Local Atomic Arrangements and Band Structure of Boron Carbide.
Boron carbide, the simple chemical combination of boron and carbon, is one of the best-known binary ceramic materials. Despite that, a coherent description of its crystal structure and physical properties resembles one of the most challenging problems in materials science. By combining ab initio computational studies, precise crystal structure determination from diffraction experiments, and state-of-the-art high-resolution transmission electron microscopy imaging, this concerted investigation reveals hitherto unknown local structure modifications together with the known structural alterations. The mixture of different local atomic arrangements within the real crystal structure reduces the electron deficiency of the pristine structure CBC+B12 , answering the question about electron precise character of boron carbide and introducing new electronic states within the band gap, which allow a better understanding of physical properties.
Icosahedral Boron‐Rich Solids
Boron‐rich molecules and solids hold a special place within chemistry. They do not follow the general bonding rules we are taught in chemistry classes. For example, some boron‐rich solids are composed of 12‐atom clusters of boron atoms in which each boron atom resides on a vertex of an icosahedron. These solids are very stable refractory materials with melting temperatures up to 2400 °C—a thousand degrees greater than silicon's. Beyond this, they possess numerous novel structural, electronic and thermal properties that are not only interesting but useful.
Electronic structure of molecular icosahedra films
Using angle-resolved photoemission and inverse photoemission, the electronic structure of films of the molecular icosahedron orthocarborane (C2B10H12) on Cu(100) has been studied. The measured gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals is in good agreement with modified neglect of differential overlap calculations. An unoccupied exopolyhedral state has been found and is ascribed to molecular orbital hybridization. This hybridization is consistent with the observed dispersion of the orthocarborane molecular orbitals. This molecular orbital dispersion indicates a surface Brillouin zone edge with an average radius of 0.7 AA-1, and suggests that the molecules adopt local close-packed ordering in the overlayers, with an intermolecular distance of 5.58 AA.