1,721,246 research outputs found
Growth and Characterisation of Boron Rich Nanomaterials
Full text linkIn this study nanomaterials are grown in a solid state reaction at 1300C of boron, barium oxide and iron(II/III)oxide powders in an argon atmosphere. The nanomaterials are shown to be grown via vapour based method by growing the nanomaterials on a separate silicon wafer that has been sputtered with iron and placed downstream of the powders in the flow of argon. An area of the silicon wafer is kept free of iron by using a mask when sputtering the wafer. When nanomaterials are grown, the masked area remains free of nanomaterials. This shows that the presence of iron is vital for the nucleation of the nanomaterials and also indicates the possibility of growing these nanomaterials on targeted sites.
The nanomaterials produced are examined and it is found that we have a presence of amorphous, crystalline and multiple twinned nanowires. The evidence collected suggests that 70% of the nanowires are twinned. The single crystal nanowires can be identified as boron carbide by comparing to diffraction pattern simulations of a boron carbide unit cell. The twinned diffraction pattern is shown to be due to different segments of the nanowire being in different diffraction condition by using Dark Field imaging. The Twinned wires are also shown to have at least four segments in a cyclic [001] twinning orientation in simultaneous diffraction condition by comparing to a twinned structure constructed from simulations. Elemental analysis using Electron Energy Loss Spectroscopy and Energy Dispersive X-ray shows that the composition of the nanomaterials is mainly boron and carbon.
The role of the iron layer on the wafer is investigated to see how varying the thickness will affect the nanomaterials grown. It is successfully shown that an increase in the thickness of the iron layer results in a greater density of nanomaterials. However there is no great variation in the average diameter of the nanomaterials produced.
The absence of a visible signal for iron in the Elemental analysis of nanostructure covered silicon wafer shows that the amount of iron in the sample has decreased during the reaction. However iron is found in small amounts in droplet structures at the tips of nanomaterials this is different to work done on a similar system at 1100C. This suggests that the role of the iron in the growth of these nanomaterials at this temperature is not yet understood. However this work has confirmed that the iron is essential for the nucleation of the nanomaterials, but post nucleation growth that was previously assumed to be a conventional VLS growth may switch to an oxide assisted growth mode
Síntesis y caracterización de nanotubos de titania (TiO2) y posibles aplicaciones en fotocatálisis
Full text link"En 1991, en el laboratorio de investigación fundamental NEC en Tsukuba Japón, Sumio Iijima observaría a través de un microscopio electrónico unas extrañas fibras nanométricas depositadas sobre una mota de hollín, estas fibras constituidas por carbón poseían una gran longitud y debido a su forma no tardaron en llamarlos nanotubos"
Nanotubes
No full textCarbon nanotubes are long structures of cylindrical shape with a diameter from one to several tens of nanometers. They consist of one or several rolled into a tube hexagonal graphite planes. Sumio Iijima synthesized them by the method of arc evaporation. In the mid-twentieth century there were two research teams from the USA and New Zealand
Nanotechnik - der integrative Ansatz macht's
No full textS.IW2Als die Kohlenstoffnanoröhren (englisch: Carbon Nanotubes, CNT) im Jahre 1991 von Sumio Iijima entdeckt wurden, war die Euphorie groß. Die hervorragenden mechanischen und elektrischen Eigenschaften der Carbon Nanotubes, genau genommen der einzelnen CNTs, versprachen Verbesserungen in vielen Bereichen: Für Kompositmaterialien mit Metallen, Keramiken oder Kunststoffen als Matrixmaterialien und CNTs als Füllstoffe versprach man sich stark verbesserte Eigenschaften.Nr.11/1
Synthesis and characterization of carbon nanotube
No full text70 p.Since the discovery in 1991 by Sumio Iijima, carbon nanotubes (CNTs) have attracted much research attention because of their mechanical, thermal and electrical properties. CNTs can be produced by methods of arc discharge, laser ablation, thermal synthesis and chemical vapor deposition (CVD). CVD is probably the most versatile production method of CNTs as well as the most promising method for producing Single-walled CNTs (SWCNTs) with high quality and yield.Master of Science (Precision Engineering
Work functions of functionalized singled-walled carbon nanotubes
Full text linkThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (leaves 39-40).Introduction: Carbon nanotube (CNT) structures were discovered by Sumio Iijima in 1991 at NEC laboratories in Japan. Since their discovery, scientists and engineers have been fascinated by their electrical and mechanical properties. Their unique characteristics, in addition to their nanoscale size, have generated much excitement about the possible applications of this novel. material.by Janet Ryu.S.B
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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