Double-positioning twinning in icosahedral B₁₂As₂ thin films grown by chemical vapor deposition

Analysis of synchrotron white-beam X-ray Laue patterns of thin epitaxial films of icosohedral boron arsenide (B₁₂As₂) prepared by chemical vapor deposition at 1300 °C on 6H-SiC (0001) (on-axis) substrates using hydrides as reactants indicated the epitaxial relationship (111)〈101̄〉∥(0001)〈112̄0〉 and the presence of double-positioning twins of B₁₂As₂. Diffractometry showed that the two twinning variants existed in a ratio of 2:1. A reciprocal space map of the epilayer showed a single peak (12 arc min wide in the ω scan direction and 1.6 arc min wide in the θ - 2θ scan direction), high degrees of both of tilt, and strain broadening. Consistent with these observations, cross-sectional transmission electron micrographs showed twin domains, with one twin orientation appearing as a matrix holding grains between 0.2 and 4 μm wide of the second twin orientation. A high density of dislocations was also noted.