SYNTHESIS, IDENTIFICATION, AND GROWTH-MECHANISM OF FE, NI, AND CO CRYSTALS ENCAPSULATED IN MULTIWALLED CARBON NANOCAGES

Nanometer size crystalline particles of alpha-Fe, gamma-Fe, Ni, beta-C o, and Co3C encapsulated in multiwalled carbon cages are synthesized b y a standard dc arc evaporation of composite anodes containing 10-15 w t.% each of the metals or their compounds. The typical particle size i s approximately 10 nm. Elemental analysis is made by x-ray energy disp ersive spectroscopy. The spectra show only the peaks associated with t he respective metal and carbon. The stoichiometry and phase of the cry stals are assigned from the characteristic lattice spacings obtained b y high-resolution transmission electron microscopy and x-ray diffracto metry. Particle size distribution is obtained from a statistical surve y of electron micrographs. A statistical growth model is adequate for explaining the crystalline particle size distribution of the encapsula ted crystals consisting of alpha-Fe and gamma-Fe smaller than 15 nm. S ignificant deviation from the model is found for the encapsulated crys tals consisting of alpha-Fe and gamma-Fe larger than 15 nm, those of N i larger than 4 nm, and those consisting of beta-Co and Co3C larger th an 6 nm. The deviation is discussed in terms of encapsulation effect o n the particle growth mechanism.