The self-assembly process of Ge islands on patterned Si (0 0 1) substrates is investigated using scanning tunneling microscopy. The substrate patterns consist of one-dimensional stripes with "V"-shaped geometry and sidewalls inclined by an angle of 9 degrees to the (0 0 1) surface. Onto these stripes, Ge is deposited in a step-wise manner at different temperatures from 520 degrees C to 650 degrees C. At low temperature, the Ge first grows nearly conformally over the patterned surface but at about 3 monolayers a strong surface roughening due to reconstruction of the surface ridges as well as side wall ripple formation occurs. At 600 degrees C, a similar roughening takes place, but Ge accumulates within the grooves such that at a critical thickness of 4.5 monolayers, 3D islands are formed at the bottom of the grooves. This accumulation process is enhanced at 650 degrees C growth, so that the island formation starts about 1 monolayers earlier. At 600 and 650 degrees C, all islands are all aligned at the bottom of the stripes, whereas at 550 degrees C Ge island form preferentially on top of ridges. The experimental observations are explained by the strong temperature dependence of Ge diffusion over the patterned surface. (C) 2011 Elsevier B.V. All rights reserved.