Matchstick Nanotubes: Structure Control and Properties
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Matchstick Nanotubes: Structure Control and Properties Vincent Jourdain 1,3, Matthieu Paillet 1, Philippe Poncharal 1, Ahmed Zahab 1, Annick Loiseau 2, Patrick Bernier 1, John Robertson 3 1 GDPC, Université Montpellier II, Place Eugène Bataillon, CC26, 34095 Montpellier Cedex 5, France 2 LEM, UMR 104 CNRS-ONERA, ONERA, BP 72, 92322 Châtillon Cedex, France 3 Cambridge University, Engineering Department, Trumpington St, Cambridge CB2 1PZ, UK ABSTRACT We report here on the catalyst features found critical in order to induce the growth of matchstick nanotubes by a sequential catalytic growth mechanism. The presence of phosphorus is required to form metal phosphide particles active for the formation of carbon nanotubes with a matchstick morphology. The metal composition does not influence the nanofilament type but strongly affect the nanotube yield. Original properties of these new periodic nanostructures are also highlighted, such as the preferential breaking at the thin nanomatch interjunctions, giving rise to individual nanomatches in suspension after ultrasonic treatment. The possibility to use this mechanism to insert carbon nanotubes with ferromagnetic nanoparticles is also reported. INTRODUCTION We recently reported on an original growth mode enabling to periodically insert carbon nanotubes with catalyst nanoparticles during their growth.[1, 2] This mechanism was so-called “sequential catalytic growth”. Key for inducing this growth mechanism is the use of phosphorus as a co-catalyst with the appropriate ratio of mixed metal catalyst. The as-produced nanofilaments were named “matchstick nanotubes” because of the shape of their elementary units. The thin nanomatch interjunctions constitute preferential breaking points efficiently cleaved by ultrasonic treatment. One other particular interest lies in the possibility to insert small (usually monocrystalline) and separated particles along the whole length of the carbon nanofilament. The resulting nanostructures could find applications in magnetic storage [3] and nano-spintronics [4]. Until now, the nanoparticles inserted in these matchstick nanotubes were only nickel iron phosphides. We also report here on the insertion of iron cobalt phosphide nanoparticles and their characterisation by Magnetic Force Microscopy. EXPERIMENTAL Layers of nickel, iron and cobalt were deposited by evaporation on different flat catalyst supports: silicon, silica, alumina (Alfa Aesar, single crystal, 99.9 %), phosphoric acidimpregnated alumina and anodic alumina membranes (AAM, Anodisc Whatman 0.02µm). AAMs intrinsically contain ~1.5% at. of phosphorus due to the phosphoric acid used during their synthesis. The supported catalysts were heated at 10°C/min, in air until 600°C and under argon flow until the growth temperature (880-1160°C). A CH4/H2 gas mixture was introduced into the reactor during 5 min. The influence of the CH4 flow rate was studied in the range 36-300 sccm, while keeping the H2 flow rate constant at 730 sccm. The reactive species were purged during 15 min with an a
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