Graphene’s newest cousin, germanene

As interest in graphene has exploded over the past decade, so, too, has interest in other two-dimensional materials, in the expectation that they will likewise exhibit unusual and impressive electrical and optical properties. Boron nitride, in which B and N alternately replace carbon atoms in graphene’s honeycomb lattice, was quick out of the gate. A Turkish team predicted in 2009 that silicon and germanium would be stable in a free-standing, low-buckled honeycomb geometry. Within a few years, several groups reported success in synthesizing single layers of silicene, the Si analogue of graphene. Now María E. Dávila (Madrid Institute of Materials Science), Angel Rubio (University of the Basque Country), Guy Le Lay (Aix-Marseille University), and their colleagues present compelling evidence for the Ge version, germanene. Although Le Lay and his coworkers had successfully used a silver template in 2012 for silicene, initial attempts to synthesize germanene on a silver substrate failed. But noting that gold deposited on Ge forms clean interfaces, the researchers switched to depositing Ge on Au. And among the many phases in the resulting Ge film were large domains that showed a telltale honeycomb pattern in scanning tunneling micrographs. Earlier this year a Chinese team reported observations of buckled germanene on platinum in STM. The European researchers went further: Low- energy electron diffraction, x-ray spectroscopy, and advanced density functional calculations all pointed to the regions indeed being nearly flat, single-layer germanene, though perhaps with some Au atoms sneaking in. (M. E. Dávila et al., New J. Phys. 16, 095002, 2014, doi:10.1088/1367-2630/16/9/095002 .)