The Electrodeposition of Germanene

Abstract

Germanene is the Ge analogue Silicene or Graphene. A number of ab-initio calculations in the literature suggest that Germanene sheets should exist. Those reports suggest that the material would have a buckled structure, where half the atoms are about 0.7 nm higher than the other half. Micro Raman, electrochemistry and in-situ scanning tunneling microscopy (EC-STM) have been used to better understand the electrochemical growth of Ge from aqueous solutions, from the first atomic layers on Au(111). Our initial studies of the electrodeposition of Ge resulted in some interesting, though not clearly understood results, such as why only about 2 ML of Ge could be formed by direct electrodeposition on Au, depending on the pH. Some reports in the literature indicate that thicker deposits of Ge can be formed by electrodeposition on electrode surfaces other than Au. It is not yet clear why Au would be different. In-situ STM studies of the first atomic layers of Ge have shown a number of processes which indicate that nanoscopic atomically flat layers are forming on the surface. The authors believe that Germanene is being formed. In addition, there is clear evidence of the formation of a surface alloy with the Au substrate, though the phase diagram suggests no significant alloying at room temperature, used in these studies. Further, though Au(111) displays the expected reconstructed (√3X23) “herringbone” structure expected, incorporation of Ge into the this structure occurs very slowly by reduction at negative potentials, starting at defects and step edges. Previous work by this group, lead to development of an electrochemical ALD cycle for the growth of thicker Ge films. That cycle is being further investigated, as some spots in early deposits displayed a Raman spectrum indicative of the presence of germanene. Presently it appears that at sufficiently negative potentials, germanene is being formed. That is, a honeycomb structure is observed, but the domain size is on the order of one or two nm, at which point, defects result in a twist in the structure. References Liang, et al., Langmuir, 26(4) (2010) 2877-2884 Xuehai Liang and John L. Stickney, Chemistry of Materials, 23(7)(2011)1742-1752 Xuehai Liang, et al., J. Am. Chem. Soc., 133(2011)8199-8204 M. A. Ledina, et al., ECS Transactions, 66 (6) 129-140 (2015)