During molecular beam epitaxy (MBE) growth of materials such as Bi2Se3, a spiral growth mode is commonly observed; an unexpected observation since these materials interact only weakly with the substrate, and are therefore unlikely to form dislocations at the interface to seed the growth of spirals. In this work, we discovered a novel mechanism that facilitates spiral core formation – the pinning of the growth front at substrate step edges – a mechanism that should be generally applicable to van der Waals epitaxy of other 3D topological insulators on weakly interacting substrates.
Using scanning tunneling spectroscopy, we have also verified the linear dispersion of the Dirac states for films thicker than 6 quintuple layers (QLs), consistent with our DFT calculations that these Dirac states are fully developed at 6 QLs. We further confirmed experimentally that the 1D mode associated with screw dislocations is indeed prohibited in the strong topological insulator Bi2Se3.
Published in Physical Review Letters:
“Spiral Growth Without Dislocations: Molecular Beam Epitaxy of the Topological Insulator Bi2Se3 on Epitaxial Graphene/SiC(0001)“, Y. Liu, M. Weinert, and L. Li, Phys. Rev. Lett. 108, 115501 (2012).