. The TEM studies on this system are reported for the first time depicting a unique morphology. A comparison in the morphology and the dielectric constant values of the sol–gel derived MgO powder was carried out with MgO powder obtained by Mg ribbon oxidation process. The sol–gel derived MgO powder was characterised by dielectric constant measurement in the compacted form and it was observed to exhibit a dielectric constant value, quite matching with the polycrystalline MgO in thin film form.

Development of Water Dispersible Powder (WDP) Formulation of Bacillus thuringiensis var. kurstaki and evaluation against Helicoverpa armigera (Hubner)

Abstract: Thirty two recipes of 7% WDP formulation of Bacillus thuringiensis var. kurstaki (HD-1) were prepared in the laboratory using eight carriers viz barium sulphate, bentonite, dolomite, fuller's earth, kaolinite, precipitate of silica, pyrophyllite and talc, two dispersing agents viz lignosulphonate (LS) and naphthalene sulphonate condensate (NSC) and two wetting agents viz sodium lauryl sulphate (SLS) and linear alkyl benzene sulphonate (LABS). The LC50 values ranged from 0.025–0.154% against neonates of Helicoverpa armigera. Recipe containing grecipitata of silica was found more effective (LC50 0.025%) compared to commercial formulation Halt 5%WP (LC50 0.043). Physico chemical properties of the carriers influenced the bioactivity of Bacillus thuringiensis in WDD formulation.

Ferroelectric and Thermal Properties of L-Methionine Doped Triglycine Sulphate Crystal

Abstract: L-Methionine doped TGS single crystals were grown using solution method. Ferroelectric hysteresis loop could be traced at room temperature under conditions of external electric field. The measurements in the present study were performed on single domain samples of 7 mm thick L-.Methionine doped TGS. X-ray diffraction (XRD) studies have been carried out to confirm the peak position. TGA and DTA studies were also carried out and the thermal properties have been analyzed. Electrical conductivity measurements were carried out at different temperatures and as a function of low and high frequency ranges. The conductivity of the L-Methionine doped TGS crystals was found to depend strongly on the frequency of the measuring electric field at different temperatures.

Swift heavy ion irradiation-induced modifications of tris-(8-hydroxyquinoline)aluminum thin films

Abstract: Tris-(8-hydroxyquinoline)aluminum (Alq3), one of the most widely used light emitting and electron transport materials in organic luminescent devices, has been synthesized. Alq3 thin films have been deposited by a thermal evaporation process on glass substrates. The effect of swift heavy ion (SHI) irradiation using 40 MeV Li3+ on the Alq3 thin films has been studied by UV-visible, infrared, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. From TRPL studies, it is found that the PL of Alq3 thin films arises from two species corresponding to its two geometrical isomers, namely facial and meridional having two different life times. It is also confirmed that the PL and lifetimes of excitons decrease with the increase of ion fluences of SHI of 40 MeV Li3+, indicating a transfer of exciton energy to unstable cationic Alq3 species generated by SHI irradiation.