Uniformly distributed nickel nanoparticles created by heating the carbon nanotube
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in Gao Max-Planck-Institut für Metallforschung, Heisenbergstrasse 3, D-70569 Stuttgart, Germany (Received 8 August 2002; accepted 6 December 2002)
Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discharge were studied by electron diffraction, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and x-ray energy dispersive spectrometer (EDS). The nanoparticles have diameters in the range of 3–15 nm. Electron diffraction pattern and HRTEM images analysis both show that the nanoparticles can be nickel or diamond. EELS and EDS analysis in a dedicated scanning transmission electron microscope showed that the nanoparticles are face-centered-cubic nickel particles rather than diamond nanocrystals. The mechanism of formation of nickel nanoparticles below its melting point is discussed.
I. INTRODUCTION
Nanoparticles, including metal and diamond nanoparticles, have been intensively investigated over the years since they display many unusual properties compared to bulk materials.1 In particular, metal particles, such as indium,2 lead,3 germanium,4 nickel, and iron,5,6 received much more interest for their particular importance in fundamental research and potential applications. It is well known that small particle of face-centered-cubic (fcc) materials with a diameter less than several hundred nanometers are either single crystalline, twinned, or even multiply twinned particles.1 Unusual crystallographic structure and its fluctuation in germanium,7 indium,2 and lead3 nanoparticles were often found. Recent research about the magnetization of nickel nanoparticles indicated that nanoparticles behave like a superparamagnet and a spin glass above and below the irreversibility temperature.5 On the other hand, the discovery of carbon nanotubes stimulated considerable interest to synthesize diamond nanocrystals from carbon nanotubes. It has been found that diamond nanocrystal can be obtained from carbon nanotubes under extreme conditions, such as shock waves and laser irradiation.8,9 Moreover, under electron beam irradiation some of the carbon nanotubes can also transform into diamond nanocrystals.10 However, it is interesting to know what can be obtained when
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J. Mater. Res., Vol. 18, No. 3, Mar 2003 Downloaded: 16 Mar 2015
carbon nanotubes are evaporated at high temperature. To our knowledge only a little work has been done on the evaporation of carbon nanotubes at elevated temperature under the vacuum. In this letter, we report our results on the evaporation of carbon nanotubes at elevated temperature in a vacuum system. II. EXPERIMENTAL
The carbon nanotubes used in this experiment were synthesized by arc-discharge using nickel catalyst and were purified. The preparation and processing are shown in Ref. 11 in detail. A two-step vacuum system was used to evaporate carbon nanotubes. After purification, the carbon nanotubes were placed on the molybdenum boat an
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