Formation of germanene with free-standing lattice constant

Two-dimensional sheets of ultra-thin germanium with the lattice parameter of free-standing germanene, i.e., 0.41 nm, are formed by atomic segregation epitaxy on face-centered-cubic Ag0.9Al0.1(111) thin films grown on a Ge(111) template. Low-energy electron diffraction clearly shows a square-like (root 13 x root 13)R +/- 46(degrees) super-structure, expressed as ( (4 1)(1 4)) in Matrix form, whose 92(degrees) angle between the two vectors is clearly observed, as well as incommensurate (1.41 x 1.41)R +/- 27(degrees) spots. Scanning tunneling microscopy (STM) images show the square-like superstructure and a defective honeycomb-like arrangement with this characteristic 0.41 nm lattice constant, corresponding to LEED patterns. Complimentary high-resolution synchrotron radiation photoemission spectroscopy measurements reveal the electronic structure of the honeycomb-like germanene sheet and further demonstrate that it overlays the surface of the Ag0.9Al0.1(111) alloy.