The structural changes of polycrystalline film C 60 /C 70 :Ni caused by Ni diffusion
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The structural changes of polycrystalline film C60yC70 : Ni caused by Ni diffusion E. Czerwosz Institute of Vacuum Technology, 00-241 Warsaw, Poland
P. Byszewski Institute of Vacuum Technology, 00-241 Warsaw, Poland and Institute of Physics, Polish Academy of Sciences, 02-628 Warsaw, Poland
R. Diduszko and H. Wronka Institute of Vacuum Technology, 00-241 Warsaw, Poland
P. Dłu´zewski and E. Mizera Institute of Physics, Polish Academy of Sciences, 02-628 Warsaw, Poland (Received 19 May 1995; accepted 24 July 1996)
C60yC70 : Ni films with 1.5 wt. % Ni concentration obtained by vacuum deposition under different thermal conditions have been investigated. The structural changes of the layers were investigated by transmission electron microscopy, electron and x-ray diffraction, and Raman spectroscopy. The polycrystalline structure was detected for the layers grown at approximately 450 K on the substrate. At elevated temperature and maintained temperature gradient on the substrate during the process, the changes of the layer’s structure and the formation of Ni microcrystals were observed. The Ni microcrystals (5–10 nm in the diameter) and the elongated shapes dimensioned 10 3 150 nm were perceived.
I. INTRODUCTION
The properties of C60 compounds with several alkali metals1,2 or alkali earth metals3–5 are widely investigated because they have proved to be superconducting. Superconductivity was also searched for in ICl doped fullerenes compounds,6 though later only magnetic properties in C60 I were found.7 The possibility of obtaining fullerene derivatives with transition metals was much less intensively investigated though their magnetic or electric properties could also be interesting.8,9 The transition metals form a number of coordination compounds where metal atoms donate electrons to ligands. A similar situation seems to be possible in the case of C60 FeC60 . In fact, it proved possible to perform the ligands exchange reaction substituting cyclopentadienyl (C5 H5 ) in ferrocene by C60 and to obtain crystalline powder of the composition C60 Fe2 .10–12 The same procedure applied to cobaltocene and to nickelocene proved unsuccessful because of the high reactivity of these compounds toward C60 . In further attempts to obtain C60 Nin compound, we use the vacuum deposition method. In this paper we show that it is possible to obtain the polycrystalline C60 : Ni structure in the for of thin film, but in certain thermal conditions, this structure is transformed into a system containing Ni microcrystals and a carbon-fullerene structure. We suggest that Ni atoms interacting with the fullerenes lead to the degradation of the fullerene molecule. The role of Ni atoms in the 3146
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 12, Dec 1996
Downloaded: 24 Mar 2015
degradation of fullerenes has been already noticed when a Ni target has been bombarded with C60 .13 At the same time several authors have observed long, single-shell nanotubes extending from ultrafine metal par
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