An intermediate hybridization in diamond: edge-shared tetrahedra

The crystal structure of the diamond is a model for a whole family of Group IV elements and A(III)B(V) and A(II)B(VI) semiconductor compounds. A common feature of these structures is a connection of tetrahedra at the corners. It takes place in the cubic diamond (sphalerite), hexagonal diamond (wurtzite) and polytypes. Stacking faults and twinning on {111} planes are well-established defects of the tetrahedral family of structures, based on the connection at the corners. The exact atomic configurations of carbon atoms in disordered chemical vapor deposition diamond materials are unknown. We are responding to the present ambiguity relating to the sp(3)/sp(2) concepts created by the assignment of sp(3) to diamond and sp(2) to graphite structure. We will consider a hypothesis of twinning on the (001) plane as a new type of defect. The (001) twinning implies that the tetrahedra share edges. This is contrary to accepted rules of crystal chemistry. The tetrahedra are connected along the (110) direction, and the twinning on (001) creates chains of carbon atoms arranged as rhombi lying in the (110) plane. The interatomic distance in such four-member rings is anticipated to be an intermediate between diamond and graphite. This particular atomic configuration is considered as an intermediate hybridization in between single and double bonds. We posit that the oriented growth of the diamond on (001) silicon generates (001) twins in the diamond structure. Raman spectra from these materials show non-cubic diamond features. We suggest that this demonstrates their connection to twinning. (C) 2003 Elsevier B.V. All rights reserved.