PECVD of boron carbide/aromatic composite films: Precursor stability and resonance stabilization energy

Abstract

Semiconducting composite films have been formed by plasma enhanced chemical vapor deposition (PECVD) from orthocarborane and aromatic precursors. Aromatic/orthocarborane composite films exhibit exciting potential in areas such as neutron detection and photocatalysis. An important factor in determining the electronic properties of these materials is the existence of an intact π system in the deposited film, indicating deposition of a (more or less) intact aromatic precursor. X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) data for films formed by co-deposition of orthocarborane and pyrimidine, pyridine, aniline, indicate that the integrity or decomposition of the aromatic π electron network correlates closely with aromatic resonance stabilization energy. The resonance stabilization energy of pyrimidine is low (8 kcal/mol), and the resulting films exhibit no evidence of a π network. Pyridine and aniline have resonance stabilization energies of 24.2 and 39.5 kcal/mol, respectively, and both exhibit FTIR and XPS core level shakeup features indicating intact π networks. This trend permits the prediction of film properties for a broad variety of aromatic precursors in such films.