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. Dissociati on results in films that form a heterogeneous intermediate phase betwe en 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 con densed orthocarborane and the electronic structure anticipated for rho mbohedral boron-carbide (based on the B-12 icosahedral ''building bloc k''). With the synchrotron radiation exposure at room temperature ther e is dissociative adsorption of this icosahedral molecule and the grow th of boron-carbide film is enhanced. The composition of the growing h im changes for very thin films on Si(111), as determined by the boron to carbon ratio. The boron concentration of the film increases with in creasing film thickness until the boron to carbon ratio reaches 5 when the film thickness is approximately 12 Angstrom. After about 12 Angst rom of film growth the composition is constant, i.e. B5C.