Tip-enhanced Rayleigh and Raman scatterings from Ge/Si quantum dots

Tip-enhanced Rayleigh scattering images of Ge quantum dots grown on a Si substrate have been observed. Changing the wavelength of the incidence light, the contrast of the images is reversed. It is found that the scattering intensity depends on the dielectric constants of the materials under the probe. Tip-enhanced Raman scatterings have also been reported. It is found that Ge-Ge and Si-Ge modes in the Raman spectra are significantly enhanced only when the atomic force microscope tip with a gold nanoparticle is positioned on the dots. The Ge content reduces at the center of the dots. This result suggests that the dots consist of a Si-rich core and a Ge-rich shell.