Preparation and characterization ofBxC1−xthin films with the graphite structure

Abstract

Using chemical vapor deposition (CVD), we have prepared ${\mathrm{B}}_{\mathit{x}}$ ${\mathrm{C}}_{1\mathrm{-}\mathit{x}}$ solid solutions for 0<x<0.17, which have the graphite structure. By varying the relative proportions of benzene and boron trichloride in the CVD reactor, we are able to control the boron concentration in our thin-film samples. Grazing-incidence x-ray diffraction shows that for a series of films prepared at 900 °C, ${\mathrm{B}}_{\mathit{x}}$ ${\mathrm{C}}_{1\mathrm{-}\mathit{x}}$ becomes more graphitic (with less turbostratic disorder) as x increases. There is a discontinuity between x=0.12 and x=0.15 in the variation of the distance between boron-carbon layers, as measured by the (002) plane spacing, which suggests the formation of an ordered ${\mathrm{BC}}_5$ compound. Using synchrotron radiation, we measured the near-edge x-ray absorption of these films at the boron and carbon 1s edges as a function of the angle between the photon beam and the substrate. The dependence of the absorption with angle at both edges shows the same behavior as that reported for highly oriented pyrolytic graphite, where transitions to unoccupied π bands are suppressed when the photon beam is normal to the graphite layers, proving that the boron substitutionally replaces carbon in these materials.