Figure 4

Left: RHEED patterns recorded during Ge growth at 520°C on the stripe-patterned Si substrates at Ge thicknesses of 0, 2, 4.2, 4.8, and 7 ML from (a) to (f), respectively. Ripple formation on the surface results in the appearance of V-shaped diffraction spots as indicated in (f) by the dashed square. Before Ge growth, 45 nm Si was deposited, resulting in a “V”-shaped stripe geometry as shown in Fig. 2 b. Right: Panel g shows the normalized RHEED intensity evolution of the specular spot and two 3D diffraction spots indicated by the dashed square and circle in (f) as a function of Ge coverage. Accordingly, an onset of ripple formation and at a critical coverage of 4.1 ML is found