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Closo-1,2-dicarbadodecaborane (C2B10H12) is a source compound found to be suitable for the deposition of a high resistivity form of boron-carbide (B5C), and the fabrication of boron-rich semiconductor devices. A scanning tunneling microscope (STM) was used to image these molecular icosahedra on Si(111)-(7 x 7). Molecular decomposition (tip induced and otherwise) produced a boron-carbide/silicon interface with pronounced heterojunction electronic characteristics. In STM, this interface is characterized by a disordering of the Si(111)-(7 x 7) reconstruction. We suggest, based on Auger electron spectroscopy data and low-energy electron diffraction observations, that boron atoms from the dissociated source molecules substitutionally occupy selvedge sites, as in the boron-induced (√3 x √3)R30° reconstruction of Si(111).