Formation of two-dimensional-like Ge 1− y Sn y ultra-thin crystal by segregation method

Abstract We demonstrated the formation of a two-dimensional-like Ge 1− y Sn y ultra-thin crystal by a segregation method using an Al/Ge 1− x Sn x stacked structure formed on a Ge(111) substrate. We verified the formation of the Ge 0.88 Sn 0.12 epitaxial layer, the Al epitaxial layer on Ge 0.88 Sn 0.12 , and the Ge 1− y Sn y -segregation layer with a Sn composition of 4.3%–7.4% on the Al epitaxial layer with the simultaneous formation of the Al 2 O 3 cap layer by scanning transmission electron microscopy (STEM) analysis with energy dispersive X-ray spectroscopy. Furthermore, a high-resolution STEM observation clarified that the Ge 1− y Sn y segregation layer showed a two-dimensional-like structure rather than a diamond structure. We also evaluated the crystallographic properties of segregated Ge 1− y Sn y -nanosheet, such as a lattice spacing of out-of-plane direction, the lattice constant, and the buckling height to be 2.6 Å, 3.0 Å, and ∼0.7–1.0 Å, respectively. This report suggests the segregation method featuring a group-IV compound epitaxial layer is a possible approach to develop various new materials of group-IV compound nanosheets.