M. Arivanandhan

An investigation of flower shaped NiO nanostructures by microwave and hydrothermal route

The face centered cubic phase of NiO nanostructures were successfully synthesized from microwave and hydrothermal methods. The structural properties of the synthesized material were analyzed by X-ray diffraction (XRD) studies. The thermal analysis revealed the transformation of Ni(OH)2 into NiO at about 380xa0°C. The obtained scanning electron microscopy images exhibited less agglomerated flowers for hydrothermal reacted NiO than the microwave processed samples. The sheet like morphologies of NiO nanostructures were confirmed by transmission electron microscope and the obtained particles sizes were comparable to the calculated values from XRD data. The UV–Vis and photoluminescence spectra results showed that the absorption edges of the NiO nanoflowers have a blue-shift due to quantum confinement effect. The Raman spectrum exhibited the transformation of antiferromagnetic to superparamagnetic transition confirmed from the absence of magnon peak. The XPS spectrum presented the observation of Ni 2p and O 1s levels with higher intense peak nature for hydrothermal treated NiO than microwave. The hysteresis loops of the NiO samples prepared by both hydrothermal and microwave heating methods revealed the weak ferromagnetic behaviors at room temperature. Based on the experimental observations and analysis, a possible hydrothermal reaction mechanism is proposed to synthesize flower shaped NiO nanostructured materials with improved structural, optical, morphological and magnetic properties compared to microwave synthesis.

Synthesis, growth, crystal structure and characterization of a new organic NLO crystal: l-Lysine 4-nitrophenolate monohydrate (LLPNP)

L-lysine 4-nitrophenolate monohydrate (LLPNP) has been synthesized and grown by solution growth method at room temperature using deionised water as a solvent. The crystal structure of the materials was solved by single crystal X-ray diffraction analysis and it was found that the material has orthorhombic system. The crystallinity of the grown crystals was studied by the powder X-ray diffraction analysis. Molecular structure of the grown crystal was investigated by 1H NMR spectroscopy. The various functional groups of the sample were identified by Fourier transform infrared and Fourier transform-Raman spectroscopic analyses. Thermal stability of the grown crystal has been studied by Thermogravimetric and Differential thermal (TG&DTA) analysis. The optical absorption of the grown crystals has been ascertained by UV-Vis-NIR absorption studies. Second harmonic generation (SHG) efficiency of the material has been determined by Kurtz and Perry technique and the efficiency was found to be 4.45 and 1.4 times greater than that of standard KDP and urea samples, respectively.

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals.

Single crystals of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of l-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vickers microhardness method.

Effect of solvents on the bulk growth of 4-aminobenzophenone single crystals: a potential material for blue and green lasers.

Although 4-aminobenzophenone (4-ABP) is the best derivative of benzophenone with 260 times higher second harmonic generation (SHG) efficiency than potassium dihydrogen phosphate (KDP), growth of high quality bulk crystal still remains a difficult task. In the present work, the effect of solvents on solubility and growth aspects of 4-ABP was investigated to grow inclusion free 4-ABP crystals. The growth processes were discussed based on solute-solvent interaction in two different growth media of ethyl acetate and ethanol. The growth rate and thereby solvent inclusions are relatively higher in ethyl acetate grown crystal than the crystal grown from ethanol. The structural, thermal and optical properties of 4-ABP crystals were studied. The enthalpy of 4-ABP melting process was estimated from differential thermal analysis. The optical transmission study shows that 4-ABP crystals grown from ethanol has high transparency compared to ethyl acetate grown sample due to solvent inclusion in the later crystal.

Investigations on the growth aspects and characterization of semiorganic nonlinear optical single crystals of L-histidine and its hydrochloride derivative.

Semiorganic single crystals of l-histidine and l-histidine hydrochloride monohydrate have been obtained in a single solution prepared from the mixture of l-histidine and hydrochloric acid in 1:2M ratio. Growth aspects of the single crystals have been discussed along with characterization studies. Crystal system and lattice parameters have been identified by X-ray diffraction analyses. It has been observed that the grown crystals possess orthorhombic system but with different set of lattice parameters. Presence of various functional groups has been identified and formation of two different crystals has been confirmed by Fourier transform infrared spectral analyses and FT-Raman studies. Linear and nonlinear optical properties have been studied by UV-Vis spectral analyses and Kurtz-Perry powder technique respectively. The thermal stability of the grown crystals was determined by thermal analyses. From the characterization studies it is found that both the crystals are useful for second harmonic generation applications.

Tailoring bismuth telluride nanostructures using a scalable sintering process and their thermoelectric properties

Bismuth telluride (Bi2Te3) nanocrystals were synthesized using a wet chemical method, and 1 mm thick pellets of nanocrystals with a 10 mm diameter were made using a high pressure and high temperature sintering (HPHTS) process. The nanostructures were tailored using the sintering process, and the impact of the sintering temperature on the morphological evolution and phase transformation of the pelletized Bi2Te3 nanocrystals were studied using standard analytical techniques. A phase change from Bi2Te3 to BiTe was observed in pellets sintered at high temperatures, and the BiTe phase dominated in the pellets sintered at 773 K. The thermoelectric properties of the as-prepared and sintered pellets were measured. The Seebeck coefficient of the Bi2Te3 nanocrystals increased with sintering temperature, and decreased at higher sintering temperatures (>673 K). Moreover, the power factor of the Bi2Te3 nanocrystals was significantly enhanced by sintering. The variations in the Seebeck coefficient and power factor are explained with a proposed model using the phase and morphological changes in the sintered Bi2Te3 pellets.

Determination of gas sensing properties of thermally evaporated WO 3 nanostructures

Thin films of tungsten oxide (WO3) nanostructures were grown on indium tin oxide coated glass substrates by thermal evaporation technique under oxygen and argon (O2/Ar) mixed gas atmosphere. The films were characterized by X-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy to study the structural and morphological properties of the grown films. Three different shapes of nanostructures (one dimensional nanorods, two dimensional nanosheets and three dimensional nanosized orthorhombic structures) were formed due to the variations of growth conditions such as substrate temperature and oxygen/argon flow rate. In particular, the flow rate of oxygen plays an important role in controlling the nucleation and growth of WO3 nanostructures. The ethanol gas sensing properties of the films were investigated under different concentrations (10–50xa0ppm) at room temperature, which reveals that the sensitivity of the sensor was greatly enhanced with the increasing gas concentration. This result indicates that the WO3 films are good candidate for sensing ethanol gas in low concentration at room temperature.

Growth and characterization of a novel nonlinear optical borate crystal--yttrium calcium borate (YCB).

A new nonlinear optical single crystal yttrium calcium borate Y2CaB10O19 (YCB) was grown for the first time from its melt. The starting materials were prepared by the solid-state reaction method. The melting point of the synthesized material was identified to be 967 °C. YCB crystal exhibits monoclinic crystal structure with the space group C2. The crystalline perfection of the grown YCB crystal was found to be good. From the UV-VIS-NIR studies, the lower cutoff wavelength of the crystal occurs below 200 nm. The functional groups of the grown crystal were assigned using the FTIR data. The second harmonic generation (SHG) of the YCB crystal was observed using a Nd:YAG laser with a fundamental wavelength of 1064 nm. The laser damage threshold value of the YCB crystal was found to be very high - 10.5 GW/cm(2).

Effect of deposition time on the chemical bath deposition method of ZnO thin films

Highly conductive and transparent zinc oxide thin films were prepared on well cleaned glass substrates by chemical bath deposition (CBD) and effect of deposition time were investigated. The crystalline nature increases with increase in deposition time whereas the diffraction angle remains same for ali the films. The flower shapes were initially formed as assemblies on glass substrates and the optical property of the ZnO nanostructure were characterized by UV-Vis spectroscopy analysis.

Electro optic properties of DAST single crystal

4 N, N-dimethylamino N methyl stilbazolium tosylate (DAST) is an excellent organic nonlinear optical material. Single crystal of DAST has been grown by solution growth method using allyl alcohol as a solvent for the first time. Its electro optic properties such as half wave voltage and electro optic figure of merit have been measured for the first time by field induced birefringence method corresponding to the wavelength of 632 nm.