Suchergebnisse

Development of a method of formation of chiral free-standing films from carbon nanotubes (CNTs), which circumvents the limitations of the established techniques, is presented. CNT macroassemblies of any size and shape can be made from desired CNT feed including those synthesized or sorted with the objective of chirality control. Free-standing CNT films were created from various starting CNT materials the most interesting being of predominantly (6,5) and (7,6) chirality. The technique offers the advantages of technical simplicity, scalability and non-destructive nature representing an important step toward the research, development and implementation of monochiral single-wall CNT tangible objects. ; The European Research Council (Grant Agreement - 259061). National Science Center, Poland (Grant Agreement - UMO-2015/19/P/ST5/03799). The European Union's Horizon 2020 research and innovation programme (Grant Agreement - 665778).

2010/2011 ; In the last decade the nanostructured carbon materials, especially single walled carbon nanotubes (SWNTs), had emerged as probable substitutes for Silicon in the next generation of electronic devices. This is due to their unique physic and chemical properties. Likewise, scientists all around the world have made a huge effort to introduce carbon materials into the market. Despite this effort, commercial application for carbon nanotubes in electronic devices has not yet been achieved. The hindrances are due to two reasons mainly: the first one is for the physico-chemical properties of carbon nanotubes; for example, the strong π-π interactions between nanotube creates thick bundles; in the pristine form CNTs are almost indispersible in any solvent; nanotubes are practically inert chemically; and finally the synthesis of SWNTs produces a mixture of semiconducting and metallic nanotubes. The second hindrance is related to the device construction and characteristics, e. g. the high contact resistance between SWNT and electrodes, the selection of electrode materials, the gate dielectric structure and material are also importants, and finally how the SWNT is contacted with electrodes. In my opinion, if it is desired to use a new material in high technology applications, will be necessary to use new methodologies and break paradigms. In this work I try to mimic what nature does, assemble objects from the bottom up. So, for the bottom up construction of the device I combine the assembly qualities of organic chemistry and the physical properties of inorganic materials. In this way, to deal with the challenges of construction and improvement of the "next device generation" I used non-conventional procedures in electronic devices: sol-gel process for the synthesis of the gate dielectric; organic chemistry for improvement on the electrodes-nanotube resistance; and propose the use of DNA origami as general assembly process for the device. For the sorting of nanotubes it is applied a top-down approach, the current technologies in the synthesis of SWNTs are not able to render a single electric behaviour yet. The scope of this work is to demonstrate that it is feasible to use bottom up techniques in the construction of devices, replacing the use of "top down" processes that are currently in use in the silicon industry. The thesis is organized as follows: • In the chapter 1 the carbon materials characteristics are introduced and how they can change the actual Silicon technologies. Additionally a brief review the electronic and optical properties of SWNTs, including the optical spectroscopy techniques used for their characterization: absorption and Raman. • Chapter 2 discuses briefly the grow methodologies of SWNTs, the as-produced characteristics, purification techniques and sorting by electronic behaviour. Graphene exfoliation is reviewed. • Chapter 3 deals with the design and synthesis of the dielectric material on SWNTs and over graphene. Sol gel process is briefly explained. • In chapter 4 is explained the synthesis of metallic nanoparticles and the selective linking with SWNTs. • Chapter 5 is dedicated to perspectives and further work, concerning mainly to device assembly, focusing in the manipulation of DNA and SWNTs. This work has been supported by the National Council for Science and Technologies, CONACyT (Mexican Government). ; XXIV Ciclo ; 1982

There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers. Am. J. Ind. Med. 55:395–411, 2012. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

This study assessed the health risks via inhalation and derived the occupational exposure limit (OEL) for the carbon nanotube (CNT) group rather than individual CNT material. We devised two methods: the integration of the intratracheal instillation (IT) data with the inhalation (IH) data, and the "biaxial approach." A four‐week IH test and IT test were performed in rats exposed to representative materials to obtain the no observed adverse effect level, based on which the OEL was derived. We used the biaxial approach to conduct a relative toxicity assessment of six types of CNTs. An OEL of 0.03 mg/m3 was selected as the criterion for the CNT group. We proposed that the OEL be limited to 15 years. We adopted adaptive management, in which the values are reviewed whenever new data are obtained. The toxicity level was found to be correlated with the Brunauer‐Emmett‐Teller (BET)‐specific surface area (BET‐SSA) of CNT, suggesting the BET‐SSA to have potential for use in toxicity estimation. We used the published exposure data and measurement results of dustiness tests to compute the risk in relation to particle size at the workplace and showed that controlling micron‐sized respirable particles was of utmost importance. Our genotoxicity studies indicated that CNT did not directly interact with genetic materials. They supported the concept that, even if CNT is genotoxic, it is secondary genotoxicity mediated via a pathway of genotoxic damage resulting from oxidative DNA attack by free radicals generated during CNT‐elicited inflammation. Secondary genotoxicity appears to involve a threshold.

Recently, copper-nanocarbon composites have become the focal point of many research groups around the world. The reason for this phenomenon is that carbon nanotubes or graphene have proven that they can bring the technology of copper to a whole new level due to their extraordinary electrical, thermal and mechanical properties. Addition of even small amounts of nanocarbon into copper matrix can significantly enhance its performance, but unfortunately integration of these two materials is not trivial. In this review article we highlight methods of manufacture of Cu-nanocarbon composites and properties of the resulting material. We stress their strong and weak points as well as indicate pending challenges remaining to be sorted out to produce the nanocomposite of significantly improved properties as compared to neat Cu. Finally, we identify future R&D directions, which must be taken to bring these materials closer to mass-production and eventually real-life applications. ; National Science Center, Poland (Grant Agreement - UMO-2015/19/P/ST5/03799). The European Union's Horizon 2020 research and innovation programme (Grant Agreement - 665778).

Carbon nanotubes (CNT) are an attractive reinforcement material for several composites, due to their inherently high strength and high modulus of elasticity. There are controversial results for cement paste with admixed CNT up to 500 µm in length. Some results show an increase in flexural or compressive strength, while others showing a decrease in the values. Our experiments produced results that showed a small increase in fracture energy and tensile strength. Micromechanical simulations on a CNT-reinforced cement paste 50×50 µm proved that CNT clustering is the crucial factor for an increasein fracture energy and for an improvement in tensile strength.