The intramolecular features of carbon 60 and carbon 84 molecules on Si(1 1 1)-7 x 7 surfaces were studied under a UHV-scanning tunneling microscope. Carbon molecules preferentially appear in faulted halves, rather than in unfaulted halves and corner holes; they are embedded in silicon substrates. The orientation and details of the structure of carbon molecules are determined by applying various sample biases to the silicon substrate. As compared with other fullerenes, a bright pentagonal ring with nebulous clusters which represents the cage structure is clearly observed on top of carbon 60 molecules. The bright stripes associated with partitioned curves which depict eight features of asymmetrical C-84 molecules are also investigated on Si(1 1 1)-7 x 7 surfaces. The orientations and possible configurations of C-60 and C-84 are considered in this work. The energy differences for various features of C-60 and C-84 molecules are estimated and discussed. The corresponding models with respect to each intramolecular feature are proposed and compared with recent theoretical calculation. (C) 2008 Elsevier B.V. All rights reserved.