  The thermoelectric properties in one- and two-dimensional silicon and
germanium structures have been investigated using first-principle density
functional techniques and linear response for the thermal and electrical
transport. We have considered here the two-dimensional silicene and germanene,
together with nano-ribbons of different widths. For the nano-ribbons, we have
also investigated the possibility of nano-structuring these systems by mixing
silicon and germanium. We found that the figure of merit at room temperature of
these systems is remarkably high, up to 2.5.
