The effect of a focusing electric field on the formation of carbon nanotubes in a
direct current arc-plasma is investigated. The hard deposits on the surface of the
cathode are the main products, rich in multi-walled carbon nanotubes. It is seen
that the focusing electric field has a distinct influence on the yield, purity and
morphology of the nanotubes. The yield of the carbon nanotubes under the ‘focused
field condition’ has been found to be higher than that derived from the normal
electrode configuration. It has been observed that the deposition of carbonaceous
soot on the reactor wall is considerably reduced on application of the focusing
electric field. Transmission electron microscopy has been used to determine the
morphology of the nanotubes. In addition, Raman spectroscopy has helped in
distinguishing the graphene-like structures from the disordered carbon networks
and helped in analysing the morphology of the tubes. Thermal analysis gave a
qualitative estimation of the relative yield of carbon nanotubes within the cathode
deposits and their thermal stabilities. The crystalline nature of the samples has
been confirmed by x-ray diffraction analysis. The results clearly indicate that the
focusing electric field confines the positively charged carbon precursors within the
cathode–anode space causing high relative yield and purity and has a distinct
effect on controlling the inner diameter of the as-synthesized carbon nanotubes.
Films of nanocrystalline g-Fe 2 O 3 were deposited on silicon substrates by using the technique of electrophoretic deposition. The precursor powder was nanocrystalline g-Fe 2 O 3 , which was synthesized, using DC arc plasma in the oxygen ambient by vapourYvapour interaction in gas phase condensation; at a stabilized arc current of 40 A. This powder was characterized by X-ray diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and Mössbauer Spectroscopy. An increase in directional coercivity was observed in case of films deposited on silicon substrates, which is dramatically significant. Preferred orientation of almost similar sized nanocrystalline magnetic domains in deposited films is evident from the results of X-ray diffraction and Transmission Electron Microscopy results. The preferred alignment of the nanocrystallites seems to be responsible for the significant changes observed in magnetic properties of films.
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