Investigations on the growth,optical behaviour and factor group of an NLO crystal: L‐alanine alaninium nitrate

Amino acid family crystals exhibit excellent nonlinear and electro‐optical properties. L‐alanine alaninium nitrate (LAAN) single crystal belonging to the amino acid group was grown by slow cooling solution growth technique. The High resolution X‐ray diffraction (HRXRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, UV‐Vis., Photoluminescence (PL) and Factor group analyses were carried out. The factor group analysis reveals 183 internal vibrations for the title compound. The second harmonic generation property was tested by Kurtz‐Perry powder technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lie group analysis for the effect of temperature-dependent fluid viscosity and thermophoresis particle deposition on free convective heat and mass transfer under variable stream conditions

This paper examines a steady two-dimensional flow of incompressible fluid over a vertical stretching sheet. The fluid viscosity is assumed to vary as a linear function of temperature. A scaling group of transformations is applied to the governing equa- tions. The system remains invariant due to some relations among the transformation parameters. After finding three absolute invariants, a third-order ordinary differential equation corresponding to the momentum equation and two second-order ordinary differential equations corresponding to energy and diffusion equations are derived. The equations along with the boundary conditions are solved numerically. It is found that the decrease in the temperature-dependent fluid viscosity makes the velocity decrease with the increasing distance of the stretching sheet. At a particular point of the sheet, the fluid velocity decreases but the temperature increases with the decreasing viscosity. The impact of the thermophoresis particle deposition plays an important role in the concentration boundary layer. The obtained results are presented graphically and discussed.     

Effect of an external electric field on two-dimensional nucleation

Summary Two-dimensional nuclei of different possible shapes are considered in the presence of an external electric field which is applied either perpendicular or parallel to the nucleation surface. The additional driving force needed for the formation of a nucleus due to the electric field is found and used in the nucleation theory. The results show that the electric field can either stimulate or inhibit the nucleation process depending on the ratio of the dielectric constants and the orientation of the applied electric field with respect to the nucleation surface. The dependence of the two-dimensional nucleation rate on the intensity of electric field is also determined.

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Riassunto Si considerano nuclei bidimensionali di differenti forme possibili in presenza di un campo elettrico esterno che è applicato sia perpendicolare che parallelo alla superficie di nucleazione. Si trova e si usa nella teoria di nucleazione l’ulteriore forza guida necesaria per la formazione di un nucleo a causa del campo elettrico. I risultati mostrano che il campo elettrico può sia stimolare che inibire il processo di nucleazione che dipende dal rapporto delle costanti dielettriche e dell’orientamento del campo elettrico applicato rispetto alla superficie di nucleazione. Si determina anche la dipendenza del valore di nucleazione bindimensionale dall’intensità del campo elettrico.

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Резюме Рассматриваются двумерные ядра различных возможиых форм в присутствии внешнего электрического поля, которое либо перпендикулярно, либо параллельно поверхности вародышеобразования. Определяется и используется в теории зародяшеобразования дополнительная движущая сила, необходимая для образования ядра, всл⪟дствие действия электрического поля. Полученные результатя показяают, что электрическое поле может либо стимулировать, либо тормозить процесс зародышеобразования в зависимости от отношения диэлектричеких постоянных и от ориентации приложенного электричеслог поля отнонительно поверхности зародышеодразования. Такзе определяется зависимость скорости образвания двумерных ядер от интенсивности электрического поля.

     

Antioxidant,Anti-Bacterial,and Congo Red Dye Degradation Activity of AgxO-Decorated Mustard Oil-Derived rGO Nanocomposites

Scaling up the production of functional reduced graphene oxide (rGO) and its composites requires the use of low-cost, simple, and sustainable synthesis methods, and renewable feedstocks. In this study, silver oxide-decorated rGO (Ag_xO−rGO) composites were prepared by open-air combustion of mustard oil, essential oil-containing cooking oil commercially produced from the seeds of Brassica juncea. Silver oxide (Ag_xO) nanoparticles (NPs) were synthesized using Coleus aromaticus leaf extract as a reducing agent. Formation of mustard seed rGO and Ag_xO NPs was confirmed by UV-visible characteristic peaks at 258 nm and 444 nm, respectively. rGO had a flake-like morphology and a crystalline structure, with Raman spectra showing clear D and G bands with an I_D/I_G ratio of 0.992, confirming the fewer defects in the as-prepared mustard oil-derived rGO (M−rGO). The rGO-Ag_xO composite showed a degradation efficiency of 81.9% with a rate constant k⁻¹ of 0.9506 min⁻¹ for the sodium salt of benzidinediazo-bis-1-naphthylamine-4-sulfonic acid (known as the azo dye Congo Red) in an aqueous solution under visible light irradiation. The composite also showed some antimicrobial activity against Klebsilla pneomoniae, Escherichia coli, and Staphylococcus aureus bacterial cells, with inhibition zones of ~15, 18, and 14 mm, respectively, for a concentration of 300 µg/mL. At 600 µg/mL concentration, the composite also showed moderate scavenging activity for 2,2-diphenyl-1-picrylhydrazyl of ~30.6%, with significantly lower activities measured for Ag_xO (at ~18.1%) and rGO (~8%) when compared to control.     

Growth and optical characterization of organic nonlinear optical crystal: indole-3-aldehyde

The metastable zone width for the solution of organic nonlinear material: indole-3-aldehyde (IA) has been determined for the various solvents of acetone, methanol and ethyl acetate and the corresponding IA crystals have been grown by temperature lowering technique. The surface analysis on different planes of the grown crystals has been carried out. The range of transmission and powder second harmonic generation efficiency of IA have been reported.     

Electronic properties of Chevrel phases by positron angular correlation

A comparative study of the Chevrel phases Mo₆S₈, Mo₆Se₈, PbMo₆S₈ and Cu_1.8Mo₆S₈ is made by the positron angular correlation technique at room temperature. Electronic properties like the number of conduction electrons per cluster, the density of states at the Fermi level, the electron effective masses and the Fermi velocities are obtained within the framework of the free electron model. The results are discussed in terms of available theoretical and other experimental data.     

Synthesis, growth, thermal, optical, dielectric and mechanical properties of semi-organic NLO crystal: Potassium hydrogen malate monohydrate

Potassium hydrogen malate monohydrate (PHMM), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from aqueous solution. Single crystals of PHMM have been grown by slow evaporation of solvent at room temperature up to dimensions of 22 mm×16 mm×14 mm. Single-crystal X-ray diffraction study on grown crystals shows that they belong to monoclinic system and non-centrosymmetry spacegroup Cc. The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectroscopic study was performed for the identification of different modes of functional groups present in the compound. The UV–Vis transmission spectrum has been recorded in the range 200–1100 nm. The thermal stability of the compound has been determined by TG-DTA curves. The dielectric studies were performed. From the microhardness measurements, Vicker's hardness number (H_v), Stiffness constant (C₁₁), fracture toughness (k_c), Brittle index (B_i) and yield strength (σ_y) have been calculated. The Young's modulus was calculated using the Knoop hardness measurement. The SHG relative efficiency of PHMM crystal was found to be 1.2 times higher than that of KDP.     

Radon isotope assessment of submarine groundwater discharge (SGD) in Coleroon River Estuary,Tamil Nadu,India

Submarine groundwater discharge is the fresh groundwater discharge to sea that impacts the coastal regions. Radon (²²²Rn) isotope has been used to quantify SGD in coleroon river estuary, India. Continuous ²²²Rn analyses were attempted for 10 days in groundwater and pore water samples at three different locations. ²²²Rn in groundwater ranges between 35.0 and 222.0 Bq m^?3 and in pore water between 14.0 and 150.0 Bq m^?3 irrespective of locations. The radon mass balance estimated total SGD rate ranges between 2.37 and 7.47 m days^?1. The SGD increases with distance from coast, influenced by tides and hydrological features.     

On the Analysis of Hydrogen in as grown and Ion Implanted GaAs Single Crystals

Hydrogen detection and analysis was carried out on the undoped semi‐insulating (S.I.) gallium arsenide (GaAs) single crystal using conventional elastic recoil detection analysis (ERDA) technique with high energy, heavy ion beam. Presence of hydrogen (nearly 3 x 1020 atoms/cc) has been observed on the as‐grown samples and further high concentration of atomic hydrogen (total concentration of 7 x 1020 atoms/cc) was found at the surface and was found to be decreasing with depth after 100 nm. Further the low energy hydrogen and oxygen ions implanted separately in GaAs at room temperature were also analysed by ERDA technique. From the analysis, the projected range (Rp) of 100 keV hydrogen and oxygen ions in GaAs was determined to be 891 nm (with Δ Rp equal to 320 nm), 170 nm (with Δ Rp equal to 120 nm) respectively. The experimentally determined values of both Rp and Δ Rp are more as compared with the values obtained using the TRIM theoretical program. Low temperature (4K) photoluminescence (PL) measurements of un‐implanted and H⁺ implanted samples show the passivation of intrinsic deep level defect EL2 and shallow acceptor impurity carbon by the low energy implanted hydrogen ions. The low energy hydrogen implantation may be used as a method of hydrogenation for passivation.