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Transmission Electron Microscopy Measurements (transmission + electron_microscopy_measurement)
Selected AbstractsGaN nanorods and LED structures grown on patterned Si and AlN/Si substrates by selective area growthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Shunfeng Li Abstract GaN nanorods (NRs) show promising applications in high-efficiency light emitting diodes, monolithic white light emission and optical interconnection due to their superior properties. In this work, we performed GaN nanostructures growth by pre-patterning the Si and AlN/Si substrates. The pattern was transferred to Si and AlN/Si substrates by photolithography and inductively-coupled plasma etching. GaN NRs were grown on these templates by metal-organic vapour phase epitaxy (MOVPE). GaN grown on Si pillar templates show a truncated pyramidal structure. Transmission electron microscopy measurements demonstrated clearly that the threading dislocations bend to the side facets of the GaN nanostructures and terminate. GaN growth can also be observed on the sidewalls and bottom surface between the Si pillars. A simple phenomenological model is proposed to explain the GaN nanostructure growth on Si pillar templates. Based on this model, we developed another growth method, by which we grow GaN rod structures on pre-patterned AlN/Si templates. By in-situ nitridation and decreasing of the V/III ratio, we found that GaN rods only grew on the patterned AlN/Si dots with an aspect ratio of about 1.5 - 2. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Carbon Nanotube Junctions: Multibranched Junctions of Carbon Nanotubes via Cobalt Particles (Adv. Mater.ADVANCED MATERIALS, Issue 44 200944/2009) Junctions between different carbon nanotubes (CNTs) created using cobalt particles as central nodes (background) are demonstrated by Ming-Sheng Wang and co-workers on p. 4477. The process involves high-temperature electron irradiation of areas where a metal particle is located at the overlapping region of two CNTs. In situ transmission electron microscopy measurements show that the junctions are electrically conductive and mechanically robust. The extension of this technique towards creating more complicated structures, such as a 3D CNT network, is also depicted in the cover. [source] Multibranched Junctions of Carbon Nanotubes via Cobalt ParticlesADVANCED MATERIALS, Issue 44 2009Julio A. Rodríguez-Manzo Junctions between different carbon nanotubes are created using cobalt particles as central nodes (see image). The process involves high temperature and electron irradiation of areas where a metal particle is located at the overlapping region of two nanotubes. In situ transmission electron microscopy measurements show that the junctions are electrically conductive and mechanically robust. A high breaking strength of 1,5,GPa is found for the junctions. [source] Fast and Almost Complete Nitridation of Mesoporous Silica MCM-41 with Ammonia in a Plug-Flow ReactorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Fumitaka Hayashi The title reaction proceeded well to yield silicon (oxy)nitride at 973,1323 K using a plug-flow reactor. The degree of nitridation was studied as a function of temperature and time of nitridation, the sample weight, and the flow rate of ammonia. It was dependent on the reaction temperature and the amount of ammonia supplied per sample weight. The nitridation at 1273 K for 10,25 h yielded the oxynitride with 36,39 wt% nitrogen, which was very close to 40 wt% of Si3N4. Characterization with X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy measurements, and nitrogen adsorption revealed the conversion of MCM-41 to the corresponding oxynitride without essential loss of the mesoporous structure, the decrements of the lattice constant and the pore diameter by 20,35%, and the increments of the wall thickness by ca. 45%. Solid-state 29Si nuclear magnetic resonance spectra during the nitridation clearly showed fast decrease in SiO4 species and slow in SiO3(OH). Various intermediate species, SiOxNy(NH2 or NH)z, were observed to be formed and finally, ca. 70% SiN4 species, ca. 20% SiN3(NH2 or NH), and ca. 10% SiON2(NH2 or NH) were produced, being consistent with the results of the above mentioned elemental analysis. [source] Dispersing silicon nanoparticles in a stirred media mill , investigating the evolution of morphology, structure and oxide formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007A. Reindl Abstract Silicon nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions (in regard to aggregation) of Si nanoparticles were produced after 6 hours of dispersing. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy as a function of dispersing time. The average crystallite size decreased from about 18 nm down to about 10 nm within 24 hours of milling as determined by X-ray diffraction and Raman scattering measurements. In addition careful analysis of the Raman spectra revealed a decrease of the crystalline volume fraction from 75% down to 24% and a corresponding increase of the amorphous phase. The microstructural development with varying crystallite size and crystalline volume fraction was directly confirmed by transmission electron microscopy measurements. Elemental analysis showed an increase of oxygen content that was directly proportional to the increase in specific surface area of the silicon nanoparticles during the dispersing process. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscopy that indicated vibrational bands of HSi,Si3,xOx, SiOx, and residual 1-butanol. The final product of the dispersing process seems to be a two-phase mixture of amorphous Si and Si nanocrystallites covered with SiOx on the surface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hybrid metal/silicon nanocomposite systems and their catalytic activityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009Sergej Polisski Abstract In this work we studied the reduction of metal salts and their mixtures on extended hydrogen-terminated porous silicon surfaces. For these experiments we employed salts of Au, Ag, Pt and their mixtures. We show that the size and shape of resulting metal and metal alloy nanoparticles depends on the pore morphology. This has been confirmed by transmission electron microscopy measurements and plasmon resonance experiments. Finally we demonstrate catalytic activity of formed Pt nanoparticles in PSi matrix via monitoring the conversion of carbon monoxide. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis, and structural and morphological characterization of iron oxide,ion-exchange resin and ,cellulose nanocomposites,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2001Lorenza Suber Abstract The synthesis and the comparative structural and morphological study of iron oxide nanoparticles in polystyrene-based ion-exchange resins and cellulosics are reported. The synthesis of magnetite was performed under nitrogen atmosphere by an in situ method in the presence of the matrix itself. Scanning and transmission electron microscopy measurements led to a detailed characterization of matrix morphology and of magnetic particle structure, size and morphology. The results show that the matrix influences the iron oxide particle size; the average size is about 7,nm in the resins and 25,nm in the celluloses. In the resins, particles are present inside the pores and as aggregates on the surface of the resin beads, whereas in the cellulose they are present on the surface and in the swollen network of the microfibers constituting the single fibers. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||