SixGe1-x alloy as efficient phonon barrier in Ge/Si superlattices for thermoelectric applications Riccardo Dettori, Claudio Melis and Luciano Colombo Eur. Phys. J. B, 88 1 (2015) 27 Published online: 21 January 2015 DOI: 10.1140/epjb/e2014-50628-8