Electrochemically deposited Ni on Ge(111) investigated with X-ray standing waves

Ni was electrodeposited on Ge(111) surfaces from an aqueous solution containing 0.5M Na₂SO₄ and 10^-3M NiSO₄, using a standard three-electrode electrochemical cell. Cyclic voltammetry was used to yield information about the cleanliness of the immersed, p-type Ge(111) surfaces. After deposition at a fixed potential, the samples were removed from the cell and investigated with X-ray standing waves while kept under an inert gas atmosphere. The analysis of the X-ray standing wave data shows that several monolayers of Ni occupy a well defined lattice location. From these results together with the results of the cyclic voltammetric measurements we conclude that the first layers of Ni react with the Ge(111) surface forming a few layers of ordered germanide.