**Acknowledgements**

We acknowledge W. Sigle and P.A. van Aken from MPI Stuttgart for Solid State Physics for their help with EELS measurements and TEM-EDX of our nanowires. The authors thank C. Trautmann for fruitful discussion and her continuous support during the project, as well as L. Burr for his contribution in the synthesis and characterization of Au-based nanowires.
