The discovery of graphene, a single-atom thin sheet of carbon, led to the worldwide race for the discovery of similar two-dimensional materials of other elements, especially of common semiconductor ma- terials such as silicon and germanium. Although graphene may be electrically the most conductive material, it is not suitable for making a transistor because of the lack of an energy band gap. In contrast, silicene and germanene, single-atom layers of silicon and germanium, pose a small band gap that can be used for making nanoelectronic transistors. A recent work has demonstrated the proof of concept of this transistor, which is made of a single layer of silicon atoms.