The morphology and crystal structure of rhombohedral B12As2, thin films prepared by chemical vapor deposition on Si (100), Si (I 10) and Si (I 1 1) substrates were examined. For short depositions, 30s at 1300 degrees C, the B12As2 nucleated in patterns that were unique to each substrate orientation, probably due to variations in the surface atomic structure and surface activation energy of the substrates. Small square domains, one-dimensional straight lines, and irregular lines were the representative morphologies on Si (100), Si (I 1 1) and Si (I 10), respectively. For long depositions, 30 min at 1300 degrees C, continuous thin films of B 1 As, formed with distinct morphologies also depend on the orientation of the substrates. "Cross", "wire" and "chain" morphologies were formed on the Si (10 0), Si (I 1 1) and Si (110) substrates, respectively. X-ray diffraction (XRD) showed that the B12As2 films had the following predominant oriented textures: B12As2 (110) on Si (100), B12As2 (101) on Si (111), and B12As2 (001) on Si (I 10). The in-plane orientations of the B12As2 films as determined by XRD pole figures is also reported. Crown Copyright (c) 2006 Published by Elsevier B.V. All rights reserved.