Examples of μ-Raman spectroscopy results obtained from single island inside the pattern (black data) and island outside the pattern (red data). The data refer to islands grown with a total amount of 2.8 nm of Ge with a 0.1 nm s−1 rate with a substrate temperature of 750°C. a Semilogarithmic plot of the Raman spectra with the indication of the three bands related to the islands (marked with Si–Si, Si-Ge and Ge–Ge) and the single band related to the Si bulk substrate. b Composition-strain plane showing the calibration curves extracted from Ref.  corresponding to the peaks shown in panel (a). The intersection of the curves is highlighted with the dot and marks the value of composition and strain for the islands. The method is described in detail in Ref.