SYNCHROTRON-RADIATION-INDUCED DECOMPOSITION OF CLOSO-1,2-DICARBADODECABORANE

We have observed that molecular films of closo-1,2-dicarbadodecaborane (C2B10H12) decompose due to exposure to synchrotron light. Dissociation results in films that form a heterogeneous intermediate phase between associative molecular fragments and solid, thin film boron-carbide. This heterogeneous phase has an observed electronic structure that is an admixture of the electronic structure observed for molecularly condensed orthocarborane and the electronic structure anticipated for rhombohedral boron-carbide (based on the B-12 icosahedral ''building block''). With the synchrotron radiation exposure at room temperature there is dissociative adsorption of this icosahedral molecule and the growth of boron-carbide film is enhanced. The composition of the growing him changes for very thin films on Si(111), as determined by the boron to carbon ratio. The boron concentration of the film increases with increasing film thickness until the boron to carbon ratio reaches 5 when the film thickness is approximately 12 Angstrom. After about 12 Angstrom of film growth the composition is constant, i.e. B5C.