Fig. 3

(color online) (a) Micro-Raman spectra obtained from three different points along a single GaAs/InGaAs core-shell nanowire with ≈50-nm shell thickness. The Raman spectrum of a GaAs (111)B substrate is also plotted as reference. b Optical microscope images indicating the three points on the nanowire from which the Raman spectra are obtained. c SEM image showing details of the same nanowire in higher resolution