Formation of silicene-germanene heterostructures by Ge deposition on epitaxial silicene

Silicene and germanene are two dimensional honeycomb sheets composed of Si and Ge atoms. Epitaxial silicene and germanene form spontaneously on ZrB2(0001) thin films grown on Si(111) [1] and Ge(111) [2] substrates and can be identified by (2X2)- and ($\surd $3X$\surd $3)-reconstruction of ZrB2(0001) respectively. In the present work, we demonstrate that silicene-germanene heterostructures can be formed by deposition of Ge on epitaxial silicene and by subsequent annealing. LEED and STM analysis revealed the growth of the following Si-Ge structures depending on preparation conditions. (1): After annealing at 830 K, (2X2)- and ($\surd $3X$\surd $3)-reconstructed areas existed side by side, which suggests that a two-dimensional silicene-germanene heterostructures is formed. (2): After annealing at 1070 K, the surface is (2X2)-reconstructed, with a heterogenous atomic contrast different from silicene which suggests the incorporation of Ge atoms in the silicene lattice. (3): After annealing this mixed Si-Ge layer at 830 K, a (2$\surd $3X2$\surd $3)-reconstruction is observed, in agreement with the overlapping of ($\surd $3X$\surd $3)- and (2X2)-reconstructed layers. The structure is presumably a silicene-germanene heterostack structure. [1] A.Fleurence, et al., Phys. Rev. Lett. 108 245501(2012). [2] A.Fleurence, et al., APS March Meeting 2016.