Site-specific electron-induced cross-linking of ortho-carborane to form semiconducting boron carbide

Semiconducting boron carbide (B10C2Hx) films have been formed by bombardment of condensed ortho-carborane (closo-1,2-dicarbadodecaborane) multilayers on polycrystalline copper substrates by 200 eV electrons under ultra-high vacuum conditions. The film formation process was characterized by X-ray and ultraviolet photoelectron spectroscopies. Electron bombardment results in the cross-linking of the icosahedral units. The cross-linking is accompanied by a shift in the B(1s) binding energy indicating site-specific cross-linking between two boron sites on adjacent carborane icosahedra. An additional shift in valence band binding energies attributed to the surface photovoltage effect is indicative of the formation of a p-type semiconductor. This is the first report of B10C2Hx formation by electron bombardment of condensed films, and the data indicate that this method is a viable route towards formation of ultra-thin films of tailored composition and cross-linkages for emerging nanoelectronics and sensor applications.