(Invited) Investigations into the Formation of Germanene Using Electrochemical Atomic Layer Deposition (E-ALD)

Germanene would be the Ge analogue of Graphene.   A number of ab-initio calculations in the literature suggest that Germanene sheets would display unique properties, similar to those observed in Graphene.  Those reports indicate the deposits should have a buckled structure, where half the atoms are about 0.7 nm higher than the other half.   MicroRaman, electrochemistry and in-situ scanning tunnelling 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).    The studies to be discussed have resulted in some interesting, though not clearly understood results, such as why only about 3 ML of Ge can be formed by direct electrodeposition on Au, depending on the pH. Subsequent deposition, under those aqueous conditions, simply stopped after three ML. Reports in the literature indicate that thicker deposits of Ge can be formed on other electrode surfaces, though it is not clear why growth on Au is different.  In-situ STM studies of the first atomic layers of Ge have shown a number of processes which are not yet well understood, such as the formation of nanoscopic atomically flat chips on the surface.  There are suggestions 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 relatively high 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.