Semiconducting boron carbides based on cross-linked carborane (BCH) icosahedra, developed several decades ago, are of significant interest in a variety of emerging areas, including photocatalysis, spintronics, and especially neutron detection. These materials, however, display generally poor charge carrier mobility, high defect levels and other properties that pose significant drawbacks. A class of nanocomposite carborane-based materials has recently been developed, that addresses many of these issues. The films consist of polymerized mixtures of carboranes and aromatic species, including benzene, 1,4-diaminobenzene, pyridine or aniline. In these materials, electronic states corresponding to the aromatic moiety appearing near the top of the valence band, and states associated with the carborane moiety occupy the bottom of the conduction band. Band gap energies are substantially reduced relative to films without aromatic content. Transport measurements also indicate that charge scattering lifetimes are substantially enhanced in aromatic/carborane films compared to corresponding films without aromatic content. This combination of superior electron-hole separation, narrower band gaps, and superior charge scattering lifetimes, yields markedly enhanced charge collection in neutron voltaics studies compared to conventional carborane-derived boron carbides. The implications of these enhanced properties for neutron detection and other applications are discussed.

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Closo-1, 7-dicarbadodecaborane (metacarborane) and aniline or pyridine have been used to fabricate semiconducting composite films by plasma enhanced chemical vapor deposition (PECVD). Chemical and electronic structures of films with aniline/metacarborane or pyridine/metacarborane ratios of ~3:1 were characterized by x-ray photoelectron spectroscopy (XPS), variable angle spectroscopic ellipsometry (VASE), and first-principles density functional theory (DFT)-based electronic structure calculations. Aniline moieties are coordinated to carborane icosahedra by C-B bond formation, whereas N-B and possibly C-B bonding was observed for pyridine/metacarborane films. The aniline/metacarborane film displayed indirect and direct band gaps of 1.0 eV and 2.9 eV, respectively, with corresponding values for the pyridine/metacarborane film of 1.4 eV and 3.3 eV. In contrast, the metacarborane film without aromatic doping exhibits indirect and direct band gaps of 2.6 and 4.9 eV, respectively. DFT results indicate that in both aniline/metacarborane and pyridine/metacarborane film, states near the valence band maximum are associated with the aromatic species, while states near the bottom of the conduction band are associated with either the aromatic or metacarborane moiety. These results indicate that aromatically-doped boron carbide films derived from metacarborane isomers exhibit very similar structures and characteristics to those formed by orthocarborane isomers. Due to the n-type (p-type) nature of boron carbide films formed by PECVD metacarborane (orthocarborane), the results reported here suggest that aromatic doped boron carbide p-n junctions are possible for neutron detection or other applications.

The chemical structures of Co oxynitrides – in particular, interactions among N and O atoms bonded to the same cobalt – are of great importance for an array of catalytic...