Probing local strain and composition in Ge nanowires by means of tip-enhanced Raman scattering
J S Reparaz, N Peica, R Kirste, A R Goñi, M R Wagner, G Callsen, M I Alonso, M Garriga, I C Marcus, A Ronda, I Berbezier, J Maultzsch, C Thomsen and A Hoffmann;
Local strain and Ge content distribution in self-assembled, in-plane Ge/Si nanowires grown by combining molecular beam epitaxy and the metal-catalyst assisted-growth method were investigated by tip-enhanced Raman scattering. We show that this technique is essential to study variations of physical properties of single wires at the nanoscale, a task which cannot be achieved with conventional micro-Raman scattering. As two major findings, we report that (i) the Ge distribution in the (001) crystallographic direction is inhomogeneous, displaying a gradient with a higher Ge content close to the top surface, and (ii) in contrast, the (uncapped) wires exhibit essentially the same small residual compressive strain everywhere along the wire.
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