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Nanoparticles, submicron-diameter tubes, and rods of Si3N4 were synthesized from the thermal treatment of wheat and rice husks at temperatures at and above 1300°C in a nitrogen atmosphere. The whole pattern Rietveld analysis of the observed diffraction data from treatments at 1300°C showed the formation of only hexagonal α-phase of Si3N4 with an R-factor of 1%, whereas samples treated at 1400°C and above showed both α- and β-phases with an R-factor of 2%. Transmission electron microscopy showed the presence of tubes, rods, and nanoparticles of Si3N4. In a two-step process, where pure SiC was produced first from rice or wheat husk in an argon atmosphere and subsequently treated in a nitrogen atmosphere at 1450°C, a nanostructured composite material having α- and β-phases of Si3N4 combined with cubic phase of SiC was formed. The thermodynamics of the formation of silicon nitride is discussed in terms of the solid state reaction between organic matter (silica content), which is inherently present in the wheat and rice husks, with the nitrogen from the furnace atmosphere. Nanostructures of silicon nitride formed by a single direct reaction or their composites with SiC formed in a two-step process of agricultural byproducts provide an uncomplicated sustainable synthesis route for silicon nitride used in mechanical, biotechnology, and electro-optic nanotechnology applications. [ABSTRACT FROM AUTHOR]

Nanotubes, nanowires, nanobelts, and nanorods of SiC were synthesized from the thermal treatment of wheat husks at temperatures in excess of 1450 °C. From the analysis based on x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy, it has been found that the processed samples of wheat husk consisted of 2H and 3C polytypes of SiC exhibiting the nanostructure shapes. These nanostructures of silicon carbide formed from wheat husks are of technological importance for designing advance composites, applications in biotechnology, and electro-optics. The thermodynamics of the formation of SiC is discussed in terms of the rapid solid state reaction between hydrocarbons and silica on the molecular scale, which is inherently present in the wheat husks. [ABSTRACT FROM AUTHOR]

We have investigated the thermally induced transformation of various residues of the corn plant into nanoparticles and nanorods of different silicon carbide (SiC) polytypes. This has been accomplished by both microwave-induced and conventional furnace pyrolysis in excess of 1450 °C in an inert atmosphere. This simple process of producing nanoparticles of different polytypes of SiC from the corn plant opens a new method of utilizing agricultural waste to produce viable industrial products that are technologically important for nanoelectronics, molecular sensors, nanophotonics, biotechnology, and other mechanical applications. Using x-ray and Raman scattering characterization, we have demonstrated that the processed samples of corn husk, leaves, stalks, and cob consist of SiC nanostructures of the 2H, 3C, 4H, and 6H polytypes. [ABSTRACT FROM AUTHOR]

Time resolved, in-situ, energy dispersive x-ray diffraction was performed in an electrolysis cell during electrochemical loading of palladium foil cathodes with hydrogen and deuterium. Concentrations of H:Pd (D:Pd) up to 1:1 in 0.1 M LiOH (LiOD) in H2O (D2O) electrolyte were obtained, as determined by both the Pd lattice parameter and cathode resistivity. In addition, some indications on the kinetics of loading and deloading of hydrogen from the Pd surface were obtained. The alpha-beta phase transformations were clearly delineated but no new phases at high concentration were determined. [ABSTRACT FROM AUTHOR]

Cobalt Oxide (Co3O4) was reduced to metallic Co using the nut shells of pistachio by heat treatment at temperatures of 1400°C and 1500°C in an argon gas atmosphere. This method for reducing Cobalt Oxide may provide a valuable route for reclaiming nanoparticles of metallic Co from waste material. Rietveld analysis of the x-ray diffraction profiles showed the presence of two phases of Co; FCC (γ-Co), and ΒCC phase of Co in addition to the presence of C in the graphite phase. The samples synthesized by processing at 1400°C showed only the FCC phase of Co whereas mixed phases of FCC and BCC Co were formed for samples heat treated at 1500°C. The magnetic properties were determined using VSM and FMR measurements. A magnetic saturation value of 160 emu/g was determined for the FCC phase which is consistent with the literature value. On the other hand, the magnetic saturation value of BCC Co was measured to be 214 emu/g. Magnetic data suggest the average magnetic moment is consistent with FCC cobalt. This simple method of producing BCC-Co has potential industrial and possible medical applications such as magnetic sensors, electromagnetic shielding, magnetic memory, magnetic fluids, magnetic composites and catalysis. [ABSTRACT FROM AUTHOR]

The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces. [ABSTRACT FROM AUTHOR]

Responsivity measurements are reported for LiNbO3 electro-optic field sensors operated under applied electric fields at ac frequencies in the vicinity of the acoustic resonance values of the crystals. At these frequencies, piezoelectric effects dominate the sensor output. These resonance effects are well known and commonly considered parasitic. However, we propose their use as a sensitivity-enhancing mechanism for electric-field detection. We have found that our field sensors operated within these resonances responded linearly with the applied field strength and exhibited increases in their intrinsic sensitivities as high as 350 times larger than their normal, electro-optic values. Our modeling of the data suggests that the sensitivity enhancements are produced by the interplay between photoelastic shifts in the refractive indices and the physical vibration modes of the crystals. Aside from narrowband applications, these resonant enhancements can be exploited with fields at frequencies well beyond the narrow bandwidth of the acoustic resonance, if the fields are properly modulated. [ABSTRACT FROM AUTHOR]

We have measured the electro-optic response of LiNbO3 and SrxBa1-xNb2O6 crystals to be used for electric-field sensors. Our results indicate that optically induced refractive index variations (photorefractivity) in the crystals affect the temporal stability and sensitivity of the sensors. Spatial distributions of the refractive indices produced from the photorefractivity create incoherence in the polarization of the probing laser passing through the crystal (optical probe). In LiNbO3 crystals, this spatial incoherence was negligible and sensor responsivities close to the theoretical maximum were attained. However, in SrxBa1-xNb2O6 crystals, strong spatial variations of the principal refractive indices resulted in an extremely incoherent polarization of the optical probe and reduced the electro-optic responsivity dramatically. The photorefractive-induced sensitivity loss is modeled using a distribution function (rather than a constant value) to describe the phase of the optical probe. These results emphasize the importance of an optically stable material, with little or no photorefractivity, when designing an electro-optic field sensor. [ABSTRACT FROM AUTHOR]

Studies of pressure induced phase transformations of ZnS nanoparticles using diamond anvil cells and synchrotron radiation were carried out to 20.0 GPa. Nanoparticles initially in the zinc-blende and wurtzite phases both transformed to the NaCl phase under the application of pressure. The zinc-blende particles, which were of 2.8 nm size, and the wurtzite particles, which were of 25.3 nm size, transformed to the NaCl phase at 19.0 and 15.0 GPa, respectively. Nanoparticles of the wurtzite phase never regained their initial wurtzite structure but returned to the zinc-blende phase upon downloading the pressure. The resultant zinc-blende nanoparticles transformed to the NaCl phase upon the reapplication of a pressure of 15.0 GPa. Nanoparticles initially in the zinc-blende phase returned to their original phase. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on microwave dielectric properties of strained thin films grown on manganese oxide by pulsed laser deposition. Correlation between thin films' structure and microwave dielectric properties; Tetragonal distortion of epitaxially grown films; Phenomenological thermodynamic theory based on the strain along in-plane direction of films.