Ion beam synthesis of boron carbide thin films

We have grown boron carbide (BxC) thin films via direct ion beam deposition using mass selected 11B+ and 12C+ ions. The films were deposited on silicon and ITO-coated quartz glass substrates with an ion energy of 100 eV at room temperature. The B+:C+ ion ratio during deposition was varied between 0:1 (pure carbon) and 1:0 (pure boron), and the resulting composition of the films matched this ratio, as observed by X-ray photoelectron spectroscopy (XPS). A detailed analysis of the XPS-spectra revealed that the deposited films undergo a transition from sp3-bonded diamond-like carbon to a boron carbide phase with a lower density with increasing B concentration. The formation of carbide bonds has been observed by means of XPS, and the valence band spectra showed a strong transition from the amorphous semiconductor ta-C to metallic boron. This transition has also been observed by optical and electrical measurements.