Local order and electrical properties of boron carbonitride films

Thin films of carbon-boron-nitrogen alloys were prepared by chemical vapor deposition from gaseous mixtures of C2H2, BCl3, NH3, and H-2. Their turbostratic graphitic structure was investigated by electron probe micro analysis (EPMA), X-ray diffraction (XRD), Raman spectroscopy, and nuclear magnetic resonance. Those compounds were shown to be solid solutions with compositions varying in a continuous domain bounded by carbon, boron nitride, and BC3. Measurements of the electrical transport properties (conductivity and Hall coefficient) were performed from 295 down to 4.2 K and in the presence of magnetic fields up to 5 T. The behavior of these solid solutions can be interpreted in terms of a metal-non metal transition, when the carbon content decreases. Heat-treatment of these compounds between 1400 and 2000 degrees C involves strongly modified transport properties. The resistivity of all materials is lowered. But the main property change is that of the magnetoresistance.