(Invited) Germanium at the Atomic Scale

Similar to how carbon networks can be sculpted into low-dimensional allotropes such as fullerenes, nanotubes, and graphene with fundamentally different properties, it is possible to create similar “allotropes” of Si or Ge with unique optoelectronic properties as well.  Here, we will describe our recent success in the creation of hydrogen and organic-terminated germanium graphane analogues, or germananes, from the topochemical deintercalation of CaGe2.  We will discuss how the optical, electronic, and thermal properties of these materials can be controlled by substituting either the surface ligand or via alloying with other Group IV elements.   Additionally, we have also developed an epitopotaxial approach for integrating precise thicknesses of Germanane layers onto Ge wafers that combines the epitaxial deposition of CaGe2 precursor phases with the topotactic interconversion into the 2D material.  These materials represent a new class of covalently terminated graphane analogues and have great potential for a wide range of electronic, optoelectronic and sensing applications, especially since theory predicts these materials to have direct and tunable band gaps around 1.5 eV and electron mobilities that are around five times higher than that of bulk Ge.